University of Nevada, Reno

The evolution of seed dispersal syndromes in Prunus

A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Ecology, Evolution and Conservation Biology

by

Maurie J. Beck

Stephen B. Vander Wall, Dissertation Advisor

August, 2009

THE GRADUATE SCHOOL

We recommend that the dissertation prepared under our supervision by

MAURIE BECK

entitled

The Evolution Of Seed Dispersal Syndromes In Prunus

be accepted in partial fulfillment of the requirements for the degree of

DOCTOR OF PHILOSOPHY

Stephen B. Vander Wall, Advisor

Stephen H. Jenkins, Committee Member

William S. Longland, Committee Member

David W. Zeh, Committee Member

Thomas J. Nickles , Graduate School Representative

Marsha H. Read, Ph. D., Associate Dean, Graduate School

August, 2009

i

ABSTRACT

There are two fruit types in the genus Prunus. The majority of species have fleshy- fruited drupes, which are considered the ancestral phenotype. In the deserts of Eurasia

and North America there are also species that produce dry fruits and large nuts,

suggesting this fruit type has originated independently on numerous occasions in response to dry conditions.

Fleshy-fruited Prunus are dispersed by frugivorous animals, primarily birds and some mammalian carnivores. In this dissertation, by documenting complete seed fate pathways, I demonstrate that desert peach (Prunus andersonii), a dry, nut-producing

species in the western Great Basin of North America, is only dispersed by scatter-

hoarding rodents. Additionally, I demonstrate that western chokecherry (P. virginiana

var. demissa, Rosaceae) is also dispersed by scatter-hoarding rodents, following primary

dispersal by endozoochorous frugivores. This type of two-phased seed dispersal is a

form of diplochory, a process that employs different modes of dispersal during sequential

dispersal phases and usually offers unique benefits during each phase. Although not well

documented, frugivory followed by scatter hoarding is believed to be more common than

previously thought. In this case I show that phase I dispersal by frugivores transports

seeds, often long distances, away from the parent plants. Scatter-hoarding rodents then

harvest the seeds from feces and bury them in soil during phase II dispersal. Caching

chokecherry seeds not only moves them away from the parent plant, but constitutes

directed dispersal, a form of seed dispersal that disproportionately enhances seed and

seedling survival. ii

The transition in Prunus from primary dispersal by fruit-consuming animals to nut dispersal by scatter-hoarding rodents is difficult to envision. However, if the ancestor to desert peach or other dry-fruited species utilized diplochory, then the most parsimonious explanation is that the transformation from fleshy fruits to dry nuts was accompanied by the loss of frugivory and the reliance only on dispersal by scatter-hoarding rodents.

In chapter 3 I review to similarities and differences between frugivory and dispersal by scatter-hoarding animals. iii

ACKNOWLEDGEMENTS

I am indebted to my major professor, Stephen B. Vander Wall, a consummate experimental ecologist and naturalist. I would also like to thank my graduate committee,

Stephen H. Jenkins, William S. Longland, David W. Zeh, and Thomas J. Nickles for contributing to my dissertation and my development as a researcher.

I would especially like to thank the Vander Wall lab, including Jenny Briggs, Julie

Roth, Ted Thayer, Jennifer Armstrong, Jennifer Hollander, and Kellie Kuhn. They were like a family to me, helping tirelessly in the field and as supportive critics, separating the grain of ideas with merit from the chaff of those without.

I thank Jenny Francis, Jessica Hay, and Chris Farrar for assistance in the field. Dr.

Chris Ross provided me with one of my field sites. I received help with statistics from G.

C. J. Fernandez, I. Aban, and D. Board for help. I received financial support from the

Ecology, Evolution, and Conservation Biology (EECB) program and the Graduate

Student Association at the University of Nevada, Reno and the Whittell Forest and

Wildlife Area. I received additional financial assistance from C. Richard Tracy. Lucy

Morris, Pauline Jasper, Lou Christiansen, and Cheri Briggs provided logistical support.

I owe much to my family and friends for their companionship and love during this long journey, including my parents, Barbara Beck and Sam Sokolow, my godmother,

Marion Kamins, my friends Dave and Betsy Harden, the Scarpaci family, Robby Weaver and Stacy Daghliesh, Jenseen Brons, Patti Doty, and the Jahn Family for providing a space conducive to finishing my dissertation, along with the fine food and well-timed threats. iv

TABLE OF CONTENTS

GENERAL INTRODUCTION...... I REFERENCES...... 3

Chapter 1. Desert peach (Prunus andersonii) and the transition in seed dispersal mode from frugivory to scatter-hoarding...... 5

ABSTRACT...... 6

INTRODUCTION...... 8

METHODS ...... 10 Description of study sites...... 10 Fruit development and production ...... 11 Foraging and removal of nuts ...... 12 Rodent community composition...... 15 Caching behavior of rodents in field enclosures ...... 15 Seed dispersal from source shrubs ...... 16 Seedling germination, emergence, and survival...... 17

RESULTS ...... 18 Fruit development and production ...... 18 Foraging and removal of nuts ...... 20 Rodent community composition...... 24 Seed dispersal from source shrubs ...... 24 Seedling germination, emergence, and survival...... 26

DISCUSSION ...... 29

ACKNOWLEDGEMENTS...... 39

REFERENCES...... 39

TABLES ...... 43

FIGURES...... 51

Chapter 2. Diplochory in western chokecherry: you can’t judge a fruit by its mesocarp 61

ABSTRACT...... 62

INTRODUCTION...... 64

v

METHODS ...... 66 Study area and species...... 66 Fruit development and crop size...... 67 Foraging on chokecherry...... 67 Seed removal transects ...... 70 Rodent community composition...... 70 Caching behavior of rodents in field enclosures ...... 71 Secondary dispersal by rodents ...... 71 Seedling emergence and survival ...... 72 Recruitment potential...... 74

RESULTS ...... 74 Fruit development and crop size...... 74 Foraging on chokecherry...... 75 Seed removal transects ...... 77 Rodent community composition...... 78 Secondary dispersal by rodents ...... 79 Seedling emergence and survival ...... 82 Recruitment potential...... 84

DISCUSSION ...... 85

ACKNOWLEDGEMENTS...... 98

REFERENCES...... 98

TABLES ...... 104

FIGURES...... 112

Chapter 3. A review of two seed dispersal syndromes: frugivory and dispersal by scatter- hoarding rodents...... 119

ABSTRACT...... 120

INTRODUCTION...... 122

TAXA...... 124

REWARD ...... 128

SEED DEPOSITION ...... 131

SPATIAL PATTERNS OF SEED DISPERSAL...... 133

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DURATION OF THE INTERACTION ...... 135

SEED DORMANCY...... 139

INTERANNUAL VARIATION IN CROP SIZE ...... 141

PHYSICAL AND CHEMICAL TRAITS OF FRUITS AND SEEDS...... 143

HABITAT AND GEOGRAPHIC REGION ...... 145

GENE FLOW, POPULATION DIFFERENTIATION, AND SPECIATION ...... 147

FUTURE DIRECTIONS ...... 149

ACKNOWLEDGEMENTS...... 150

REFERENCES...... 150

vii

LIST OF TABLES

Chapter 1. Desert peach (Prunus andersonii) and the transition in seed dispersal mode from frugivory to scatter-hoarding

Table 1. Nutrient and amygdalin content of desert peach fruit pulp and seed kernels.

Table 2. Fate of desert peach fruits and nuts from focal shrubs at the Park and Pine Nut Range sites during the summers of 1999 – 2001.

Table 3. Number of captures of rodent species at four trapping grids at the Park site and Pine Nut Range in August of 1999-2001.

Table 4. Fates of 200 radioactively-labeled desert peach nuts placed under 12 source shrubs at the Pine Nut site during the summer of 1999, 2001-2002.

Table 5. Cache characteristics of four rodent species at 8 source shrubs at the Pine Nut site during the summer of 1999, 2001-2002.

Table 6. The fates of 100 desert peach nuts in caching trials by six rodent species in 15 x 15 m rodent enclosures at the Pine Nut site during the summer of 1999, 2001-2003.

Table 7. The caching characteristics of six species of rodents in caching trials in 15 x 15 m rodent enclosures at the Pine Nut site.

Table 8. Recruitment potential for abiotic dispersal and dispersal by four species of rodents at the Pine Nut site.

Chapter 2. Diplochory in western chokecherry: you can’t judge a fruit by its mesocarp

Table 1. Nutrient and amygdalin content of chokecherry fruit pulp and seed kernels.

Table 2. Species of birds that foraged on chokecherry, type of forager, and index of abundance at Verdi in 1999, and Verdi and Purdy Creek in 2001.

Table 3. Fate of chokecherry fruits and stones from focal plant seed traps at Cliff Ranch in 2000 and Purdy Creek in 2001.

Table 4. Number of captures of rodent species at trapping grids in two habitats at Purdy Creek in September 2001.

Table 5. Fates of 200 radioactively labeled chokecherry stones placed under 3 source plants at Purdy Creek during the fall of 2002. viii

Table 6. Cache characteristics of chokecherry stones scatter-hoarded by rodents at 3 source plants at Purdy Creek during the fall of 2002.

Table 7. Caches placed in different types of microsites compared to the availability of those microsites at 3 source plants at Purdy Creek during the fall of 2002.

Table 8. Recruitment potential for abiotic fruit fall, primary dispersal by birds, and diplochory by birds and then scatter-hoarding rodents in two habitats at Purdy Creek. ix

LIST OF FIGURES

Chapter 1. Desert peach (Prunus andersonii) and the transition in seed dispersal mode from frugivory to scatter-hoarding

Figure 1. Seed fate pathway diagram of desert peach (Prunus andersonii).

Figure 2. Fruit and seed development in desert peach and chokecherry from weekly sampling during the summer of 1999.

Figure 3. The timing of desert peach nut harvest in relation to energy content from focal shrubs at the Park and Johnson Lane sites during the summer of 1999 – 2001.

Figure 4. Removal rate of desert peach fruit and nuts by rodents along transects during the summer of 1999 and 2001 at the Park and Johnson Lane sites.

Figure 5. Cache microsite and substrate use by four species of rodents at eight source shrubs at the Pine Nut site.

Figure 6. Seedling emergence and one-year survival from simulated caches planted in exclosures in response nut size, cache size and microhabitat.

Figure 7. Seedling emergence and one-year survival from simulated caches planted in exclosures in response to six depths (0-5 cm).

Chapter 2. Diplochory in western chokecherry: you can’t judge a fruit by its mesocarp

Figure 1. Seed fate pathway diagram of western choke cherry (Prunus virginiana var. demissa).

Figure 2. The timing of chokecherry fruit harvest from by birds from 12 focal plants at Verdi in 1999, Cliff Ranch in 2000 and, Purdy Creek in 2001.

Figure 3. Removal rate of chokecherry fruits and bird-processed stones by rodents from transects in riparian and upland habitats during the fall at Verdi in 1999, Cliff Ranch in 2000, and Purdy Creek in 2001.

Figure 4. The distribution of caches made by rodents around source plant 2 (large circle) in 2002 at Purdy Creek.

Figure 5. Percentage of seedlings that emerged from simulated caches planted in exclosures in response to six dispersal categories and two habitat types 1

GENERAL INTRODUCTION

Seed dispersal syndromes are often defined by devices associated with a specific

mode of dispersal (Vander Wall 2008). Thus winged-seeds are dispersed by wind, seeds

that are rapidly launched away from plants by specialized structures are ballistically

dispersed, and eliasome-bearing seeds are ant dispersed. There are also many plants with

seeds that lack recognizable dispersal devices, which has created some confusion among

plant ecologists as to whether seed dispersal is even important in these taxa (Ellner and

Shmida 1981; Van Rheede van Oudtshoorn and Van Rooyen 1999; Willson and Traveset

2000). Currently, there is a growing appreciation that specific dispersal devices often do

not sufficiently elucidate the fates of seeds (Vander Wall 2008), suggesting more detailed

seed-fate studies are needed. For many seeds, the dispersal device usually informs us

only about the initial phase of a multi-step seed dispersal process that may sequentially

utilize a number of different dispersal modes (polychory), each providing one or more

dispersal-related benefits. Those benefits include dispersal away from distance-

dependent mortality near parents or conspecifics, colonization of new habitats, sometimes

far from the initial seed source, or non-random directed dispersal to sites with

disproportionately high recruitment potential (Howe and Smallwood 1982).

Animal-mediated seed dispersal syndromes generally form diffuse coevolutionary

networks between a group of seed plants and a guild of animal dispersers (Herrera 1982;

Thompson 1999; Wenny 2001). The network is usually characterized by a web of

mutualists with asymmetric interactions of dependency among each other (Bascompte et al. 2006; Jordano et al. 2003; Thompson 2006). These interactions show a nested pattern of specialization, with specialists nested within a core of generalists (see Fig. 1 in 2

Bascompte et al. 2006). One well-known seed dispersal syndrome defined by a dispersal-related structure is frugivory, in which an animal ingests fleshy fruit, then subsequently carries the seeds some distance from the plant where they are defecated or regurgitated onto the ground or, less commonly, onto another plant. Succulent fruits are ubiquitous and are found in a diverse array of plant taxa, suggesting that fleshy fruits evolved repeatedly and with apparent ease in numerous independent origins. Another less well documented mode of animal dispersal involves vertebrate seed predators (e.g. rodents, corvid birds, a few marsupials) that store seeds, many lacking specific dispersal devices, in shallow caches for later use and then fail to recover some of the seeds. Both mutualisms involve an exchange of food (i.e. fruit pulp or seed kernel) for seed transport

(Herrera 2002).

Considering the diversity of primary modes of seed dispersal found in some plant taxa (pines in Benkman 1995; Gnetales in Hollander and Wall 2009; Rosaceae in Potter et al. 2007; Fabaceae and Liliaceae in Willson and Traveset 2000), the transition from one mode of primary dispersal to another mode apparently presents no great evolutionary challenge. Prunus is a large genus (> 200 species) in the family Rosaceae that is distributed worldwide, primarily in the temperate regions of Eurasia and North America.

Most species produce fleshy fruits (~ 85%; e.g. cherries, plums, apricots, peaches), which are considered ancestral in Prunus, suggesting a long reliance on frugivory for primary seed dispersal (Bortiri et al. 2006). A smaller number of species in arid environments produce dry fruit with large nuts that are putatively dispersed by scatter-hoarding rodents.

The almonds of central Asia are the most familiar, comprising 26 species in two subgenera and five sections (Bortiri et al. 2006; Browicz and Zohary 1996; Watkins 3

1995). In deserts of western North America and Mexico there are two, apparently

convergent, nut-bearing clades of at least eight species (Bortiri et al. 2006; Bortiri et al.

2001; Lee and Wen 2001; Mason 1913).

In the first two chapters of this dissertation, I provide evidence for primary dispersal

by scatter-hoarding rodents of desert peach (P. andersonii), a dry-fruited endemic of the

western Great Basin of North America, and diplochory in chokecherry (Prunus

virginiana var. demissa), involving phase I dispersal by frugivorous birds and phase II

dispersal by scatter-hoarding rodents. I also discuss the transition in primary dispersal

from frugivory to scatter-hoarding in Prunus, which accompanied the transformation of a

fleshy fruit to a dry-fruited nut in arid environments in both Asia and North America on a

number of independent occasions. Finally, I review the differences between frugivory

and dispersal by scatter-hoarding animals in chapter 3.

REFERENCES

Bascompte, J., P. Jordano, and J. M. Olesen. 2006. Asymmetric coevolutionary networks facilitate biodiversity maintenance. Science 312:431-433. Benkman, C. W. 1995. Wind dispersal capacity of pine seeds and the evolution of different seed dispersal modes in pines. Oikos 73:221-224. Bortiri, E., B. V. Heuvel, and D. Potter. 2006. Phylogenetic analysis of morphology in Prunus reveals extensive homoplasy. Plant Systematics and Evolution 259:53-71. Bortiri, E., S. H. Oh, J. G. Jiang, S. Baggett, A. Granger, C. Weeks, M. Buckingham et al. 2001. Phylogeny and systematics of Prunus (Rosaceae) as determined by sequence analysis of ITS and the chloroplast trnL-trnF spacer DNA. Systematic Botany 26:797-807. Browicz, K., and D. Zohary. 1996. The genus Amygdalus L (Rosaceae): species relationships, distribution and evolution under domestication. Genetic Resources and Crop Evolution 43:229-247. Ellner, S. P., and A. Shmida. 1981. Why are adaptations for long range seed dispersal rare in desert plants. Oecologia 51:133-144. Herrera, C. M. 1982. Seasonal variation in the quality of fruits and diffuse coevolution between plants and avian dispersers. Ecology 63:773-785. 4

—. 2002. Seed dispersal by vertebrates, Pages 185-208 in C. M. Herrera, and O. Pellmyr, eds. Plant-animal interactions: an evolutionary approach. Oxford, UK, Blackwell. Hollander, J. L., and S. B. V. Wall. 2009. Dispersal syndromes in North American Ephedra. International Journal of Plant Sciences 170:323-330. Howe, H. F., and J. Smallwood. 1982. Ecology of seed dispersal. Annual Review of Ecology and Systematics 13:201-228. Jordano, P., J. Bascompte, and J. M. Olesen. 2003. Invariant properties in coevolutionary networks of plant-animal interactions. Ecology Letters 6:69-81. Lee, S., and J. Wen. 2001. A phylogenetic analysis of Prunus and the Amygdaloideae (Rosaceae) using ITS sequences of nuclear ribosomal DNA. American Journal of Botany 88:150-160. Mason, S. C. 1913. The pubescent-fruited species of Prunus of the southwestern states. Journal of Agricultural Research 1:147-186. Potter, D., T. Eriksson, R. C. Evans, S. Oh, J. E. E. Smedmark, D. R. Morgan, M. Kerr et al. 2007. Phylogeny and classification of Rosaceae. Plant Systematics and Evolution 266:5-43. Thompson, J. N. 1999. The raw material for coevolution. Oikos 84:5-16. —. 2006. Mutualistic webs of species. Science 312:372-373. Van Rheede van Oudtshoorn, K., and M. W. Van Rooyen. 1999, Dispersal biology of desert plants Adaptations of desert organisms, 1430-9432. Berlin, Springer- Verlag. Vander Wall, S. B. 2008. On the relative contributions of wind vs. animals to seed dispersal of four Sierra Nevada pines. Ecology 89:1837-1849. Watkins, R. 1995. Cherry, plum, peach, apricot and almond, Pages 423-428 in J. S. a. N. W. Simmonds, ed. Evolution of Crop Plants. London, Longman. Wenny, D. G. 2001. Advantages of seed dispersal: a re-evaluation of directed dispersal. Evolutionary Ecology Research 3:51-74. Willson, M. F., and A. Traveset. 2000. The ecology of seed dispersal, Pages 85-110 in M. Fenner, ed. Seeds: the ecology of regeneration in plant communities. Wallingford, UK, C.A.B. International.

5

Chapter 1.

Desert peach (Prunus andersonii) and the transition in seed dispersal mode from frugivory to scatter-hoarding

Maurie J. Beck

Program in Ecology, Evolution and Conservation Biology; University of Nevada, Reno 6

Desert peach (Prunus andersonii) and the transition in seed dispersal mode from frugivory to scatter-hoarding

Maurie J. Beck

ABSTRACT

Plants have made the transition from one mode of primary seed dispersal to another mode on numerous occasions, often in response to changing selective pressures that transform reproductive morphology and dispersal syndrome. In Prunus, dry fruits arose independently in Eurasia and North America, apparently in response to arid environments. This transformation in diaspore morphology was accompanied by a transition in the mode of seed dispersal from frugivory to scatter hoarding by seed caching rodents. Here I show that dry-fruited desert peach (P. andersonii) relies only on dispersal of its nuts by scatter hoarding rodents.

The mesocarp of desert peach fruits dried out and dehisced at maturity (late June).

No vertebrate frugivores consumed the fruits, but rodents avidly harvested the nuts

throughout July and August, scatter-hoarding 50.9% and larder-hoarding 46.2% of

radioactive nuts placed under source shrubs. Most nuts were harvested (89%) and

removed (74%) from the plant canopy by scansorial rodents such as white-tailed antelope

ground squirrels (Ammospermophilus leucurus), which scatter-hoarded them in many 1-2

seed caches, buried 10-30 mm deep. Deer mice (Peromyscus maniculatus) also made

many shallow (<10 mm deep) one-nut caches. Great Basin pocket mice (Perognathus

parvus) and Panamint kangaroo rats (Dipodomys panamintinus), in contrast, primarily

larder hoarded nuts (≈ 60%) in burrows too deep for seedling emergence, but also scatter-

hoarded many nuts (4-20 nuts/cache) in a few caches 10-40 mm deep. Antelope ground 7

squirrels were the most effective dispersers and deer mice were the least effective. Nuts

or fruits that fell from the canopy had virtually no recruitment (<1% emergence), but nuts

buried in soil to simulate rodent caches had 32% emergence and 5.6% survived one year,

suggesting that scatter-hoarding rodents are responsible for nearly all recruitment in

desert peach.

Desert peach arose from a fleshy-fruited ancestor that was probably dispersed by

endozoochorous frugivores. All other dry-fruited species of this genus independently

evolved dry fruits in arid environments across North America and Eurasia. The most

parsimonious explanation for the transition in Prunus from primary dispersal by

frugivores to primary dispersal by scatter-hoarding rodents was simply the loss of

frugivory in a diplochorous ancestor, accompanied by the transformation from fleshy

fruits to dry fruits and large nuts.

Key words: desert peach; scatter-hoarding; coevolution; mutualism; Prunus

andersonii; seed-caching rodents; seed dispersal; seed fate pathways; seed predation; seedling establishment

8

INTRODUCTION

Plant adaptations for newly colonized or changing environments may involve

transformations in reproductive morphology and dispersal mode. This would be true for

fleshy-fruited plants in deserts, which impose a selective premium on water economy.

Furthermore, frugivore-dispersed seeds that land on the surface in such dry conditions

would also be subject to desiccation and other detrimental abiotic factors. Consequently, plant populations in arid environments that substitute traits which conserve water and enhance dispersal to more favorable sites would have higher fitness than those previously adapted to frugivory. Dispersal of seeds in succulent fruits by endozoochorous frugivores is therefore rare or absent in deserts (Jordano 2000). Dispensing with fleshy fruits in arid environments might be relatively simple, but achieving a transition in dispersal mode between different guilds of animal dispersers would appear to be more difficult.

However, plants have made the transition from one mode of primary seed dispersal to another mode on numerous occasions. For example, a number of plant taxa (Betulaceae,

Fagaceae, Juglandaceae, Pinus) that relied primarily on wind dispersal subsequently utilized food-hoarding animals to disperse enlarged nuts (Vander Wall 2001). Vander

Wall (2001) suggested that vertebrate seed predators were consuming the winged nutlets of extinct species and hoarding them in caches as a response to seasonal food shortages.

He then hypothesized that this additional incipient dispersal mechanism was already in place, and the plant lineage was relying, to some degree, on diplochory; i.e. two-phase seed dispersal in which a primary dispersal agent initially transports seeds and then there is subsequent movement by an entirely different mechanism that often provides different 9

benefits from those of phase I dispersal (Vander Wall and Longland 2004). The

morphological transformation in the diaspore associated with changing ecological

circumstances then formed the basis for a shift to a new mode of primary dispersal. Such

changes in fruit morphology and seed dispersal may have occurred in nut-bearing

members of Prunus (almonds), all of which are found in arid environments.

Prunus is a widespread genus in Rosaceae, found predominantly in holarctic regions,

and consisting of over 200 species of cherries, plums, apricots, peaches, and almonds

(Bortiri et al. 2006; Lee and Wen 2001; Watkins 1995; Wilken 1993). A succulent drupe

appears to be ancestral (Bortiri et al. 2006) and ~ 85% of species produce small, fleshy

fruits that are initially dispersed by vertebrate frugivores (birds, carnivores). Some of

these species also rely on secondary dispersal by seed-caching animals (Beck Chapter 2;

Li and Zhang 2007; Lu and Zhang 2004; Zhang and Wang 2001). In arid and semi-arid regions of Eurasia and North America, up to seven clades are composed of dry-fruited species with large nuts that are putatively dispersed by scatter hoarding rodents. The almonds of central Asia are the most familiar, comprising 26 species in two subgenera and five sections (Bortiri et al. 2006; Browicz and Zohary 1996; Watkins 1995). In deserts of western North America there are two, apparently convergent, nut-bearing

clades of at least eight species (Bortiri et al. 2006; Bortiri et al. 2001; Lee and Wen 2001;

Mason 1913).

Desert peach (Prunus andersonii) is a small (< 3 m in height), desert-adapted endemic

shrub of the western Great Basin of Nevada and California (Wilken 1993). Its pink flowers bloom in April and are pollinated by insects. The fruits develop in May and June with a green fleshy mesocarp (similar to fleshy-fruited Prunus) that turns yellow-orange 10

and dehisces when ripe. The nuts (mean ± SD = 267.5 ± 119.3 mg; range = 46.6-686.4

mg; n = 421) are then harvested until late August by scatter-hoarding rodents from either

the shrub canopy or the ground. There is a great deal of variation in crop size. In some

years large plants can produce up to 10,000 nuts, while in other years there may be hardly any crop at all.

Here I investigate the seed dispersal ecology of desert peach by following complete seed fate pathways from fruit production through harvest and dispersal to germination and establishment (Fig. 1). There have been no previous studies that document nut dispersal in any dry-fruited Prunus. Specifically, I 1) explore the effects of nut morphology on early life stages of desert peach (pre-dispersal mortality, dispersal, and germination and emergence), 2) explore the influence of physical and chemical traits of nuts on rodent dispersal behavior, 3) quantify disperser effectiveness, and 4) link behavior and effectiveness to differential benefits of dispersal, including directed dispersal (the non-random dispersal of seeds to sites with disproportionally high establishment; Wenny 2001).

METHODS

Description of study sites

I conducted this study at three locations in northwestern Nevada from spring 1999 –

spring 2004. All sites had desert peach in association with other Great Basin desert

shrubs, including big sagebrush (Artemesia tridentata), rubber rabbitbrush

(Chrysothamnus nauseosus), antelope bitterbrush (Purshia tridentata), Mormon tea

(Ephedra viridis), and plateau gooseberry (Ribes velutinum). In the Pine Nut Range, 20 km southeast of Carson City, NV, the Pine Nut (39º05’10”N, 119º39’0”W, elev. 1920 m) 11 and Johnson Lane sites (39º02’40”N, 119º37’35”W, elev. 1822 m) were in piñon juniper woodland. Silver Knolls Park (Park site; 39º39’55”N, 119º55’56”W, elev. 1600 m) is 2 km northwest of Stead, NV and lacks trees. Yearly precipitation (1 October – 30

September) in Carson City (elevation 1432 m) was 231 mm in 1998-1999, 175 mm in

1999-2000, 89 mm in 00-01, and 178 mm in 01-02. Precipitation at Stead (elevation

1539 m) was 294 mm in 98-99, 197 mm in 99-00, 109 mm in 00-01, and 168 mm in 01-

02. Most precipitation falls during the winter, with occasional local summer thunderstorms.

Fruit development and production

I documented fruit development in desert peach from June to August of 1998 – 2000 at the Park site, using 10 shrubs in 1998 and 12 shrubs during the other years. I placed 6 mm mesh hardware cloth baskets around fruit for protection from animal foragers, then collected one undamaged fruit per plant each week until all fruits were gone. I weighed and measured the length and width of each fruit, separated the pulp and removed the seed kernel from the nut, weighed those two samples, then reweighed the samples after drying in a convection oven at 60° C for 72 h. I calculated percent water content and dry mass for the pulp and kernel by subtracting the dry weight from the wet weight, then plotted the weekly mean (± 1 SD) for water content and mass for the pulp and seed kernel over the whole season. To compare desert peach fruit development with fleshy-fruited

Prunus, I followed the same protocol for choke cherry (P. virginiana) (Beck Chapter 2), which I collected at Verdi (39º31’00” N, 119º58’40” W, elev.1500 m), ≈15 km west of

Reno, NV. I also calculated mean water savings per fruit (n = 12 fruits) for dry fruit compared to wet fruit by subtracting the water (g) from the dry fruit pulp (5.2% water) 12 and the seed (2.3% water) from the water from wet fruit pulp (74.9% water) and the seed

(34.5%). I then estimated water savings for an individual plant during a year of heavy fruit production by multiplying the water saved (ml) times the average number of fruits/shrub.

Ward Laboratories, Inc. (Kearney, Nebraska, USA) determined nutrient content and amygdalin concentration (cyanogenic glycosides) for desert peach fruit pulp and seed kernels individually from the combined samples of ≈ 150 fruits from 10 plants for unripe

(green fruit; 2 June 2007), semi-ripe (green-yellow fruit; 5 July 2007), and ripe fruit

(yellow-orange fruit; 22 July 2007) collected at the Park site in 2007.

I measured fruit production during June of 2001-2003 by establishing eight 10 x 10 m plots (four each at the Park and Johnson Lane sites) in patches of desert peach. I recorded the number of shrubs/plot, mapped their position, measured height, least and greatest width, and calculated the volume/shrub using the formula for an ellipsoid.

During mid-June, before nut harvest began, I counted all fruits on each shrub three times to estimate mean number of fruits per shrub, then calculated fruit production/plot by summing the estimates from all plants on the plot. I natural-log transformed the number of fruits/plot, then analyzed fruit production across years using a repeated measures mixed model ANCOVA with shrub volume/plot as a covariate, plots nested within location as random covariates, and Tukey-Kramer adjustments for multiple comparisons

(SAS Institute 2004).

Foraging and removal of nuts

From June through August of 1999-2001, I documented the nut harvest from 12 productive desert peach focal shrubs at the Park and Johnson Lane sites (24/year). I 13

marked three representative branches/shrub with numbered plastic bands, then recorded

the number of intact healthy, insect-infested (aborted or damaged but appearing viable),

and aborted fruits during weekly visits. Aborted fruit turned brown, shriveled, and fell

off the branches (Fig. 1, path 1). Healthy fruit remained firmly attached to the peduncle.

Fruits that disappeared from the branches were either harvested directly from the canopy

(path 2) or fell to the ground (path 3) during foraging.

I also placed a 10 cm deep seed trap covering 0.21 m2 in area underneath each focal

shrub in early June 1999 – 2001 to measure fruit and nut harvest from the canopy.

Wooden-framed seed traps had aluminum screening on the bottom, 12 mm mesh

hardware cloth on top, and wire mesh extending ~ 10 cm above the frame along the perimeter to prevent fruit from bouncing out. I also marked a 0.21 m2 open seedfall plot

on the opposite side of the focal shrub to determine the combined fruit and nut harvest

from the canopy and ground at each shrub. I collected seed trap and open plot contents

weekly, then sorted the material into intact fruits, insect-infested (lethal or non-lethal) and

aborted fruits, fruit husks, nuts, and shells. As an index of pre-dispersal insect infestation and nut mortality (path 1), I counted aborted, lethal insect (seed kernel eaten by larvae), and viable insect-damaged fruits (seed kernel undamaged) and nuts from traps and open plots. I used seed trap contents as an index of fruit fall (intact or viable insect-damaged fruits; path 3), harvest (fruit husks, gnawed fruit; path2), minimum eaten (empty shells; path 4), discarded (nuts, gnawed fruit), and removal (the number of fruit husks minus nuts eaten and discarded; paths 7 and 13) from the shrub canopy. I used open plot contents as a measure of the combined harvest (fruit husks, gnawed fruit), eaten (empty shells), discarded (nuts, gnawed fruit), and removed nuts (the number of fruit husks 14 minus nuts eaten and discarded) from the ground and canopy of the shrub. I also estimated total, viable, insect infested, and foraged fruits/shrub (the number of fruit husks and gnawed fruits) by combining the contents of the seed trap and open plot for each focal shrub, dividing by the area (0.42 m2), and multiplying by the total canopy area

(length x width) of the shrub. I natural-log transformed the number of fruits/plant, then analyzed fruit production across years using a mixed model repeated measures ANCOVA with plant shrub volume as a covariate, plants nested within location as random covariates, and Tukey-Kramer adjustments for multiple comparisons. A repeated measures mixed model ANOVA with year and location as fixed effects and plant as a random covariate was used to analyze differences in arcsine transformed percent insect infestation, lethal insect infestation, abortion, and total pre-dispersal mortality

(SAS Institute 2004).

I measured removal rate (path 5), eaten (path 9), and un-harvested (path 6) fruits or nuts from the ground by placing a single intact fruit or nut at each of 200 stations along a transect, spaced 10 m apart. Each station was uniquely marked with sticks, pebbles, or cones under desert peach shrubs during harvest in 1999 and 2001. I determined a baseline harvest rate by placing one intact fruit at each of 50 stations along an open transect away from shrubs in 2001. I recorded whether the fruit or nut was present, absent, or eaten (shell fragment) at transect stations daily for one week and then weekly thereafter. I analyzed removal rate with a failure rate model using interval and right censoring and a Weibull distribution in Proc Lifereg (Allison 1995; Klein and

Moeschberger 1997; SAS Institute 2004). 15

Rodent community composition

I determined rodent community composition by trapping at each site with Sherman live traps spaced 15 m apart and baited with mixed birdseed. I tagged each animal with a numbered ear tag and recorded species, gender, and mass. In 1999, I established a 5 x 5 m grid at the Park site and trapped for 2 days and nights (6-7 July), checking traps in the morning and early evening. In 2000 and 2001 I established two 5 x 10 trapping grids at the Park site and trapped for 4 days and nights (7-10 July 2000, 19-22 June 2001). I established 50 trap grids at the two Pine Nut sites and trapped for 4 days and nights (19-

22 August 1999, 24-27 August 2000, and 16-19 August 2001).

Caching behavior of rodents in field enclosures

I examined the caching of desert peach nuts by six species of rodents in behavioral trials in two 15 x 15 m rodent-proof enclosures (June-September 2000-2002) in the Pine

Nut Range (see Hollander and Vander Wall 2004 for complete details). I released an animal in the nest bucket after placing 100 nuts labeled with scandium-46, a gamma- emitting radionuclide with a half-life of 84.5 days, in a feeder in the center the enclosure.

Trials lasted up to five days. I then removed the animal from the enclosure, collected all larder-hoarded nuts and shells from the nest bucket, and surveyed for caches with a

Geiger counter. I mapped each cache location, carefully excavated the cache, measured the cache depth, and recorded the number of nuts/cache, cache substrate (mineral soil, light litter [< 5 mm thick], heavy litter [≥ 5 mm thick]), and microhabitat (open [> 10 cm from edge of shrub in the open], edge [± 10 cm from edge of shrub], under [> 10 cm from edge of canopy under shrub]). 16

Seed dispersal from source shrubs

I used radioactively-labeled desert peach nuts to determine post dispersal seed fates

by free-ranging rodents at productive desert peach shrubs (Vander Wall 1994; Vander

Wall 2002). During July – September, I placed 200 numbered, radioactively-labeled nuts

in ten piles (20 nuts/pile) under each desert peach source shrub (one source shrub in

1999, six source shrubs in 2000, and five in 2002). I deployed a Trail Master active

infrared camera (Goodson & Associates 1995-2006) at each source shrub. Once the nuts

were removed from the source shrub, I also set out Sherman live traps to learn the

identity of the foraging rodent(s), which was usually mildly radioactive from handling the

nuts. After all the nuts were taken (usually within 24 h), I surveyed with a portable

Geiger counter for caches (pathway 8, Fig. 1) and shell fragments (eaten nuts; pathway 9)

within 50 m of the source shrub. I mapped each cache location relative to the source

shrub, excavated each cache, and recorded the nut identification numbers, number of

nuts/cache, cache depth, substrate (mineral soil, light litter, or heavy litter), and

microhabitat (under shrub, edge, open), then re-cached the seeds so that the site appeared

undisturbed. I re-surveyed source shrubs at least twice that season before the first snow

to determine seed fates (paths 11-12, 16-18) and recorded whether nuts in caches were

missing (path 11), present (path 12), moved to new secondary caches (secondary, tertiary, quaternary, etc.; path 17, 18), or eaten (shells; path 16). In late April or May of the following spring I resurveyed all source shrubs and recorded cache and nut fates

(pathways 16-19, 22-25), and the fate of all seedlings (26-30) until the fall of 2004. In some cases, rodents larder hoarded seeds in burrows (path 14-15, 21-22). I recovered larders because they were too deep for seedlings to emerge. I analyzed cache distance to 17

source shrub with a general linear mixed-model, using source shrub as a random effect

and cache type (primary, secondary) as a fixed effect (Proc Mixed; SAS Institute 2004).

To characterize available cache sites I placed a 40 x 40 m grid centered on the source

shrub. At 2 m intervals (400 random points), I recorded substrate (see above) and

microhabitat (open, under shrub). I analyzed used versus available cache sites with a mixed model logistic regression (Proc Glimmix; SAS Institute 2004), with substrate and

microhabitat as fixed effects and source shrub as a random variable. I also used a mixed-

model logistic regression to analyze which cache site characteristics (cache size, cache

depth, substrate, microhabitat) affected seedling emergence in caches with and without

seedlings.

Seedling germination, emergence, and survival

I planted nuts in simulated caches in rodent-proof exclosures in the fall of 1999 –

2001 to examine cache characteristics affecting seedling emergence and survival (paths

26-30). The 46 x 46 cm exclosures were constructed of 6 mm wire mesh, extended 10

cm below and 14 cm above the soil surface, and were covered with mesh lids to exclude

large animals. At the Park site, I placed 10 pairs of exclosures (20 total) in open and

shade microhabitat (under shrubs with shade cloth on the lids to ensure equal shading) in

1999 and 2000, and 20 pairs in 2001. At the Pine Nut site I placed 10 paired exclosures in 2000 and 20 pairs in 2001. I randomly assigned one unique combination of nut size

(small nut: <200 mg, 130.2 ± 27.3, range = 46.7-195.9 mg; large nut: > 300 mg, 388.5 ±

66.4, range = 300.6 – 686.4 mg), cache size (1 or 3 nuts/cache), and depth (6 depths: 0 –

5 cm) to each of 24 caches in a 5x5 array/exclosure (one cache was unassigned). Surface

caches (0 cm) represented abiotic dispersal (path 6, 10, 25). Buried nuts simulated rodent 18

caches over a range of natural conditions. I recorded emergence in late April or early

May and then monitored seedling survival until the fall of 2004. I also planted 300 nuts,

2 cm deep in a 1 m2 exclosure to determine percent germination. I analyzed seedling

emergence using mixed-model logistic regression (Proc Glimmix SAS Institute 2004)

with nut size, cache size, depth, and microhabitat as fixed effects and plot, location, and

year as random effects. The experimental unit was the cache, which was nested within

plots within microhabitat, year, and location. I analyzed seedling survival using the

Lifereg procedure (SAS Institute 2004). Data are means ± SD and I controlled alpha =

0.05 using Monte Carlo simulations for all multiple comparisons.

I also calculated an index of recruitment (recruitment potential) by multiplying the

proportion of nuts from four seedling regeneration state categories. The product was then

multiplied by 100. The categories were: 1) nuts removed from focal plant, 2) nuts cached, 3) nuts remaining in spring caches and, 4) emergent seedlings. I used data from

focal plants for removal, source shrub data for the proportion being cached and remaining

in spring caches, and germination enclosure data for emergence.

RESULTS

Fruit development and production

Desert peach whole fruit wet mass increased to a maximum in mid-July 1999 (1106.8

± 465.0 mg, range 437-2193; n = 12), then decreased to less than half that (349.9 ± 147.4

mg; range 220-1010) as foraging concluded at the end of August (Fig. 2A). There was a corresponding decrease in pulp percent water from 79.2 ± 1.3% early in development (2

June 1999) to 5.2 ± 1.0% (25 August). This decrease in pulp water content resulted in a

water savings of 0.57 ml/fruit and 534 ml/shrub. As the nuts matured (1 July – 15 July), 19

fruit color changed from green to yellow-orange and the husk dehisced. In contrast,

choke cherry, like most fleshy-fruited Prunus, increased in both fruit wet mass (4 July =

287.4 ± 66.0 mg, range 199-455 mg; 17 September = 1000.0 ± 251.7 mg, range 421-1453

mg; n = 12) and pulp percent water (4 July = 72.3 ± 2.0, range 69-77%, 17 September =

79.5 ± 1.7, range 77-82%) as fruit color changed from green to purple (Fig. 2A).

However, contrary to the divergence in mesocarp development, the endocarp (the woody

seed coat enclosing the seed kernel) of desert peach developed similarly to that of other

species of Prunus (see chokecherry for comparison in Fig. 2B). Percent water decreased

(2 June = 91.1 ± 1.3%, 25 August = 2.3 ± 0.7%) and dry seed kernel mass increased (3.9

± 2.0 to 74.1 ± 26.6 mg, range 41-125 mg). There were changes in nutrient composition

and energy content of desert peach as well (Table 1). Although the fruit pulp appeared to

contain nutrients (primarily carbohydrates) with substantial energy content, it remained

astringent and unpalatable throughout development, and the pulp was not consumed by

vertebrate foragers (personal observation; see data below). In contrast, the energy

content of the seed kernel not only increased with seed mass as nuts ripened, but also

increased in fat content from 4% early in development (5 June) to 49.1% at maturity (22

July). Toxic amygdalin concentrations in the seed kernel decreased by half as the nut

matured, but were nearly absent in the husk (Table 1). Fruit and nut development varied

among years in association with mean spring temperatures (March – June 1998 = 17.6°

C, ripe fruit = 29 July 1998; 1999 = 20.1° C, ripe fruit = 14 July 1999; 2000 = 22.7° C,

ripe fruit = 3 July 2000).

Fruit production on the 10 x 10 m plots was significantly affected by year (F2,12 =

98.9, P < 0.0001), location (F1,5 = 8.3, P = 0.0344), and year X location interaction (F2,12 20

= 10.1, P = 0.0027), whereas shrub volume/plot (19.3 ± 8.1 m3/plot, range = 9.2–36.4

3 m /plot; n = 8 plots) was almost significant (F1,5 = 5.9, P = 0.059). Fruit production was

much greater in 2003 (636.7 ± 261.8 fruits/m3/plot, n = 8 plots) than 2001 (36.3 ± 34.0

fruits/ m3/plot; t = 11.1, P < 0.0001) or 2002 (14.2 ± 7.0 fruits/m3/plot; t = 13.0, P <

0.0001), but there was no difference between 2001 and 2002 (t = 1.9, P = 0.085). In

2001, the Pine Nut Range (64.6 ± 23.1 fruits/m3/plot) had significantly higher fruit

production than the Park site (8.0 ± 4.8 fruits/m3/plot; t = 4.6, P = 0.0058), but there was

no difference between locations in 2002 (t = 1.1 P = 0.304) and 2003 (t = 0.25, P =

0.804). Shrub volume (range = 0.007–17.4 m3/shrub; n = 90 shrubs) accounted for 30%

of the variation in fruit production (range = 0–5900 fruits/shrub) among plants (F1,268 =

253.0, P < 0.0001, Adj. R2 = 0.303), although some plants consistently produced more

fruit than others. Fruit production among plots within locations within years was similar

(F1,245 = 0.15, P = 0.99), indicating synchronous fruit crops within the Park site or Pine

Nut Range.

After accounting for shrub volume (range 0.6-22.7 m3/shrub, n = 72 focal shrubs;

F1,65 = 21.3, P < 0.0001), year was the only factor affecting focal plant nut production

(F2,65 = 9.5, P = 0.0002). There were significantly larger crops in 1999 (1183.9 ± 968.0 nuts/m3/shrub; n = 12 focal shrubs) than 2000 (679.3 ± 333.8 nuts/m3/shrub; t = 2.9, df =

65, P = 0.015) and 2001 (538.7 ± 347.2 nuts/ m3/shrub; t = 4.3, df = 65, P = 0.0002).

There was no difference in crop size between 2000 and 2001 (t = 0.8, df = 65, P = 0.72).

Foraging and removal of nuts

Based on combined seed trap and open plot contents, pre-dispersal nut mortality

(pathway 1, Fig. 1) accounted for 39.8 ± 14.2% (range = 9.9-98.4%, n = 71 focal shrubs) 21

of the total nut crop (Table 2). Insects (weevil Rhynchites velatus, Coleoptera,

Curculionidae; stinkbug Chlorochroa uhleri, C. ligata, Hemiptera: Pentatomidae) were responsible for 61.6 ± 25.4% (range = 1.5-97.9%) of pre-dispersal mortality, whereas fruit abortion (pollination failure, self-pruning, pathogens) accounted for the rest (38.4 ±

25.4%, range = 0.5-75.8%). Pre-dispersal mortality was highest in 2001 (60.9 ± 24.6%), followed by 2000 (37.8 ± 21.6%), and 1999 (33.4 ± 21.1%). Insect infestation and mortality was also much higher at the lower elevation Park site (elevation = 1600 m; insect infestation = 65.6 ± 29.7%, mortality = 51.8 ± 26.2%; n = 36 focal plants) than in the Pine Nut Range (elevation = 1920 m; insect infestation = 39.0 ± 26.4%, mortality =

36.8 ± 22.4%) (Table 2).

Vertebrate frugivores (e.g. birds, carnivores) failed to respond to changing fruit color as a foraging cue and did not feed on the fruit or fruit pulp. Nut harvesting by rodents, however, closely tracked nut development (Fig. 3). Rodents “sampled” immature nuts as they developed, but they did not intensively forage until fruit color began to change from green to yellow, the husk dehisced, seed percent water decreased to ≈ 35%, and seed mass increased to ≈ 65 mg as nuts matured (Fig. 3). Nut harvest by rodents was much higher during the very large nut crop of 1999 compared to 2000 and 2001 (Fig. 3).

During peak foraging (mid June to early August depending on year), 91.4 ± 9.1% of nuts were harvested at both locations across years, although the percent of the nut crop harvested per week was consistently higher and the duration of foraging was shorter at the Pine Nut site (30.1 ± 1.9% of the nuts/week; foraging duration = 3.0 ± 0.0 weeks) than the Park site (18.9 ± 2.9% nuts/week; duration = 4.0 ± 1.7 weeks). This was probably due in part to larger shrub size and crop size, and a greater abundance of rodents 22 in the Pine Nut Range (Table 3). Much of the individual variation among shrubs in foraging intensity and timing was due to larger crop size (F1,229 = 93.5, P < 0.0001) and an interaction indicating rodents preferred foraging at shrubs with ripe nuts (nut maturity) and larger crops (F1,183 = 61.1, P < 0.0001). The timing of foraging at the two sites was very similar, except in 2001, when peak foraging was 1-2 weeks earlier at the Park site

(18 June) than the Pine Nut Range (30 June) (Fig. 3). Foraging, which corresponded to nut development, began earliest in 2001 (warmest spring), followed by 2000 (3 July), and

1999 (15 July; coldest spring).

Based on the discarded husks in seed traps, rodents harvested 88.6 ± 2.6% (range = 0-

100%/shrub) of the viable nut crop per year from the canopy of focal shrubs (pathway 2;

Fig. 1, Table 2). The rest were knocked off or fell to the ground (pathway 3; Fig. 1). In the open seedfall plots, only 5.9 ± 4.6% were not harvested and 7.5 ± 4.0% were discarded (gnawed fruits, intact nuts) (pathway 6; Fig. 1). However, unharvested or discarded propagules were an artifact of removing the open plot contents every week, but not replacing them. Most of the viable nuts in these two categories would have been eaten or removed from underneath the shrubs by rodents. Furthermore, 67.1% of the nuts discarded by rodents suffered lethal insect damage. Therefore, of the total nuts harvested

(94.1%), rodents removed 74.7 ± 31.3% from the canopy or the ground (pathways 7, 8,

13, 14) and ate 25.3 ± 26.6% at the focal plants (pathways 4, 9; Fig. 1, Table 2). Many eaten nuts in the open plots had holes gnawed in them, indicating they were consumed by smaller rodents, such as pocket mice and deer mice. Other nuts were cracked in half by larger rodents such as sciurids and kangaroo rats. In the seed traps, in contrast, almost all eaten nuts (>99%) were cracked in half, indicating they were eaten by scansorial sciurids. 23

The shrub canopies also showed signs of foraging by these larger rodents (small branches

cracked, ripped peduncles). Antelope ground squirrels were the most commonly seen

rodents feeding in canopies, and I frequently caught them in traps placed next to burrows

beneath productive shrubs.

The percentage of nuts removed intact from the focal shrubs was always higher in the

Pine Nut Range (> 80%) than the Park site (< 60%), probably because the viable nut crop

was reduced by the greater pre-dispersal mortality at the lower elevation Park site (Table

2). For example, in 2001, after discounting the unharvested nuts, 83.8% were removed

from the Pine Nut Range focal plants, but only 11.7% were removed and 88.3% eaten by

rodents at the Park site. However, at the Park site that year, 63.3% of the total crop was

destroyed by insects, leaving little for the rodents (Table2).

Propagule removal from transect stations under shrubs was affected by propagule

type (χ2 = 6.84, df = 1, P = 0.0089), year (χ2 = 18.26, df = 1, P < 0.0001), location (χ2 =

17.34, df = 1, P < 0.0001), microhabitat (χ2 = 68.7, df = 1, P < 0.0001), and the

interactions between year and location (χ2 = 26.53, df = 1, P < 0.0001) and microhabitat

and location (χ2 = 7.26, df = 1, P = 0.007) (Fig. 4). Removal rate was 4.3 times faster in

1999 than 2001 (χ2 = 44.42, df = 1, P = 0.007). In 1999, intact fruits were removed 1.6

times more rapidly than nuts under shrubs (χ2 = 6.48, df = 1, P = 0.0109), and removal

rate was 4.2 times faster at the Johnson Lane than the Park site (χ2 = 29.78, df = 1, P <

0.0001). In 2001, there was no difference in removal rate between fruit or nuts (P =

0.1817) or locations (P = 0.6403) under shrubs, but nuts under productive shrubs at the

Park and Johnson sites were removed 58.9 times faster than nuts in open microhabitats (χ 24

2 = 68.7, df = 1, P < 0.0001) (Fig. 4). Rodents removed 91.1% (pathways 8, 14, Fig 1) of the healthy fruits or nuts, ate 4.1% (pathway 9), and failed to harvest 4.9% (pathway 6) from under shrubs. In the open, where foraging activity was less, only 34% of nuts were removed, 66% were unharvested, and none were eaten.

Rodent Community

I trapped six rodent species (Table 3). Species richness and abundance was higher in the Piñon-Juniper woodland of the Pine Nut Range than the Park site, which lacked trees.

At all locations I also observed California ground squirrels, but they were too big to fit into the traps.

Seed dispersal from source shrubs

Rodents harvested all radioactively-labeled desert peach nuts from under the 12 source shrubs within a few days. Rodents ate only 0.2% of the nuts at source shrubs. I was able to locate 84.2 ± 19.3% (range = 32.5 to 100%) of the radioactively-labeled nuts

(Table 4). For those nuts removed from source shrubs, rodents scatter hoarded 50.9 ±

43.3% (pathway 8, Fig. 1), larder hoarded 46.2 ± 44.2 % (pathway 14), and ate 2.8 ±

4.7%. Most of the nuts that I failed to find were likely carried outside the survey areas.

I identified four species of rodents (Table 4) that removed desert peach nuts from source shrubs either from Trail Master photographs (n = 4), from captured animals with residual radiation (n = 8), or from unique cache or larder characteristics (n = 2).

There was substantial variation in the way the four species handled desert peach nuts

(Table 4). Pocket mice and kangaroo rats predominantly larder hoarded nuts (pathway

14, Fig. 1) in burrows 20-50 cm deep (66.9 ± 29.3%, n = 5 and 61.4 ± 51.7%, n = 5, respectively) but scatter hoarded (pathway 7) most of the remaining nuts in shallow 25

surface caches (31.2 ± 30.7% and 37.9 ± 52.0%, respectively). In contrast, an antelope

ground squirrel scatter hoarded all of the 168 nuts that I found in 85 primary caches. Six

additional trials inside enclosures with white-tailed antelope ground squirrels confirmed

that this species only scatter hoarded nuts (Table 6). Deer mice also primarily scatter

hoarded nuts (83.8 ± 7.9% of nuts, n = 3; Table 4). Because I removed almost all nuts

placed in larders, I underestimated the number of larder hoarded nuts that eventually

would have been eaten or, perhaps, scatter hoarded.

There were differences in the characteristics of caches made by the four species of

rodents that scatter hoarded nuts at source shrubs (Table 5). Kangaroo rats and pocket

mice made relatively few, large caches. The antelope ground squirrel typically made 2-

seed caches whereas deer mice typically made 1-seed caches (see also Table 7). Deer

mice made relatively shallow caches and kangaroo rats the deepest. Kangaroo rats made

caches farthest from source shrubs and the antelope ground squirrel the closest.

Across all source shrubs, rodents placed caches non-randomly with regard to

substrate (F2,3619 = 3.81, P = 0.0223), microhabitat (F1,3619 = 3.47, P = 0.0627), and the interaction between substrate and microhabitat (F2,3619 = 4.95, P = 0.007). In

comparisons among species, antelope ground squirrels, deer mice, and kangaroo rats

were more likely to cache in the open, whereas pocket mice cached in heavy litter under

shrubs (Fig. 5). Deer mice were also more likely to cache in mineral soil or light litter

than heavy litter.

The characteristics of caches varied at different source shrubs (Table 4), largely because different rodent species were involved in caching nuts at different source shrubs.

Across all source shrubs, animals recovered 79.9 ± 17.8% of the nuts from primary 26

caches, and recached 32.7 ± 28.3% in 101 secondary, 8 tertiary, and 2 quaternary caches.

Of the 893 nuts that I found scatter hoarded around source shrubs in 433 caches, 273

(30.6%) nuts remained in 76 caches (open microhabitat = 35, edge = 20, under shrubs =

30, unknown = 1) until the time of germination the following spring (Table 4). The other

nuts (69.4%) were gone by the spring survey. Seventy-four seedlings emerged (27.1%;

pathways 22 and 24, Fig. 1) from the nuts that remained (range 1-5 seedlings/cache) in 30

spring caches (Fig. 5), but only one seedling survived into the fall (pathway 27). Sources

of seedling mortality included biotic (rodents grazed 31 seedlings and uprooted 1

seedling; pathway 26) and abiotic factors (42 desiccated; pathways 28 and 30).

Seedling germination, emergence, and survival

In the seedling emergence plots, nut size, cache size, and depth of burial all had

significant effects on the probability of seedling emergence (nut size: F1,3090 = 15.6, P =

0.008; cache size: F1,3090 = 47.2, P < 0.0001; depth: F5,3090 = 22.1 P < 0.0001; Fig. 6, 7),

but not survival. In 2001 and 2002, large nuts were 1.6 times more likely to produce emergent seedlings than small nuts at 4-5 cm deep (t = 3.05, df = 50, P = 0.0039). At 0-3

cm, there was no difference (P > 0.15). In contrast, seedling emergence in 2000 was 2.8

times more likely with small nuts than large nuts (t = 2.83, df = 192, P = 0.0051). As

would be expected, across all years three-nut caches were 2.6 times more likely to

produce at least one seedling per cache than one-nut caches (t = 6.9, df = 3090, P <

0.0001), although cache size had no effect on the percentage of seedlings that emerged

(1-nut = 27.0%, 3-nut = 26.8% , t = 0.86, df = 6198, P = 0.388). Nuts placed on the

surface, simulating abiotic dispersal, rarely germinated (7.3%) or produced a seedling

(0.78%) compared to buried nuts (85.6% germination and 42.6% emergence) at all other 27

cache depths across all years (t = 10.3, df = 3094, P < 0.0001; Fig. 7). Intact fruit (the dried mesocarp covering the nut) on the surface produced no emergent seedlings.

Therefore, burial is necessary for germination and emergence of desert peach.

Emergence from buried nuts varied across depths (1-5 cm) and by year. A greater percentage of seedlings emerged in 2000 from 2 cm (t = 2.44, df = 192, P = 0.015, odds

ratio = 4.9) and 4 cm caches (t = 2.23, df = 192, P = 0.027, odds ratio = 4.3) than from 1

cm caches. Emergence was poor in 2001 and there were no differences among caches 1-

5 cm deep. In 2002 there was significantly greater emergence from caches 2-5 cm deep

than at 1 cm deep (2 cm: odds ratio = 1.4; 3 cm: odds ratio = 2.1; 4 cm: odds ratio = 1.7,

5 cm: odds ratio = 1.4) (Fig. 7). Microhabitat only had an effect on seedling emergence

(F1,32 = 4.2, P = 0.0493) and one-year survival (F1,55 = 8.0, P = 0.0065) at the Park site in

2002, when seedlings were 1.7 times more likely to emerge (shrub: 50.4%, open: 37.0%)

and 5.8 times more likely to survive under shrubs than in the open. There was no

difference in emergence and survival under shrubs (35.8%) compared to the open

(30.6%) in the Pine Nut Range (P > 0.18; Fig. 6).

Year had a significant effect on seedling emergence (F2,79 = 33.2, P < 0.0001; Fig. 6)

and one-year survival (F2,67 = 9.5, P = 0.0002), primarily because of differences in

precipitation. The spring of 2000 followed the wettest winter (187.7 mm at Carson City,

Nevada), followed by 2002 (164.5 mm), and 2001 (83.6 mm). The winter of 2001 was

one of the driest years on record. Caches in 2002 (43.7% emergence) were 3.8 more

likely to produce emergent seedlings than in 2000 (20.0% emergence; t = 5.8, df = 100, P

< 0.0001) and 2.9 times more likely than 2001 (23.5% emergence; t = 6.8, df = 62, P <

0.0001). There was no significant difference in emergence between 2000 and 2001 (P = 28

0.57). In contrast, one year seedling survival in 2000 (37.7%) was 21.9 times more likely

than 2001 (1%; t = 3.9, df = 129, P = 0.0006) and 6.4 times more likely than 2002 (4.9%;

t = 3.6, df = 35, P = 0.0013). Seedling survival was also more likely in 2002 than in

2001, but the difference was not significant (P = 0.177). One year seedling survival was

11.4 times more likely at the Park site (8.7%) than at the Pine Nut site (0.8%; F1,192 =

20.8, P < 0.0001). Most seedling mortality occurred from desiccation during the first

summer. However, 3.3% of seedlings from the 2000, no seedlings from the 2001, and

2.4% of seedlings from the 2002 survived until the end of the study (Spring 2004).

Recruitment potential for all rodents was 3.4% and all recruitment resulted from nuts

buried by scatter-hoarding rodents (Table 8). Abiotic recruitment was negligible

(0.016%; fruit or nuts remaining on the surface). Differences in behavior among rodent

species also influenced recruitment potential. There was no difference in removal rate (≈

100%) from source shrubs among all species. However, pocket mice (31.5%) and

kangaroo rats (37.9%) were much less likely to scatter hoard than deer mice (83.8%) or

the antelope ground squirrel (100%; see also Table 6). The greater likelihood of larder

hoarding was, therefore, most responsible for the lower recruitment potential of pocket

mice (4.1%) and kangaroo rats (3.6%) compared to the antelope ground squirrel (8.9%).

Deer mice had the lowest recruitment potential (0.39%), primarily because fewer nuts

remained in spring caches (14.2% compared to > 25% for all other species) and seedling

emergence was only 3.3% from shallow deer mouse caches compared to more than 30%

for all other species (Table 8).

29

DISCUSSION

Desert peach, unlike most species of Prunus (plums, peaches, apricots, cherries), does

not have morphological adaptations (fleshy-fruit) associated with seed dispersal by endozoochorous frugivores (birds, carnivorous mammals). Although the fruit changes from green to yellow-orange during development, frugivores fail to respond to this visual

signal of ripe fruit. This is not surprising, given that the husk (the mesocarp) loses water

and remains astringent instead of becoming more succulent and sweet at maturity (Table

1). Thus, there was no fleshy-fruit to provide a reward for the seed dispersal services of

mutualist frugivores. In thousands of hours of casual observation at my study sites, I

never saw any birds consume desert peach fruits. Dry fruit, therefore, probably deters

frugivores from consuming desert peach fruits and subsequently dispersing the nuts away

from shrubs where scatter hoarding rodents forage.

Rodents appeared to be the primary (and perhaps only) vertebrate seed predators and

dispersers of desert peach nuts. They often cracked open green, immature fruits to

determine the palatability of the seeds. High concentrations of amygdalin made the

immature seed kernels bitter early in development (Table 1). Then, responding to the

change in fruit color, rodents rapidly harvested and removed almost the entire nut crop

(92.5%) within 3-5 weeks of nut maturity (Fig. 3). By the end of foraging, all nuts had been harvested and dried husks littered the ground underneath shrubs. Based on the

number of shells in seed traps and plots under focal shrubs, 25.3% of the nuts were eaten

during harvest. The much larger number of husks than shells indicated most of the nuts

were carried away intact (74.7%), to be scatter-hoarded, placed in larders, or eaten

elsewhere. Daily removal rate was 31.1 ± 11.6%/day (range = 24.1-76.0%/day; Fig. 4) 30

for nuts under desert peach shrubs compared to 2.4 ± 5.0%/day (range = 1.1-3.2%) for

nuts placed in the open, suggesting that animals preferentially foraged at profitable sites

under productive shrubs. Desert peach nuts were valued food items (range = 335.6-

1997.6 J/nut), especially in contrast to other, much smaller seeds that were available in mid-summer, including antelope bitterbrush, plateau gooseberry, and Mormon tea.

Disperser effectiveness refers to the effect a particular seed disperser has on the future reproduction of a plant (Herrera and Jordano 1981; Schupp 1993). There are two components to disperser effectiveness: the quantity of seeds dispersed and the quality of seed dispersal, including the effect the dispersal site has on seed germination and establishment. Seed traps provided a measure of the quantity component. The large quantity of husks indicated that most of the nuts were harvested and removed from the canopy by scansorial rodents (Table 2), including white-tailed antelope ground squirrels,

California ground squirrels, and least chipmunks. The rest were harvested beneath shrubs after falling to the ground or being knocked off during foraging. Of all the sciurids I observed, only white-tailed antelope ground squirrels avidly scatter hoarded desert peach nuts (Tables 4 and 5), which was consistent with the behavior of six individuals in enclosure trials that only scatter hoarded and did not larder hoard (Table 6). Although not the most abundant species at my study sites, antelope ground squirrels were the rodents I most frequently saw in shrub canopies. After establishing temporary burrows beneath productive shrubs, they often stripped the nut crop within a few days. I also observed California ground squirrels removing nuts from desert peach shrub canopies, but it is assumed that these animals only larder hoard. Hollander and Vander Wall (2004) found that least chipmunks scatter hoarded singleleaf piñon pine nuts, but only one of 31

three captive chipmunks I tested scatter hoarded a few nuts in very shallow caches.

Panamint kangaroo rats, Great Basin pocket mice, deer mice, and piñon mice (Pine Nut

Range site only) also harvested desert peach nuts, but they appeared to forage primarily

from the ground after the scansorial rodents had taken most of the crop. Kangaroo rats

are bipedal and are poor climbers. The three remaining species can climb, but desert

peach canopies generally showed signs of vigorous foraging by larger rodents (cracked

smaller branches, ragged peduncles, torn husks). More importantly, the nuts were too

hard for these smaller species to crack in half. Instead they gnawed small holes in the

shells to extract the seed kernels (personal observation). Nuts opened this way were predominantly found in the open seedfall plots, indicating they were eaten on the ground, not in the seed traps, which almost always contained only shells that were cracked in half.

Further, nuts eaten by the smaller species in the caching enclosure trials also had small holes gnawed in them. Therefore, white-tailed antelope and California ground squirrels probably accounted for most of the desert peach nut harvest and the quantity component of disperser effectiveness (Schupp 1993).

Cache site placement by animals and the attributes of those sites clearly have important consequences for seed and seedling survival and affect the quality component of disperser effectiveness (Schupp 1993). One of the potential benefits of seed dispersal is directed dispersal (Briggs et al. 2008; Howe and Smallwood 1982; Wenny 2001), the non-random dispersal of seeds to “safe” sites where the probability of seedling establishment is disproportionally high. This might be especially true in arid environments where water is limited and the difference between survival and death is often a fine scale microhabitat feature. Burial of seeds even millimeters below the 32

surface is likely to mitigate the effects of harsh abiotic conditions (desiccation,

temperature extremes, UV radiation, fire; Chambers and MacMahon 1994; Roth and

Vander Wall 2005), decrease the chances of detection by some seed predators (Briggs

and Vander Wall 2004; Wenny 1999), and substantially increase the probability of

germination (Garcia et al. 2002; Wenny 1999). For nuts placed on the surface simulating

abiotic dispersal, few germinated and emerged compared to buried nuts (Fig. 7A).

Because large nuts are unlikely to be buried abiotically (Chambers and MacMahon

1994), dispersal by scatter hoarding animals was crucial for successful recruitment of

desert peach. In accord with Hollander and Vander Wall (see table 2; 2004), antelope

ground squirrels, Panamint’s kangaroo rats, and Great Basin pocket mice buried desert

peach nuts 10-40 mm deep (Table 5, 7), from which seedling emergence was common

(Fig. 7). Seedling emergence declined for nuts buried > 40 mm deep. Deer mice, in

contrast, scatter hoarded most nuts in very shallow caches (6.0 ± 3.6 mm) from which

few seedlings emerged (3.3%), probably due to less soil moisture associated with

shallower depths (Table 4). Cache depth and its effect on emergence appeared to be the

primary reason deer mice had such low recruitment potential (Table 8).

Rodents that primarily larder hoard, such as California ground squirrels and, to a

lesser extent, Great Basin pocket mice, and Panamint’s kangaroo rats, are less effective dispersers because they store many seeds in larders where seedlings fail to emerge (Table

4). Pocket mice (31.5%) and kangaroo rats (37.9%) scatter hoarded much less than they

larder-hoarded, whereas deer mice (83.8%) primarily scatter hoarded, and antelope

ground squirrels (100%) exclusively scatter hoarded (Table 4) (see table 1 in Hollander

and Vander Wall 2004). The difference in recruitment potential (Table 8) between the 33

antelope ground squirrel (8.9%) and pocket mice (4.1%) or kangaroo rats (3.6%) was,

therefore, most likely affected by the propensity of the species to cache or larder hoard.

Both heteromyids have large external cheek pouches, which probably accounted for the

fewer large caches they made. Although antelope ground squirrels have internal cheek pouches, they (Table 5 and 7) and the deer mice (Table 5) made numerous small caches

(see Fig. 2 in Hollander and Vander Wall 2004). Rodents that make many small caches are generally more effective dispersers than species that make a few large caches because of the greater number of potential emergence sites. Furthermore, seeds placed in large caches often have lower survival because of higher detection by other foragers (Geluso

2005), greater seedling expulsion by adjacent seedlings emerging from large clumps

(Vander Wall 1994), and seedling competition (Howe 1989). However, cache size did not affect seedling survival during the course of this study. Nevertheless, over longer time scales there was evidence of attrition; most adult shrubs were alone or with one or two other mature plants (personal observation).

I found caches up to 34 m away from source shrubs, although this was probably an

underestimate because rarely I searched beyond 50 m from the source shrubs. Nuts in

primary caches were often recovered within a month of initial caching and recached

further away from source shrubs in secondary caches. Many of these nuts were

subsequently recached in tertiary and quaternary caches, suggesting a spatially and

temporally dynamic seed environment.

Although there was considerable variation in where rodents placed their caches (Fig.

5), microhabitat had little effect on seedling emergence and survival (Fig. 6). For the

most part, seedlings emerged and survived equally well in emergence plots in the open or 34

under shrubs. However, studies of other plants have shown beneficial nurse plant effects,

including lower ambient temperature in the shade (Chambers et al. 1999; Hollander and

Vander Wall 2004; Legras 2008).

Seedling survival in caches from source shrubs (1 of 74 seedlings that emerged the

previous spring survived to the following October) or emergence plots (1 year survival in

2000 = 8.2%, 2001 = 2.0%, 2002 = 5.0%; Fig. 6, 7) were low, especially in 2001, one of

the driest years on record. Regardless of year, most seedlings died from desiccation by

the end of their first summer. In addition, I rarely saw emergent seedlings at either of my

study sites. Nonetheless, such low survival is not surprising, especially in desert adapted

plants, where recruitment is often episodic or infrequent (Humphrey and Schupp 1999;

Van Rheede van Oudtshoorn and Van Rooyen 1999; Alan Muth personal communication). Nor is such low recruitment necessarily critical for persistence of desert peach, which, like many species of Prunus, reproduces vegetatively (Kiviniemi

2001) and is fairly long lived. Perhaps only during years with frequent thunderstorms through the dry season does desert peach reproduce via dispersed seeds.

This is the first study to demonstrate a reliance on scatter hoarding for seed dispersal

in any dry-fruited species of Prunus. I have documented abundant scatter hoarding of

desert almond (P. fasciculata) nuts (M. Beck and S. Vander Wall, unpublished data), one

of six species of an older North American clade of dry-fruited Prunus (Bortiri et al.

2006). Presumably other North American and Asian nut-bearing Prunus, all of which

occur in arid environments, are dispersed in a similar way, but the rodents that disperse these plants are unknown. Desert peach and closely related desert apricot (P. fremontii) form one of the two North American clades (section Penarmeniaca), which is sister to 35

fleshy-fruited Bessey's cherry (P. besseyi), indicating they are recently derived from a fleshy-fruited ancestor (Bortiri et al. 2006). The five almond clades in Asia show

evidence of allopatric speciation (Browicz and Zohary 1996) and suggest that dry fruit

arose independently numerous times, always in arid environments. There also might

have been a reversal back to succulent fruits, but the phylogenetic evidence is weak (see peach (P. persica) in section Amygdalus; Bortiri et al. 2006).

There are a number of features indicating that nut-bearing species of Prunus evolved dry fruits and large nuts in tandem with dispersal by scatter hoarding rodents. In deserts,

large seeds and nuts are thought to enable seedling emergence from greater depths and

rapid root growth (Baker 1972; Leishman and Westoby 1994; Parciak 2002). Larger

desert peach nuts buried in simulated caches at the deepest depths (4 and 5 cm) were

much more likely to produce emergent seedlings than those from smaller nuts.

Additionally, adult plants have very deep tap roots (see plate XI, Fig. 2 in Mason 1913).

Arid environments would also initially favor dry fruits not only to conserve water, but to deter frugivory, which would otherwise result in the deposition of nuts on the ground in very dry conditions, increasing the likelihood of desiccation. Furthermore, in contrast to the smooth stones of most fleshy-fruited Prunus, desert peach nuts have sharp edges that might deter ingestion by endozoochorous frugivores and hinder long-range dispersal

(antitelochory). Ellner and Shmida (1981) and others (Gutterman 1994; Murbeck 1920;

Van Rheede van Oudtshoorn and Van Rooyen 1999; Zohary 1937) have suggested that deserts favor seeds that lack devices for long-range dispersal (atelechory) or have traits

that hinder dispersal because microsites that enhance seedling establishment are rare and

dispersal is therefore not favored under these conditions. This is clearly not the case for 36

desert peach. Although dry fruits deter frugivores from dispersing the nuts away from

the parent plants where rodents forage, the nuts, unadorned with dispersal devices, supply

an energy-rich reward for scatter-hoarding animals, which provide the only avenue for

successful recruitment. As this mutualism coevolved in dry-fruited Prunus, there might

also have been additional selection for larger nuts to provide a more profitable reward for

the dispersers as well as an adaptation for establishment in arid environments (Jansen et

al. 2002; Jansen et al. 2004; Zhang et al. 2008).

In common with other dry-fruited Prunus, desert peach nuts have hard shells and

bitter seed kernels containing amygdalin, presumably for defense against pre and post-

dispersal seed predators (Browicz and Zohary 1996; Kester et al. 1991). Amygdalin

levels fall by half as desert peach nuts mature, unlike the seeds in some frugivore- dispersed species of Prunus (chokecherry; Majak et al. 1981; black cherry; Swain et al.

1992), which maintain high concentrations throughout development (Table 1). For desert

peach, this is probably not an adaptation to deter pre-dispersal insect seed parasites before

the shell hardens. High glycoside levels would no longer be necessary after the shell

hardens and becomes an effective barrier. Cherry stones also become very hard as they

mature, but amygdalin concentrations, in contrast, remain high (Beck Chapter 2; Swain

et al. 1992). A more likely explanation is that decreased amygdalin levels at nut maturity

would be less likely to deter scatter-hoarding rodents from harvesting and dispersing

nuts. A similar pattern occurs in the pulp of most fleshy-fruited species; levels of toxic

metabolites found in immature fruits often fall upon ripening (Cipollini and Levey 1997).

Whether a similar decrease in amygdalin during development occurs in the seed kernels

of other species of dry-fruited Prunus is unknown. 37

The hard shells and cyanogenic glycosides of desert peach may also influence the behavior of its rodent seed dispersers (Cristol 2001; Guimarães et al. 2003) by increasing their propensity to initially cache seeds instead of eating them (Jacobs 1992). Seeds with high handling costs (long handling time, toxins that need to be metabolized) cause animals to defer consumption and store nuts instead. Further, rodents may retrieve costly items more slowly from caches than higher value items that lack those costs, increasing the probability for those seeds to remain buried until germination and emergence. Xiao et al. (2008) supported this conclusion by showing that nuts with high tannin concentrations were recovered more slowly and had a higher probability of remaining in caches than nuts with low tannin levels (the high tannin hypothesis; Smallwood and

Peters 1986). In desert peach, these traits might deter seed predation and induce scatter- hoarding animals to cache more and retrieve less, thereby exploiting their dispersal services while lowering the cost of eaten seeds. This is especially important in a community where seed predators can choose from a variety of cached seeds. In piñon - juniper woodland, for example, the more preferred piñon pine seeds (thinner shells and lack of toxins) become available shortly after desert peach nuts have been harvested and stored. When both seed types have been cached, the lower handling costs associated with retrieving piñon seeds increases the probability that desert peach nuts will remain in caches until the following spring.

The transition from one mode of dispersal to another (from frugivory to scatter- hoarding dispersal) would appear to present a formidable evolutionary challenge. Yet such transitions are relatively common. Multiple modes of dispersal have been described in several plant taxa including pines in Benkman (1995), Fabaceae and Liliaceae in 38

Willson and Traveset (2000), and Gnetales in Hollander and Vander Wall (2009). Many of these transitions can be linked to diplochory, the presence of two or more dispersal agents in a multi-phase seed dispersal process (Vander Wall and Longland 2004). A similar transition probably occurred in dry-fruited Prunus. Initially most consumers of the stones of fleshy-fruited ancestors acted strictly as seed predators. Those animals that incidentally scatter hoarded the nuts and failed to recover them enhanced recruitment and exerted positive selection for larger seeds and the subsequent evolution of diplochory

(Vander Wall and Longland 2004). As the environment dried out or Prunus populations colonized more arid habitats, two-phased dispersal, in concert with changing abiotic selective forces, may then have provided the mechanism for the transition from fleshy- fruited ancestors that relied on diplochory (sequential two-phased dispersal, first by endozoochorous frugivores, then by scatter hoarding animals) to dispersal of nuts solely by scatter hoarding animals. Diplochory in Prunus and other fleshy-fruited taxa appears to be much more prevalent than previously recognized (Beck Chapter 2; Forget and

Milleron 1991; Vander Wall et al. 2005; Wenny 1999). Zhang and colleagues (Li and

Zhang 2007; Lu and Zhang 2004; Zhang and Wang 2001) found that wild apricot was secondarily dispersed by scatter hoarding rodents in China. I have found that phase two dispersal in western chokecherry markedly increases successful recruitment, primarily because of seed burial. Thus, the most parsimonious explanation for the transition in

Prunus from primary dispersal utilizing frugivores in fleshy-fruited species to primary dispersal by scatter hoarding rodents in dry-fruited Prunus was simply the loss of frugivory in a diplochorous ancestor, which accompanied the transformation from fleshy fruits to dry fruits and large nuts. 39

This research was conducted according to the guidelines for the use of animals published by the Animal Behavior Society and was carried out in accordance with the legal requirements of the United States of America and the University of Nevada, Reno

(IACUC Protocol no. A04/05-04).

ACKNOWLEDGEMENTS

I thank S. B. Vander Wall, S. H. Jenkins, W. S. Longland, D. W. Zeh, and T. J.

Nickles for helpful comments on an earlier draft of this manuscript. I thank Jenny

Briggs, Julie Roth, Ted Thayer, Jennifer Armstrong, Jennifer Hollander, Kellie Kuhn,

Jenny Francis, Jessica Hay, and Chris Farrar for assistance in the field. I thank G. C. J.

Fernandez, I. Aban, and D. Board for help with statistical analysis. Financial support was provided by the Program in Ecology, Evolution, and Conservation Biology and the

Graduate Student Association at the University of Nevada, Reno.

REFERENCES

Allison, P. D. 1995, Survival analysis using the SAS system: a practical guide. Cary, NC, SAS Institute, Inc. Baker, H. G. 1972. Seed weight in relation to environmental conditions in California. Ecology 53:997-1010. Beck, M. J. Chapter 2. Diplochory in western chokecherry: you can’t judge a fruit by its mesocarp, University of Nevada-Reno, Reno. Benkman, C. W. 1995. Wind dispersal capacity of pine seeds and the evolution of different seed dispersal modes in pines. Oikos 73:221-224. Bortiri, E., B. V. Heuvel, and D. Potter. 2006. Phylogenetic analysis of morphology in Prunus reveals extensive homoplasy. Plant Systematics and Evolution 259:53-71. Bortiri, E., S. H. Oh, J. G. Jiang, S. Baggett, A. Granger, C. Weeks, M. Buckingham et al. 2001. Phylogeny and systematics of Prunus (Rosaceae) as determined by sequence analysis of ITS and the chloroplast trnL-trnF spacer DNA. Systematic Botany 26:797-807. 40

Briggs, J., S. B. Vander Wall, and S. H. Jenkins. 2008. Forest rodents provide directed dispersal of Jeffrey pine seeds. Ecology. Briggs, J. S., and S. B. Vander Wall. 2004. Substrate type affects caching and pilferage of pine seeds by chipmunks. Behavioral Ecology 15:666-672. Browicz, K., and D. Zohary. 1996. The genus Amygdalus L (Rosaceae): species relationships, distribution and evolution under domestication. Genetic Resources and Crop Evolution 43:229-247. Chambers, J. C., and J. A. MacMahon. 1994. A day in the life of a seed: movements and fates of seeds and their implications for natural and managed systems. Annual Review of Ecology and Systematics 25:263-292. Chambers, J. C., S. B. Vander Wall, and E. W. Schupp. 1999. Seed and seedling ecology of piñon and juniper species in the pygmy woodlands of western North America. Botanical Review 65:1-38. Cipollini, M. L., and D. J. Levey. 1997. Secondary metabolites of fleshy vertebrate- dispersed fruits: adaptive hypotheses and implications for seed dispersal. American Naturalist 150:346-372. Cristol, D. A. 2001. American crows cache less preferred walnuts. Animal Behaviour 62:331-336. Ellner, S. P., and A. Shmida. 1981. Why are adaptations for long range seed dispersal rare in desert plants. Oecologia 51:133-144. Forget, P. M., and T. Milleron. 1991. Evidence for secondary seed dispersal by rodents in Panama. Oecologia 87:596-599. Garcia, D., M. J. Banuelos, and G. Houle. 2002. Differential effects of acorn burial and litter cover on Quercus rubra recruitment at the limit of its range in eastern North America. Canadian Journal of Botany-Revue Canadienne De Botanique 80:1115- 1120. Geluso, K. 2005. Benefits of small-sized caches for scatter-hoarding rodents: influence of cache size, depth, and soil moisture. Journal of Mammalogy 86:1186-1192. Goodson & Associates. 1995-2006. Trail Master active infrared camera. Lenexa, Kansas, USA. Guimarães, P. R., J. Jose, M. Galetti, and J. R. Trigo. 2003. Quinolizidine alkaloids in Ormosia arborea seeds inhibit predation but not hoarding by agoutis (Dasyprocta leporina). Journal of Chemical Ecology 29:1065-1072. Gutterman, Y. 1994. Strategies of seed dispersal and germination in plants inhabiting deserts. Botanical Review 60:373-425. Herrera, C. M., and P. Jordano. 1981. Prunus mahaleb and birds: the high efficiency seed dispersal system of a temperate fruiting tree. Ecological Monographs 51:203-218. Hollander, J. L., and S. B. Vander Wall. 2004. Effectiveness of six species of rodents as dispersers of singleleaf piñon pine (Pinus monophylla). Oecologia 138:57-65. Hollander, J. L., and S. B. V. Wall. 2009. Dispersal syndromes in North American Ephedra. International Journal of Plant Sciences 170:323-330. Howe, H. F. 1989. Scatter dispersal and clump dispersal and seedling demography: hypothesis and implications. Oecologia 79:417-426. Howe, H. F., and J. Smallwood. 1982. Ecology of seed dispersal. Annual Review of Ecology and Systematics 13:201-228. 41

Humphrey, L. D., and E. W. Schupp. 1999. Temporal patterns of seedling emergence and early survival of Great Basin perennial plant species. Great Basin Naturalist 59:35-49. Jacobs, L. F. 1992. The effect of handling time on the decision to cache by gray squirrels. Animal Behaviour 43:522-524. Jansen, P. A., M. Bartholomeus, F. Bongers, J. A. Elzinga, J. Den Ouden, and S. E. Van Wieren. 2002. The role of seed size in dispersal by a scatterhoarding rodent, Pages 209-225 in D. Levey, W. R. Silva, and M. Galetti, eds. Seed dispersal and frugivory: ecology, evolution and conservation. New York, CABI. Jansen, P. A., F. Bongers, and L. Hemerik. 2004. Seed mass and mast seeding enhance dispersal by a neotropical scatter-hoarding rodent. Ecological Monographs 74:569-589. Jordano, P. 2000. Fruits and frugivory in M. Fenner, ed. Seeds: the Ecology of Regeneration in Plant Communities. Wallingford, UK, C.A.B. International. Kester, D. E., T. M. Gradziel, and C. Grasselly. 1991. Almonds (Prunus). Acta Horticulturae 290:701-758. Kiviniemi, K. 2001. Evolution of recruitment features in plants: a comparative study of species in the Rosaceae. Oikos 94:250-262. Klein, J. P., and M. L. Moeschberger. 1997, Survival analysis: techniques for censored and truncated data. New York, Springer-Verlag. Lee, S., and J. Wen. 2001. A phylogenetic analysis of Prunus and the Amygdaloideae (Rosaceae) using ITS sequences of nuclear ribosomal DNA. American Journal of Botany 88:150-160. Legras, E. 2008. Microhabitat is critical for sugar pine seedling emergence and survival in xeric Jeffrey pine dominated forest, University of Nevada-Reno, Reno. Leishman, M. R., and M. Westoby. 1994. The role of seed size in seedling establishment in dry soil-conditions: experimental evidence from semiarid species. Journal of Ecology 82:249-258. Li, H. J., and Z. B. Zhang. 2007. Effects of mast seeding and rodent abundance on seed predation and dispersal by rodents in Prunus armeniaca (Rosaceae). Forest Ecology and Management 242:511-517. Lu, J. Q., and Z. B. Zhang. 2004. Effects of habitat and season on removal and hoarding of seeds of wild apricot (Prunus armeniaca) by small rodents. Acta Oecologica- International Journal of Ecology 26:247-254. Majak, W., R. E. McDiarmid, and J. W. Hall. 1981. The cyanide potential of Saskatoon serviceberry (Amelanchier alnifolia) and chokecherry (Prunus virginiana). Canadian Journal of Animal Science 61:681-686. Mason, S. C. 1913. The pubescent-fruited species of Prunus of the southwestern states. Journal of Agricultural Research 1:147-186. Murbeck, S. V. 1920. Beitrage zur biologie der wustenpflanzen: die synaptospermie. Lunds University Arsskr 17:1-52. Parciak, W. 2002. Seed size, number, and habitat of a fleshy-fruited plant: consequences for seedling establishment. Ecology 83:794-808. Roth, J. K., and S. B. Vander Wall. 2005. Primary and secondary seed dispersal of bush chinquapin (Fagaceae) by scatterhoarding rodents. Ecology 86:2428-2439. 42

SAS Institute. 2004.SAS proprietary software release, version 9.1, version 9.1.SAS Institute, Inc., Cary, NC. Schupp, E. W. 1993. Quantity, quality and the effectiveness of seed dispersal by animals. Vegetatio 108:15-29. Smallwood, P. D., and W. D. Peters. 1986. Gray squirrel food preferences: the effects of tannin and fat concentration. Ecology 67:168-174. Swain, E., C. P. Li, and J. E. Poulton. 1992. Development of the potential for cyanogenesis in maturing black-cherry (Prunus-Serotina Ehrh) fruits. Plant Physiology 98:1423-1428. Van Rheede van Oudtshoorn, K., and M. W. Van Rooyen. 1999, Dispersal biology of desert plants Adaptations of desert organisms, 1430-9432. Berlin, Springer- Verlag. Vander Wall, S. B. 1994. Seed fate pathways of antelope bitterbrush: dispersal by seed- caching yellow pine chipmunks. Ecology 75:1911-1926. —. 2001. The evolutionary ecology of nut dispersal. Botanical Review 67:74-117. —. 2002. Masting in animal-dispersed pines facilitates seed dispersal. Ecology 83:3508- 3516. Vander Wall, S. B., K. M. Kuhn, and J. R. Gworek. 2005. Two-phase seed dispersal: linking the effects of frugivorous birds and seed-caching rodents. Oecologia 145:282-287. Vander Wall, S. B., and W. S. Longland. 2004. Diplochory: are two seed dispersers better than one? Trends in Ecology & Evolution 19:155-161. Watkins, R. 1995. Cherry, plum, peach, apricot and almond, Pages 423-428 in J. S. a. N. W. Simmonds, ed. Evolution of Crop Plants. London, Longman. Wenny, D. G. 1999. Two-stage dispersal of Guarea glabra and G. kunthiana (Meliaceae) in Monteverde, Costa Rica. Journal of Tropical Ecology 15:481-496. —. 2001. Advantages of seed dispersal: a re-evaluation of directed dispersal. Evolutionary Ecology Research 3:51-74. Wilken, D. H. 1993. Prunus, Pages 969-970 in J. C. Hickman, ed. The Jepson manual: higher plants of California. Berkeley, CA, University of California Press. Willson, M. F., and A. Traveset. 2000. The ecology of seed dispersal, Pages 85-110 in M. Fenner, ed. Seeds: the ecology of regeneration in plant communities. Wallingford, UK, C.A.B. International. Xiao, Z. S., G. Chang, and Z. B. Zhang. 2008. Testing the high-tannin hypothesis with scatter-hoarding rodents: experimental and field evidence. Animal Behaviour 75:1235-1241. Zhang, H. M., Y. Chen, and Z. B. Zhang. 2008. Differences of dispersal fitness of large and small acorns of Liaodong oak (Quercus liaotungensis) before and after seed caching by small rodents in a warm temperate forest, China. Forest Ecology and Management 255:1243-1250. Zhang, Z. B., and F. S. Wang. 2001. Effect of rodents on seed dispersal and survival of wild apricot. Acta Ecologica Sinica 21:839-845. Zohary, M. 1937. Die verbreitungsokologischen verhaltnisse der pflanzen Palaestinas Beih. Bot. Centralbl. 56:1-155.

43

TABLES

TABLE 1. Nutrient analyses and cyanogenic glycoside (amygdalin) content of desert peach fruit pulp and seed kernels during development. NFE: Nitrogen free extract (carbohydrates).

Date Fruit maturity Dry mass (mg) Energy Energy Protein NFE Fat Amygdalin (fruit color) content content (%) (%) (%) content (KJ/g) (J/fruit) (ppm HCN) Pulp 2 Jun Unripe (green) 134.2 ± 24.3 7.9 1064 10.8 78.3 0.7 1 5 Jul Pre-ripe (yellow green) 202.4 ± 53.3 7.9 1601 6.2 81.9 1.0 12 22 Jul Ripe (yellow orange) 200.0 ± 104.9 7.8 1562 4.5 81.2 1.4 1

Seed kernel 2 Jun Unripe (watery kernels) 13.4 ± 1.9 7.6 101 39.5 37.2 4.0 4947† 5 Jul Pre-ripe (filled kernels) 62.4 ± 17.4 14.1 878 29.4 14.7 49.1 3100† 22 Jul Ripe (filled kernels) 73.2 ± 29.6 14.0 1029 30.5 13.4 49.1 2448† † Denotes toxic concentration of HCN in Rattus rattus 44

TABLE 2. Fate of desert peach fruits and nuts from 72 focal shrubs (12shrubs/year at each site†) at the Park and Pine Nut Range sites during the summers of 1999 – 2001. Park site Pine Nut Range sites ______

Seed traps Seedfall plots Seed traps Seedfall plots ______Fates Year Mean ± SD % Mean ± SD % Mean ± SD % Mean ± SD % Pre-dispersal mortality 1999 84.5 ± 58.1 32.3 57.3 ± 57.8 34.2 91.5 ± 78.4 28.8 48.0 ± 45.6 24.4 2000 56.8 ± 32.5 45.6 58.2 ± 33.2 47.8 46.5 ± 26.1 28.4 31.8 ± 22.7 21.7 2001 74.1 ± 51.3 65.0 66.0 ± 47.8 61.4 51.5 ± 26.8 45.1 56.0 ± 25.9 40.5 Fruit fall 1999 22.3 ± 23.1 12.9 6.6 ± 9.6 5.8 19.0 ± 15.4 8.6 4.5 ± 7.9 2.9 2000 9.5 ± 5.6 13.3 8.8 ± 8.0 14.9 12.0 ± 14.7 10.2 3.9 ± 5.0 3.4 2001 5.5 ± 6.3 14.6 2.4 ± 2.8 5.4 5.5 ± 5.4 8.8 2.5 ± 3.8 3.9 Nuts eaten 1999 15.8 ± 8.4 9.1 24.2 ± 32.6 21.2 16.2 ± 13.3 7.4 19.5 ± 24.8 12.7 2000 5.2 ± 8.6 8.2 7.0 ± 7.1 11.9 7.6 ± 6.7 6.5 8.1 ± 11.2 7.0 2001 27.6 ± 44.7 73.4 33.1 ± 56.0 74.3 4.2 ± 2.9 6.7 13.6 ± 16.1 15.7 Fruits/nuts discarded 1999 19.1 ± 13.4 11.0 11.3 ± 15.7 9.9 5.9 ± 6.8 2.7 6.4 ± 11.2 4.2 2000 1.9 ± 1.8 2.7 5.5 ± 6.9 9.4 2.1 ± 2.9 1.8 1.0 ± 2.0 0.9 2001 1.2 ± 1.2 3.1 4.1 ± 5.6 9. 2 4.0 ± 6.8 6.4 7.0 ± 7.7 8.1 Nuts removed‡ 1999 116.5 ± 99.9 67.0 72.1 ± 101.9 63.1 179.4 ± 126.6 81.3 122.8 ± 127.8 80.1 2000 54.8 ± 55.7 76.8 37.5 ± 33.2 63.8 95.5 ± 62.0 81.5 101.7 ± 72.0 88.7 2001 3.3 ± 4.4 8.9 4.9 ± 6.7 11.1 48.5 ± 57.2 78.0 63.7 ± 72.8 73.3 Notes. Percentages for all sources of pre-dispersal mortality were calculated from total contents of seed traps and plots, whereas all other categories were based on viable propagules (what was left after pre-dispersal mortality was removed). † Seed trap data were incomplete from one focal shrub at the Park site in 1999 and the Pine Nut site in 2001, and were excluded from the calculations. ‡ The number of dried fruit husks minus the number eaten and the number discarded. 45

Table 3. Number of individual rodents captured at four trapping grids in August of 1999- 2001. All grids had 50 traps open 4 days (200 trap days), except in 1999 at Park east, which had 25 traps open for 2 days (50 trap days). Park west was not trapped in 1999. California ground squirrels (Spermophilus beecheyi) were observed but were too large to enter traps. Trapping grids ______Park Park Pine Johnson Species Year east west nut lane White-tailed antelope ground squirrel 1999 0 0 2 Ammospermophilus leucurus 2000 5 1 0 1 2001 0 0 0 3 Least chipmunk 1999 0 13 0 Tamius minimus 2000 0 0 1 1 2001 0 0 0 1 Deer mouse 1999 7 23 24 Peromyscus maniculatus 2000 1 1 0 0 2001 0 0 3 4 Piñon mouse 1999 0 0 8 Peromyscus truei 2000 0 0 0 0 2001 0 0 0 0 Great Basin pocket mouse 1999 5 16 8 Perognathus parvus 2000 5 1 3 3 2001 3 4 12 11 Panamint’s kangaroo rat 1999 0 6 5 Dipodomys panamintinus 2000 3 2 0 4 2001 1 4 3 9

46

Table 4. Fates of 200 radioactively labeled desert peach nuts deployed under 12 source shrubs during 1999, 2001-2002. Percentages for nuts accounted for are based on the number of nuts harvested. Percentages for scatter hoarded, larder hoarded, and eaten are based on the number of nuts accounted for. Percentage of nuts in spring caches is based on the number of nuts cached. Percentage of seedlings is based on the number of nuts in spring caches. At source shrub DP99-1, both captured animals had residual radiation. At source shrub DP02-5, both animals were photographed. Source Rodent species† Nuts Scatter Larder Eaten‡ Nuts in No. of Shrub accounted for Hoarded hoarded spring caches seedlings ______# % # % # % # % # % # % 1999-1 Panamint kangaroo rat 72 36.0 0 0.0 71 98.6 1 1.4 0 0.0 0 0.0 Deer Mouse 66 33.0 59 89.4 0 0.0 7 10.6 3 2.2 0 0.0 2001-1 Panamint kangaroo rat 200 100.0 0 0.0 197 98.5 3 1.5 0 0.0 0 0.0 2001-2 Panamint kangaroo rat 175 87.5 158 90.3 17 9.7 0 0.0 70 40.0 5 7.1 2001-3 Great Basin pocket mouse 196 98.0 142 72.4 54 27.6 0 0.0 85 43.3 34 40.0 2001-4 Great Basin pocket mouse 196 99.5 0 0.0 189 96.4 7 3.6 0 0.0 0 0.0 2001-5 Great Basin pocket mouse 197 98.5 5 2.5 187 94.9 5 2.5 5 2.5 1 20.0 2001-6 Panamint kangaroo rat 135 67.5 134 99.3 0 0.0 1 0.7 9 6.7 6 66.7 2002-1 Deer Mouse 165 82.5 129 78.2 10 6.1 26 15.8 30 18.2 2 6.7 2002-2 Great Basin pocket mouse 183 91.5 61 33.3 116 63.4 6 3.3 18 9.8 5 27.8 2002-3 Great Basin pocket mouse 65 32.5 31 47.7 34 52.3 0 0.0 11 16.9 3 4.6 2002-4 Antelope ground squirrel 168 84.0 168 100.0 0 0.0 0 0.0 39 23.2 15 38.5 2002-5 Panamint kangaroo rat 192 96.0 0 0.0 192 100.0 0 0.0 0 0.0 0 0.0 Deer mouse 6 3.0 6 100.0 0 0.0 0 0.0 3 1.5 3 100.0 † Identity based on Trail Master photographs, captured animals at source shrubs with residual radiation, or unique caching characteristics of known animals from enclosure studies. ‡ Includes only nuts initially eaten at the source shrubs or found during the first survey. Actual number eaten (including from recovered caches) is higher. 47

Table 5. Cache characteristics of four rodent species at 8 source shrubs during 1999, 2001-2002. Rodent species† n Cache type‡ No. of caches Nuts/cache Cache depth (mm) Cache distance (m) ______Mean ± SD Mean ± SD Range Mean ± SD Range Mean ± SD Max. Antelope ground squirrel 1 Total 118 1.8 ± 1.4 1-9 17.2 ± 12.3 0-45 4.6 ± 3.2 19.0 Primary 85 2.0 ± 1.6 1-9 17.6 ± 13.0 0-45 3.9 ± 3.0 10.4 Secondary 33 1.4 ± 0.8 1-5 16.2 ± 10.3 0-40 6.2 ± 3.3 19.0 Panamint kangaroo rat 2 Total 22.0 ± 5.7 8.3 ± 4.6 1-20 25.3 ± 11.1 5-67 22.7 ± 8.8 34.5 Primary 14.5 ± 0.7 9.2 ± 4.6 1-20 27.5 ± 12.9 5-67 21.6 ± 9.7 34.5 Secondary 7.5 ± 6.4 5.3 ± 2.6 2-11 17.7 ± 6.0 8-28 25.7 ± 4.6 30.8 Great Basin pocket mice 3 Total 23.3 ± 9.2 4.2 ± 2.8 1-10 13.5 ± 4.5 0-45 16.5 ± 6.6 33.6 Primary 14.7 ± 10.0 5.3 ± 3.0 1-10 10.8 ± 5.8 0-45 14.0 ± 5.1 33.6 Secondary 8.0 ± 2.5 2.9 ± 2.0 1-8 14.6 ± 3.5 2-30 19.7 ± 5.1 33.4 Deer mice 2 Total 98.5 ± 41.7 1.1 ± 0.3 1-4 6.0 ± 3.7 0-40 10.6 ± 7.2 30.8 Primary 79.0 ± 28.3 1.2 ± 0.3 1-4 6.0 ± 3.6 0-26 9.2 ± 6.7 30.8 Secondary 19.0 ± 12.7 1.0 ± 0.2 1-3 6.7 ± 5.4 0-40 17.0 ± 7.5 27.4 † Identity based on Trail Master photographs, captured animals at source shrubs with residual radiation, or unique caching characteristics of known animals from enclosure studies. ‡ Primary caches were made from nuts harvested under source shrubs. Secondary caches (including tertiary, quaternary) were made from nuts that were recovered from primary caches and recached, either by the original scatter hoarding animal or a different animal. 48

Table 6. The fates of 100 desert peach nuts in caching trials by six rodent species in 15 x 15 m rodent enclosures at the Pine Nut site. Rodent species n Nut fates ______Harvested Scatter Larder Eaten Misc.† hoarded hoarded ______

Mean ± SD Mean ± SD Mean ± SD Mean ± SD Mean ± SD Antelope ground squirrel 8 75.8 ± 32.4 31.2 ± 34.2 0.0 ± 0.0 38.0 ± 40.5 6.5 ± 6.1 Least chipmunk 2 7.0 ± 5.7 5.5 ± 7.8 0.0 ± 0.0 1.0 ± 1.4 0.5 ± 0.7 Deer mouse 4 44.8 ± 14.0 4.5 ± 2.5 16.8 ± 21.6 22.5 ± 9.0 1.0 ± 1.4 Piñon mouse 3 33.0 ± 3.6 18.3 ± 2.1 1.7 ± 2.9 10.7 ± 9.3 2.3 ± 1.5 Great Basin pocket mouse 5 75.4 ± 29.6 3.4 ± 3.4 47.4 ± 30.4 15.8 ± 9.4 8.8 ± 11.6 Panamint’s kangaroo rat 9 72.4 ± 35.5 33.8 ± 40.4 24.9 ± 24.2 10.7 ± 3.1 ± 3.5 12.8 † Miscellaneous fates include nuts we could not find, including nuts small shell fragments that were eaten 49

Table 7. The caching characteristics of six species of rodents in caching trials in 15 x 15 m rodent enclosures at the Pine Nut site. Rodent species n Cache characteristics ______No. of Nuts/cache Cache depth caches ______Mean ± SD Mean ± SD Range Mean ± SD Range Antelope ground squirrel 6 26.2 ± 15.3 1.4 ± 0.5 1–5 13.9 ± 6.9 2–45 Least chipmunk 1 10.0 1.1 ± 0.3 1–2 1.7 ± 2.5 0–7 Deer mouse 3 4.0 ± 2.1 1.1 ± 0.1 1–2 2.3 ± 3.9 0–11 Piñon mouse 3 16.6 ± 0.6 1.1 ± 0.1 1–2 4.6 ± 1.2 0–14 Great Basin pocket mouse 3 3.0 ± 1.0 2.3 ± 1.7 1–7 4.6 ± 2.2 0–10 Panamint’s kangaroo rat 4 8.5 ± 3.3 9.9 ± 3.0 1–19 20.2 ± 4.6 5–44 50

TABLE 8. Recruitment potentials for four species of rodent, all rodents combined and for abiotic dispersal. Recruitment potentials were calculated as the product of four states (proportions) in the seedling regeneration process by 100. Dispersal category Seedling regeneration states Recruitment ______potential (%) Initial Cached‡ Spring Emergence§ deposition† cache‡ Abiotic dispersal 0.04 0.004 0.016 All rodents 0.784 0.443 0.306 0.321 3.403 Antelope ground squirrel 1.0 1.0 0.232 0.385 8.929 Great Basin pocket mouse 1.0 0.312 0.416 0.317 4.114 Panamint kangaroo rat 1.0 0.379 0.255 0.369 3.569 Deer mouse 0.983 0.838 0.142 0.033 0.389 † For abiotic dispersal, the initial deposition state value was from removal transects and refers to the propagules landing on the soil and not being removed by animals. The proportion removed for all rodents was derived from focal plant open plot data. The proportion removed for individual species was the proportion removed from source shrubs. ‡ Values from source shrub data. § Emergence data for abiotic dispersal and all rodents combined are from the seedling emergence study. Emergence data for individual species are from source shrub data. 51

FIGURES

Figure 1. Seed fate pathway diagram of desert peach (Prunus andersonii).

Figure 2. Fruit development in desert peach (dry-fruited) and chokecherry (fleshy-

fruited) from weekly sampling (mean ± 1 SD; 1 fruit/plant; n = 12 plants) during the

summer of 1999. (A) Percent water of fruit pulp (closed squares are desert peach; open squares are chokecherry) and whole fruit mass (closed diamonds are desert peach; open diamonds are chokecherry). (B) Percent water of seed kernel (closed squares are desert peach; open squares are chokecherry), and dry seed kernel mass (mg) (closed diamonds are desert peach; open diamonds are chokecherry). The duration of fruit development was from 16 June – 25 August for desert peach and 4 July – 17 September 1999 for chokecherry. The primary (on left) and secondary (on right) y-axis are percent water and mass, respectively.

Figure 3. The timing of desert peach nut harvest from seed trap and open plot contents at

the Park (closed diamonds = mean number of foraged nuts; n = 12 source shrubs/year)

and Johnson Lane sites (open diamonds = mean number of foraged nuts; n = 12/year)

during 1999 – 2001 in relation to energy content (closed triangles are joules/nut). The

primary y-axis (on left) is the number of nuts foraged and the secondary y-axis (on right)

is energy content in joules/nut (see Table 1).

Figure 4. Removal rate of desert peach fruit (filled black) and nuts (unfilled) by rodents

from stations along transects during the summer of 1999 and 2001 at the Park (squares) 52

and Johnson Lane sites (diamonds). Removal rate was faster in 1999 than 2001. In

1999, intact fruits were removed more quickly than nuts under shrubs, and removal rate

was faster at the Pine Nut than the Park site. In 2001, there was no difference between

fruit or nuts or sites under shrubs, but fruit placed along transects in open microhabitats

(filled gray) at the Park and Pine Nut sites were removed very slowly compared to

propagules under shrubs.

Figure 5. Cache (A) microsite and (B) substrate use by four species of rodents at eight

source shrubs. Data are means + SD. Sample sizes are in parentheses in the legend.

Microsites: Open = in the open > 10 cm from canopy edge, Edge = ± 10 cm of canopy edge, Shrub = under shrub > 10 cm from canopy edge. Substrate: Mineral soil = no litter,

Light litter < 5 mm thick, Heavy Litter ≥ 5 mm thick.

Figure 6. Seedling emergence (A) and one-year survival (B) from simulated caches

planted at the Park and Pine Nut sites for 3 years in response three treatments; 1) nut size

[small (< 200 mg) or large nuts (> 300 mg)], 2) cache size (one or three nuts/cache), and

3) microhabitat (in the open or under shrubs). For all years, I randomly assigned one

treatment combination per cache in all exclosures (e.g. nut size, cache size, depth (see

Fig. 7); n = 24 caches/ exclosures). I placed an equal number of exclosures in the open or

under shrubs (covered with shade cloth). For 2000, I only planted exclosures at the Park

site, and the under shrub exclosures contained only caches with one large or small nut on

the surface or buried 2 cm deep. Seedling emergence is based on the number of nuts 53

planted that year for that category. Seedling survival is based on the number of seedlings that emerged that year for that category.

Figure 7. Seedling emergence (A) and one-year survival (B) from simulated caches

planted at the Park and Pine Nut sites for 3 years in response to six depths (0-5 cm).

Surface caches (0 cm) represent abiotic dispersal. For all years, I randomly assigned one

treatment combination per cache in all exclosures (nut size, cache size, depth (see Fig. 6);

n = 24 caches/enclosure). I placed an equal number of exclosures in the open or under

shrubs (covered with shade cloth). For 2000, I only planted exclosures at the Park site,

and the under shrub exclosures contained only caches with one large or small nut on the surface or buried 2 cm deep. Seedling emergence is based on the number of nuts planted that year for that category. Seedling survival is based on the number of seedlings that emerged that year for that category. 54

Desert peach fruit on shrubs

1 2 3

Nut harvest from shrubs Fruit fall Pre-dispersal mortality

4 5 6

Eaten Ground harvest Not harvested

7 89 10

Scatter hoarded Eaten Die

11 12

Seeds recovered Seeds not recovered

13 14 15 16 17 18 19 20

Larder hoarded Eaten Recached Die

21 22 23 24 25

Die Eaten Germination and emergence

2627 28

Biotic mortality Seedling establishment Abiotic mortality

29 30

Growth and maturation Seedling attrition Figure 1. 55

100 1400 A 1200 80 1000

60 800

40 600

Percent water Percent 400

20 (mg) mass Whole fruit 200

0 0 0 1428425670

100 180 B 80 150

120 60 90 40 60 Percent water Percent 20 30 Seed kernel(mg) mass

0 0 01428425670 Days

Figure 2 56 180 1200 1999

150 1000 t

s 120 800

90 600

Number of nut of Number 60 400

30 200 (joules/nu Energy content

0 0 17-Jun 1-Jul 15-Jul 29-Jul 12-Aug 100 1200 2000

1000 t 80

s 800 60 600 40

Number of nut of Number 400

20 (joules/nu content Energy 200

0 0 12-Jun 26-Jun 10-Jul 24-Jul 7-Aug 100 1200 2001

1000 t 80

s 800 60 600 40

Number of nut of Number 400

20 200 (joules/nu content Energy

0 0 4-Jun 18-Jun 2-Jul 16-Jul 30-Jul Date

Figure 3. 57

100 1999

10

1 Propagules remaining Propagules

0.1 0714

100 2001

10

1 Propagules remaining Propagules

0.1 071421 Days

Figure 4. 58

80 A Antelope ground squirrel (1) Deer mouse (2) 60 Panamint's kangaroo rat (2) Great Basin pocket mouse (3)

40

20 Percentage of caches of Percentage

0 Open Edge Shrub

80 B

60

40

20 Percentage of caches of Percentage

0 Mineral soil Light litter Heavy litter

Figure 5. 59

2000 80 A 2001 2002 60

40

20 Seedling emergence (%) Seedling emergence 0 Small Large 1 nut 3 nuts Open Shrub

80 B )

60

40

20 Seedling survival (%) (%) Seedling survival

0 Small Large 1 nut 3 nuts Open Shrub Nut size Cache size Microsite

Figure 6. 60

80 A 2000 2001 60 2002

40

20 Seedling emergence (%) Seedling emergence 0 012345

80 B )

60

40

20 Seedling survival (%) (%) survival Seedling

0 012345 Depth (cm)

Figure 7. 61

Chapter 2.

Diplochory in western chokecherry: you can’t judge a fruit by its mesocarp

Maurie J. Beck

Program in Ecology, Evolution and Conservation Biology; University of Nevada, Reno

62

Diplochory in western chokecherry: you can’t judge a fruit by its mesocarp

Maurie J. Beck

ABSTRACT

Western chokecherry (Prunus virginiana var. demissa, Rosaceae) is diplochorous, and relies on phase I seed dispersal by endozoochorous frugivores and phase II dispersal by scatter-hoarding rodents. Here, I quantify the benefits provided by each phase of seed dispersal for this plant. Between August and September, avian frugivores (mostly

American robins, Turdus migratorius, and cedar waxwings, Bombycilla cedrorum)

consumed and dispersed most of the fruit crop (87%) onto the soil surface, primarily

throughout the riparian corridor. Mammalian carnivores also ate the fruit and provided

some primary dispersal. During phase II dispersal, animals removed 89% of fruits and

seeds from transects in riparian areas and 58% from upland habitats. Rodents scatter-

hoarded 91.6% of the seeds they found, burying most in small caches (2-8 seeds), 8–25

mm deep. Only 3.8% of seeds placed on the soil surface, simulating primary dispersal by

avian frugivores, produced emergent seedlings. In contrast, 52.1% of seeds buried in

simulated rodent caches produced seedlings, 29.7% of which were still alive after 1 year.

Two benefits commonly associated with frugivory are escape from distance-

dependent mortality (seed predation, pathogens) near the parent plant and colonization of

new habitats. Endozoochorous frugivores dispersed 67% of the cherry seeds they

harvested away from chokecherry focal plants. Rodents removed seeds and fruit that fell

beneath the plant canopy, and then cached seeds in widely scattered sites, further

reducing mortality near the parent plant. More importantly, rodents buried seeds, which 63

significantly improved seedling emergence and provided directed dispersal to microsites that disproportionately enhanced recruitment, a crucial benefit often associated with seed dispersal by scatter-hoarding animals. Combining different mechanisms of seed dispersal

during sequential dispersal phases significantly enhanced chokecherry seedling

recruitment by providing more dispersal-related benefits than either frugivory of scatter- hoarding could provide alone.

Key words: food hoarding; frugivory; germination; mutualism; Prunus virginiana var.

demissa; seed-caching rodents; seed dispersal; seed fate pathways; seed predation;

seedling establishment; western choke cherry 64

INTRODUCTION

Diplochory is a multi-step seed dispersal process that utilizes different dispersal

agents during sequential dispersal phases (Borchert 2006; Longland et al. 2001; Seiwa et al. 2002; Vander Wall and Longland 2004). Different modes of seed dispersal between one phase and another may provide very different benefits. For example, frugivory or wind during phase I dispersal may carry seeds away from distance-dependent mortality near the parent plant (Packer and Clay 2000) and/or provide long-distance colonization of unoccupied habitat (Fragoso 1997; Thornton et al. 1996). Subsequently, during phase II dispersal, seeds may move to their ultimate destination via another mechanism (seed- caching rodents, ants, dung beetles). Different benefits, such as directed dispersal to sites where the probability of establishment is disproportionately high, are often provided by the new agent of secondary dispersal compared to the benefits of primary dispersal

(Briggs et al. 2009; Howe and Smallwood 1982; Wenny 2001).

Diplochory has rarely been documented in nature, perhaps because dispersal devices

(winged-seeds, fleshy-fruits) define most seed dispersal syndromes and researchers have failed to appreciate the possibility of subsequent seed movements. For example, studies of frugivore-mediated seed dispersal seldom consider seeds taken from feces by rodents

as anything more than seed predation (Hulme and Hunt 1999; Moles et al. 2003; Whelan

et al. 1991). A detailed seed fate study however, may instead reveal a more complex

seed dispersal process, involving phase I dispersal by vertebrate frugivores, followed by

phase II dispersal by scatter hoarding rodents (Forget and Milleron 1991; Vander Wall

and Longland 2004; Wenny 1999). 65

Prunus is a large genus (> 200 species) in the family Rosaceae that is distributed

worldwide, primarily in the temperate regions of Eurasia and North America. About

85% of species produce fleshy fruits (cherries, plums, apricots, peaches), which are

considered ancestral in Prunus, suggesting a long reliance on frugivory for primary

dispersal (Bortiri et al. 2006). For example, Herrera and Jordano (1981) documented the

dispersal of St. Lucie cherry (P. mahaleb) in Spain by avian frugivores during their fall

migration. Most previous studies of seed dispersal in fleshy-fruited Prunus have reported post-dispersal seed predation by scatter hoarding rodents (Holl and Lulow 1997; Hulme

1997; Kollmann et al. 1998; LoGiudice and Ostfeld 2002; Osunkoya 1994), but few studies have actually followed seed fates and demonstrated seed predation or secondary dispersal by rodents (Li and Zhang 2007; Vander Wall et al. 2005b; Zhang and Wang

2001).

In the riparian areas of western North America, chokecherry (P. virginiana var. demissa), like P. mahaleb in Spain, produces large crops of small, succulent drupes during the fall that correspond to a classic bird-dispersal syndrome. Other studies of chokecherry have generally assumed that rodents act strictly as seed predators and provide no seed dispersal services (Parciak 2002b; Webb and Willson 1985). By following seed fates from fruit production through harvest and dispersal to germination and establishment (Fig. 1), I document diplochory in western chokecherry and quantify the seed dispersal benefits provided by phase I and phase II dispersal. I demonstrate that rodents are not only post-dispersal seed predators, but provide secondary, directed dispersal to sites that enhance seed survival and plant fitness, a benefit which is different from the dispersal benefits provided by frugivorous birds. I also discuss the evolution of 66 diplochory and its implications for the evolutionary transition from one mode of primary dispersal to a different mode within Prunus.

METHODS

Study area and species

I conducted parts of this study in four riparian drainages with thickets of western chokecherry in northwestern Nevada during the summers of 1999 – 2004. At all sites, riparian vegetation included willow (Salix spp.), aspen (Populus tremuloides), and mountain rose (Rosa woodsii). Great Basin Desert shrubs, including big sagebrush

(Artemesia tridentata), rubber rabbitbrush (Chrysothamnus nauseosus), and antelope bitterbrush (Purshia tridentata), were the dominant upland vegetation. The Verdi site

(39º31’00”N, 119º58’40”W Elev.1500 m) in Verdi, NV, was a disturbed residential area overlooking the Truckee River, with larger chokecherry. The Cliff Ranch site

(39º15’23”N, 119º50’30”W Elev.1600 m) was in Washoe Valley, NV at the base of the

Carson Range. Purdy Creek (39º37’15”N, 120º02’10”W, elev. 1840 m) and Ball’s

Ranch (39º39’27”N, 120º03’15”W Elev.1854) were 5 km west of Bordertown, NV in

Sierra County, California. The latter three sites were in narrow riparian corridors with a pine (Pinus jeffreyi, P. ponderosa) overstory, and steep upland slopes. I changed locations to Cliff Ranch in 2000 because of human disturbance and the lack of a chokecherry crop in Verdi that year. At Cliff Ranch there was no chokecherry crop in

2001, so I changed locations to Purdy Creek for the rest of the study. Most precipitation fell from November to April.

67

Fruit development and crop size

To document fruit development, I selected 10 focal plants in 1998 and 12 focal plants

in 1999 in Verdi, placed 6 mm mesh hardware cloth baskets around fruit for protection from animal foragers, and then picked one undamaged fruit/plant/week from July –

September until all fruits were harvested. In the lab I weighed and measured (length, width) each fruit, separated the pulp and removed the seed kernel from the cherry stone, weighed each of those samples, dried them in a convection oven at 60° C for 72 h, and then reweighed the sample. I calculated percent water content and mass for the pulp and seed samples by subtracting the dry weight from the wet weight, and then plotted the weekly mean (± 1 SD) for pulp and seed percent water and dry mass over the whole season. Nutrient content and amygdalin concentration for chokecherry fruit pulp and seed kernels were determined by Ward Laboratories, Inc. (Kearney, Nebraska, USA) from the combined samples of ≈ 500 fruits from 10 plants for unripe (green cherries; 22

July 2007) and ripe (purple cherries; 10 August 2007) fruit collected at Purdy Creek in

2007.

I calculated fruit production on twelve arbitrarily selected focal shrubs at the Cliff

Ranch in 2000 and Purdy Creek in 2001. I estimated fruit production by counting the

number of racemes for each focal shrub three times, averaging those counts, and then

multiplying the average number of racemes/plant by the average number of fruits/raceme

(n = 10 racemes/plant).

Foraging on chokecherry

I assessed avian species richness and abundance by scan sampling at fruiting

chokecherry plants during random times of the day. Scan samples were 1 – 5 minutes, 68

depending on bird abundance and only included counts at plants where at least one bird

was present. I recorded bird counts at 7 plants per day during twelve days from 24

August – 23 September 1999 in Verdi. In 2001, I sampled 7 plants/day over five days at both Verdi (12 August – 10 September) and Purdy Creek (20 August - 16 September). I

developed an index of abundance for each species by averaging the number of

individuals per scan (1 scan/plant) times the proportion of scans that that species was

present each day, then averaged over the number of days sampled. I used mixed model repeated measures (Proc Mixed in SAS Institute 2004, version 9.1) to analyze avian frugivore abundance with natural log-transformed number of birds as the response variable, the number of fruit and fruit color as fixed effects, location-year as a random effect, and plant within date as the repeated measure.

I monitored fruit harvest, fruit fall, and pre-dispersal fruit mortality from July through

October on twelve focal chokecherry plants at Verdi in 1999, Cliff Ranch in 2000, and

Purdy Creek in 2001. I selected three branches/plant, marked each with a numbered plastic band, then during weekly visits, I recorded the number of aborted, fungus-infested

(Fig. 1; pathway 1a), insect-infested (pathway 1b; Fig. 1), and intact fruit on the marked branches of focal shrubs. Cherries that disappeared from the branches were either harvested by animals directly from the focal shrub (pathway 2; Fig. 1) or had fallen to the ground (pathway 3; Fig. 1). I also placed a 10 cm deep seed trap covering 0.21 m2 in area underneath each focal plant to monitor the harvest and fall of fruits and cherry stones.

Seed traps consisted of a wooden frame with aluminum screening on the bottom, 12 mm mesh hardware cloth on top, and wire mesh perimeter extending ~ 10 cm above the frame to prevent fruits from bouncing out. I also marked a 0.21 m2 open plot on the opposite 69

side of the focal plant to determine total fruit and nut harvest from the ground. I collected

seed trap and open plot contents weekly, sorting the material and calculating fruit

abortion (including fungal infected; pathway 1 in part), lethal insect infestation (pathway

1 in part), total mortality (abortion and insect lethal; path 1), fruit fall (intact and nonlethal insect damaged fruits; path 3), clean stones defecated or regurgitated by endozoochorous birds (pathway 5 in part, Fig. 1), stones pecked or depulped by pulp

consuming birds (pathway 5 in part), and minimum eaten from the canopy (empty shells

from traps; pathway 4) and the ground (difference between shells on open plots and traps;

pathway 11).

I used the formulas below to calculate the number of fruits eaten by avian pulp

consumers, endozoochorous birds, seeds available for secondary dispersal by scatter

hoarding rodents, and depredated seeds (shells), then determined percentages by dividing

each of these categories by the fruit crop (see above) for each focal shrub (see Parciak

2002a).

1) avian pulp consumers = D/a

2) endozoochorous birds = N – (F + D + P)/a

3) propagules available for secondary dispersal = N – P/a

4) depredated seeds = P/a where N is the number of fruits per plant, D is number of pecked or depulped fruit in seed traps, P is the number of shells in traps, F is the number of fallen fruits in traps, and a is

the proportion of the surface area of the canopy sampled (i.e. ¼ pi x length x width). 70

I collected chokecherry fruit from non focal plants in 1999 and 2001, fed them to

captive American robins, and recovered the regurgitated or defecated cherry stones for

use in removal rate and emergence studies (see below).

Seed removal transects

As a measure of harvest rate from the ground (Fig. 1; pathways 7, 8), I used intact

chokecherries, representing fallen or dropped fruit from plants, and bird-processed

stones, representing seeds defecated or regurgitated by birds, at stations every 10 m along

transects in upland habitat away from the riparian zone and under chokecherry plants

along the riparian corridor. I deployed transects in each habitat at Verdi on 25 October

1999 (100 stations), Cliff Ranch beginning 15 October 2000 (80 stations), and Purdy creek on 3 September 2001 (100 stations). A single chokecherry or cherry stone was

placed at each of the stations, uniquely marked with sticks, pebbles, or pine cones, along

a wandering transect in the riparian or upland habitat (Vander Wall 1994a). I checked transects daily for one week and then weekly thereafter, recording whether the fruit or stone was present, absent, or eaten (shell fragment). I analyzed removal rate with survival analysis using interval and right censoring and a Weibull distribution (Allison

1995; Klein and Moeschberger 1997; Proc Lifereg in SAS Institute 2004).

Rodent community composition

At Purdy Creek, I assessed rodent community composition by establishing two, 5 x

10 trapping grids with 50 Sherman live traps spaced 12 m apart, one grid in riparian habitat and the other in upland Jeffrey pine forest. From 20-23 September 2001, I deployed traps baited with sunflower seeds, checked them twice daily for four days and 71

four nights, tagged each animal with a numbered ear tag and recorded species, gender,

and mass.

Caching behavior of rodents in field enclosures

I examined the caching of chokecherry stones by four species of rodents in behavioral

trials in five 10 x 10 m rodent-proof enclosures (June-November 2000-2002) in the

Whittell Forest and Wildlife Area (Little Valley), in the Carson Range ≈30 km south of

Reno, NV (39º 15´ 10" N, 119º 52´ 35" W, elev. 1975 m). I placed 50 chokecherry stones labeled with scandium-46, a gamma-emitting radionuclide with a half-life of 84.5

days (see Vander Wall 1994b for methods) in the enclosure feeder, then released an

animal in a nest bucket. Because some rodents responded so poorly to chokecherry seeds

as a food source, trials lasted for up to five days.

Secondary dispersal by rodents

To determine post dispersal seed fates, I placed 20 radioactively labeled chokecherry

stones (see above) in each of ten piles under three widely spaced source plants in October

2002. I deployed a Trail Master infrared active camera (Goodson & Associates 1995-

2006) at each source plant and trapped after all seeds were gone to learn the identity of

the foraging rodent. Rodents remained mildly radioactive for a day after handling

chokecherry stones. After all the seeds were taken (usually within 24 h), I surveyed out

50 m from the source shrub with a portable Geiger counter to locate caches (path 10) and

shell fragments (path 11). I mapped cache locations relative to the source shrub, carefully excavated each cache, and recorded the number of seeds/cache, cache depth, substrate (mineral soil, light litter (<5mm thick), heavy litter (>5 mm thick), distance from edge and center of the nearest shrub, and percent tree cover, then re-cached the 72 seeds so that the site appeared undisturbed. I resurveyed source shrubs twice before the first snow to determine seed fates (pathways 13-14, 17-19; Fig. 1) and recorded whether caches were missing (pathway 13), present (pathway 14), redistributed into new secondary caches (pathways 18, 19), or eaten (e.g. shells; path 17). The following spring

I resurveyed all source shrubs, recording cache fates (pathways 17-20, 23, 25-26), and the fate of all seedlings (pathways 29-32) until the fall of 2004. I analyzed caches with seedlings versus caches without seedlings using a mixed model logistic regression (Proc

Glimmix in SAS Institute 2004), with number of nuts/cache, cache depth, substrate (soil, light litter <5 mm thick, heavy litter ≥ 5 mm thick), and microsite (under shrub cover, under tree cover, or in direct sunlight in the open) as fixed effects. I used the same variables to analyze seedling survival (Allison 1995; Proc Lifereg in SAS Institute 2004), except I substituted number of seedlings/cache instead of nuts/cache. To compare rodent cache sites to available cache sites I placed a 40 x 40 m grid centered on the source plant, then recorded substrate and microsite at 2 m intervals. I used mixed model logistic regression (Proc Glimmix in SAS Institute 2004) to determine whether rodents placed cache locations non-randomly.

Seedling emergence and survival

I planted chokecherry fruit and stones in simulated caches in rodent-proof exclosures to examine the importance of abiotic dispersal (pathways 12, 27), primary avian dispersal

(pathways 6, 24), and secondary dispersal by rodents (pathways 20, 26) on seedling emergence and survival (pathways 28-32; Fig. 1). The 30 x 30 cm exclosures were constructed of 6 mm wire mesh, extended 10 cm below and 14 cm above the soil surface, and covered with mesh lids to exclude animals. At the Ball Ranch site, I placed 81 cages 73

in riparian microhabitat in December 1999, and 41 cages each in riparian and upland habitat in November 2001. I used a 2 x 3 factorial design of depth (0, 2 cm deep) and propagule type (intact chokecherries, bird-processed stones, hand-processed stones) planted in a 2 x 3 array within exclosures. Intact fruit on the surface represented abiotic dispersal (pathways 12, 27). I also included buried fruit to balance the design. Bird- processed cherry stones placed on the surface simulated primary dispersal by avian frugivores (pathways 6, 24). Hand-processed stones were a control to test whether gut

passage through frugivores affected seedling emergence and survival. Buried stones

simulated secondary dispersal by rodents (pathways 20, 26). I recorded emergence the

following spring and then monitored seedling survival until the spring of 2004. The three

levels of propagule treatment (intact cherries, bird-processed cherry stones, hand-

processed stones) not only tested the gut passage hypothesis (Janzen 1983; Traveset

1998; Traveset et al. 2001), which predicts that passage through a vertebrate digestive

tract will affect germination patterns (often positively; Traveset 1998), but permitted me

to differentiate between the mechanical/chemical effects of gut passage (bird-processed

vs. hand-processed) from germination inhibition caused by the biochemical effects of

pulp secondary compounds (intact fruit vs. hand-processed) on germination (Samuels and

Levey 2005). I used mixed-model logistic regression (Proc Glimmix in SAS Institute

2004) to analyze seedling emergence and survival analysis (Allison 1995; Proc Lifereg in

SAS Institute 2004) to analyze seedling survival, with microhabitat, depth, and propagule

type as fixed effects, and exclosure nested within year as random effects.

74

Recruitment potential

I determined the recruitment potential in under chokecherry plants and in upland

habitat away from plants for each of the following dispersal categories: 1) intact fruit on

the surface, 2) bird-processed seeds on the surface simulating dispersal by an endozoochorous bird, and 3) bird-processed seeds cached by a rodent. To calculate the recruitment potential for each dispersal category, I took the product of the proportions of

1) intact fruit that fell from plants or stones dispersed by frugivores, 2) seeds removed by seed-caching rodents or remaining in place following initial deposition for intact fruit or

bird processed stones, 3) seeds cached (only for scatter-hoarding rodents), 3) seeds

remaining in spring caches (only for scatter-hoarding rodents) and, 4) seedling

emergence. I then multiplied the product by 100. I used data from focal plants for the

initial deposition category, removal transects for the removal category, source plant data

for the proportion being cached and remaining in spring caches, and germination

enclosure data for emergence. Data for initial deposition of bird-processed seeds in

upland habitat away from focal plants was from Fig. 7 in Parciak (2002a).

RESULTS

Fruit development and crop size

Over the course of development, chokecherry whole fruit wet mass increased from

287.4 ± 66.0 mg (range 194-457 mg, n = 12) in June to 863.6 ± 149.6 mg (range 421-

1453 mg) in September. Although there was considerable individual variation among

plants, chokecherries matured (fruit color turned from green to purple) from late July

through early September. Maturation corresponded to an increase in pulp percent water

(unripe = 72.3% ± 2.0; ripe = 79.5 ± 1.7%), a decrease in seed percent water (unripe = 75

85.8 ± 2.4%; ripe = 29.9 ± 1.5%), and an increase in seed dry mass (unripe = 6.6 ± 1.9

mg; ripe = 44.5 ± 9.6 mg). Nutrient content of the pulp and seed kernel also increased,

both in relative (KJ/g) and absolute terms (J/fruit) (Table 1). The cyanogenic glycoside

amygdalin decreased in concentration as the fruit pulp ripened, but this toxin remained

high in the mature seed kernels (Table 1). At maturity, the peduncle and fruit remained

firmly attached to the plant, common to many species that rely on canopy-feeding

frugivores.

Chokecherry fruit crop varied greatly over the course of this study. Qualitatively,

there were very large crops at Verdi in 1999 and Purdy Creek in 2001, but only

moderately small crops at Cliff Ranch in 2000 and Purdy Creek in 2002. I changed

locations to Cliff Ranch in 2000 because there was no fruit crop at Verdi (in addition to

being a residential area) and to Purdy Creek in 2001 because there was no fruit crop at

Cliff Ranch. Analysis of quantitative data showed that year/location (F1,21 = 18.12, P =

0.0004) and plant volume (F1,21 = 62.66, P < 0.0001) were significant in explaining crop size. There was a significantly larger fruit crop at Purdy Creek in 2001 (297.4 ± 78.6 fruits/m3 of foliage, range 179.2-444.4 fruits/m3, n = 12 focal plants) than at Cliff Ranch

in 2000 (49.3 ± 7.3 fruits/m3 of foliage, range 31.3-59.0 fruits/m3; t = 4.26, df = 21, P =

0.0004).

Foraging on chokecherry

Based on seed trap and seedfall plot contents, pre-dispersal seed mortality (pathway

1, Fig. 1) by insects, fungal pathogens, and fruit abortion accounted for 35.6 ± 21.0%

(range = 8.2-84.0%/shrub, n = 32 focal shrubs) of the total fruit crop. Pre-dispersal 76

mortality was highest in 1999 (47.4 ± 20.4%, n = 12), followed by 2001 (37.4 ± 15.6%, n

= 12), and 2000 (22.7 ± 18.3%, n = 8).

I recorded 22 total species of birds foraging on chokecherry (Table 2), including17

species at Verdi in 1999, 14 species at Verdi in 2001, and 15 species at Purdy Creek in

2001. By far the most common frugivorous birds were American robins (Turdus

migratorius) and cedar waxwings (Bombycilla cedrorum), which ingested whole cherries

and subsequently defecated or regurgitated the stones, often away from plants. These

avian endozoochores accounted for 85.3 ± 6.4% of the birds recorded during scan

sampling, whereas sparrows, finches, and other pulp consumers, which pecked or

depulped the fruit before dropping the seeds under the plant, accounted for 14.7 ± 6.4%.

Frugivores began removing fruit in late July to mid August, which coincided with the

ripening fruit crop (Fig. 2). However, once fruit had ripened, there was also substantial

variation in foraging among focal plants. Depending on when chokecherries matured and

the size of the crop, foraging began sometime in August and ended between early

September at Cliff Ranch in 2000 when there was a small crop, and late October at Verdi

in 1999 when there was a very large crop (Fig. 2). Fruit maturity (based on color) (F3,83 =

22.2, P < 0.0001), crop size (F3,71.5 = 21.8, P < 0.0001), and the interaction between maturity and crop size (F6,85 = 4.4, P = 0.0007) significantly affected frugivore foraging

abundance. Birds were more abundant at plants with ripe (14.4 ± 27.3 birds) than unripe

fruit (0.04 ± 0.37 birds; t = 7.89, df = 51, P < 0.0001) and large (21.0 ± 32.0 birds) than

small crops (4.8 ± 9.5 birds; t = 4.48, df = 55, P = 0.0032).

Based on the total viable fruit crop, endozoochorous birds consumed 79.7 ± 6.7 % of

the seed crop, defecated or regurgitated 13.1 ± 8.6% of the seeds under plant canopies, 77 while dispersing the rest (66.7 ± 15.3%) away from focal plants (Table 3; pathway 5 in part, Fig. 1). Pulp consumers dropped 7.0 ± 2.0% under canopies, seed predators such as scansorial rodents and grosbeaks ate 5.4 ± 3.7% (pathway 4, Fig. 1), and 8.0 ± 5.0% of intact cherries fell to the ground (pathway 3). I also found cherry stones in the scat of black bears (Ursus americanus), coyotes (Canis latrans), and raccoons (Procyon lotor), indicating that mammalian carnivores also dispersed chokecherry. Aside from loss to canopy seed predators, 94.6 ± 3.7% of the crop (fruit and seeds) fell to ground and was available to rodents for secondary dispersal.

I occasionally observed scansorial chipmunks and golden-mantled ground squirrels eating or removing cherries from the plant canopy. I also found many dried fruit pulp fragments in the seed traps and open plots, indicating that rodents often stripped the pulp from the stones before eating the seeds under the plant (pathway 11), or removing the stones to be scatter hoarded (pathway 10), larder hoarded (pathway 15), or eaten elsewhere (pathways 17 and 21). Most of the stones were probably carried away from focal plants instead of eaten on site (see removal transects and source shrub data below for reliable estimates).

Seed removal transects

Intact fruits were removed 3.6 times faster than stones from transect stations under chokecherry shrubs (χ2 = 62.2, df = 1, P < 0.0001) (Fig. 3; pathway 8, Fig. 1), probably because cherries were consumed by ground foraging frugivores (such as quail and carnivores) in addition to being removed by rodents. Cherry stones were removed 10.8 times faster in riparian habitat under plants where seed rain was higher than in open upland habitat (χ2 = 70.8, df = 1, P < 0.0001) (Fig. 3; pathway 5, Fig. 1). Animals 78

removed 88.9% of the intact fruit and stones from riparian areas (intact fruit = 98.6%,

stones = 79.3%) and 57.9% from upland habitat (fruit = 71.4%, stones = 44.3%) during

the study. By the onset of winter two months later, however, all of the propagules would

probably have been taken from the ground. Only 3.2% of the stones (shells from both

fruit and stones) were eaten at the stations (pathway 11, Fig. 1). The effect of site was significant (χ2 = 26.8, df = 2, P < 0.0001). Propagule removal at Verdi in 1999 was 2.9

times slower than at Cliff Ranch in 2000 and 1.9 times slower than at Purdy Creek in

2001, but there was no difference in removal rate between the latter two sites/years (Fig.

3).

Rodent community composition

At Purdy Creek, most rodents were yellow pine chipmunks (Tamias amoenus) and

deer mice (Peromyscus maniculatus) (Table 4). I also caught bushy-tailed wood rats

(Neotoma cinerea), long-eared chipmunks (Tamias quadrimaculatus), and golden- mantled ground squirrels (Spermophilus lateralis). California ground squirrels

(Spermophilus beecheyi) were present but were too large to be trapped by my methods. I

did not trap at Cliff Ranch or Verdi. However, Cliff Ranch and Purdy Creek both had

narrow riparian zones with a pine overstory and probably shared a similar complement of

rodents. In contrast, Verdi was a residential area with few trees and I only saw California

ground squirrels. I also found chokecherry shells that were either cracked in half or had

small holes gnawed in one end, indicating they were eaten by ground squirrels or deer

mice, respectively.

79

Secondary dispersal by rodents

During enclosure caching trials at the Little Valley site, deer mice, golden-mantled

ground squirrels, yellow pine chipmunks, and long-eared chipmunks harvested only

24.3% of the stones after 5 days even though no other food was available. However,

there was no chokecherry in Little Valley and rodents were presumably unfamiliar with

chokecherry stones as a food source. Harvest rates for the four species ranged from 0.3%

for yellow pine chipmunks to 68.9% for deer mice and more seeds were eaten (16.6%)

than scatter hoarded (3.3%).

At Purdy Creek, which had chokecherry all along the riparian corridor, rodents

harvested all radioactively labeled cherry stones from under the three source plants.

Rodents scatter hoarded 91.6% (Table 5; pathway 10, Fig. 1), larder-hoarded 7.6%, and initially ate 0.8% (pathway 11, Fig. 1) of the seeds harvested at source plants. I was able to locate from 46 to 100% of the stones that were removed from source plants (Table 5).

However, at plant 3, an unreachable burrow under a boulder probably contained most of the 37 stones that were unaccounted for, since there was a moderately strong signal from the Geiger counter (pathway 15, Fig. 1). I failed to locate 18.5% of the cherry stones taken from source plants, most of which were either carried outside the survey areas or buried in winter larders deep underground. Across all 3 source plants, rodents subsequently recovered 365 (81.5%) of the stones in primary caches (pathway 13, Fig. 1), then ate 31 (6.9%; pathway 17, Fig. 1) or re-cached 56 stones (12.5%; pathway 18, Fig.

1) in 25 secondary caches (including subsequent recovery and recaching).

From Trail Master photographs and captured animals with traces of residual radiation,

I identified yellow pine and long-eared chipmunks that initially removed chokecherry 80

stones from source plants. However, it was likely that more than one animal (including

other species) might have harvested radioactively-labeled seeds or pilfered them from the caches of other individuals and re-cached them. For example, after most of the seeds were removed from source plant 1 by two long-eared chipmunks, on the third day, a yellow-pine chipmunk and a Douglass squirrel (Tamias douglassii) were photographed

harvesting the remaining seeds over the next few days.

The caching dynamics varied substantially among source plants (Table 5). At plants

1 and 3, the cherry stones were removed gradually over 6 days, 90.5% were buried in

primary caches (pathway 10, Fig. 1), and by mid November rodents had recovered

(pathways 13 and 19, Fig. 1) and eaten ≈ 11% (pathway 17) and transported 86.3% of the

seeds outside the study area or into winter larders (pathway 16). No caches remained at

source plant 1 and only eight seeds in six shallow caches (4.0 ± 7.3 mm deep) were still

present at source plant 3 the following spring. None produced emergent seedlings (Table

5; pathways 20 and 23, Fig. 1). In contrast, a yellow pine chipmunk removed all seeds

from source plant 2 within 1 day and scatter hoarded 197 stones in 36 primary caches

(pathway 10, Fig. 1; Fig. 4). After the first week, rodents had recovered 70 seeds from 13

primary caches (36.1%; pathway 13, Fig. 1) and recached 24 seeds in 10 secondary

caches (pathway 18). By the last survey before winter, three seeds had been eaten

(pathway 17) and 136 seeds (69.0%) in 19 primary (pathway 14) and 19 secondary

caches (pathway 18) were still present. The following spring (2003), 104 seeds (52.8%)

in 14 primary (pathway 14) and 19 secondary caches (Fig. 4) remained unrecovered.

Caching characteristics also varied among the source plants (Table 6). At source

plant 2, rodents made 36 primary and 23 secondary caches, most of which were small 81

(3.9 ± 3.3 seeds/cache, range 1-16 seeds). In contrast, there were fewer, larger caches at

source plant 1 and source plant 3 (Table 6)). For all source plants, cache depths ranged

from 0 to 60 mm (mean = 11.3 ± 9.7 mm). Secondary caches were further from source

plants (23.6 ± 11.8 m, range 1.0-35.7 m) than primary caches (18.6 ± 12.6 m, range 2.1-

41.4 m), but this was not significant.

Rodents placed 62.2 ± 1.9% of caches in soil (Table 7); the rest were placed in litter

or the soil/litter interface (37.3%). Most caches (66.7 ± 15.5%) were in the open, 15.4 ±

5.3% were at the edge of shrubs, and 18.0 ± 13.9% were under shrubs. Because of the

presence of a forest overstory in the Purdy Creek riparian zone, 54.9 ± 32.0% of caches

were in the shade. Across all source shrubs, rodents used substrate (F2,1010 = 2.97, P =

0.052) and overstory (F1,1010 = 12.94, P = 0.0003) non-randomly and understory

randomly (P = 0.82) (Table 7). Rodents were 2.4 times more likely to cache in soil than

heavy litter (t = 2.34, df = 1010, P = 0.186), 2.8 times more likely in shade than in direct sunlight (t = 3.60, df = 1010, P = 0.005), and 6 times more likely in soil in the shade than

in light litter (t = 3.22, df = 1010, P = 0.017) or heavy litter (t = 2.93, df = 1010, P =

0.043) in the open (Table 7). Substrate use for source plant 1 was nonrandom (F2,343 =

6.87, P = 0.001), overstory use for plants 1 (F2,343 = 5.23, P = 0.023) and 2 (F2,383 = 5.71,

P = 0.017) were nonrandom, and combined substrate-overstory categories for plant 2

(F2,383 = 2.74, P = 0.066) were also used nonrandomly (Table 7).

Thirty-five seedlings (33.7%; 29 from primary caches, pathway 26; 6 from secondary

caches, pathway 25) emerged from 48.5% (11 primary, 5 secondary) of the unrecovered

caches at source plant 2 (Fig. 4). Nine additional seeds germinated (pathways 20 and 23).

Burial depth did not differ between caches with and without seedlings (P = 0.308), but 82

seedlings were 6.6 times more likely to emerge from caches in mineral soil (12 caches,

75%; 30 seedlings, 85.7%) than in litter (4 caches, 25%; 5 seedlings, 14.3%; t = 2.96, df

= 23, P = 0.007) and 3.1 times more likely to emerge from caches under tree cover (11

caches, 68.7%; 24 seedlings, 68.6%) than in direct sunlight (5 caches, 31.3%; 11

seedlings, 31.4%; t = 1.99, df = 11, P = 0.07).

Substrate (χ2 = 24.7, df = 2, P < 0.0001), tree cover (χ2 = 21.9, df = 1, P < 0.0001), the interaction between substrate and tree cover (χ2 = 12.4, df = 2, P = 0.0021), and

seedling density (χ2 = 47.3, df = 4, P < 0.0001) all affected seedling survival. There was

no difference in seedling survival between mineral soil and light litter (P = 0.69), but

seedlings survived ≈ 9 times longer in soil or light litter than in heavy litter (P < 0.0001).

Seedlings also survived 11.5 times longer in shade than in direct sunlight (χ2 = 30.2, df =

1, P < 0.0001) and 5.1 times longer in small clumps (1-2 seedlings) than in large clumps

(3-5 seedlings; χ2 = 42.2, df = 1, P < 0.0001). Of the 35 emergent seedlings, 3 seedlings

(8.6%) in 2 caches survived until the end of the study (fall 2004; pathway 29, Fig. 1).

Five seedlings were killed by foraging rodents (pathway 28), 19 from desiccation

(pathway 30), and 8 from unknown causes.

Seedling emergence and survival

In the emergence enclosure studies, fruit type (whole fruit vs. stone; F2,896 = 4.56, P =

0.01), depth (surface vs. buried; F1,896 = 101.28, P < 0.0001), and the interaction between fruit type and depth (F1,898 = 5.59, P = 0.0039) significantly affected chokecherry

seedling germination and emergence, but year did not (F1,139.6 = 2.66, P = 0.1052) (Fig.

5). I found no difference in emergence between bird (28%) and hand-processed cherry stones (25.9%; F1,599 = 0.26, P = 0.62), so I pooled the data. There was no difference in 83

emergence between cherry stones on the surface (primary avian dispersal; emergence =

3.0%; pathway 24, Fig. 1) or intact fruit on the surface (fruit fall; emergence = 3.4%; t =

0.20, df = 898, P = 0.9987; pathway 27). However, buried chokecherry stones

(secondary dispersal by rodents = 52.1%; pathways 25 and 26, Fig. 1) were more than 30 times more likely to produce seedlings than stones or fruit on the surface (P < 0.0001;

Fig. 5), indicating burial by rodents enhanced germination and emergence. In 2001, there was higher emergence in riparian (20.3%) than upland habitat (15.7%), but the difference was not significant (t = 1.35, df = 69, P = 0.1812, odds ratio = 1.6 times more likely in riparian).

Removal of the fruit pulp from the seed or digestion by robins enhanced germination, supporting the gut passage hypothesis. Hand-processed stones (48.7%) were 6.3 times more likely to germinate than intact cherries (14.1%; t = 6.28, df = 452, P < 0.0001), but

there was no difference between hand or bird-processed cherry stones (50.3%; t = 0.57,

df = 452, P = 0.83) (Fig. 5), indicating that there was no additional effect of digestion on

germination beyond the removal of the fruit pulp from the seed by the digestive tract.

Because the propagules were buried 2 cm deep in mineral soil and deprived of sunlight, there was more support for the hypothesis that alkaloids in the pulp inhibited germination via biochemical pathways rather than for the hypothesis that the pulp blocked or otherwise physically affected light regime.

As evidence of delayed germination, 26 of 189 (13.8%) seedlings emerged the second

(23 seedlings) or third spring (3 seedlings; Fig. 5) after planting. Fruit type (F2,119 =

18.79, P < 0.0001) and depth (F1,64 = 11.1, P = 0.0015) were both significant factors

affecting germination schedule. Intact fruits (73.1%) were 169.7 and 46.6 times more 84 likely to delay germination than bird (7.7%; t = 5.11, df = 137, P < 0.0001) or hand- processed (19.2%; t = 5.23, df = 79, P < 0.0001) cherry stones, respectively, but there was no difference between bird and hand-processed stones (t = 1.34, df = 184, adj. P =

0.4686). Given that germination and emergence were very unlikely for surface propagules, delayed germination was also 22.8 times more likely for fruit or seeds placed on the surface than for those that were buried.

The year seeds were planted was the only factor significantly affecting seedling survival (χ2 = 30.9, df = 1, P < 0.0001). Emergent seedlings from the 1999 cohort were

24.3 times more likely to survive one year than seedlings that emerged from the 2001 cohort. By the end of the study (spring 2004), 8.6% of all the seedlings were still alive

(pathways 29 and 31, Fig. 1), desiccation had accounted for 43.4% of the mortality

(pathway 30), 30.7% died from unknown causes, and 7.9% died from unknown winter related losses.

Recruitment potential

Almost all recruitment resulted from seeds buried in caches by scatter-hoarding rodents (Table 8). Recruitment was poor to negligible for all other types of dispersal onto the soil surface, particularly intact fruit fall or primary dispersal by avian frugivores.

Delayed germination also occurred, but this source of emergence accounted for less than

15% of all recruitment. Recruitment potential was 10.2 times higher for seeds in rodent caches in riparian than in upland habitats. However, recruitment potential varied considerably for individual source plants. At source plant 2, 17.8% of the seeds produced emergent seedlings, but at source plants 1 and 3, there was no emergence among the seeds I was able locate. 85

DISCUSSION

Western chokecherry has an avian frugivore dispersal syndrome (Almeida-Neto et al.

2008; Jordano 1995a; Tamboia et al. 1996; Tiffney 1984). Most of the conspicuously

displayed, red to purple berries were consumed by birds, which then defecated or

regurgitated the seeds elsewhere. As in other berry-producing species (Koike et al. 2008;

Otani 2002), mammalian carnivores (personal observation) also dispersed chokecherry

(see Parciak 2002a). Avian frugivore visitation of chokecherry plants, measured during

scan sampling (Table 2) and weekly cherry counts from focal plants (Fig. 2), was correlated with fruit maturity and fruit crop size, results that have been reported in some

studies of Prunus (Jordano 1995b), but not others (Parciak 2002a). In this study, 85.3%

of avian foragers detected during scan sampling were endozoochorous birds

(predominantly American robins and cedar waxwings; Table 2), which swallowed cherries intact, then regurgitated or defecated the seeds either under or away from the

parent plant. Pulp-consuming birds, which pecked or depulped the fruit and dropped the

stones beneath the parent plant, accounted for the rest (14.7%) of the avian foraging

community.

Aside from seed predation (5.4%) by birds or scansorial rodents foraging in the plant

canopy, endozoochorous birds consumed 79.7% of the chokecherries and dispersed

66.6% of the seeds away from focal plants, pulp consumers depulped 7.0%, and 8.0% of

the crop fell as intact cherries under the plant (Table 3). All of these propagules (94.6%)

were available for secondary dispersal by scatter hoarding rodents.

The fate of chokecherry seeds depended in part on propagule type (whole cherries or

stones), disperser type (avian endozoochores or pulp consuming birds), and destination 86

(under parent plants in riparian habitat or in the open in upland habitat). Intact chokecherries could have remained under the parent plant (pathway 9, Fig. 1) where the seeds inside the fruit either died (pathway 12, Fig. 1), were eaten (< 1%; pathway 11), or a seedling subsequently germinated and emerged (pathway 27). Aside from being eaten, the other two outcomes were improbable because the traffic of fruit and seed consumers under plants was intense, as indicated by the higher rate of propagule removal at transect stations under plant canopies (28.1%/day; Fig. 3) than in the open (4.1%/day) (see

Parciak 2002b for similar conclusions), and the much larger number of rodents captured in riparian compared to upland habitats (Table 4). The most likely reason intact cherries were removed 3.6 times faster than cherry stones under plants was that whole cherries were not only consumed or removed by rodents, but were also eaten and dispersed by ground-foraging frugivores (Fig. 3). California quail were often seen foraging under chokecherry during scan sampling and the scat of carnivores of all types was filled with cherry stones when fruit was available (personal observation). In contrast, cherry stones were not only deposited directly under chokecherry plants by both types of frugivorous birds (pulp consumers and legitimate dispersers), but were dispersed by endozoochorous avian frugivores throughout the riparian zone as well as away from those areas into upland habitat (pathway 5).

Habitat type also affected the likelihood that frugivore-dispersed seeds were removed by rodents, remained undisturbed to germinate (pathway 24), or died (pathway 6).

Rodents not only harvested 85% of cherry stones under plant canopies in riparian areas, but removed them 10.8 times faster than in open upland habitats. In the unlikely event that stones deposited in riparian areas by frugivores remained on the surface until 87

germination (15%), seedling emergence was only 3.8% (Fig. 5) and recruitment potential

was 0.52% (Table 8). There was no emergence for any seeds on the surface in upland

habitats, but emergence from rodent caches was lower and seedling desiccation was

higher on dry slopes than in the wetter riparian habitat (see below and Parciak 2002b). In

addition to the larger rodent population mentioned above, the higher seed removal rate by

rodents under plants in riparian corridors was probably the result of the much higher seed

rain falling in the riparian zone, which concentrated foraging activity there, rather than in

upland habitats (see Parciak 2002b for similar conclusions). Only 5.7% of the seeds were

eaten at transect stations under plants in riparian habitat and no seeds were consumed at

upland stations in the open, indicating rodents generally removed intact seeds from where

they found them to be cached or eaten elsewhere (Fig. 3).

Naïve rodents in enclosure trials in Little Valley that were unfamiliar with

chokecherry showed much less interest in the seeds as a food source than rodents exposed to the abundant chokecherry along Purdy Creek. Perhaps this relative avoidance was also related to the toxic seed kernels found in the stones (Table 1), but rodents in Purdy Creek avidly harvested (100%) and scatter-hoarded 91.6% of the radioactive cherry stones I was able to locate (81.5%).

The difference in how rodents perceive cherry stones as food items among locations with and without chokecherry may have important consequences for recruitment and colonization. In areas without chokecherry, rodents unfamiliar with cherry stones may ignore seeds deposited in feces by frugivores, few of which would produce emergent seedlings unless they were buried abiotically. Under such circumstances, successful colonization may be infrequent. 88

Unlike the long dispersal distances that are often provided by avian and mammalian frugivores during primary dispersal (Fragoso et al. 2003; Jordano et al. 2007), all seeds in rodent caches that I accounted for were within 50 m of source plants (Fig. 4, Table 6), consistent with dispersal distances by rodents found in many other studies (Forget et al.

2005; Roth and Vander Wall 2005; Thayer and Vander Wall 2005; Xiao et al. 2004).

Because many species of rodents have very good spatial memory and olfactory ability, they are able to relocate their own caches or detect and pilfer the caches of other animals

(Briggs and Vander Wall 2004; Guimarães et al. 2005; Vander Wall et al. 2006; Vander

Wall and Jenkins 2003). Thus, phase II dispersal by scatter hoarding rodents placed chokecherry seeds in a spatiotemporally dynamic seed environment; 81.5% of the seeds in primary caches and 42.9% in secondary caches at the source plants were recovered

(pathways 13 and 19, Fig. 1). Unfortunately, I have no way of knowing whether the initial seed caching animal or other individuals recovered these seeds. Only 6.9% of the

seeds removed from caches were eaten (pathway 17), but the seed loss from this pathway

was probably significantly higher because I lost track of many of the radioactively-

labeled stones, either into winter larders or carried outside the study area. Nonetheless,

12.5% of the recovered seeds were recached (pathway 18), probably in sequential cache

sites (Roth and Vander Wall 2005) potentially much further from the caches I was able to

locate (Fig. 4). Previous studies have found seeds in up to six different cache sites before

germination (Beck Chapter 1; Roth and Vander Wall 2005; Vander Wall 2002; Vander

Wall and Joyner 1998).

At source plant 1, no seeds remained in caches until the following spring and only 8

seeds in 6 caches remained unrecovered at source plant 3, but no seedlings emerged 89

(Table 5). In contrast, 52.8% of the seeds deployed at source plant 2 were still in caches in the spring, 42.3% of those germinated, and 33.7% of seeds in spring caches produced emergent seedlings (pathways 25 and 26), three of which survived beyond the end of the study (Fig. 4). Most seeds were buried in soil (62.1%; Table 6)) where they were more likely to emerge compared to those placed in litter or on the surface (see below).

Furthermore, 82.5% of stones were cached at depths (5 – 40 mm) from which seedling emergence was common (Table 6) and rodents made caches in the shade of riparian trees where seedling survival was higher than in open sunlight (Table 7). There was also density dependent seedling mortality in caches with many seedlings compared to those with one or two seedlings (pathway 29, Fig. 1). All of these cache characteristics, including cache placement, indicate that secondary dispersal by rodents provides high quality, effective seed dispersal (Schupp 1993).

Seed handling had a marked effect on chokecherry seedling emergence in the germination study (Fig. 5). Emergence was poor for all propagules on the soil surface; there was no difference in emergence from cherries (3.4%), simulating fallen fruit, or seeds (3.0%), simulating avian dispersal. Although abiotic dispersal was rare, some intact cherries placed on the surface germinated and emerged one or two years later, suggesting there was delayed germination beyond that imposed by winter dormancy. In contrast, simulated rodent caches (buried 2 cm deep) of bird-processed cherry stones were ≈ 15 times more likely to produce emergent seedlings (52.1%) than all other unburied propagule types (≈ 3%). Differences in food-handling behavior among rodent species would also have significantly influenced recruitment potential. Although ground squirrels (golden-mantled and California) primarily larder hoard in burrows deep 90

underground or cache seeds too deeply for successful emergence (Briggs et al. 2009),

chipmunks scatter-hoarded nearly all the chokecherry stones they encountered and

accounted for almost all of the recruitment in riparian or upland habitat (Table 8), an

indication that secondary dispersal by scatter hoarding rodents, a mechanism different

than primary dispersal, likely plays an important and perhaps necessary role in

chokecherry demography throughout western North American watersheds. Although I

never measured abiotic burial, fruit and seeds could also have been buried by water,

especially during flooding in riparian corridors.

It should be noted that successful dispersal and colonization of seeds carried by

frugivores to riparian zones that lack chokecherry may be limited because scatter-

hoarding rodents might not harvest or cache the few, unfamiliar seeds they encountered.

Consequently, recruitment appears to be rare from seeds on the soil surface that arrive via

endozoochorous frugivores because they generally fail to germinate. Seed dispersal

interactions, therefore, are not uniform across geographic areas, which creates mosaics of

coevolutionary selection regimes that may enhance or diminish recruitment depending on

local conditions (Thompson 2005).

Diplochory is a seed dispersal process that utilizes different dispersal agents during

sequential dispersal phases and usually offers unique benefits during each phase (Vander

Wall and Longland 2004). The syndrome of frugivory (phase I) subsequently linked to

secondary dispersal by scatter hoarding rodents (phase II) is a potentially common form

of diplochory, but there are few well-documented studies (Vander Wall et al. 2005b;

Wenny 1999; Zhang and Wang 2001). During phase I in chokecherry, endozoochorous frugivores (small to medium sized birds and mammalian carnivores) ingest the cherries 91

and disperse the seeds, sometimes long distances away from the parent plant. There are

two benefits commonly associated with frugivory; colonization of suitable habitat and

escape from density or distance dependent mortality near the parent plant (see the Janzen-

Connell model in Connell 1971; Howe and Smallwood 1982; Janzen 1970). Although I

did not measure colonization or long distance dispersal, Jordano and colleagues (Garcia et al. 2007; Jordano et al. 2007) found that medium-sized birds and carnivores accounted for most long-distance dispersal and gene flow (up to 17 km away) into their local study population of P. maheleb, a congener that has similar fruit and seed morphology as chokecherry. It would not be surprising to find comparable primary dispersal patterns in chokecherry.

Seed predation by insects is frequently the cause of mortality near the parent plant.

Seed movement away from the parent plant via seed dispersal may reduce this substantial source of predispersal seed mortality (Janzen 1969; Janzen 1971; Janzen 1980).

However, predispersal seed predation in chokecherry (26.0-40.1% of the total crop; unpublished data; pathway 3, Fig. 1) occurs before fruit ripens, precluding any positive effect provided by escape from distance-dependent mortality near the parent plant. In this study, endozoochorous birds dispersed 88.9% of the seeds they consumed away from focal plants. If rodents acted exclusively as seed predators, primary dispersal by frugivores might reduce post dispersal seed losses in chokecherry by carrying seeds away from sources of post dispersal seed predation near the parent plant, as was described by

Parciak (2002b). Parciak (2002b), although adding a caveat concerning the lack of data on dispersal by scatter hoarding rodents, reported very high levels of post-dispersal seed predation, based on the assumption that seed removal by rodents was equivalent to seed 92

predation (but see Vander Wall et al. 2005a). This is not valid because I demonstrated that seeds that fall as intact cherries, depulped cherry stones dropped beneath plants, or dispersed by legitimate frugivores, face similar fates whether they land near or far from the parent plant; most seeds are harvested and cached by scatter hoarding rodents, which account for a majority of seedlings for the next cohort. Of course, frugivores may move seeds away from other sources of mortality near the parent plant. Packer and Clay (2000) showed that high concentrations of soil pathogens near black cherry trees (Prunus serotina) substantially increased seedling mortality nearby and accounted for the greater number of seedlings further from cherry trees.

A secondary benefit of fruit handling by endozoochorous frugivores on germination may be removal of fruit pulp from the seed. The use of intact cherries, bird-processed cherry stones, and hand-processed stones buried in soil in the emergence study permitted me to test the gut passage hypothesis (see Samuels and Levey 2005 for experimental design) and assess the quality of treatment of cherry seeds following consumption and regurgitation or defecation by avian frugivores (Schupp 1993). The gut passage hypothesis (Janzen 1983; Traveset 1998; Traveset et al. 2001; Traveset and Verdu 2002)

proposes that seed survival and germination may be affected by passage through the digestive tract of vertebrate frugivores. Emergence was much higher for seeds with the

fruit pulp removed by hand (hand-processed stones; 48.7%) than for intact fruit (14.1%),

but there was no difference between hand-processed and bird-processed stones (51.9%).

Therefore, no additional effect of digestion (scarring of the seed coat from digestive enzymes or mechanical effects) on germination was evident beyond the removal of the fruit pulp following passage through the digestive tract, suggesting reduced germination 93

was caused by either the physical effects of fruit pulp (osmotic pressure, interrupted light

regime) or fruit pulp chemistry, which, in many cases, is known to inhibit seed

germination (Barnea et al. 1990; Cipollini and Levey 1997; Samuels and Levey 2005).

Thus, gut passage by endozoochorous frugivores probably improved germination more

than the partial removal of the fruit pulp by pulp consumers and provided an extra benefit

in addition to dispersal away from mortality near the parent plant.

Phase II dispersal by scatter-hoarding rodents is unlikely to contribute much to long distance dispersal and colonization of new habitats. Most rodents have limited home ranges and previous studies have shown that rodents disperse seeds relatively short distances (Forget 1994; Forget et al. 1999; Hoshizaki et al. 1999; Silvius and Fragoso

2003; Vander Wall and Longland 2004) (Fig. 4, Table 6). However, burying seeds in caches may disproportionately enhance seed and seedling survival through directed dispersal (Briggs et al. 2009; Wenny 2001) by hiding them from other seed predators

(Vander Wall 1993; but see Vander Wall et al. 2006 with regard to pilfering by conspecifics), diminish harsh abiotic effects encountered on the soil surface (desiccation, temperature extremes, UV radiation, fire; Chambers and MacMahon 1994; Roth and

Vander Wall 2005), and increase germination if the seeds remain buried (Borchert 2004;

Longland et al. 2001; Seiwa et al. 2002). In this study, seeds cached in soil at the most common depths had substantially higher emergence and recruitment potential (8.4%) than seeds deposited on the ground (0.5%) or within the litter layer, thus qualifying as directed dispersal (Briggs et al. 2009; Vander Wall and Longland 2004; Wenny 2001)

(Table 8). In addition to burial, rodents placed caches in mineral soil more often than 94 light or heavy litter, and in the shade of overstory trees more than in sunlight, all of which enhanced either seedling emergence or survival (Table 7).

Of course, if seeds are recovered by the original cacher or another individual and eaten, then even the most favorable cache site provides no benefit. For example, Gomez et al. (2008), during a three year study, found that most acorns of Holm oak (Quercus ilex) were consumed at the supply point or the initial dispersal site, ~ 7% were cached, and only 1.3% of the acorns survived in caches until the following spring. Therefore, directed dispersal often means more than just landing or being placed in a suitable site.

The quality of treatment of the seeds by the disperser is often equally important, especially if there is a high probability of further interactions between the seed and seed- dispersing animal following initial dispersal, as is often the case with dispersal by scatter- hoarding animals (Schupp 1993). Therefore, the relative effectiveness of this form of dispersal is dependent on the proportion of seeds that enter and then remain in caches until germination.

How might plants accomplish this difficult task of remaining in caches? Large fruit crops may potentially satiate frugivores, but usually not the food hoarding behavior of seed-caching animals. Given the resources, seed-caching animals continue to cache, often storing more than they can recover and eat (Vander Wall 1990). Following very large crops, most seeds would be cached and any surplus would remain buried until germination. When plants are precluded from producing large seed crops because of small plant size or a lack of resources, costly seed traits that deter recovery could also create a surplus of cached seeds. The seeds of many plants, including chokecherry, have general anti-predator defenses (costs), such as hard seed coats (unpublished data) (Blate 95 et al. 1998; Smith and Follmer 1972) or toxic secondary chemicals (Table 1) (Janzen

1969; Janzen 1978) that deter both pre and post-dispersal seed predators. For seed- caching animals, if these traits are too effective and discourage all seed harvest, the seed is ignored and there is no dispersal into caches. In contrast, minimally defensive seed traits are likely ineffective in affecting behavior and the seeds are eaten before or shortly after they are cached and recovered. It is possible that natural selection has optimized the tradeoff between these two conflicting behavioral responses to maximize the number of seeds stored and minimize the number of those seeds that are retrieved from caches and eaten. Seed traits that balance deterrence, dispersal, and recovery could potentially create a strategy of first into and last out of a cache. Jacobs (1992) found that hard seed coats increased the probability that rodents would cache the seeds for later use, instead of eating them immediately and Xiao et al. (2006) demonstrated that high tannin cork oak acorns (Quercus variabilis ) were less likely to be recovered and eaten than low tannin

Henry’s chestnuts (Castanea henryi). In the context of a diverse seed community that changes in composition and abundance over space and time, seeds with significant costs, such as chokecherry, might enter caches in greater quantity and likely remain there until germination than seeds of more preferred species with fewer costs. In years of little seed production, few seeds will be cached, most recovered, and seed caching animals will effectively act as seed predators. In contrast, in years of high community-wide seed production, such as masting of Jeffrey pine and even a moderate crop of chokecherry, which usually ripens before pine seeds become available, there will probably be a surplus of seeds of both species remaining in caches until the following spring. 96

Because of the repeated evolution of different forms of diplochory across many plant taxa, Vander Wall and Longland (2004) proposed that diplochory is not a haphazard collection of dispersal mechanisms, but is an adaptive configuration of dispersal agents that provide different benefits for each phase of dispersal. Diplochorous plants that depend upon dissimilar dispersal guilds for phase I and II dispersal are linked to two distinct networks of animal interactors, each of which impose different selective regimes on the seeds they disperse. In diplochorous Prunus, primary dispersal is provided by a frugivore guild that treats the seeds as a foraging byproduct to be discarded, whereas rodent seed predators, through their continued interest in the seeds from harvest through caching and recovery, inadvertently provide secondary dispersal by storing seeds in microsites (burial in soil) favorable to emergence and establishment.

How might this form of diplochory have evolved? For plants that rely on endozoochory, the fleshy fruit is the unit of dispersal and the fruit pulp provides a reward to seed dispersing animals. This form of dispersal has evolved independently numerous times in a wide range of plant taxa (Howe and Smallwood 1982; Jordano 2000). In a recent phylogenetic study of Prunus, Bortiri et al. (2006) found that fleshy-fruited drupes were ancestral, suggesting an ancient history of primary dispersal by endozoochorous frugivores.

Seed predation and the subsequent evolution of dispersal by scatter hoarding animals are also very old interactions and are ubiquitous in nature (Janzen 1971; Vander Wall

1990; Vander Wall 2001). In contrast to frugivory, the seed is both the dispersal unit and an attractive food item for a wide variety of vertebrate seed consumers, some of which might store the seeds under conditions that favor food hoarding (pulses of seeds 97 interspersed with periods of food scarcity). If the benefits of caching (see above) outweighed the costs of recovery and seed predation, then secondary dispersal, accompanied by selection for larger seed size to attract scatter hoarding animals, may have evolved. In Prunus, which produces a relatively large, nutritious, single-seeded drupe, phase I and II may have arisen simultaneously, or diplochory may be ancestral, having evolved from a multi-seeded, fleshy-fruited ancestor that subsequently reduced seed number and increased seed size, possibly in response to shading in closed canopy forests and/or dispersal by scatter-hoarding rodent seed predators (Vander Wall 2001).

There are also more than thirty species of dry-fruited Prunus that evolved on multiple occasions in the deserts of Eurasia and western North American (Bortiri et al. 2006), and which likely no longer rely on primary dispersal by frugivores. Beck and Vander Wall

(Beck Chapter 1) have proposed that instead of evolving primary dispersal by seed- caching animals de novo, the most parsimonious explanation entailed selection against fleshy fruits in a diplochorous ancestor in arid environments, then the loss of phase I dispersal by frugivores, while retaining dispersal by scatter hoarding rodents.

This study highlights not only the prevalence and importance of diplochory in this and other fleshy-fruited species (Forget et al. 2005; Vander Wall and Longland 2004), but the necessity of documenting complete seed fates (Roth and Vander Wall 2005), instead of assuming that seed removal is equivalent to seed predation, as many past studies have done (Hulme 1997; Moles et al. 2003; but see Vander Wall et al. 2005a).

This research was conducted according to the guidelines for the use of animals published by the Animal Behavior Society and was carried out in accordance with the legal 98

requirements of the United States of America and the University of Nevada, Reno

(IACUC Protocol no. A04/05-04).

ACKNOWLEDGEMENTS

I thank S. B. Vander Wall, S. H. Jenkins, W. S. Longland, D. W. Zeh, and T. J.

Nickles for helpful comments on an earlier draft of this manuscript. I thank Jenny

Briggs, Julie Roth, Ted Thayer, Jennifer Armstrong, Jennifer Hollander, Kellie Kuhn,

Jenny Francis, Jessica Hay, and Chris Farrar for assistance in the field. I thank G. C. J.

Fernandez, I. Aban, and D. Board for help with statistical analysis. Dr. Chris Ross

permitted me use of his property for the chokecherry emergence study. Financial support

was provided by the Program in Ecology, Evolution, and Conservation Biology, the

Graduate Student Association at the University of Nevada, Reno, and the Whittell Forest

and Wildlife Area.

REFERENCES

Allison, P. D. 1995, Survival analysis using the SAS system: a practical guide. Cary, NC, SAS Institute, Inc. Almeida-Neto, M., F. Campassi, M. Galetti, P. Jordano, and A. Oliveira. 2008. Vertebrate dispersal syndromes along the Atlantic forest: broad-scale patterns and macroecological correlates. Global Ecology and Biogeography 17:503-513. Barnea, A., Y. Yomtov, and J. Friedman. 1990. Differential germination of two closely related species of Solanum in response to bird ingestion. Oikos 57:222-228. Beck, M. J. Chapter 1. Desert peach (Prunus andersonii) and the transition in seed dispersal mode from frugivory to scatter-hoarding, University of Nevada-Reno, Reno. Blate, G. M., D. R. Peart, and M. Leighton. 1998. Post-dispersal predation on isolated seeds: a comparative study of 40 tree species in a Southeast Asian rainforest. Oikos 82:522-538. Borchert, M. 2004. Vertebrate seed dispersal of Marah macrocarpus (Cucurbitaceae) after fire in the Western Transverse Ranges of California. Ecoscience 11:463-471. 99

—. 2006. Seed fate of Marah macrocarpus (Cucurbitaceae) following fire: do seedlings recruit from rodent burrows? Ecological Research 21:641-650. Bortiri, E., B. V. Heuvel, and D. Potter. 2006. Phylogenetic analysis of morphology in Prunus reveals extensive homoplasy. Plant Systematics and Evolution 259:53-71. Briggs, J. S., and S. B. Vander Wall. 2004. Substrate type affects caching and pilferage of pine seeds by chipmunks. Behavioral Ecology 15:666-672. Briggs, J. S., S. B. Vander Wall, and S. H. Jenkins. 2009. Forest rodents provide directed dispersal of Jeffrey pine seeds. Ecology 90:675-687. Chambers, J. C., and J. A. MacMahon. 1994. A day in the life of a seed: movements and fates of seeds and their implications for natural and managed systems. Annual Review of Ecology and Systematics 25:263-292. Cipollini, M. L., and D. J. Levey. 1997. Secondary metabolites of fleshy vertebrate- dispersed fruits: adaptive hypotheses and implications for seed dispersal. American Naturalist 150:346-372. Connell, J. H. 1971. On the role of natural enemies in preventing competitive exclusion in some marine animals and rain forest trees, Pages 298-312 in P. J. Den Boer, and P. R. Gadwell, eds. Dynamics of populations. Wageningen, Netherlands. Forget, P.-M., J. E. Lambert, P. E. Hulme, and S. B. Vander Wall. 2005. Seed fate: predation, secondary dispersal, and seedling establishmentin. ed. Wallingford, UK, CAB International. Forget, P. M. 1994. Recruitment pattern of Vouacapoua americana (Caesalpiniaceae), a rodent-dispersed tree species in French Guiana. Biotropica 26:408-419. Forget, P. M., F. Mercier, and F. Collinet. 1999. Spatial patterns of two rodent-dispersed rain forest trees Carapa procera (Meliaceae) and Vouacapoua americana (Caesalpiniaceae) at Paracou, French Guiana. Journal of Tropical Ecology 15:301-313. Forget, P. M., and T. Milleron. 1991. Evidence for secondary seed dispersal by rodents in Panama. Oecologia 87:596-599. Fragoso, J. M. V. 1997. Tapir-generated seed shadows: scale-dependent patchiness in the Amazon rain forest. Journal of Ecology 85:519-529. Fragoso, J. M. V., K. M. Silvius, and J. A. Correa. 2003. Long-distance seed dispersal by tapirs increases seed survival and aggregates tropical trees. Ecology 84:1998- 2006. Garcia, C., P. Jordano, and J. A. Godoy. 2007. Contemporary pollen and seed dispersal in a Prunus mahaleb population: patterns in distance and direction. Molecular Ecology 16:1947-1955. Gomez, J. M., C. Puerta-Pinero, and E. W. Schupp. 2008. Effectiveness of rodents as local seed dispersers of Holm oaks. Oecologia 155:529-537. Goodson & Associates. 1995-2006. Trail Master active infrared camera. Lenexa, Kansas, USA. Guimarães, P. R., B. Z. Gomes, Y. J. Ahn, and M. Galetti. 2005. Cache pilferage in red- rumped agoutis (Dasyprocta leporina) (Rodentia). Mammalia 69:431-434. Herrera, C. M., and P. Jordano. 1981. Prunus mahaleb and birds: the high efficiency seed dispersal system of a temperate fruiting tree. Ecological Monographs 51:203-218. 100

Holl, K. D., and M. E. Lulow. 1997. Effects of species, habitat, and distance from edge on post- dispersal seed predation in a tropical rainforest. Biotropica 29:459-468. Hoshizaki, K., W. Suzuki, and T. Nakashizuka. 1999. Evaluation of secondary dispersal in a large-seeded tree Aesculus turbinata: a test of directed dispersal. Plant Ecology 144:167-176. Howe, H. F., and J. Smallwood. 1982. Ecology of seed dispersal. Annual Review of Ecology and Systematics 13:201-228. Hulme, P. E. 1997. Post-dispersal seed predation and the establishment of vertebrate dispersed plants in Mediterranean scrublands. Oecologia 111:91-98. Hulme, P. E., and M. K. Hunt. 1999. Rodent post-dispersal seed predation in deciduous woodland: predator response to absolute and relative abundance of prey. Journal of Animal Ecology 68:417-428. Jacobs, L. F. 1992. The effect of handling time on the decision to cache by gray squirrels. Animal Behaviour 43:522-524. Janzen, D. H. 1969. Seed-eaters versus seed size, number, toxicity and dispersal. Evolution 23:1-27. —. 1970. Herbivores and the number of tree species in a tropical forest. American Naturalist 104:501-528. —. 1971. Seed predation by animals. Annual Review of Ecology and Systematics 2:465- 492. —. 1978. The ecology and evolutionary biology of seed chemistry as related to seed predation, Pages 163-206 in J. B. Harborne, ed. Biochemical aspects of plant and animal coevolution. New York, Academic Press. —. 1980. Specificity of seed-attacking beetles in a Costa Rican deciduous forest. Journal of Ecology 68:929-952. —. 1983. Dispersal of seeds by vertebrate guts, Pages 232-262 in D. J. Futuyma, and M. Slatkin, eds. Coevolution. Sunderland, MA, Sinauer Associates. Jordano, P. 1995a. Angiosperm fleshy fruits and seed dispersers: a comparative analysis of adaptation and constraints in plant-animal Interactions. American Naturalist 145:163-191. —. 1995b. Frugivore-mediated selection on fruit and seed size: birds and St. Lucies Cherry, Prunus mahaleb. Ecology 76:2627-2639. —. 2000. Fruits and frugivory in M. Fenner, ed. Seeds: the Ecology of Regeneration in Plant Communities. Wallingford, UK, C.A.B. International. Jordano, P., C. Garcia, J. A. Godoy, and J. L. Garcia-Castano. 2007. Differential contribution of frugivores to complex seed dispersal patterns. Proceedings of the National Academy of Sciences of the United States of America 104:3278-3282. Klein, J. P., and M. L. Moeschberger. 1997, Survival analysis: techniques for censored and truncated data. New York, Springer-Verlag. Koike, S., H. Morimoto, Y. Goto, C. Kozakai, and K. Yamazaki. 2008. Frugivory of carnivores and seed dispersal of fleshy fruits in cool-temperate deciduous forests. Journal of Forest Research 13:215-222. Kollmann, J., D. A. Coomes, and S. M. White. 1998. Consistencies in post-dispersal seed predation of temperate fleshy-fruited species among seasons, years and sites. Functional Ecology 12:683-690. 101

Li, H. J., and Z. B. Zhang. 2007. Effects of mast seeding and rodent abundance on seed predation and dispersal by rodents in Prunus armeniaca (Rosaceae). Forest Ecology and Management 242:511-517. LoGiudice, K., and R. S. Ostfeld. 2002. Interactions between mammals and trees: predation on mammal-dispersed seeds and the effect of ambient food. Oecologia 130:420-425. Longland, W. S., S. H. Jenkins, S. B. Vander Wall, J. A. Veech, and S. Pyare. 2001. Seedling recruitment in Oryzopsis hymenoides: are desert granivores mutualists or predators? Ecology 82:3131-3148. Moles, A. T., D. I. Warton, and M. Westoby. 2003. Do small-seeded species have higher survival through seed predation than large-seeded species? Ecology 84:3148- 3161. Osunkoya, O. O. 1994. Postdispersal survivorship of north Queensland rain-forest seeds and fruits: effects of forest, habitat and species. Australian Journal of Ecology 19:52-64. Otani, T. 2002. Seed dispersal by Japanese marten Martes melampus in the subalpine shrubland of northern Japan. Ecological Research 17:29-38. Packer, A., and K. Clay. 2000. Soil pathogens and spatial patterns of seedling mortality in a temperate tree. Nature 404:278-281. Parciak, W. 2002a. Environmental variation in seed number, size, and dispersal of a fleshy-fruited plant. Ecology 83:780-793. —. 2002b. Seed size, number, and habitat of a fleshy-fruited plant: consequences for seedling establishment. Ecology 83:794-808. Roth, J. K., and S. B. Vander Wall. 2005. Primary and secondary seed dispersal of bush chinquapin (Fagaceae) by scatterhoarding rodents. Ecology 86:2428-2439. Samuels, I. A., and D. J. Levey. 2005. Effects of gut passage on seed germination: do experiments answer the questions they ask? Functional Ecology 19:365-368. SAS Institute. 2004.SAS proprietary software release, version 9.1, version 9.1.SAS Institute, Inc., Cary, NC. Schupp, E. W. 1993. Quantity, quality and the effectiveness of seed dispersal by animals. Vegetatio 108:15-29. Seiwa, K., A. Watanabe, T. Saitoh, H. Kannu, and S. Akasaka. 2002. Effects of burying depth and seed size on seedling establishment of Japanese chestnuts, Castanea crenata. Forest Ecology and Management 164:149-156. Silvius, K. M., and J. M. V. Fragoso. 2003. Red-rumped agouti (Dasyprocta leporina) home range use in an Amazonian forest: Implications for the aggregated distribution of forest trees. Biotropica 35:74-83. Smith, C. C., and D. Follmer. 1972. Food preferences of squirrels. Ecology 53:82-91. Tamboia, T., M. L. Cipollini, and D. J. Levey. 1996. An evaluation of vertebrate seed dispersal syndromes in four species of black nightshade (Solanum sect Solanum). Oecologia 107:522-532. Thayer, T. C., and S. B. Vander Wall. 2005. Interactions between Steller's jays and yellow pine chipmunks over scatter-hoarded sugar pine seeds. Journal of Animal Ecology 74:365-374. 102

Thompson, J. 2005, The geographic mosaic of coevolution. Chicago, University of Chicago Press. Thornton, I. W. B., S. G. Compton, and C. N. Wilson. 1996. The role of animals in the colonization of the Krakatau Islands by fig trees (Ficus species). Journal of Biogeography 23:577-592. Tiffney, B. H. 1984. Seed size, dispersal syndromes, and the rise of the angiosperms: evidence and hypothesis. Annals of the Missouri Botanical Garden 71:551-576. Traveset, A. 1998. Effect of seed passage through vertebrate frugivores' guts on germination: a review. Perspectives in Plant Ecology Evolution and Systematics 1:151-190. Traveset, A., N. Riera, and R. E. Mas. 2001. Passage through bird guts causes interspecific differences in seed germination characteristics. Functional Ecology 15:669-675. Traveset, A., and M. Verdu. 2002. A meta-analysis of the effect of gut treatment on seed germination, Pages 339-350 in D. J. Levey, and M. Galetti, eds. Seed dispersal and frugivory: Ecology, evolution and conservation. Wallingford, UK., CABI Publishing. Vander Wall, S. B. 1990, Food hoarding in animals. Chicago, University of Chicago Press. —. 1993. Seed water content and the vulnerability of buried seeds to foraging rodents. American Midland Naturalist 129:272-281. —. 1994a. Removal of wind-dispersed pine seeds by ground-foraging vertebrates. Oikos 69:125-132. —. 1994b. Seed fate pathways of antelope bitterbrush: dispersal by seed-caching yellow pine chipmunks. Ecology 75:1911-1926. —. 2001. The evolutionary ecology of nut dispersal. Botanical Review 67:74-117. —. 2002. Masting in animal-dispersed pines facilitates seed dispersal. Ecology 83:3508- 3516. Vander Wall, S. B., J. S. Briggs, S. H. Jenkins, K. M. Kuhn, T. C. Thayer, and M. J. Beck. 2006. Do food-hoarding animals have a cache recovery advantage? Determining recovery of stored food. Animal Behaviour 72:189-197. Vander Wall, S. B., and S. H. Jenkins. 2003. Reciprocal pilferage and the evolution of food-hoarding behavior. Behavioral Ecology 14:656-667. Vander Wall, S. B., and J. W. Joyner. 1998. Recaching of Jeffrey pine (Pinus jeffreyi) seeds by yellow pine chipmunks (Tamias amoenus): potential effects on plant reproductive success. Canadian Journal of Zoology-Revue Canadienne De Zoologie 76:154-162. Vander Wall, S. B., K. M. Kuhn, and M. J. Beck. 2005a. Seed removal, seed predation, and secondary dispersal. Ecology 86:801-806. Vander Wall, S. B., K. M. Kuhn, and J. R. Gworek. 2005b. Two-phase seed dispersal: linking the effects of frugivorous birds and seed-caching rodents. Oecologia 145:282-287. Vander Wall, S. B., and W. S. Longland. 2004. Diplochory: are two seed dispersers better than one? Trends in Ecology & Evolution 19:155-161. 103

Webb, S. L., and M. F. Willson. 1985. Spatial heterogeneity in post-dispersal predation on Prunus and Uvularia seeds. Oecologia 67:150-153. Wenny, D. G. 1999. Two-stage dispersal of Guarea glabra and G. kunthiana (Meliaceae) in Monteverde, Costa Rica. Journal of Tropical Ecology 15:481-496. —. 2001. Advantages of seed dispersal: a re-evaluation of directed dispersal. Evolutionary Ecology Research 3:51-74. Whelan, C. J., M. F. Willson, C. A. Tuma, and I. Souzapinto. 1991. Spatial and temporal patterns of postdispersal seed predation. Canadian Journal of Botany-Revue Canadienne De Botanique 69:428-436. Xiao, Z. S., P. A. Jansen, and Z. B. Zhang. 2006. Using seed-tagging methods for assessing post-dispersal seed fate in rodent-dispersed trees. Forest Ecology and Management 223:18-23. Xiao, Z. S., Z. B. Zhang, and Y. S. Wang. 2004. Dispersal and germination of big and small nuts of Quercus serrata in a subtropical broad-leaved evergreen forest. Forest Ecology and Management 195:141-150. Zhang, Z. B., and F. S. Wang. 2001. Effect of rodents on seed dispersal and survival of wild apricot. Acta Ecologica Sinica 21:839-845.

104

TABLES

Table 1. Nutrient analyses and cyanogenic glycoside (amygdalin) content of choke cherry fruit pulp and seed kernels from unripe (green; 22 July 2007) and ripe (purple 20 August) fruits collected at Purdy Creek, California. Percent water and dry mass are means from 100 fruits. Energy: J/fruit (pulp or seeds) = KJ/g times dry mass mg. NFE: Nitrogen free extract (carbohydrates). Fruit Water Dry mass Energy Energy Protein NFE Fat Amygdalin maturity (%) (mg) content content (%) (%) (%) (ppm (KJ/g) (J/nut) HCN) Pulp Unripe 72.5 ± 1.8 34.0 ± 7.1 7.7 261 7.3 78.3 0.7 620† Ripe 79.5 ± 1.7 147.3 ± 42.7 8.6 1268 5.1 87.5 2.1 30 Seeds Unripe 62.4 ± 13.6 14.1 ± 7.7 11.7 164 46.4 16.9 27.8 6086† Ripe 27.4 ± 2.1 44.5 ± 9.6 12.7 565 37.6 16.5 37.7 6107† † Denotes toxic concentration of HCN in Rattus rattus 105

Table 2. Species of avian chokecherry fruit consumer, type of consumer, and index of abundance at Verdi in 1999, and Verdi and Purdy Creek in 2001. The index of abundance (mean ± SD) for each species was the average number of individuals of that species/scan, times the proportion of scans the species was present for each day, averaged over the number of days for the location/year. Index of abundance‡ Species Scientific name Type of consumer† ______Verdi 1999 Verdi 2001 Purdy Cr. 2001 American robin Turdus migratorius Frugivore 12.2 ± 3.5 11.6 ± 2.6 12.6 ± 5.5 Cedar waxwing Bombycilla cedrorum Frugivore 8.5 ± 5.0 10.4 ± 4.1 10.3 ± 4.3 European starling Sturnus vulgaris Frugivore 4.3 ± 2.5 5.1 ± 2.6 4.8 ± 1.6 House finch Carpodacus mexicanus pulp consumer 3.2 ± 3.4 3.7 ± 1.8 – Lesser goldfinch Carduelis psaltria pulp consumer 2.1 ± 1.8 1.6 ± 1.1 – California quail Callipepla californica Frugivore, seed predator 2.0 ± 2.0 3.5 ± 2.0 1.8 ± 2.1 Black-billed magpie Pica pica Frugivore 1.6 ± 1.6 2.0 ± 1.3 1.3 ± 1.0 House sparrow Passer domesticus pulp consumer 1.5 ± 1.5 2.8 ± 0.4 – Western scrub jay Aphelocoma coerulescens Frugivore 0.9 ± 0.8 1.2 ± 0.8 – Cassin's finch Carpodacus cassinii pulp consumer 0.7 ± 1.4 0.1 ± 0.1 4.0 ± 2.3 Song sparrow Melospiza melodia? pulp consumer 0.7 ± 0.9 0.4 ± 0.3 0.3 ± 0.3 Pinyon jay Gymnorhinus cyanocephalus Frugivore 0.4 ± 1.4 – 0.5 ± 0.9 White-crowned sparrow Zonotrichia leucophrys pulp consumer 0.4 ± 0.7 0.1 ± 0.2 – Morning dove Zenaida macroura Frugivore 0.2 ± 0.3 0.3 ± 0.3 0.4 ± 0.3 Steller's jay Cyanocitta stelleri Frugivore 0.1 ± 0.1 0.3 ± 0.6 1.2 ± 0.9 Lewis woodpecker Melanerpes lewis Frugivore, fruit hoarder 0.1 ± 0.2 – – Phainopepla Phainopepla nitens Frugivore 0.01 ± 0.02 – – Spotted towhee Pipilo maculatus pulp consumer – – 1.2 ± 0.6 Clark's nutcracker Nucifraga columbiana Frugivore, seed predator – – 0.3 ± 0.4 Black-headed grosbeak Pheucticus melanocephalus pulp consumer, seed predator – – 0.3 ± 0.2 Green-tailed towhee Pipilo chlorurus pulp consumer – – 0.1 ± 0.1 Western tanager Piranga ludoviciana Frugivore – – 0.1 ± 0.1 106

Note: Sampling involved scanning at each station and counting all the birds by species present, then moving to the next station † Frugivores consumed the whole fruit and regurgitated or defecated the cherry stones onto the ground. Pulp consumers depulped or pecked the fruit, then discarded the seed under the parent plant. Depending on the species, avian seed predators either cracked the stones open or destroyed the seeds in the gizzard. Fruit hoarders were seen caching whole fruits in cracks in telephone poles. ‡ The index of abundance for 1) Verdi 1999 was based on 7.2 ± 3.8 plants/day averaged over 12 days from 24 August – 23 September 1999. 2) Verdi 2001 was based on 7 plants/day averaged over 5 days from 12 August – 10 September 2001, and 3) Purdy Creek 2001 was based on 7 plants/day averaged over 5 days from 20 August – 16 September 2001. 107

Table 3. Fate of intact chokecherry fruits and stones (pathways 2-5, and 9) from focal plant seed traps at Cliff Ranch in 2000 (n = 12 plants) and Purdy Creek in 2001 (n = 8 plants). The estimates for intact fruit fall, avian pulp consumers (depulped stones), and canopy seed predators (eaten stones) were calculated by dividing the number of each item found in the seed trap by the proportion of the plant surface area sampled. The estimate for seeds dispersed by endozoochorous birds was calculated by subtracting the estimates for intact fruit fall, depulped stones, and eaten stones from the estimated crop size. Cliff Ranch 2000 Purdy Creek 2001 ______Fates Mean ± SD % Mean ± SD % Crop size† 402.3 ± 425.2 100.0 4000.5 ± 4200.4 100.0 Eaten stones‡ 32.1 ± 39.8 8.0 111.9 ± 131.8 2.8 Intact fruit fall 46.3 ± 83.0 11.5 176.6 ± 381.9 4.4 Depulped stones§ 22.3 ± 42.0 5.6 336.4 ± 329.9 8.4 Endozoochorous birds|| 301.6 ± 280.7 75.0 3375.6 ± 3717.3 84.4 Available for 2º dispersal¶ 370.2 ± 387.8 92.0 3888.6 ± 4247.1 97.2 Note: Data from 4 seed traps from 2001 were disturbed and discarded. † Estimated by multiplying the average number of chokecherries/raceme times the average number of racemes/plant ‡ Canopy seed predators were rodents or birds capable of cracking cherry stones § Depulped by birds that pecked the pulp from the fruit and dropped the seeds || Birds that ingested the fruit then defecated or regurgitated the seeds, often elsewhere ¶ Seeds available for secondary dispersal by rodents = the sum of intact fruit, depulped stones, and stones dispersed by endozoochorous frugivores.

TABLE 4. Number of rodents captured on 50 trap grids in two habitats at Purdy Creek, California from 20 - 23 September 2001. Riparian Upland ______Number of Number of Rodent species captures % Captures % Bushy-tailed woodrat 2 4.7 0 0.0 Neotoma cinerea Deer mouse 14 32.6 3 30.0 Peromyscus maniculatus Golden-mantled ground squirrel 3 7.0 0 0.0 Spermophilus lateralis Yellow-pine chipmunk 22 51.2 7 70.0 Tamias amoenus Long-eared chipmunk 2 4.7 0 0.0 Tamias quadrimaculatus Total 43 100.0 10 100.0 Note: Sampling for each grid consisted of 200 trap days 108

Table 5. Fates of 200 (pathway 7) radioactively labeled chokecherry stones placed under 3 source plants at Purdy Creek during the fall of 2002. Percentages for stones accounted for are based on the number of nuts harvested. Percentages for scatter hoarded, larder hoarded, and eaten are based on the number of stones accounted for. Percentage of stones in spring caches is based on the number of stones cached. Percentage of seedlings is based on the number of stones in spring caches. Other species or individuals may have handled cherry stones after the initial seed caching animal. Source Rodent species† Stones Scatter Larder Eaten‡ Stones in No. of plant accounted for Hoarded hoarded spring caches seedlings ______# % # % # % # % # % # % 1 Long-eared chipmunk 92 46.0 88 95.7 0 0.0 13 14.1 0 0.0 0 0.0 2 Yellow-pine chipmunk 197 98.5 197 100.0 0 0.0 4 2.0 104 52.8 35 33.7 3 Chipmunk spp. 200 100.0 163 81.5 37 18.5§ 18 9.0 8 4.9 0 0.0 † Determined from Trail Master photographs and traces of radioactivity on captured rodents ‡ Includes all seeds eaten, including at source plants and found during all surveys. § The presumed count was 37, but I was unable to verify the number of stones because they were in an unreachable burrow beneath a large boulder 109

Table 6. Cache characteristics of scatter-hoarded chokecherry stones at 3 source plants. Source Cache type† No. of Nuts/cache Cache depth Cache distance (m) plant caches (mm) ______

Mean ± SD Range Mean ± SD Range Mean ± SD Max 1 Total 10 Primary 10 8.8 ± 4.3 2-16 9.7 ± 5.6 0-15 24.4 ± 11.7 39.7 Secondary 0 2 Total 59 3.9 ± 3.3 1-16 10.8 ± 9.2 0-60 20.5 ± 12.8 41.4 Primary 36 5.5 ± 3.5 1-16 9.4 ± 4.4 0-25 18.6 ± 13.0 41.4 Secondary 23 1.9 ± 1.6 1-7 13.3 ± 14.3 2-60 23.5 ± 12.2 36.0 3 Total 11 14.0 ± 16.6 1-47 15.8 ± 14.2 0-40 14.7 ± 10.1 29.5 Primary 9 18.1 ± 17.4 1-47 17.8 ± 15.0 0-40 12.8 ± 9.0 29.4 Secondary 2 1.7 ± 1.2 1-3 8.0 ± 9.9 1-15 24.8 ± 6.5 29.5 † Primary caches were made from radioactively- labeled stones harvested under source plants. Secondary caches were made from stones that were recovered from primary caches and recached, either by the original scatter hoarding animal or a different animal. 110

TABLE 7. Caches placed in different types of microsites compared to the availability of those microsites at three source shrubs. For categories that were used non-randomly, microsite types are ranked according to relative use (preference). Microsite category Source plant† F num DF P Ranking‡ of microsite types within categories§ den DF Substrate 1 6.87 2/342 0.0012 MS>>LL>HL 2 0.18 2/383 0.8372 3 1.17 2/273 0.3120 All plants 2.97 2/1010 0.0605 MS>LL>HL Understory 1 0.59 1/342 0.4423 2 1.47 1/383 0.2254 3 1.24 1/273 0.2660 All plants 0.05 1/1010 0.8244 Overstory 1 5.23 1/342 0.0029 S>O 2 5.71 1/383 0.0173 S>O 3 1.69 1/273 0.1949 All plants 12.94 1/1010 0.0003 S>>O Substrate + overstory 1 na na na 2 2.74 2/383 0.0656 MS-S>LL-S>HL-O>HL-S>LL-O>MS-O 3 0.16 2/273 0.8484 All plants 3.13 2/1010 0.0442 MS-S>LL-S>HL-S>MS-O>HL-O>LL-O † Plant 1 = 10 caches, 337 random points; plant 2 = 59 caches, 331 random points; plant 3 = 11 caches, 269 random points ‡ >> indicates a statistically significant preference for one microsite over the next listed (P < 0.05); > indicates a non- significant trend § MS = mineral soil; LL = light litter; HL = heavy litter; S = in shade; O = in open sunlight; In the “Substrate + overstory” category, dashes (-) between 2 codes indicate combinations of microsites; e.g. MS-S = mineral soil in shade 111

TABLE 8. Recruitment potential for abiotic fruit fall, primary dispersal by birds, and diplochory by birds and then scatter- hoarding rodents in two habitats at Purdy Creek. Recruitment potentials were calculated as the product of states (with proportions) in the seedling regeneration process multiplied by 100. Habitat Dispersal category Seedling regeneration states Recruitment ______potential Primary Remaining Available Rodent Rodent Spring Emergence|| (%) deposition at initial for rodent removal‡ cached§ caches§ site† site‡ dispersal† Riparian Abiotic fruit fall 0.053 0.007 0.043 0.002 Bird-dispersed seed 0.912 0.150 0.038 0.524 Rodent-cached seed 0.965 0.793 0.916 0.229 0.521 8.367 Upland Bird-dispersed seed 0.2 0.557 0.0 0.0 Rodent-cached seed 0.2 0.443 0.916 0.229 0.441 0.820 † Values from focal shrubs, except bird-dispersed seeds in upland habitat, which were from (Parciak 2002a). ‡ Values from removal transect data. § Values from source plant data || Values from emergence enclosure study 112

FIGURES

Figure 1. Seed fate pathway diagram of western choke cherry (Prunus virginiana var. demissa).

Figure 2. The timing of chokecherry fruit harvest by birds from twelve focal plants at A) Verdi in 1999, B) Cliff Ranch in 2000 and, C) Purdy Creek in 2001. The curve with large closed diamonds is mean fruit removal from the twelve plants. Each curve with small open diamonds and dashed lines represents the removal rate for one of the focal plants. The curve with the large closed triangle is energy content (joules/fruit). The curves also reflect fruit fall prior to foraging and pre-dispersal mortality by insect infestation, mold, and fruit abortion. The primary y-axis

(on left) is the scale for percent fruit remaining, while the secondary y-axis (on right) is for energy content.

Figure 3. Removal rate of chokecherry fruits (squares; representing fallen fruit) and bird- processed stones (diamonds) by rodents from transects in riparian areas under plants (filled symbols) and upland habitats away from plants (open symbols) during the fall at Verdi in 1999,

Cliff Ranch in 2000, and Purdy Creek in 2001. Data expressed as the logarithm of propagules remaining (0 propagules remaining = 0.1). In addition to rodents, whole fruit may have been removed by ground foraging avian frugivores or mammalian carnivores. Along the open transect in Verdi in 1999, I included data up to the time the stations were disturbed.

Figure 4. The distribution of caches made by rodents around source shrub 2 (large circle) in

2002 at Purdy Creek, California. Open circles denote empty primary caches, closed circles were primary caches still present the following spring (2003), and diagonal crosses within closed 113 circles were primary caches that produced seedlings. Open squares were empty secondary caches, closed squares were secondary caches present during spring 2003, and vertical crosses within closed squares were secondary caches that produced seedlings. Primary caches were made by yellow pine chipmunk(s) within 1 day of taking radioactive chokecherry stones from under the source shrub. Secondary caches could have been made by individuals (species?) other than the original cacher.

Figure 5. Percentage of seedlings that emerged from single seed caches in rodent-proof exclosures that were planted in the fall of 1999 and 2001 at Ball Ranch, Nevada. Treatments include six dispersal categories: FB = intact chokecherry fruit buried 2 cm deep, FS = intact fruit on the soil surface simulating abiotic fruit fall, BB = buried bird-processed (by an American robin) stones simulating secondary dispersal by rodents, BS = surface bird-processed stones simulating avian primary dispersal, HB = buried hand-processed (fruit pulp removed by hand) stones (a control for BB), and HS = surface hand-processed stones (a control for BS); and two habitat types: exclosures placed in riparian and upland habitats. In 1999, all 81 enclosures were placed in riparian habitats. In 2001, 41 enclosures each were placed in riparian and upland habitats (82 enclosures). Filled bars indicate emergence the spring after planting, hatched bars indicate 1 year delayed-germination and emergence the second spring after planting, and open bars indicate 2 year delayed-germination and emergence the third spring (only in the 1999 cohort). 114

Chokecherry fruit on plants

1 2 3 Frugivore harvest Fruit fall Pre‐dispersal

4 5

Predatio Deposition

6 7 8 9

Die Ground harvest Not harvested

10 11 12

Eaten Scatter hoarded Die

13 14

Seeds recovered Seeds not

15 16 17 18 19 20

Larder hoarded Eaten Recached Die

21 22 23

Eaten Die

24 25 26 27

Germination and emergence

28 29 30

Abiotic mortality Seedling establishment Biotic mortality

31 32

Growth and maturation Seedling attrition Figure 1. 115

100 1200 ) A 80 1000 800 60 600 40 400 20 200 Cherries remaining (%)

0 0 (joules/fruit content Energy 4-Jul 18-Jul 1-Aug 15-Aug 29-Aug 12-Sep 26-Sep

100 1200 ) B 80 1000 800 60 600 40 400 20 200 Cherries remaining (%)

0 0 Energy content (joules/fruit 4-Jul 18-Jul 1-Aug 15-Aug 29-Aug 12-Sep 26-Sep

100 C 1400 ) 1200 80 1000 60 800

40 600 400 20 Cherries remaining (%) remaining Cherries 200 Energy content (joule/fruit content Energy 0 0 4-Jul 18-Jul 1-Aug 15-Aug 29-Aug 12-Sep 26-Sep Date

Figure 2. 116

100 Verdi 1999 g

10 Propagules remainin 1 0 7 14 21

Cliff Ranch 2000 100 g

10

1 Propagules remainin 0.1 0 7 14 21 28

Purdy Creek 2001 100 g

10

1 Propagules remainin 0.1 0 7 14 21 28 35 42 49 Days

Figure 3. 117

40

30

20

Distance (m) 10

0

-10 -40-30-20-100 10 Distance (m) Figure 4.

118

1999 2002 emergence 60 2001 emergence 50 2000 emergence 40 30 20 10

Seedling emergence (%) Seedling emergence 0 FB FS BB BS HB HS Riparian Upland

2001 2003 emergence 60 2002 emergence 50 40 30 20 10 Seedling emergence (%) Seedling emergence 0 FB FS BB BS HB HS Riparian Upland

Dispersal category Habitat Figure 5.

119

Chapter 3.

A review of two seed dispersal syndromes: frugivory and dispersal by scatter-hoarding animals

Maurie J. Beck

Program in Ecology, Evolution and Conservation Biology; University of Nevada, Reno 120

A review of two seed dispersal syndromes: frugivory and dispersal by scatter-hoarding animals

Maurie J. Beck

ABSTRACT

Two important animal-mediated seed dispersal syndromes are frugivory by vertebrate fruit consumers that ingest fleshy-fruits, then defecate or regurgitate seeds onto the ground, and caching behavior by food-hoarding animals that store seeds in small, widely- spaced caches to reduce seed loss to naïve conspecific and heterospecific competitors. In both instances, there is an exchange of food for seed transport. For frugivores, the fleshy pulp is the reward and seeds are nothing but contamination to be eliminated as quickly as possible. In contrast, seeds are a durable reward for food-storing animals, and aside from those seeds eaten immediately, there is a long-term interaction between seed cachers and their seed stores. Many of the other differences between frugivory and scatter-hoarding derive from the nature of the reward and the duration of the interaction.

Selective forces that enhance dispersal hold primacy in shaping fruit traits, whereas the additional selective demands of seedling germination and growth impose constraints on seeds that are not imposed on fruit pulp. Fruit morphology, therefore, varies far more than seed kernel morphology, and there is often strong selection on all seeds to remain inconspicuous. Perhaps for this reason, seeds that rely on seed-eating animals for dispersal generally lack external morphological devices associated with of seed dispersal.

Once frugivores disperse seeds, the interaction is terminated, and the resultant seed shadow does not change, unless other forces, such as wind, water, ants, or dung beetles, move seeds to future destinations. Scatter-hoarding animals, in contrast, incessantly 121 rearrange cache locations, either to protect their own seeds from competitors, or to pilfer those competitors. The ensuing seed shadows are thus repeatedly modified, creating a spatiotemporally dynamic seed environment. Seed burial also frequently places seeds in microsites that are disproportionally conducive to germination and establishment.

Key words: coevolution; frugivory; frugivore; diffuse mutualism; plant-animal interactions; scatter-hoarding; seed-caching rodents; seed dispersal; seed fate pathways; seed predation; seedling establishment 122

INTRODUCTION

Seed dispersal is an important process in plant life history, with significant

consequences for plant demography, spatial distribution, population divergence, and

evolution. Two important seed dispersal syndromes that plants utilize to effect seed

dispersal (van der Pijl 1982), each associated with distinct animal guilds, are frugivory by

vertebrate fruit consumers that ingest fleshy-fruits, then defecate or regurgitate seeds onto

the ground across the landscape (Howe 1986), and scatter-hoarding by animals that store

seeds in caches away from the parent plant (Price and Jenkins 1986; Stapanian and Smith

1978).

Frugivory and scatter-hoarding share some common features. Fundamentally, in both

seed dispersal syndromes, plants supply a nutritional reward for dispersal services

provided by vertebrate animal dispersers. Furthermore, studies have demonstrated that

frugivores and scatter-hoarding animals are capable of providing three benefits frequently ascribed to seed dispersal (Howe and Smallwood 1982): escape from density or distance dependent mortality due to predators, pathogens, or competition near the parent plant

(Connell 1971; Janzen 1970; Packer and Clay 2000), colonization of new habitats, often involving long-distance dispersal (Baker 1974; Jordano et al. 2007), and directed

dispersal to sites with disproportionately high recruitment (Briggs et al. 2009; Howe and

Smallwood 1982; Wenny 2001; Wenny and Levey 1998). These advantages are not

mutually exclusive because the selective forces associated with each benefit often operate

simultaneously. However, it is unlikely that a single mode of dispersal can provide all

three benefits concurrently. Consequently, many plants utilize diplochory, a seed

dispersal process that employs different modes of dispersal during sequential dispersal 123 phases and usually offers unique benefits during each phase (Vander Wall and Longland

2004). Although there are few well documented cases, a potentially common form of diplochory involves frugivory during phase I dispersal subsequently linked to phase II dispersal by scatter hoarding rodents (Beck Chapter 2; Enders 2009; Feer and Forget

2002; Forget 1991; Fragoso 1997; Vander Wall et al. 2005; Wenny 1999; Zhang and

Wang 2001).

Some researchers have suggested that a particular seed dispersal mode is associated with certain benefits and not others. For example, studies have demonstrated that frugivory often provides escape and/or colonization (Fragoso et al. 2003), in contrast to scatter-hoarding, which has frequently been linked to directed dispersal (Briggs et al.

2009). However, this relationship with a specific benefit of dispersal is more often a function of the type of disperser and their vagility or behavior than mode of dispersal

(Lees and Peres 2009). Frugivorous birds and mammals can move seeds great distances

(Fragoso et al. 2003; Jordano et al. 2007), but so do seed-caching corvids such as nutcrackers and jays (Johnson et al. 1997; Tomback 1980; Vander Wall and Balda 1977).

Many frugivorous birds disperse seeds away from sources of mortality near the parent plant, as do scatter-hoarding rodents by distributing seeds in widely spaced caches to reduce seed loss from other seed predators (Forget 1992). Some frugivores also disperse most seeds in highly aggregated clumps underneath parent plants or spatially restricted roost sites and nests (Howe 1989), a pattern that is similar to larder-hoarding granivores

(Jenkins and Breck 1998).

Most seed dispersal mutualisms between plants and animals are diffuse, involving weak asymmetric interactions among a network of seed plants and their animal dispersers 124

(Bascompte et al. 2006; Thompson 2006). Frugivory and scatter-hoarding both fit this model. For example, in Prunus mahaleb in southern Spain, many frugivorous birds and mammals eat the cherries, but only a few endozoochorous frugivores consume most of the fruit and provide effective dispersal services for this species, which ripens the earliest among 11 fleshy-fruited plants in the region that share many of the same dispersers

(Bascompte et al. 2006; Herrera and Jordano 1981; Jordano et al. 2007; Jordano and

Schupp 2000). Similarly, 3 species of winged pine seeds along with other seed plants in the Carson Range of Nevada provide food for a wide variety of animals and rely on a guild of seed-caching animals, including two species of birds and four species of rodents, for secondary dispersal following primary dispersal by the wind. Some of these animals are more effective seed dispersers than others, provide different dispersal benefits (see above). and rely to varying degrees on a subset of the pines and other seed plants (Roth and Vander Wall 2005; Thayer and Vander Wall 2005; Vander Wall 2008; Vander Wall and Joyner 1998).

Aside from the similarities listed above, there are many important differences between frugivory and scatter-hoarding seed dispersal syndromes. In this review, I will focus on the differences and discuss the implications that emerge on patterns and processes of these two divergent forms of seed dispersal.

TAXA

The types and diversity of animals engaged in frugivory and scatter-hoarding seed- dispersal syndromes are very different, as are the plant taxa involved. Most terrestrial

vertebrates include fruit in their diet, suggesting that frugivory requires fewer specialized

morphological, physiological, or behavioral adaptations for this food source. This is 125 certainly true for the very large number of animals that opportunistically eat fruit.

However, the smaller subset of specialist frugivores often have adaptations to cope with large amounts of fruit in their diet. Because many fruits are low in calories and lack specific nutrients, specialized frugivores are larger than their non-specialized counterparts, and tend to have digestive anatomy and physiology that permits them to process fruit quickly (Herrera 2002; Jordano 2000). Other important adaptations include flatter bills, wider gapes, and smaller gizzards in frugivorous birds. Similarly, fruit- eating bats have shorter, wider palates. Furthermore, many avian frugivores have specialized anatomical and physiological adaptations that permit them to consume a wide variety of toxic fruits, including large livers with specialized detoxifying enzymes, a lack of enzymes that would interact with chemicals within fruit to cause toxicity, and mechanisms to eliminate toxins or prevent their intestinal uptake (Cipollini 2000; Herrera

1985; Struempf et al. 1999; Witmer 2001).

Most prominent among frugivorous animals are passerine birds, such as tanagers, thrushes, cotingas, starlings, birds of paradise, waxwings; non-passerine birds, including toucans, trogons, parrots, pigeons, hornbills, touracos; mammalian carnivores such as bears, procyonids (raccoons, coatis), viverrids (civets, genets), and canids (coyotes, foxes), and, especially in tropical regions, monkeys, bats, forest ungulates (Bodmer

1991), elephants, reptiles, and fishes (Atsalis 1999; Bodmer 1989; Bravo 2008; Celedon-

Neghme et al. 2008; Clarke and Downie 2001; Dubost 1984; Duncan and Chapman 1999;

Galetti et al. 2008; Hamann and Curio 1999; Herrera 2002; Horn 1997; Jordano 2000;

Milton 1992; Morris et al. 2006; Olesen and Valido 2003). Worldwide, perhaps 5000 species of vertebrates regularly eat fruit and disperse seeds. 126

The types of scatter-hoarding animals that disperse seeds, on the other hand, are much reduced, primarily because this form of seed dispersal requires a special behavior (seed storage) that has evolved in a relatively narrow range of terrestrial vertebrates. Further, only those animals that scatter hoard (as opposed to larder hoard) seeds in soil (as opposed to in tree bark or foliage) are likely to be effective dispersers of seeds. Larder- hoarding animals, including most ground squirrels, bury seeds too deeply (usually in an underground burrow chamber) and scatter hoarding animals that hide seeds above the ground, such as tits, chickadees, and nuthatches place seeds in unfavorable substrates.

These restrictive conditions result in a relatively narrow range of effective species, including most corvids, such as jays, rooks, magpies, and nutcrackers; several groups of rodents, including many sciurids, heteromyids, spiny rats, some cavimorph rodents, gerbils, jerboas, and Australian hopping mice; and a couple of species of marsupials, such as musky-rat kangaroo and woylie (Dennis 2003; Murphy et al. 2005; Vander Wall

1990). These taxa amount to only several hundred species worldwide. Many food- hoarding animals also have strong bills or dentition to access seed kernels in hard-shelled nuts (Vander Wall 2001) and specialized anatomy to transport seeds, including sublingual pouches in nutcrackers (Vander Wall and Balda 1977) and cheek pouches in sciurid and heteromyid rodents (Vander Wall 2001).

Perhaps as a consequence of the relatively low diversity of scatter-hoarding animals, the diversity of seeds and nuts that are dispersed via scatter hoarding is also relatively low. Furthermore, selection typically favors inconspicuous seeds and nuts that usually vary only in size and generally lack any devices associated with a specific mode of seed dispersal, such as wings, fruits, and eliasomes (Vander Wall 1990; Vander Wall 2001; 127

Vander Wall 2008). Important genera of hoarder-dispersed propagules include Juglans and Carya (Juglandaceae), Fagus, Quercus, Lithocarpus, Castanea, and Castenopsis

(Fagaceae), Hippocastanea (Hippocastanaceae), Purshia and certain Prunus (Rosaceae),

Corylus (Betulaceae), certain Pinus (Pinaceae), Bertholletia (Lecythidaceae), Carapa

(Meliaceae), and Astrocaryum (Arecaceae) (Carvajal and Adler 2008; Forget 1997;

Jansen et al. 2004; Peres and Baider 1997; Vander Wall 1990)

The large variety of frugivorous animals that disperse fruit probably contributes to the much greater diversity of fleshy-fruited plants (van der Pijl 1982). Fleshy fruits are ubiquitous, are found throughout extinct and extant vascular plants, including gymnosperm and angiosperm lineages, and have originated numerous times (Herrera

2002). In some cases, whole orders, such as Cycads, have fleshy-fruited species dispersed by vertebrate frugivores. More often there are subsets of taxa with fleshy fruits within taxonomic groups, including families within orders and genera within families that reflect phylogenetic affiliation (Jordano 1995) and niche conservatism (Lord et al. 1995).

Fleshy fruits come in a diverse assortment of forms (Snow 1981; Wiesbauer et al.

2008). Berry-like fruits are the most common fruit type and often covary in size with the gape width of the animals that disperse them (Jordano 1995). Other fruit types include arillate fruits (derived from the seed coat) alone or in capsules or pods (e.g. tropical legumes), fleshy capsules, pyrenes, and many kinds of dehiscent non-capsular fruits

(Knapp 2002; Snow 1981). Bird-dispersed plants often present a conspicuous visual display of small, brightly colored propagules with a thin skin that remain attached to the plant at maturity (see Fig. 7.7 in Herrera 2002). In contrast, mammal dispersed fruits 128 frequently have a hard, dull-colored rind or husk and are advertised with a perceptible odor (Herrera 2002).

The genera of plants that produce fleshy fruits are too numerous to mention, but important plant families include Anacardiaceae (sumac, mango), Berberidaceae

(barberry), Cactaceae (cacti), Caprifoliaceae (honeysuckle), Cornaceae (dogwood),

Cucurbitaceae (cucumber, squash), Ericaceae (blueberry), Grossulariaceae (gooseberry, currant), Lauraceae (laurel), Moraceae (mulberry, fig), Myrtaceae (myrtle), Oleaceae

(olive), Arecaceae (palm), Piperaceae (piper), Rhamnaceae (buckthorn), Rosaceae

(blackberry, raspberry, cherry, plum, apple), Sapindaceae (soapberry), Solanaceae

(nightshade), Viscaceae (mistletoe), Vitaceae (grape), and many others (Jordano 2000;

Smith 1977; Snow 1981).

REWARD

The nutrients in fleshy fruit function as a reward for seed dispersal by frugivorous

animals. Seed kernels provide the same function for granivores that scatter hoard seeds.

For frugivory, the reward (fruit pulp) is independent of the unit of dispersal (seed). The

seed, in contrast, is the reward for food-hoarding animals. The degree of autonomy of

the unit of dispersal from the reward has important implications for dispersal in both seed

dispersal syndromes.

From the plants perspective in both dispersal syndromes, the reward, in the form of

fruit pulp or seeds, is a quid pro quo for dispersal services rendered. From the

perspective of the propagules, however, there are divergent interests. The frugivore is

only interested in the fruit pulp, but the seeds, as incidental contamination, are dispersed nonetheless. In contrast, the interaction between seeds and the scatter-hoarding animals 129 that disperse them is always antagonistic between both. Either the animal eats the seed and gains the reward without paying for dispersal or the seed is cached and not recovered without paying any nutritional reward whatsoever.

Selective forces that enhance dispersal hold primacy in shaping fruit traits, which appear to have originated solely to serve as an incentive for dispersal by frugivores. Fruit morphology varies far more than seed kernel morphology, and the fruit phenotype, in terms of shape, color, scent, taste, nutrient content, and display is substantially more diverse than in seeds (Janson 1983; Knapp 2002; Snow 1981). In many cases, fruit traits, including rewards, appear to be tailored to specific disperser guilds (Altshuler 2001; Dew and Wright 1998; Lomascolo et al. 2008; Martinez del Rio and Restrepo 1993; Shanahan et al. 2001). Considering the diversity in form, fruit morphology apparently changes more easily (Gottlieb 1984; Herrera 2002) than seed traits, which have functional conflicts imposed by selection for seed dispersal on the one hand, and germination and seedling establishment, on the other (Schupp 1995).

The selective demands of the seedling phase of the lifecycle impose constraints on seed contents that are not imposed on fruit pulp. Seedling resource requirements vary depending on ecological conditions. For example, heavy shade in dense forests favors the additional resources that large seeds provide to seedlings (Bruun and Ten Brink 2008;

Leishman and Westoby 1994a; Moles and Westoby 2004; Westoby et al. 2002) and also offer a more robust reward to scatter-hoarding rodents. However, these two selective forces are often not in accord. There are many instances in which ecological conditions might favor small seeds, but dispersal by scatter-hoarding animals favors larger 130 propagules. Seed nutrient contents must therefore not only supply resources for growing seedlings, but a reward for seed-caching animals.

Because of a focus by plant ecologists and physiologists on seedling nutrient requirements, seed traits are often not seen as features that might enhance seed dispersal

(Howe 1986). In fact, seed harvesting is almost always considered seed predation. This perception stems from a bias which asks why plants would “purposefully” feed their embryos to animals for dispersal services. But as Janzen (1986) suggested, whether a plant expends resources on fruit pulp or embryos to attract dispersers is equivalent and therefore immaterial. Seeds and nuts are very nutritious food items, and therefore function to attract seed predators and dispersers alike.

The types of nutrients in fruit pulp or seed kernels diverge significantly. Most fruits contain significant amounts of water, are low (< 10%) in protein (Moermond and

Denslow 1983; Moermond and Denslow 1985), but vary considerably in carbohydrate and lipid content (see appendix in Jordano 2000; Levey and Duke 1992; Levey and

Martinez del Rio 2001; Witmer 2001; Witmer and Van Soest 1998). This lack of dietary protein precludes many animals from being obligate frugivores, although some taxa are highly frugivorous, but either supplement their diet with small amounts of animal food, or are able to subsist on little dietary protein and nitrogen (Snow 1962; Witmer

1998b). Frugivores, therefore frequently consume a number of fruit species simultaneously, apparently to compensate for nutrient imbalances in fruit pulp (Levey

1987; Levey and Grajal 1991; Levey and Martinez del Rio 2001). Seeds and nuts, in contrast, typically have much higher lipid and protein than fruit, but lower water content

(see Table 2 in Vander Wall 2001). Many food-hoarding animals are able to persist 131 almost entirely as granivores, but they too, frequently consume many different seed types simultaneously.

There are also divergent selective forces on the conspicuousness of fruits and seeds.

This coincides with the harvest and post-dispersal phases of seeds, but only the actual harvest of fruits. Because frugivorous animals are a potentially limiting resource, large, conspicuous fruit displays potentially increase disperser visits in much the same way a prominent floral display attracts more pollinators. But once the fruit is consumed and the seeds are dispersed, the interaction between disperser and propagule is terminated. In contrast, the interaction for seeds and seed-caching animals continues. Selection may initially favor a large display of seeds or nuts to attract scatter-hoarding animals, but once seeds are buried, there is strong selection for them to remain inconspicuous.

SEED DEPOSITION

The site of seed deposition has important consequences for plant demography and

fitness (Chambers and MacMahon 1994; Herrera et al. 1994; Hulme 1997; Rogers et al.

1998). Most frugivore-dispersed seeds land on the ground after being depulped by pulp-

consuming birds, spat out, regurgitated, or defecated, although epiphytes and parasitic

mistletoes require host-plant substrates (Aukema and Martinez del Rio 2002b; Snow

1981). Depending on the quality of the deposition site, surface deposition may be all that

is necessary for germination and seedling establishment (Fragoso 1997; Fragoso and

Huffman 2000; Wenny and Levey 1998). Rogers and colleagues (Rogers et al. 1998;

Voysey et al. 1999) found that recruitment for three tree species was highest from dung at

lowland gorilla (Gorilla gorilla) nest sites, although others have found establishment of

seedlings in feces is sometimes very poor (Enders 2009). The soil surface can be a harsh 132 environment, often placing seeds at risk from such abiotic and biotic hazards as temperature extremes, desiccation, ultraviolet radiation, fire, and seed predation. Some frugivore-dispersed seeds may escape these risks by abiotic burial, but incorporation into the soil seed bank is dependent on seed size and soil particle size; as seed size increases the chance for abiotic burial decreases significantly (Chambers et al. 1991).

In contrast to frugivory, scatter-hoarding animals bury seeds in soil, which may constitute directed dispersal and disproportionately enhance seed and seedling survival

(Briggs et al. 2009; Wenny 2001). For example, chokecherry (Prunus virginiana) seedling emergence is sixteen times higher for buried seeds compared to seeds deposited on the soil surface (Beck Chapter 2) and some species of oaks and nut-bearing members of Prunus fail to germinate altogether unless buried (Beck Chapter 1; Chambers and

MacMahon 1994; Forget and Milleron 1991; Griffin 1971; Thompson 1987; Vander Wall

1993a). The benefits of burial on germination success include buffering of seeds from temperature fluctuations and maintenance of higher seed moisture, especially important in arid environments where access to water is crucial for seedling survival (Chambers and

MacMahon 1994; Griffin 1971; Vander Wall 2001). Caching also reduces the risk of detection by other seed predators, including insects, larger vertebrates such as peccaries

(Tayassu spp.), and conspecific or heterospecific pilferers (Forget et al. 1994; Janzen

1971; Vander Wall 1993a; Vander Wall et al. 2006a; Wenny 1999). The incidence of seed predation, though, varies with seed density, depth, soil moisture content and particle size, and olfactory ability of the animals (Vander Wall 2003; Vander Wall et al. 2003).

Finally, scatter-hoarding animals bury most seeds 5 – 50 mm deep where germination and emergence is common (Briggs et al. 2009; Hollander and Vander Wall 2004; Vander 133

Wall 1993a), but some species, such as golden-mantled ground squirrels (Spermophilus lateralis), bury seeds in deeper caches (Briggs et al. 2009; Vander Wall et al. in press), or store seeds in larders deep underground (Beck Chapter 1; Borchert 2004), where seeds fail to emerge (Elliott 1978; Kuhn and Vander Wall 2008; Seiwa et al. 2002). For example, Hollander and Vander Wall (2004) found that Great Basin pocket mice

(Perognathus parvus) larder-hoarded 38% of the piñon pine nuts they harvested and that seedling emergence decreased significantly at cache depths > 4 cm. In such cases, food- hoarding animals provide no dispersal services and only act as seed predators.

SPATIAL PATTERNS OF SEED DISPERSAL

Food-hoarding animals create strikingly different seed dispersion patterns compared

to those generated by frugivores. As the name implies, scatter-hoarding animals actively

space seed caches away from the source plant as well as away from other caches

(Stapanian and Smith 1978). By spacing caches widely enough that the probability of a

naïve animal finding one cache approaches that of a random search, seed-cachers,

through the use of well-developed spatial memories (Balda and Kamil 1992; Bednekoff

et al. 1997; Bossema 1979; Gould-Beierle and Kamil 1998; Macdonald 1997; Vander

Wall 1991), can manage their own caches without suffering excessive losses. At the

same time, cachers must balance the benefits of spacing with the costs of moving

between caches and recovering seeds (Stapanian and Smith 1978; Tamura et al. 1999).

This often results in non-random spacing of seeds away from parent plants within an

animal’s home range. Such dispersion patterns lower seed densities, thus minimizing

cache pilferage, reducing competition among seedlings, and decreasing mortality from

parasites and pathogens (Clarkson et al. 1986; Packer and Clay 2000). However, some 134 food-hoarding animals can also generate clumped dispersion patterns by placing them in larders.

Seed shadows generated by frugivores are often leptokurtic; i.e. seed density decreases monotonically with distance from the seed source, corresponding to a negative exponential curve (Willson and Traveset 2000). Most seeds are deposited close to the parent plant, although at the population level, the distribution of seeds may not be leptokurtic. Seed shadows made by frugivores can also result in clumped dispersal away from the fruit source by the patchiness of the habitat structure, which might provide perch sites for frugivores (Jordano and Schupp 2000; Wenny and Levey 1998), the phenology and spatial pattern of conspecifics and heterospecifics (Jordano et al. 2007), as well as the assemblage of dispersers present and the individual seed shadows they cast with respect to behavioral differences in fruit and seed handling (Herrera 1998; Martinez et al. 2008;

Schupp 1993).

Howe (1989) made a distinction between scattered and clumped seed shadows generated by frugivores. Dispersion patterns produced by frugivores vary considerably in configuration, often depending on body size. According to Howe (1989), small and moderate-sized birds and bats are more effective seed dispersers because they scatter seeds widely (Herrera and Jordano 1981; Morrison 1978; Shanahan et al. 2001), but large-bodied frugivores, including ungulates, carnivores, primates, and flightless birds, are not as effective because they deposit many seeds in feces, resulting in high seed predation and seedling mortality. However, even those animals that Howe (1989) categorized as scatter-dispersers often deposit most seeds in dense aggregations under the fruiting parent plant or conspecifics (Janzen et al. 1976). Furthermore, under some 135 conditions, clumped seed dispersal may result in successful recruitment. Wenny and

Levey (1998) found that the seeds of Ocotea endresiana had a bimodal distribution. Four species of birds dispersed most seeds under parents and conspecifics in forest, where recruitment was poor because of fungal pathogens and shade. Male three-wattled bellbirds (Procnias tricarunculata) also dispersed seeds in clumps, but these were under song posts in canopy gaps where mortality from pathogens was low and most recruitment occurred.

DURATION OF THE INTERACTION

The nature of the reward (seeds vs. fruit) has several important implications for

disperser behavior and the duration of the plant-animal interaction. First, seeds are much

less perishable than fleshy fruits and can be stored for long periods of time (Chambers

and MacMahon 1994; Janzen 1977; Vander Wall 2001). Second, seeds are a commodity

for food-hoarders (Price and Jenkins 1986), but little more than inedible ballast for

frugivores (Levey and Grajal 1991; Stanley and Lill 2002a; Stanley and Lill 2002b;

Witmer 1998a). For aerial frugivores such as birds and bats, discarding or eliminating

seeds quickly is advantageous by reducing the energetic costs of seed transport. Seed

loads also affect rate-limiting processes such as gut capacity (Norberg 1990), processing

time (Levey and Duke 1992), and nutritional assimilation (Levey and Grajal 1991;

Murray et al. 1993; but see Witmer 1998a) . For terrestrial frugivores, such as flightless

birds, mammals, reptiles), quickly eliminating seeds is less critical. Third, frugivores are

paid immediately for dispersal services with an energy rich food source, while payment

for scatter-hoarding animals is often not only delayed by substantial handling costs, but

sometimes deferred altogether because cached seeds are not recovered. 136

The ability of seeds and nuts to persist in the environment for a considerable length of time without spoilage permits them to be stored and eaten at a later time (Vander Wall

2001). In contrast, fruit spoils much more quickly, especially in warm, moist climates

(Janzen 1977), and frugivores almost always eat fruit immediately. Although some animals, including woodrats (Reichman 1988) and woodpeckers (personal observation), do cache and store fruit, the fruit would likely rot and perish long before the seeds could germinated. Further, many of these fruit-hoarding animals cache fruit in locations not conduce to seedling establishment, such as larders and in tree bark (personal observation). Seed caching by animals, on the other hand, is facilitated by the long-term durability of seeds. Many seeds are able to remain viable in caches over months and years (Brown 2001; Chambers 1989; Dalling et al. 1998; Fragoso and Huffman 2000;

Garcia et al. 2000; Garcia et al. 1999; Griffin 1971; Herrera 1982; Herrera 2000; Levey and Byrne 1993; Nogales et al. 2001; Vander Wall 2001). Such persistent food items make scatter-hoarding possible and permit food-hoarders to meet long-term energy requirements in habitats that provide seasonally inconsistent food supplies.

Frugivores can process seeds from seconds to weeks after eating fruit. For example, many primates eat fruit but spit seeds immediately (Lambert 1999; Lambert 2000), birds that depulp, mash, or swallow the fruit discard, regurgitate or defecate seeds within minutes or hours (Levey 1987; Stanley and Lill 2002a), and large herbivores can deposit seeds in dung days to weeks later (Janzen 1982). When food hoarders store seeds, the interaction is likely to persist for weeks, months, or even longer. This divergence in duration may also affect competition among dispersers. For frugivores, competition is only likely to occur at fruiting plants during harvest. For food-hoarders, in addition to 137 initial competition at the seed source, competition often continues throughout the interaction as animals pilfer each others' caches (Vander Wall et al. in press; Vander Wall and Jenkins 2003). Scatter-hoarders maintain control of stored food and thwart cache pilferage by actively managing their own food stores, resulting in a dynamic seed environment. Hence, seed shadows of scatter-hoarders are likely to change over time.

For frugivory, in contrast, there is no further interaction after the fruit has been eaten and the seeds dispersed. Thus, dispersion patterns don’t change following deposition, unless other dispersal agents such as ants, water, dung beetles, and food-hoarding animals initiate further seed movement as part of diplochorous seed dispersal.

Regardless of the duration, the level of interest in seeds following ingestion is quite different for frugivores and scatter hoarders. Once frugivores eat fruit, their interest in the seed is essentially terminated and following deposition the interaction is finished. In contrast, a scatter-hoarder maintains an interest in the stored food as long as the food exists. Because of the level of interest and the length of the interaction, scatter hoarders are much more likely to have well-developed spatial memories that enable them to manage caches over time (Balda and Kamil 1988; Bednekoff et al. 1997; Jacobs and

Liman 1991; Macdonald 1997; Vander Wall 1991; Vander Wall et al. 2006a). Perhaps some frugivores, such as bats (Ratcliffe 2009), may require a well-developed spatial memory to return to widely-spaced fruit sources daily or seasonally, but scatter-hoarding animals must keep track of thousands of caches that change in space and time.

Frugivores and scatter-hoarders may have significantly different effects on seeds because of the length of the interaction. Although gut passage in frugivores can enhance or retard germination (Rohner and Ward 1999; Traveset et al. 2001; Wahaj et al. 1998), 138 frugivores have no further direct effects on seeds after elimination, whereas food- hoarders will likely recover and eat many of the seeds they store some time in the future.

Aside from recovering and eating seeds, some scatter-hoarders can have additional detrimental effects. Sciurids and the red acouchies (Myoprocta exilis) turn seeds into

“zombies” for long-term storage by excising the embryo or otherwise damaging seeds without killing them (Fox 1982; Jansen et al. 2006; Pigott et al. 1991; Steele et al. 2001;

Wood 1938).

The duration of the interaction also has important consequences for the ability of plants to manipulate dispersers. There is evidence that plants can exert some degree of control over dispersal (mistletoe and Phainopepla; Aukema and Martinez del Rio 2002a;

Aukema and Martinez del Rio 2002b; Walsberg 1975). For example, secondary compounds in fruit pulp can affect gut retention time (Wahaj et al. 1998) or cause frugivores to leave fruit plants early (attraction/repulsion and protein assimilation hypotheses; Cipollini and Levey 1997), presumably with consequences for seed shadows.

However, because scatter-hoarding animals continue to manage and recover their caches after harvest, seed traits that increase handling time, such as hard seed hulls, or contain toxic secondary metabolites may impose costs that influence seed-caching behavior.

These costly seed traits frequently do not deter foraging, but instead increase the propensity for scatter-hoarders to cache the seeds rather than eat them (Jacobs 1992), and to recover cached seeds more slowly than seeds without those costs (Xiao et al. 2008). In a diverse seed community, seeds with costly traits would thus have a higher probability of remaining in caches until spring germination compared to seeds without these costs

(the cost-mediated cache recovery hypothesis; Beck unpublished manuscript). By 139 manipulating the behavior of scatter-hoarding animals to cache more and retrieve less, such seed traits can extend the interaction for the benefit of the seed at the expense of the seed-caching animal.

SEED DORMANCY

Seed dormancy is a life-history strategy that permits seeds to persist in unfavorable environments until more appropriate conditions for germination and establishment become available (Harper et al. 1970). As such, dormancy and persistent seed banks are bet-hedging strategies that prevent local extinction of plants that have poor dispersal

ability or occur in areas where habitat conditions favoring recruitment fluctuate over time

and there is a low probability of successfully reproducing while they are alive, such as in

annual or semelparous species) (Kalisz and McPeek 1993; Venable 2007; Venable and

Brown 1988). For example, three shade-intolerant pioneer tree species at Barro Colorado

Island, Panama, germinated after decades in seed banks in tree-fall gaps that occur unpredictably in space and time (Dalling and Brown 2009).

In certain respects, differences in dormancy are more often related to the effects of life history on traits such as seed size rather than dispersal syndrome. According to

Thompson (1987), small seeds are more likely to escape detection by vertebrate seed predators, although predation risk is also influenced by seed aggregation and abundance

(Kjellsson 1985), nutritional quality, defensive structures and seed toxins, and the types of potential seed consumers (Louda 1989; Thompson 1985). Small seeds are also more easily incorporated into the soil, where persistence in the soil seed bank would favor the evolution of seed longevity and dormancy (Chambers and MacMahon 1994). As seed size increases, the probability of burial by abiotic processes diminishes (Chambers et al. 140

1991) and detection by vertebrate seed consumers increases. If the probability of surviving until germination is small because there is strong selection by vertebrate seed consumers for larger seeds, any benefits attributed to dormancy would never be realized as seed size increased (Thompson 1987). Therefore, long-term dormancy in large-seeded species is not predicted under conditions where the dispersal agent has a continuing interaction with the propagule and acts both as an antagonist and a mutualist, as is the case with food hoarding animals. In some instances, the threat of predation is so high that seeds forego dormancy altogether and germinate immediately following maturity.

For example, to avoid seed predation many species of white oak (Quercus), Florida scrub hickory (Carya floridiana), and Araucaria all germinate within days or weeks of nut maturity (Smallwood et al. 2001; Vander Wall 2001). Many of these large-seeded species rely on burial by scatter-hoarding animals for dispersal, but face the same fluctuating recruitment conditions that favor dormancy. Instead of forming a persistent seed bank, large seeds in closed-canopy forests, for example, may germinate rapidly and then produce a persistent sapling stage in the understory until conditions improve.

Frugivory, in contrast, shows no such pattern with regard to seed size, seed predation, and dormancy. The fruits and seeds dispersed by frugivores vary by several orders of magnitude in size (Jordano 2000; Moles et al. 2007). This variation has been attributed to such factors as phylogeny (including phylogenetic niche conservatism), habitat, and coadaptation to frugivore phenotype, but not seed predation. Frugivores are uninterested in seeds per se, and therefore are not seed predators.

141

INTERANNUAL VARIATION IN SEED CROP SIZE

One of the fundamental differences between frugivory and dispersal by scatter-

hoarding animals involves the functional response of frugivores and food hoarding

animals to food abundance and variation in crop size. For frugivory, there is no advantage in satiating frugivores because they are likely a limiting resource, whereas conditions favoring seed-caching mutualisms are a subset of conditions that favor masting. During harvest, food-hoarding animals can be satiated, but their caching behavior cannot since they typically store more food than they can ever eat. Thus, large seed crops do not overwhelm disperser behavior, but increase the quantity of seeds dispersed and the probability that some of those seeds will not be recovered.

Frugivores, in contrast, can be satiated by large fruit crops because they consume their food immediately and this limits how much they can eat and disperse at any one

time (Hampe 2008). Because fruiting plants must compete for the limited appetite of a

limited number of frugivores, they should theoretically produce large fruit crops out of

phase with other plants within the population to monopolize potential dispersers. This is

the same strategy employed by flowering plants, which produce a large floral display to

attract the majority of pollinators (Brys et al. 2008). In support of this prediction, Herrera

et al. (1998) found that plants relying on frugivore-mediated dispersal had less variable

fruit crops compared to those relying on a means of dispersal in which satiation was

impossible, such as wind and water, or unlikely (scatter-hoarding animals).

Many trees that rely on scatter-hoarding animals for dispersal are masting species (but

see Herrera et al. 1998; Janzen 1971; Kelly 1994; Shepherd et al. 2008; Sork 1993;

Vander Wall 2002). One of the predominant hypotheses for masting is predator satiation, 142 which postulates that small crops starve seed predators, causing predator populations to fall (numerical response), followed by a year of large seed production which then satiates

(functional response) the smaller predator population, thus substantially increasing the proportion of surviving seeds (Vander Wall 2002). In this view, scatter-hoarding animals act primarily as antagonistic seed consumers, and only incidentally as seed dispersers

(Herrera et al. 1998; Kelly and Sork 2002). An alternative explanation is that masting is also a response by plants to benefit from the food-storing behavior of some vertebrate seed consumers. Seed caching essentially prevents these animals from being satiated. By producing an overabundance of seeds in some years, plants can not only satiate animals that always act as seed predators, such as insect seed parasites, but take advantage of scatter-hoarding animals that often harvest and store seeds well beyond their current and future needs. Many studies have shown that food hoarders store prodigious amounts of food (Chettleburgh 1952; Johnson and Adkisson 1985; Kallander 1978; Vander Wall and

Balda 1981; Wauters and Casale 1996), including Clark’s nutcrackers (Nucifraga columbiana), which stored between 1.8-3.3 times the number of pine seeds needed to meet their energetic requirements (Tomback 1982; Vander Wall 1988; Vander Wall and

Balda 1977). Under such ecological conditions, a much larger number of seeds are likely to enter caches and remain unrecovered until germination. As a consequence, mast years often result in disproportionately high levels of recruitment (Crawley and Long 1995;

Hoshizaki et al. 1997; Watt 1923; Wolff 1996) compared to non mast years (Downs and

McQuillen 1944; Jensen 1985; Sork and Boucher 1977), especially if a plant population produces large crops out of phase with other species within the community (Bossema

1979; Nilsson 1985). 143

PHYSICAL AND CHEMICAL TRAITS OF FRUIT AND SEEDS

In addition to defensive traits in fruit and seeds, fruit pulp often contains secondary metabolites that provide a diverse array of additional functions that are not found in seeds. Cipollini and Levey (1997) and Cipollini (2000) proposed that secondary metabolites may also affect seed germination, including germination inhibition and enhancement (Beck Chapter 2; Samuels and Levey 2005; Tewksbury et al. 2008;

Traveset 1998), and gut passage time (Janzen 1983; Murray et al. 1994; Wahaj et al.

1998). Previous studies have found secondary metabolites with laxative and constipative effects (Rogiers and Knowles 1997; Tewksbury et al. 2008), which may affect transit times that prevent seed damage or influence seed dispersion patterns.

Unlike seeds, in which selection favors post-dispersal inconspicuousness, fruits often utilize traits that function to attract seed dispersers, including large displays of fruit

(attraction/association hypothesis; Cipollini 2000). In addition to toxins, secondary metabolites also function as pigments such as anthocyanins and carotinoids (Harborne

1979), fragrances including aglycones, sesquiterpene, and nootkatone, and various flavanones that use flavor to signal the presence of nutrients (Boulanger and Crouzet

2000; Ortuno et al. 1995). Furthermore, Cipollini (2000) proposed that secondary metabolites may also provide direct nutritional benefits to frugivores, such as antioxidants and natural medicines (Bairlein 1996; Cipollini and Stiles 1993). For example, the maned wolf (Chrysocyon brachyurus) consumes large amounts of Solanum lycocarpum fruit, which has been implicated in preventing infection by the giant kidney worm, Dioctophyma renale (Bueno and Motta 2004; Santos et al. 2003). 144

Propagules share the need to deter non-dispersing consumers, including pathogens, insects, and vertebrate seed predators. To defend against these threats, propagules utilize a combination of physical barriers and toxic secondary chemistry. However, this defensive function may adversely affect or constrain seed dispersal, setting the stage for an evolutionary conflict between the deterrence of antagonists and the attraction of dispersers (Cipollini and Levey 1997; Vander Wall 2001).

The structural morphology of a seed dispersed by an endozoochorous frugivore primarily functions to protect the seed from the digestive environment and only affects dispersal insofar as it influences the rate-limiting process of gut passage and nutrient uptake. In contrast, the physical configuration of seeds dispersed by scatter-hoarding animals explicitly confronts this conflict between attractiveness and deterrence. For example, black walnuts (Juglans nigra) have very thick woody hulls that deter most foragers except the strongest-jawed sciurids that scatter hoard the nuts (Smith and

Follmer 1972).

Although some mammal-dispersed fruits have thick husks or hard rinds to prevent small birds and rodents from foraging on them, the pulp of many fleshy fruits often contains toxic secondary metabolites for defense (Cipollini and Levey 1997; Gautier-

Hion et al. 1985; Janson 1983). There have been varying levels of support for three hypotheses examining the defensive nature of fruit toxins, including the general toxicity, directed toxicity, and defense tradeoff hypotheses (Cipollini and Levey 1997). Toxic metabolites in immature fruits and seeds should deter consumers that are always detrimental, similar to toxins in foliage. Levels of toxicity in ripe fruit and seeds often depend on the level of threat posed by pathogens and invertebrates, thus the tradeoff of 145 attraction to dispersers and deterrence of antagonistic consumers. To counteract fruit toxins, frugivores frequently consume a number of fruit species at one time, either to dilute the effects of toxic secondary metabolites or to utilize pulp chemical constituents necessary for detoxification pathways (Cipollini 2000; Herrera 2002; Witmer 2001).

Cipollini and Levey (1997) also listed hypotheses for secondary compounds that could enhance the benefits of dispersal by influencing frugivore behavior. For example,

Sorensen (1983) proposed the attraction/repulsion, which suggests that nutrients in fruit attract dispersers, but toxins deter frugivores from continuing to feed, inducing them to leave the parent plant early. Similarly, the protein assimilation hypothesis also induces to frugivores to leave, but does so by interfering with protein metabolism (Izhaki 1998;

Izhaki and Safriel 1989; Izhaki and Safriel 1990).

However, plants that rely on scatter-hoarding animals for dispersal theoretically have a greater opportunity than frugivore-dispersed plants to use seed traits, such as hard seed coats and chemical toxins, to manipulate the propensity of dispersers to initially cache or subsequently recover seeds, thus more precisely controlling seed fates to the plants advantage (see length of the interaction above). Seeds with significant costs might enter caches in greater quantity and likely remain there until germination compared to more preferred seeds with fewer defenses.

HABITAT AND GEOGRAPHIC REGION

Fleshy fruits are found in a wide variety of habitats where they constitute a substantial proportion of the woody flora. In temperate deciduous and coniferous forests, fleshy- fruited plants account for 35 - 50% of the species (Jordano 2000). The proportion of frugivore-dispersed taxa increases with precipitation and moisture and decreases with 146 latitude. In the humid tropics, plants dispersed by vertebrate frugivores dominate the flora (> 70%), regardless of geographical region. For example, frugivory accounts for ≈

80% of species in African tropical rainforests, 82 – 88% in Australian rainforests, and 70

– 94% in neotropical rainforests (Jordano 2000). Although not well studied, arctic forest and tundra habitats also have a substantial proportion of fleshy-fruited species (Bruun et al. 2008; Herrera 2002). In contrast, fleshy-fruited plants are rare in grasslands and deserts. Grasslands are dominated by plants that generally rely on wind for seed dispersal, whereas natural selection would generally disfavor fleshy-fruit plants in arid environments where water economy is at a premium. Furthermore, seeds deposited on the ground by endozoochorous frugivores under such hot, dry conditions would be subject to intense desiccation-induced mortality.

Seed dispersal via scatter-hoarding animals has been much less well documented than frugivory. Thus, the proportion of plants in various habitats and geographical regions that rely on seed-caching animals for seed dispersal is unknown. Unlike frugivory, plants that rely on scatter-hoarding animals are probably quite common in arid and semiarid environments (Beck Chapter 1; Briggs et al. 2009; Demas and Bartness 1999; Giannoni et al. 2001; Roth and Vander Wall 2005; Thayer and Vander Wall 2005; Tsurim and

Abramsky 2004; Vander Wall 1997; Vander Wall et al. 2006b). Many of these plants produce large seeds, which supply the nutrients needed to fuel rapid root-growth to reach water underground (Baker 1972; Leishman and Westoby 1994b). However, large seeds are unlikely to be buried abiotically (Chambers and MacMahon 1994), but burial is often crucial to protect seeds from high surface temperatures and desiccation. Therefore, 147 scatter-hoarding animals are the only dispersal mechanism in arid and semiarid environments capable of placing large seeds in shallow underground microsites.

Theoretically, scatter-hoarding may be a relatively unimportant form of seed dispersal in mesic environments because seed burial is perhaps less crucial for germination, although this has not been tested for many species. In terms of seed caching behavior, hiding seeds in caches in wet forests may be ineffective, primarily because moist seeds are more likely to be detected by naïve rodent seed predators and scatter hoarders, many of which have acute olfactory sensitivity (Vander Wall 1993b; Vander Wall 2003).

Moreover, selection for food-hoarding behavior may also be less important in tropical habitats than in seasonally fluctuating temperate environments that are associated with food scarcity. Despite these arguments, scatter hoarding is prevalent in mesic temperate and tropical forests worldwide (Forget et al. 1999; Forget and Vander Wall 2001;

Guimarães et al. 2005). In fact, scatter-hoarding in many habitat types may be more common than is currently appreciated.

GENE FLOW, POPULATION DIFFERENTIATION AND SPECIATION

The transmission of genes between populations of terrestrial plants involves their

earliest life history stages (pollen and seeds). A substantial fraction of frugivores frequently move seeds long distances. Except for corvids, in contrast, most seed-caching animals are small terrestrial mammals, including many rodents some marsupials, that disperse seeds within a limited home range. Therefore, the tail of the dispersal curve may extend tens of kilometers for frugivores, but is often truncated in scatter-hoarding animals. 148

Although frugivores disperse most seeds short to medium distances, a significant fraction are carried long distances and enhance gene flow (Shaw and Small 2005; Shilton et al. 1999). Jordano and colleagues (Garcia et al. 2007; Jordano et al. 2007) found that medium-sized birds and carnivores accounted for most long distance dispersal and gene flow from up to 17 km away into their local study population of St. Lucie cherry (Prunus maheleb). As a consequence, many fleshy-fruited plants show little genetic differentiation and population substructure (Hampe et al. 2003; Hardesty et al. 2006;

Kelly et al. 2004; Oddou-Muratorio and Klein 2008; Voigt et al. 2009) and should show little local coevolutionary adaptation to dispersers (Herrera 2002). Furthermore, rates of speciation should be low, with large species ranges, and low extinction rates (Gaston

1998; Jablonski and Roy 2003; Oakwood et al. 1993). Yet the large number of fleshy- fruited species argues against this interpretation. A contrasting view is the peripheral isolates model (Holt 1997; Mayr 1963; Mayr 1982), which suggests broad geographical ranges increase the formation of isolated subpopulations and subsequent speciation.

Because frugivory and pollination mutualisms are characterized by diffuse, very diverse, asymmetric food-web networks, proponents of the geographic mosaic theory of coevolution (Bascompte et al. 2006; Jordano et al. 2003; Thompson 2005; Thompson

2006; Thompson 2009) have argued more recently that variation in the strength of coevolutionary interactions results in evolutionary hot and cold spots, resulting in local population differentiation and speciation.

Plants, including oaks and pines), dispersed by scatter-hoarding corvids also show evidence of long-distance dispersal (Pons and Pausas 2007), high levels of gene flow, and little population differentiation, congruent with many species dispersed by avian 149 frugivores (Richardson et al. 2002). Dispersal limitation, in contrast, is the primary driver of restricted gene flow, spatial demography, and population differentiation for plants dispersed by small scatter-hoarding terrestrial mammals. For example, nut-bearing members of Prunus are probably only dispersed by scatter-hoarding rodents with limited home ranges (Beck Chapter 1). Perhaps because of a lack of long distance-dispersal in dry-fruited Prunus, there is phylogeographic evidence of endemism and allopatric speciation in the separate lineages found in the deserts of Eurasia and western North

America (Bortiri et al. 2006; Browicz and Zohary 1996).

FUTURE DIRECTIONS

Detailed seed fate studies are needed to determine whether previous assumptions

about seed fate are justified. For example, it has often been assumed that a lack

morphological devices associated with a specific mode of seed dispersal suggests that

dispersal is perhaps unimportant for that species. This has been especially true for plants

in arid environments (Ellner and Shmida 1981; Gutterman 1994; Zohary 1937).

Recruitment in any of these species may require seed burial by scatter-hoarding animals

for effective seed dispersal. Additionally, previous studies of plants with fleshy-fruits

have assumed that seed dispersal is only by frugivorous animals, when, in fact, this may

be the beginning of a multi-step seed dispersal process and not the end, involving a

sequential series of different mechanisms and dispersal-related benefits (Vander Wall and

Longland 2004). 150

ACKNOWLEDGEMENTS

I thank S. B. Vander Wall, S. H. Jenkins, W. S. Longland, D. W. Zeh, and T. J.

Nickles for helpful comments on an earlier draft of this manuscript. Financial support

was provided by the Program in Ecology, Evolution, and Conservation Biology and the

Graduate Student Association at the University of Nevada, Reno.

REFERENCES

Altshuler, D. L. 2001. Ultraviolet reflectance in fruits, ambient light composition and fruit removal in a tropical forest. Evolutionary Ecology Research 3:767-778. Atsalis, S. 1999. Diet of the brown mouse lemur (Microcebus rufus) in Ranomafana National Park, Madagascar. International Journal of Primatology 20:193-229. Aukema, J. E., and C. Martinez del Rio. 2002a. Variation in mistletoe seed deposition: effects of intra- and interspecific host characteristics. Ecography 25:139-144. —. 2002b. Where does a fruit-eating bird deposit mistletoe seeds? Seed deposition patterns and an experiment. Ecology 83:3489-3496. Bairlein, F. 1996. Fruit-eating in birds and its nutritional consequences. Comparative Biochemistry and Physiology a-Physiology 113:215-224. Baker, H. G. 1972. Seed weight in relation to environmental conditions in California. Ecology 53:997-1010. —. 1974. The evolution of weeds. Annual Review of Ecology and Systematics 5:1-24. Balda, R. P., and A. C. Kamil. 1988. The spatial memory of Clark nutcrackers (Nucifraga columbiana) in an analog of the radial arm maze. Animal Learning & Behavior 16:116-122. —. 1992. Long-term spatial memory in Clark nutcracker, Nucifraga columbiana. Animal Behaviour 44:761-769. Bascompte, J., P. Jordano, and J. M. Olesen. 2006. Asymmetric coevolutionary networks facilitate biodiversity maintenance. Science 312:431-433. Beck, M. J. Chapter 1. Desert peach (Prunus andersonii) and the transition in seed dispersal mode from frugivory to scatter-hoarding, University of Nevada-Reno, Reno. —. Chapter 2. Diplochory in western chokecherry: you can’t judge a fruit by its mesocarp, University of Nevada-Reno, Reno. —. unpublished manuscript. A new hypothesis for seed characteristics that are costly (but not too costly) to seed dispersers. Bednekoff, P. A., R. P. Balda, A. C. Kamil, and A. G. Hile. 1997. Long-term spatial memory in four seed-caching corvid species. Animal Behaviour 53:335-341. 151

Bodmer, R. E. 1989. Frugivory in Amazonian artiodactyla: evidence for the evolution of the ruminant stomach. Journal of Zoology 219:457-467. —. 1991. Strategies of seed dispersal and seed predations in Amazonian ungulates. Biotropica 23:255-261. Borchert, M. 2004. Vertebrate seed dispersal of Marah macrocarpus (Cucurbitaceae) after fire in the Western Transverse Ranges of California. Ecoscience 11:463-471. Bortiri, E., B. V. Heuvel, and D. Potter. 2006. Phylogenetic analysis of morphology in Prunus reveals extensive homoplasy. Plant Systematics and Evolution 259:53-71. Bossema, I. 1979. Jays and oaks: an eco-ethological study of a symbiosis. Behaviour 1979:1-117. Boulanger, R., and J. Crouzet. 2000. Free and bound flavour components of Amazonian fruits: 2. cupuacu Volatile compounds. Flavour and Fragrance Journal 15:251- 257. Bravo, S. P. 2008. Seed dispersal and ingestion of insect-infested seeds by black howler monkeys in flooded forests of the Parana River, Argentina. Biotropica 40:471- 476. Briggs, J. S., S. B. Vander Wall, and S. H. Jenkins. 2009. Forest rodents provide directed dispersal of Jeffrey pine seeds. Ecology 90:675-687. Browicz, K., and D. Zohary. 1996. The genus Amygdalus L (Rosaceae): species relationships, distribution and evolution under domestication. Genetic Resources and Crop Evolution 43:229-247. Brown, K. 2001. Botany: patience yields secrets of seed longevity. Science 291:1884- 1885. Bruun, H. H., R. Lundgren, and M. Philipp. 2008. Enhancement of local species richness in tundra by seed dispersal through guts of muskox and barnacle goose. Oecologia 155:101-110. Bruun, H. H., and D. J. Ten Brink. 2008. Recruitment advantage of large seeds is greater in shaded habitats. Ecoscience 15:498-507. Brys, R., H. Jacquemyn, and M. Hermy. 2008. Pollination efficiency and reproductive patterns in relation to local plant density, population size, and floral display in the rewarding Listera ovata (Orchidaceae). Botanical Journal of the Linnean Society 157:713-721. Bueno, A. D., and J. C. Motta. 2004. Food habits of two syntopic canids, the maned wolf (Chrysocyon brachyurus) and the crab-eating fox (Cerdocyon thous), in southeastern Brazil. Revista Chilena De Historia Natural 77:5-14. Carvajal, A., and G. H. Adler. 2008. Seed dispersal and predation by Proechimys semispinosus and Sciurus granatensis in gaps and understory in central Panama. Journal of Tropical Ecology 24:485-492. Celedon-Neghme, C., L. A. San Martin, P. F. Victoriano, and L. A. Cavieres. 2008. Legitimate seed dispersal by lizards in an alpine habitat: The case of Berberis empetrifolia (Berberidaceae) dispersed by Liolaemus belii (Trop iduridae). Acta Oecologica-International Journal of Ecology 33:265-271. Chambers, J. C. 1989. Seed viability of alpine species: variability within and among years. Journal of Range Management 42:304-308. 152

Chambers, J. C., and J. A. MacMahon. 1994. A day in the life of a seed: movements and fates of seeds and their implications for natural and managed systems. Annual Review of Ecology and Systematics 25:263-292. Chambers, J. C., J. A. MacMahon, and J. H. Haefner. 1991. Seed entrapment in alpine ecosystems: effects of soil particle size and diaspore morphology. Ecology 72:1668-1677. Chettleburgh, M. R. 1952. Observations on the collection and burial of acorns by jays in Hainault Forest. British Birds 45:359-364. Cipollini, M. L. 2000. Secondary metabolites of vertebrate-dispersed fruits: evidence for adaptive functions. Revista Chilena De Historia Natural 73:421-440. Cipollini, M. L., and D. J. Levey. 1997. Secondary metabolites of fleshy vertebrate- dispersed fruits: adaptive hypotheses and implications for seed dispersal. American Naturalist 150:346-372. Cipollini, M. L., and E. W. Stiles. 1993. Fruit rot, antifungal defense, and palatability of fleshy fruits for frugivorous birds. Ecology 74:751-762. Clarke, F. M., and J. R. Downie. 2001. A bat (Chiroptera) survey of mora rainforest in Trinidad's Victoria-Mayaro Forest Reserve. Biodiversity and Conservation 10:725-736. Clarkson, K., S. F. Eden, W. J. Sutherland, and A. I. Houston. 1986. Density dependence and magpie food hoarding. Journal of Animal Ecology 55:111-121. Connell, J. H. 1971. On the role of natural enemies in preventing competitive exclusion in some marine animals and rain forest trees, Pages 298-312 in P. J. Den Boer, and P. R. Gadwell, eds. Dynamics of populations. Wageningen, Netherlands. Crawley, M. J., and C. R. Long. 1995. Alternate bearing, predator satiation and seedling recruitment in Querrcus robur L. Journal of Ecology 83:683-696. Dalling, J. W., and T. A. Brown. 2009. Long-term persistence of pioneer species in tropical rain forest soil seed banks. American Naturalist 173:531-535. Dalling, J. W., M. D. Swaine, and N. C. Garwood. 1998. Dispersal patterns and seed bank dynamics of pioneer trees in moist tropical forest. Ecology 79:564-578. Demas, G. E., and T. J. Bartness. 1999. Effects of food deprivation and metabolic fuel utilization on food hoarding by jirds (Meriones shawi). Physiology & Behavior 67:243-248. Dennis, A. J. 2003. Scatter-hoarding by musky rat-kangaroos, Hypsiprymnodon moschatus, a tropical rain-forest marsupial from Australia: implications for seed dispersal. Journal of Tropical Ecology 19:619-627. Dew, J. L., and P. Wright. 1998. Frugivory and seed dispersal by four species of primates in Madagascar's eastern rain forest. Biotropica 30:425-437. Downs, A. A., and W. E. McQuillen. 1944. Seed production of southern Appalachian oaks. Journal of Forestry 42:913-920. Dubost, G. 1984. Comparison of the diets of frugivorous forest ruminants of Gabon. Journal of Mammalogy 65:298-316. Duncan, R. S., and C. A. Chapman. 1999. Seed dispersal and potential forest succession in abandoned agriculture in tropical Africa. Ecological Applications 9:998-1008. 153

Elliott, L. 1978. Social behavior and foraging ecology of the eastern chipmunk (Tamias striatus) in the Adirondak Mountains. Smithsonian Contributions to Zoology 265:1-107. Ellner, S. P., and A. Shmida. 1981. Why are adaptations for long range seed dispersal rare in desert plants. Oecologia 51:133-144. Enders, M. S. 2009. Are black bears (Ursus americanus) effective seed disperrsal agents? With a little help from their friends., University of Nevada-Reno, Reno. Feer, F., and P. M. Forget. 2002. Spatiotemporal variations in post-dispersal seed fate. Biotropica 34:555-566. Forget, P. M. 1991. Comparative recruitment patterns of 2 non-pioneer canopy tree species in French Guiana. Oecologia 85:434-439. —. 1992. Regeneration ecology of Eperua grandiflora (Caesalpiniaceae), a large seeded tree in French Guiana. Biotropica 24:146-156. —. 1997. Effect of microhabitat on seed fate and seedling performance in two rodent- dispersed tree species in rain forest in French Guiana. Journal of Ecology 85:693- 703. Forget, P. M., F. Mercier, and F. Collinet. 1999. Spatial patterns of two rodent-dispersed rain forest trees Carapa procera (Meliaceae) and Vouacapoua americana (Caesalpiniaceae) at Paracou, French Guiana. Journal of Tropical Ecology 15:301-313. Forget, P. M., and T. Milleron. 1991. Evidence for secondary seed dispersal by rodents in Panama. Oecologia 87:596-599. Forget, P. M., E. Munoz, and E. G. Leigh. 1994. Predation by rodents and bruchid beetles on seeds of Scheelea palms on Barro-Colorado Island, Panama. Biotropica 26:420-426. Forget, P. M., and S. B. Vander Wall. 2001. Scatter-hoarding rodents and marsupials: convergent evolution on diverging continents. Trends in Ecology & Evolution 16:65-67. Fox, J. F. 1982. Adaptation of gray squirrel behavior to autumn germination by white oak acorns. Evolution 36:800-809. Fragoso, J. M. V. 1997. Tapir-generated seed shadows: scale-dependent patchiness in the Amazon rain forest. Journal of Ecology 85:519-529. Fragoso, J. M. V., and J. M. Huffman. 2000. Seed-dispersal and seedling recruitment patterns by the last Neotropical megafaunal element in Amazonia, the tapir. Journal of Tropical Ecology 16:369-385. Fragoso, J. M. V., K. M. Silvius, and J. A. Correa. 2003. Long-distance seed dispersal by tapirs increases seed survival and aggregates tropical trees. Ecology 84:1998- 2006. Galetti, M., C. I. Donatti, M. A. Pizo, and H. C. Giacomini. 2008. Big fish are the best: seed dispersal of Bactris glaucescens by the pacu fish (Piaractus mesopotamicus) in the Pantanal, Brazil. Biotropica 40:386-389. Garcia, C., P. Jordano, and J. A. Godoy. 2007. Contemporary pollen and seed dispersal in a Prunus mahaleb population: patterns in distance and direction. Molecular Ecology 16:1947-1955. 154

Garcia, D., R. Zamora, J. M. Gomez, P. Jordano, and J. A. Hodar. 2000. Geographical variation in seed production, predation and abortion in Juniperus communis throughout its range in Europe. Journal of Ecology 88:436-446. Garcia, D., R. Zamora, J. A. Hodar, and J. M. Gomez. 1999. Age structure of Juniperus communis L. In the Iberian peninsula: conservation of remnant populations in Mediterranean mountains. Biological Conservation 87:215-220. Gaston, K. J. 1998. Species-range size distributions: products of speciation, extinction and transformation. Philosophical Transactions of the Royal Society of London Series B-Biological Sciences 353:219-230. Gautier-Hion, A., J. M. Duplantier, R. Quris, F. Feer, C. Sourd, and J. P. D. Decoux, G. 1985. Fruit characters as a basis of fruit choice and seed dispersal in a tropical forest vertebrate community. Oecologia 65:324–337. Giannoni, S. M., M. Dacar, P. Taraborelli, and C. E. Borghi. 2001. Seed hoarding by rodents of the Monte Desert, Argentina Austral Ecology 26:259-263. Gottlieb, L. D. 1984. Genetics and morphological evolution in plants. American Naturalist 123:681-709. Gould-Beierle, K. L., and A. C. Kamil. 1998. Use of landmarks in three species of food- storing corvids. Ethology 104:361-377. Griffin, J. R. 1971. Oak regeneration in the upper Carmel Valley, California. Ecology 52:862-868. Guimarães, P. R., B. Z. Gomes, Y. J. Ahn, and M. Galetti. 2005. Cache pilferage in red- rumped agoutis (Dasyprocta leporina) (Rodentia). Mammalia 69:431-434. Gutterman, Y. 1994. Strategies of seed dispersal and germination in plants inhabiting deserts. Botanical Review 60:373-425. Hamann, A., and E. Curio. 1999. Interactions among frugivores and fleshy fruit trees in a Philippine submontane rainforest. Conservation Biology 13:766-773. Hampe, A. 2008. Fruit tracking, frugivore satiation, and their consequences for seed dispersal. Oecologia 156:137-145. Hampe, A., J. Arroyo, P. Jordano, and R. J. Petit. 2003. Rangewide phylogeography of a bird-dispersed Eurasian shrub: contrasting Mediterranean and temperate glacial refugia. Molecular Ecology 12:3415-3426. Harborne, J. B. 1979. Flavonoid pigments, Pages 619-656 in G. A. Rosenthal, and D. H. Janzen, eds. Herbivores: their interaction with secondary metabolites. New York, Academic Press. Hardesty, B. D., S. P. Hubbell, and E. Bermingham. 2006. Genetic evidence of frequent long-distance recruitment in a vertebrate-dispersed tree. Ecology Letters 9:516- 525. Harper, J. L., P. H. Lovell, and K. G. Moore. 1970. The shapes and sizes of seeds. Annual Review of Ecology and Systematics 1:327-356. Herrera, C. M. 1982. Defense of ripe fruit from pests: its significance in relation to plant- disperser interactions. American Naturalist 120:218-241. —. 1985. Aposematic insects as 6-legged fruits: incidental short circuiting of their defense by frugivorous birds. American Naturalist 126:286-293. —. 1998. Long-term dynamics of Mediterranean frugivorous birds and fleshy fruits: A 12-year study. Ecological Monographs 68:511-538. 155

—. 2000. Individual differences in progeny viability in Lavandula latifolia: A long-term field study. Ecology 81:3036-3047. —. 2002. Seed dispersal by vertebrates, Pages 185-208 in C. M. Herrera, and O. Pellmyr, eds. Plant-animal interactions: an evolutionary approach. Oxford, UK, Blackwell. Herrera, C. M., and P. Jordano. 1981. Prunus mahaleb and birds: the high efficiency seed dispersal system of a temperate fruiting tree. Ecological Monographs 51:203-218. Herrera, C. M., P. Jordano, J. Guitian, and A. Traveset. 1998. Annual variability in seed production by woody plants and the masting concept: Reassessment of principles and relationship to pollination and seed dispersal. American Naturalist 152:576- 594. Herrera, C. M., P. Jordano, L. Lopezsoria, and J. A. Amat. 1994. Recruitment of a mast- fruiting, bird-dispersed tree: bridging frugivore activity and seedling establishment. Ecological Monographs 64:315-344. Hollander, J. L., and S. B. Vander Wall. 2004. Effectiveness of six species of rodents as dispersers of singleleaf piñon pine (Pinus monophylla). Oecologia 138:57-65. Holt, R. D. 1997. Rarity and evolution: some theoretical considerations, Pages 209-234 in W. E. Kunin, and K. J. Gaston, eds. The biology of rarity. Population and community biology series; 17. London, Chapman & Hall. Horn, M. H. 1997. Evidence for dispersal of fig seeds by the fruit-eating characid fish Brycon guatemalensis Regan in a Costa Rican tropical rain forest. Oecologia 109:259-264. Hoshizaki, K., W. Suzuki, and S. Sasaki. 1997. Impacts of secondary seed dispersal and herbivory on seedling survival in Aesculus turbinata. Journal of Vegetation Science 8:735-742. Howe, H. F. 1986. Seed dispersal by fruit-eating birds and mammals, Pages 123-189 in D. R. Murray, ed. Seed dispersal. Orlando, FL, Academic Press. —. 1989. Scatter dispersal and clump dispersal and seedling demography: hypothesis and implications. Oecologia 79:417-426. Howe, H. F., and J. Smallwood. 1982. Ecology of seed dispersal. Annual Review of Ecology and Systematics 13:201-228. Hulme, P. E. 1997. Post-dispersal seed predation and the establishment of vertebrate dispersed plants in Mediterranean scrublands. Oecologia 111:91-98. Izhaki, I. 1998. Essential amino acid composition of fleshy fruits versus maintenance requirements of passerine birds. Journal of Chemical Ecology 24:1333-1345. Izhaki, I., and U. N. Safriel. 1989. Why are there so few exclusively frugivorous birds: experiments on fruit digestibility. Oikos 54:23-32. —. 1990. Weight losses due to exclusive fruit diet: interpretation and evolutionary implications: reply. Oikos 57:140-142. Jablonski, D., and K. Roy. 2003. Geographical range and speciation in fossil and living molluscs. Proceedings of the Royal Society of London Series B-Biological Sciences 270:401-406. Jacobs, L. F. 1992. The effect of handling time on the decision to cache by gray squirrels. Animal Behaviour 43:522-524. Jacobs, L. F., and E. R. Liman. 1991. Gray squirrels remember the locations of buried nuts. Animal Behaviour 41:103-110. 156

Jansen, P. A., F. Bongers, and L. Hemerik. 2004. Seed mass and mast seeding enhance dispersal by a neotropical scatter-hoarding rodent. Ecological Monographs 74:569-589. Jansen, P. A., F. Bongers, and H. H. T. Prins. 2006. Tropical rodents change rapidly germinating seeds into long-term food supplies. Oikos 113:449-458. Janson, C. H. 1983. Adaptation of fruit morphology to dispersal agents in a neotropical forest. Science 219:187-189. Janzen, D. H. 1970. Herbivores and the number of tree species in a tropical forest. American Naturalist 104:501-528. —. 1971. Seed predation by animals. Annual Review of Ecology and Systematics 2:465- 492. —. 1977. Why fruits rot, seeds mold, and meat spoils. American Naturalist 111:691-713. —. 1982. Differential seed survival and passage rates in cows and horses, surrogate pleistocene dispersal agents. Oikos 38:150-156. —. 1983. Dispersal of seeds by vertebrate guts, Pages 232-262 in D. J. Futuyma, and M. Slatkin, eds. Coevolution. Sunderland, MA, Sinauer Associates. —. 1986. Seeds as products. Oikos 46:1-2. Janzen, D. J., G. A. Miller, J. Hackford-Jones, C. M. Proud, K. Hooper, and C. P. Janos. 1976. Two Costa Rican bat-generated seed shadows of Andira inermis (Leguminosae) Ecology 57:1068-1075. Jenkins, S. H., and S. W. Breck. 1998. Differences in food hoarding among six species of heteromyid rodents. Journal of Mammalogy 79:1221-1233. Jensen, T. S. 1985. Seed-seed predator interactions of European beech, Fagus silvatica and forest rodents, Clethrionomys glareolus and Apodemus flavicollis. Oikos 44:149-156. Johnson, W. C., and C. S. Adkisson. 1985. Dispersal of beech nuts by blue jays in fragmented landscapes. American Midland Naturalist 113:319-324. Johnson, W. C., C. S. Adkisson, T. R. Crow, and M. D. Dixon. 1997. Nut caching by blue jays (Cyanocitta cristata L.): implications for tree demography. American Midland Naturalist 138:357-370. Jordano, P. 1995. Angiosperm fleshy fruits and seed dispersers: a comparative analysis of adaptation and constraints in plant-animal Interactions. American Naturalist 145:163-191. —. 2000. Fruits and frugivory in M. Fenner, ed. Seeds: the Ecology of Regeneration in Plant Communities. Wallingford, UK, C.A.B. International. Jordano, P., J. Bascompte, and J. M. Olesen. 2003. Invariant properties in coevolutionary networks of plant-animal interactions. Ecology Letters 6:69-81. Jordano, P., C. Garcia, J. A. Godoy, and J. L. Garcia-Castano. 2007. Differential contribution of frugivores to complex seed dispersal patterns. Proceedings of the National Academy of Sciences of the United States of America 104:3278-3282. Jordano, P., and E. W. Schupp. 2000. Seed disperser effectiveness: The quantity component and patterns of seed rain for Prunus mahaleb. Ecological Monographs 70:591-615. Kalisz, S., and M. A. McPeek. 1993. Extinction dynamics, population growth and seed banks. Oecologia 95:314–320. 157

Kallander, H. 1978. Hoarding in the rook Corvus frugilegus. Anser. Suppl. 3:124-128. Kelly, D. 1994. The evolutionary ecology of mast seeding. Trends in Ecology & Evolution 9:465-470. Kelly, D., J. J. Ladley, and A. W. Robertson. 2004. Is dispersal easier than pollination? Two tests in new Zealand Loranthaceae. New Zealand Journal of Botany 42:89- 103. Kelly, D., and V. L. Sork. 2002. Mast seeding in perennial plants: why, how, where? Annual Review of Ecology and Systematics 33:427-447. Kjellsson, G. 1985. Seed fate in a population of Carex pilulifera L .2. seed predation and its consequences for dispersal and seed bank. Oecologia 67:424-429. Knapp, S. 2002. Tobacco to tomatoes: a phylogenetic perspective on fruit diversity in the Solanaceae. Journal of Experimental Botany 53:2001-2022. Kuhn, K. M., and S. B. Vander Wall. 2008. Linking summer foraging to winter survival in yellow pine chipmunks (Tamias amoenus). Oecologia 157:349-360. Lambert, J. E. 1999. Seed handling in chimpanzees (Pan troglodytes) and redtail monkeys (Cercopithecus ascanius): Implications for understanding hominoid and cercopithecine fruit-processing strategies and seed dispersal. American Journal of Physical Anthropology 109:365-386. —. 2000. The fate of seeds dispersed by African apes and cercopithecines. American Journal of Physical Anthropology:204-204. Lees, A. C., and C. A. Peres. 2009. Gap-crossing movements predict species occupancy in Amazonian forest fragments. Oikos 118:280-290. Leishman, M. R., and M. Westoby. 1994a. The role of large seed size in shaded conditions: experimental evidence. Functional Ecology 8:205-214. —. 1994b. The role of seed size in seedling establishment in dry soil-conditions: experimental evidence from semiarid species. Journal of Ecology 82:249-258. Levey, D. J. 1987. Seed size and fruit-handling techniques of avian frugivores. American Naturalist 129:471-485. Levey, D. J., and M. M. Byrne. 1993. Complex ant plant interactions: rain-forest ants as secondary dispersers and postdispersal seed predators. Ecology 74:1802-1812. Levey, D. J., and G. E. Duke. 1992. How do frugivores process fruit: gastrointestinal transit and glucose absorption in cedar waxwings (Bombycilla cedrorum). Auk 109:722-730. Levey, D. J., and A. Grajal. 1991. Evolutionary implications of fruit processing limitations in cedar waxwings. American Naturalist 138:171-189. Levey, D. J., and C. Martinez del Rio. 2001. It takes guts (and more) to eat fruit: lessons from avian nutritional ecology. Auk 118:819-831. Lomascolo, S. B., P. Speranza, and R. T. Kimball. 2008. Correlated evolution of fig size and color supports the dispersal syndromes hypothesis. Oecologia 156:783-796. Lord, J., M. Westoby, and M. Leishman. 1995. Seed size and phylogeny in six temperate floras: constraints, niche conservatism, and adaptation. American Naturalist 146:349-364. Louda, S. M. 1989. Predation in the dynamics of seed regeneration, Pages 25-51 in M. A. Leck, V. T. Parker, and R. L. Simpson, eds. Ecology of soil seed banks. San Diego, Academic Press. 158

Macdonald, I. M. V. 1997. Field experiments on duration and precision of grey and red squirrel spatial memory. Animal Behaviour 54:879-891. Martinez del Rio, C., and C. Restrepo. 1993. Ecological and behavioral consequences of digestion in frugivorous animals. Vegetatio 108:205-216. Martinez, I., D. Garcia, and J. R. Obeso. 2008. Differential seed dispersal patterns generated by a common assemblage of vertebrate frugivores in three fleshy- fruited trees. Ecoscience 15:189-199. Mayr, E. 1963, Animal species and evolution. Cambridge, MA, Harvard Univ. Press. —. 1982. Speciation and macroevolution. Evolution 36:1119-1132. Milton, S. J. 1992. Plants eaten and dispersed by adult leopard tortoises Geochelone pardalis (Reptilia, Chelonii) in the Southern Karoo. South African Journal of Zoology 27:45-49. Moermond, T. C., and J. S. Denslow. 1983. Fruit choice in neotropical birds: effects of fruit type and accessibility on selectivity. Journal of Animal Ecology 52:407-420. —. 1985. Neotropical avian frugivores: patterns of behavior, morphology, and nutrition, with consequences for fruit selection, Pages 865-897 in P. A. Buckley, M. S. Foster, E. S. Morton, R. S. Ridgley, and N. G. Smith, eds. Neotropical Ornithology. Ornithological Monographs. Washington, D. C., American Ornithologists Union. Moles, A. T., D. D. Ackerly, J. C. Tweddle, J. B. Dickie, R. Smith, M. R. Leishman, M. M. Mayfield et al. 2007. Global patterns in seed size. Global Ecology and Biogeography 16:109-116. Moles, A. T., and M. Westoby. 2004. Seedling survival and seed size: a synthesis of the literature. Journal of Ecology 92:372-383. Morris, S., D. Humphreys, and D. Reynolds. 2006. Myth, marula, and elephant: an assessment of voluntary ethanol intoxication of the African elephant (Loxodonta africana) following feeding on the fruit of the marula tree (Sclerocarya birrea). Physiological and Biochemical Zoology 79:363-369. Morrison, D. W. 1978. Foraging ecology and energetics of frugivorous bats Artibeus jamaicensis. Ecology 59:716-723. Murphy, M. T., M. J. Garkaklis, and G. E. S. Hardy. 2005. Seed caching by woylies Bettongia penicillata can increase sandalwood Santalum spicatum regeneration in western Australia. Austral Ecology 30:747-755. Murray, K. G., S. Russell, C. M. Picone, K. Winnettmurray, W. Sherwood, and M. L. Kuhlmann. 1994. Fruit laxatives and seed passage rates in frugivores: consequences for plant reproductive success. Ecology 75:989-994. Murray, K. G., K. Winnettmurray, E. A. Cromie, M. Minor, and E. Meyers. 1993. The influence of seed packaging and fruit color on feeding preferences of American robins. Vegetatio 108:217-226. Nilsson, S. G. 1985. Ecological and evolutionary interactions between reproduction of beech Fagus silvatica and seed eating animals. Oikos 44:157-164. Nogales, M., F. M. Medina, V. Quilis, and M. Gonzalez-Rodriguez. 2001. Ecological and biogeographical implications of yellow-legged gulls (Larus cachinnans Pallas) as seed dispersers of Rubia fruticosa Ait. (Rubiaceae) in the Canary Islands. Journal of Biogeography 28:1137-1145. 159

Norberg, U. M. 1990, Vertebrate flight: mechanics, physiology, morphology, ecology and evolution: Zoophysiology, v. 27. Berlin, Springer Verlag. Oakwood, M., E. Jurado, M. Leishman, and M. Westoby. 1993. Geographic ranges of plant species in relation to dispersal morphology, growth form and diaspore weight. Journal of Biogeography 20:563-572. Oddou-Muratorio, S., and E. K. Klein. 2008. Comparing direct vs. indirect estimates of gene flow within a population of a scattered tree species. Molecular Ecology 17:2743-2754. Olesen, J. M., and A. Valido. 2003. Lizards as pollinators and seed dispersers: an island phenomenon. Trends in Ecology and Evolution 18:177-181. Ortuno, A., D. Garciapuig, M. D. Fuster, M. L. Perez, F. Sabater, I. Porras, A. Garcialidon et al. 1995. Flavanone and nootkatone levels in different varieties of grapefruit and pomelo. Journal of Agricultural and Food Chemistry 43:1-5. Packer, A., and K. Clay. 2000. Soil pathogens and spatial patterns of seedling mortality in a temperate tree. Nature 404:278-281. Peres, C. A., and C. Baider. 1997. Seed dispersal, spatial distribution and population structure of Brazilnut trees (Bertholletia excelsa) in southeastern Amazonia. Journal of Tropical Ecology 13:595-616. Pigott, C. D., A. C. Newton, and C. Zammit. 1991. Predation of acorns and oak seedlings by grey squirrel. Quarterly Journal of Forestry 85:173-178. Pons, J., and J. G. Pausas. 2007. Acorn dispersal estimated by radio-tracking. Oecologia 153:903-911. Price, M. A., and S. H. Jenkins. 1986. Rodents as seed consumers and dispersers, Pages 191-235 in D. R. Murray, ed. Seed dispersal. Orlando, FL, Academic Press. Ratcliffe, J. M. 2009. Neuroecology and diet selection in phyllostomid bats. Behavioural Processes 80:247-251. Reichman, O. J. 1988. Caching behavior by eastern woodrats, Neotoma floridana, in relation to food perishability. Animal Behaviour 36:1525-1532. Richardson, B. A., J. Brunsfeld, and N. B. Klopfenstein. 2002. DNA from bird-dispersed seed and wind-disseminated pollen provides insights into postglacial colonization and population genetic structure of whitebark pine (Pinus albicaulis). Molecular Ecology 11:215-227. Rogers, M. E., B. C. Voysey, K. E. McDonald, R. J. Parnell, and C. E. G. Tutin. 1998. Lowland gorillas and seed dispersal: The importance of nest sites. American Journal of Primatology 45:45-68. Rogiers, S. Y., and N. R. Knowles. 1997. Physical and chemical changes during growth, maturation, and ripening of saskatoon (Amelanchier alnifolia) fruit. Canadian Journal of Botany-Revue Canadienne De Botanique 75:1215-1225. Rohner, C., and D. Ward. 1999. Large mammalian herbivores and the conservation of arid Acacia stands in the Middle East. Conservation Biology 13:1162-1171. Roth, J. K., and S. B. Vander Wall. 2005. Primary and secondary seed dispersal of bush chinquapin (Fagaceae) by scatterhoarding rodents. Ecology 86:2428-2439. Samuels, I. A., and D. J. Levey. 2005. Effects of gut passage on seed germination: do experiments answer the questions they ask? Functional Ecology 19:365-368. 160

Santos, E. F., E. Z. F. Setz, and N. Gobbi. 2003. Diet of the maned wolf (Chrysocyon brachyurus) and its role in seed dispersal on a cattle ranch in Brazil. Journal of Zoology 260:203-208. Schupp, E. W. 1993. Quantity, quality and the effectiveness of seed dispersal by animals. Vegetatio 108:15-29. —. 1995. Seed seedling conflicts, habitat choice, and patterns of plant recruitment. American Journal of Botany 82:399-409. Seiwa, K., A. Watanabe, T. Saitoh, H. Kannu, and S. Akasaka. 2002. Effects of burying depth and seed size on seedling establishment of Japanese chestnuts, Castanea crenata. Forest Ecology and Management 164:149-156. Shanahan, M., S. So, S. G. Compton, and R. Corlett. 2001. Fig-eating by vertebrate frugivores: a global review. Biological Reviews 76:529-572. Shaw, J., and R. L. Small. 2005. Chloroplast DNA phylogeny and phylogeography of the North American plums (Prunus subgenus Prunus section Prunocerasus, Rosaceae). American Journal Of Botany 92:2011-2030. Shepherd, J. D., R. A. Ditgen, and J. Sanguinetti. 2008. Araucaria araucana and the Austral parakeet: pre-dispersal seed predation on a masting species. Revista Chilena De Historia Natural 81:395-401. Shilton, L. A., J. D. Altringham, S. G. Compton, and R. J. Whittaker. 1999. Old World fruit bats can be long-distance seed dispersers through extended retention of viable seeds in the gut. Proceedings of the Royal Society of London Series B- Biological Sciences 266:219-223. Smallwood, P. D., M. A. Steele, and S. H. Faeth. 2001. The ultimate basis of the caching preferences of rodents, and the oak-dispersal syndrome: Tannins, insects, and seed germination. American Zoologist 41:840-851. Smith, C. C., and D. Follmer. 1972. Food preferences of squirrels. Ecology 53:82-91. Smith, J. P. J. 1977, Vascular plant families: an introduction to the families of vascular plants native to North America and selected families of ornamental or economic importance. Eureka, Calif., Mad River Press. Snow, D. W. 1962. The natural history of the oilbird, Steatornis caripensis, in Trinidad, W. I. Part 2. Population breeding ecology and food. Zoologica 47:199-221. —. 1981. Tropical frugivorous birds and their food plants: a world survey. Biotropica 13:1-14. Sorensen, A. E. 1983. Taste aversion and frugivore preference. Oecologia 56:117-120. Sork, V. L. 1993. Evolutionary ecology of mast-seeding in temperate and tropical oaks (Quercus Spp). Vegetatio 108:133-147. Sork, V. L., and D. H. Boucher. 1977. Disperal of seet pignut hickory in a year of low fruit production, and the influence of predation by a curculionid beetle. Oecologia 28:289-299. Stanley, M. C., and A. Lill. 2002a. Does seed packaging influence fruit consumption and seed passage in an avian frugivore? The Condor 104:136-145. —. 2002b. Importance of seed ingestion to an avian frugivore: an experimental approach to fruit choice based on seed load. Auk 119:175-184. Stapanian, M. A., and C. C. Smith. 1978. A model for seed scatterhoarding: coevolution of fox squirrels and black walnuts. Ecology 59:884-896. 161

Steele, M. A., G. Turner, P. D. Smallwood, J. O. Wolff, and J. Radillo. 2001. Cache management by small mammals: experimental evidence for the significance of acorn-embryo excision. Journal of Mammalogy 82:35-42. Struempf, H. M., J. E. Schondube, and C. Martinez del Rio. 1999. The cyanogenic glycoside amygdalin does not deter consumption of ripe fruit by cedar waxwings. Auk 116:749-758. Tamura, N., Y. Hashimoto, and F. Hayashi. 1999. Optimal distances for squirrels to transport and hoard walnuts. Animal Behaviour 58:635-642. Tewksbury, J. J., D. J. Levey, M. Huizinga, D. C. Haak, and A. Traveset. 2008. Costs and benefits of capsaicin-mediated control of gut retention in dispersers of wild chilies. Ecology 89:107-117. Thayer, T. C., and S. B. Vander Wall. 2005. Interactions between Steller's jays and yellow pine chipmunks over scatter-hoarded sugar pine seeds. Journal of Animal Ecology 74:365-374. Thompson, J. 2005, The geographic mosaic of coevolution. Chicago, University of Chicago Press. Thompson, J. N. 1985. Postdispersal seed predation in Lomatium Spp. (Umbelliferae): variation among individuals and species. Ecology 66:1608-1616. —. 2006. Mutualistic webs of species. Science 312:372-373. —. 2009. The coevolving web of life. American Naturalist 173:125-140. Thompson, K. 1987. Seeds and seed banks. New Phytologist 106:23-34. Tomback, D. F. 1980. How nutcrackers find their seed stores. Condor 82:10-19. —. 1982. Dispersal of whitebark pine seeds by Clark nutcracker: a mutualism hypothesis. Journal of Animal Ecology 51:451-467. Traveset, A. 1998. Effect of seed passage through vertebrate frugivores' guts on germination: a review. Perspectives in Plant Ecology Evolution and Systematics 1:151-190. Traveset, A., N. Riera, and R. E. Mas. 2001. Passage through bird guts causes interspecific differences in seed germination characteristics. Functional Ecology 15:669-675. Tsurim, I., and Z. Abramsky. 2004. The effect of travel costs on food hoarding in gerbils. Journal of Mammalogy 85:67-71 van der Pijl, L. 1982, Principles of dispersal in higher plants. New York, Springer- Verlag. Vander Wall, S. B. 1988. Foraging of Clarks nutcrackers on rapidly changing pine seed resources. Condor 90:621-631. —. 1990, Food hoarding in animals. Chicago, University of Chicago Press. —. 1991. Mechanisms of cache recovery by yellow pine chipmunks. Animal Behaviour 41:851-863. —. 1993a. A model of caching depth: implications for scatter hoarders and plant dispersal. American Naturalist 141:217-232. —. 1993b. Seed water content and the vulnerability of buried seeds to foraging rodents. American Midland Naturalist 129:272-281. —. 1997. Dispersal of singleleaf piñon pine (Pinus monophylla) by seed caching rodents. Journal of Mammalogy 78:181-191. 162

—. 2001. The evolutionary ecology of nut dispersal. Botanical Review 67:74-117. —. 2002. Masting in animal-dispersed pines facilitates seed dispersal. Ecology 83:3508- 3516. —. 2003. How rodents smell buried seeds: a model based on the behavior of pesticides in soil. Journal of Mammalogy 84:1089-1099. —. 2008. On the relative contributions of wind vs. animals to seed dispersal of four Sierra Nevada pines. Ecology 89:1837-1849. Vander Wall, S. B., and R. P. Balda. 1977. Coadaptations of the Clark's nutcracker and the piñon pine for efficient seed harvest and dispersal. Ecological Monographs 47:89-111. —. 1981. Ecology and evolution of food-storage behavior in conifer-seed- catching corvids. Zeitschrift Fur Tierpsychologie-Journal of Comparative Ethology 56:217-242. Vander Wall, S. B., M. J. Beck, J. S. Briggs, J. K. Roth, T. C. Thayer, J. L. Hollander, and J. M. Armstrong. 2003. Interspecific variation in the olfactory abilities of granivorous rodents. Journal of Mammalogy 84:487-496. Vander Wall, S. B., J. S. Briggs, S. H. Jenkins, K. M. Kuhn, T. C. Thayer, and M. J. Beck. 2006a. Do food-hoarding animals have a cache recovery advantage? Determining recovery of stored food. Animal Behaviour 72:189-197. Vander Wall, S. B., M. S. Enders, and B. A. Waitman. in press. Difference in cache pilferage between yellow pine chipmunks and golden-mantled ground squirrels. Vander Wall, S. B., T. Esque, D. Haines, M. Garnett, and B. A. Waitman. 2006b. Joshua tree (Yucca brevifolia) seeds are dispersed by seed-caching rodents. Ecoscience 13:539-543. Vander Wall, S. B., and S. H. Jenkins. 2003. Reciprocal pilferage and the evolution of food-hoarding behavior. Behavioral Ecology 14:656-667. Vander Wall, S. B., and J. W. Joyner. 1998. Recaching of Jeffrey pine (Pinus jeffreyi) seeds by yellow pine chipmunks (Tamias amoenus): potential effects on plant reproductive success. Canadian Journal of Zoology-Revue Canadienne De Zoologie 76:154-162. Vander Wall, S. B., K. M. Kuhn, and J. R. Gworek. 2005. Two-phase seed dispersal: linking the effects of frugivorous birds and seed-caching rodents. Oecologia 145:282-287. Vander Wall, S. B., and W. S. Longland. 2004. Diplochory: are two seed dispersers better than one? Trends in Ecology & Evolution 19:155-161. Venable, D. S. 2007. Bet hedging in a guild of desert annuals. Ecology 88:1086–1090. Venable, D. S., and J. S. Brown. 1988. The selective interactions of dispersal, dormancy and seed size as adaptations for reducing risk in variable environments. American Naturalist 131:360–384. Voigt, F. A., R. Arafeh, N. Farwig, E. M. Griebeler, and K. Bohning-Gaese. 2009. Linking seed dispersal and genetic structure of trees: a biogeographical approach. Journal of Biogeography 36:242-254. Voysey, B. C., K. E. McDonald, M. E. Rogers, C. E. G. Tutin, and R. J. Parnell. 1999. Gorillas and seed dispersal in the Lope Reserve, Gabon. II: survival and growth of seedlings. Journal of Tropical Ecology 15:39-60. 163

Wahaj, S. A., D. J. Levey, A. K. Sanders, and M. L. Cipollini. 1998. Control of gut retention time by secondary metabolites in ripe Solanum fruits. Ecology 79:2309- 2319. Walsberg, G. E. 1975. Digestive adaptations of Phainopepla nitens associated with the eating of mistletoe berries. Condor 77:169-174. Watt, A. S. 1923. On the ecology of British beechwoods with special reference to their regeneration. Journal of Ecology 11:1-48. Wauters, L. A., and P. Casale. 1996. Long-term scatterhoarding by Eurasian red squirrels (Sciurus vulgaris). Journal of Zoology 238:195-207. Wenny, D. G. 1999. Two-stage dispersal of Guarea glabra and G. kunthiana (Meliaceae) in Monteverde, Costa Rica. Journal of Tropical Ecology 15:481-496. —. 2001. Advantages of seed dispersal: a re-evaluation of directed dispersal. Evolutionary Ecology Research 3:51-74. Wenny, D. G., and D. J. Levey. 1998. Directed seed dispersal by bellbirds in a tropical cloud forest. Proceedings of the National Academy of Sciences of the United States of America 95:6204-6207. Westoby, M., D. S. Falster, A. T. Moles, P. A. Vesk, and I. J. Wright. 2002. Plant ecological strategies: some leading dimensions of variation between species. Annual Review of Ecology and Systematics 33:125-159. Wiesbauer, M. B., E. L. H. Giehl, and J. A. Jarenkow. 2008. Morphological patterns of diaspores from animal-dispersed tree and treelet species at Parque Estadual de Itapua, Rio Grande do Sul State, Brazil. Acta Botanica Brasilica 22:425-435. Willson, M. F., and A. Traveset. 2000. The ecology of seed dispersal, Pages 85-110 in M. Fenner, ed. Seeds: the ecology of regeneration in plant communities. Wallingford, UK, C.A.B. International. Witmer, M. C. 1998a. Do seeds hinder digestive processing of fruit pulp? Implications for plant/frugivore mutualisms. Auk 115:319-326. —. 1998b. Ecological and evolutionary implications of energy and protein requirements of avian frugivores eating sugary diets. Physiological Zoology 71:599-610. —. 2001. Nutritional interactions and fruit removal: cedar waxwing consumption of Viburnum opulus fruits in spring. Ecology 82:3120-3130. Witmer, M. C., and P. J. Van Soest. 1998. Contrasting digestive strategies of fruit-eating birds. Functional Ecology 12:728-741. Wolff, J. O. 1996. Population fluctuations of mast-eating rodents are correlated with production of acorns. Journal of Mammalogy 77:850-856. Wood, O. M. 1938. Seedling production of oak in southern New Jersey. Ecology 19:276- 293. Xiao, Z. S., G. Chang, and Z. B. Zhang. 2008. Testing the high-tannin hypothesis with scatter-hoarding rodents: experimental and field evidence. Animal Behaviour 75:1235-1241. Zhang, Z. B., and F. S. Wang. 2001. Effect of rodents on seed dispersal and survival of wild apricot. Acta Ecologica Sinica 21:839-845. Zohary, M. 1937. Die verbreitungsokologischen verhaltnisse der pflanzen Palaestinas Beih. Bot. Centralbl. 56:1-155.