Insect pollinators and predators of Spalding’s catchfly (Silene spaldingii) of the Zumwalt , Final Report – January 2012

USFWS Agreement # F10AC00090 (old #13420-A-J002)

Robert V. Taylor Sandra J. DeBano The Nature Conservancy Oregon State University 906 S River St Hermiston Agricultural Research & Extension Center Enterprise, OR 97828 PO Box 105 [email protected] Hermiston, OR 97838 [email protected]

Abstract Spalding’s catchfly (Silene spaldingii) is a rare, threatened, perennial wildflower which depends on insect pollinators for reproduction. We studied the pollinators insect predators, and ungulate browse rates on S. spaldingii in 2010 and 2011 on the Zumwalt Prairie. We also examined fruit and seed production to assess reproductive output and conducted a greenhouse experiment to examine seed viability. We found that and B. appositus were the principal pollinators of S. spaldingii and confirmed that bees carried S. spaldingii pollen and that 34% of muli- visits involved 6 or more catchfly . Bees were also more likely to visit dense patches of S. spaldingii and areas having high numbers of blooming forbs. We found that 70% of S. spaldingii stems were browsed or had their flowers eaten by insect predators such as the noctuid moth Heliothis oregonica. Only 10% of stems produced mature fruits with an average of 119 (±42 SD) seeds per fruit. Seed germination rates were low (9%) compared to rates found in previous research on this plant; seeds produced later in the season had slightly higher rates (16%) than those produced earlier (6%). Although S. spaldingii on the Zumwalt Prairie appears to have adequate insect pollinators available, low seed production and viability may present a threat to this population of this federally-listed, threatened plant.

Introduction Spalding’s catchfly (Silene spaldingii S Watson) is a perennial wildflower that once grew throughout the bunchgrass of the inland Pacific Northwest. Due primarily to the plowing of its habitat, this plant is now very rare and was listed as a threatened species under the U.S. Endangered Species Act (ESA) in 2001(US Fish and Widlife Service 2007). Currently, this plant’s geographic range includes small portions of , Oregon, and , where populations are mostly small and fragmented (Figure 1). Fourteen populations occur in the Blue Mountains Basin ecoregion in Spalding’s s catchfly pollination and predation northeast Oregon, an area that encompasses both the Zumwalt Prairie and the adjacent Wallowa Valley and Wallowa Lake moraines, and varies in elevation from approximately 1100 to 1600 m. A large population of S. spaldingii (>10,000 individuals) inhabits rolling loess-influenced bunchgrass hills and plateaus on The Nature Conservancy’s Zumwalt Prairie Preserve and adjacent lands (Figure 1; Jansen and Taylor 2010). Due to its large size and distance from other catchfly populations, this area is significant for conservation of this species. With funding from the US Fish and Wildlife Service and other sources, we conducted a study to investigate how insect pollinators and insect predators affect reproductive success in this large population S. spaldingii. Our study addressed three key issues identified in the Recovery Plan relating to insect pollination, insect predation, and catchfly’s ability to successfully reproduce by seed (US Fish and Widlife Service 2007).

First, S. spaldingii reproduces only via seed and has been shown to rely on insect pollinators for production of fertile seed (Hitchcock and Maguire 1947, Lesica 1993). One study observed an overall reduction in catchfly fitness of more than 95% in the absence of insect pollinators due to decreases in the proportion of fruits maturing, the number of seeds per fruit, rates of germination, and seedling growth and survival (Lesica 1993). Lesica and Heidel (1996) found that the rate of fruit abortion was negatively correlated with the rate of insect visitation. Thus, there is ample evidence that insect-mediated cross-pollination is critical to maintaining viable populations of this species. In recent years, however, many insects that perform important pollination services have been declining raising concerns that native plant species may be inadequately served by pollinator populations (Allen-Wardell et al. 1998). Although at least one thorough study of the pollinators of S. spaldingii has been done in the past (Lesica 1993), it did not include the Zumwalt Prairie as a study site and was done over two decades ago. In this study we sought to identify the principal pollinators, compare them to the available pool of pollinators in the area and document rates of visitation. Because the effectiveness of pollinators is also influenced by contextual factors (Kremen et al. 2007) we also evaluated two factors that might influence visitation rates: the density of S. spaldingii plants in the area and the abundance of other flowering plants. We use these data to test predictions made by resource concentration (Root, 1973 , facilitation (Waser, 1979), and competition (Pleasants, 1980) hypotheses which provide alternate explanations of how the abundance of plants influence the abundance of associated insects.

Second, observers of S. spaldingii have documented various insect predators (e.g., weevils and other beetles, lepidopteran larvae), which prey on the flowers and fruits of S. spaldingii with rates as high as 90% reported in some studies (US Fish and Widlife Service 2007). Although, it is clear that insect predators can reduce the number of fruits and seeds produced by S. spaldingii, to date there have been no studies examining the

2 Taylor & Debano US FWS Agreement# F10AC00090 Spalding’s s catchfly pollination and predation extent to which they actually affect catchfly populations. As part of this study, we tracked all catchfly plants in six plots throughout the growing season and documented rates of predation by insects and other predators. By following plants until senescence we also were able to determine how many catchfly plants successfully produced fruits.

Finally, the long-term viability of S. spaldingii populations depends ultimately on its ability to produce a sufficient number of viable seeds. Whereas lack of pollination services might be one cause for low seed production and/or low seed viability, other factors, including small population size, genetic isolation, and inbreeding, are other possibilities. To understand whether pollination or some other factor might be limiting reproductive output of S. spaldingii, we collected fruits and counted seeds from approximately 90 plants and tested the viability of the seeds. Using these data, along with observations we made on fruit production by catchfly plants, we present some rough, but intriguing estimates of total reproductive output of this rare plant on the Zumwalt Prairie.

In the sections below we describe our methods and report the results of our study. We conclude this report with a discussion of our findings and how they relate to the conservation of S. spaldingii. By coupling the results of this study to recent investigations of the effects of cattle grazing on the food web (including pollinators) we make recommendations to land managers and policy makers which, if followed, should serve to benefit populations of key pollinators and in doing so help secure the viability of S. spaldingii populations across its geographic range, thus significantly advancing efforts for recovery of the species.

Methods

Study Area The study was conducted at the Zumwalt Prairie Preserve (ZPP, lat 45º 3’ N, long 116º 6’ W) located in Wallowa County in northeastern Oregon (Figure 2 a,b). The 13,269-ha preserve is owned and managed by The Nature Conservancy (TNC) and lies in the southwestern portion of the Pacific Northwest Bunchgrass Prairie (Tisdale 1982). At 1,060-1,680 m elevation, the preserve is dominated by native bunchgrasses, including Idaho fescue (Festuca idahoensis Elmer), Sandberg bluegrass (Poa secunda J. Presl), prairie Junegrass (Koeleria macrantha [Ledeb.] Schult.), and bluebunch wheatgrass (Pseudoroegneria spicata [Pursh] A. Löve). It has a diverse assemblage of over 112 forb species including Aster L. spp., western yarrow (Achillea millefolium L.), lupines (Lupinus L. spp.), prairie smoke (Geum triflorum Pursh), and cinquefoil (Potentilla L. spp.) (Kennedy et al. 2009). S. spaldingii tends to have a patchy yet relatively

3 Taylor & Debano US FWS Agreement# F10AC00090 Spalding’s s catchfly pollination and predation substantial distribution within the preserve, with more than 50,000 plants estimated to occur across 112 ha (Jansen and Taylor 2009).

Pollinator Observations Pollinator observations were conducted between 3-12 August 2010 at 30 randomly located sites in the southern portion of the preserve (Harsin pasture), which is known to have a large concentration of the species and has been excluded from livestock grazing since 2005 (Figure 2c; Jansen and Taylor 2009). Timing of the observations coincided with the peak blooming period; S. spaldingii was observed blooming in the area from 22 July-2 September and 85% of all blooms were observed before 13 August (R.V. Taylor, unpublished data). We made observations by walking from site to site recording all instances of potential pollinators visiting S. spaldingii, following pollinators to multiple plants, and capturing visitors when possible. A total of 91.25 person-hours were spent doing observations, including 7 person-hours after dusk between 2000 and 2300 using red-tinted lights. All bees captured were frozen, pinned, labeled, sexed, and identified to species. We treat B. californicus and B. fervidus as one species (B. fervidus), although uncertainty over their taxonomic status is ongoing (Williams 2010). Representative specimens of all species were vouchered at the Oregon State Arthropod Collection at Oregon State University (OSU) in Corvallis.

We estimated the potential pool of native bee pollinators by sampling bees for 24 hours with four UV-reflective blue vane traps (Stephen and Rao 2007) in an adjacent area of similar habitat on 4-5 August 2010. Blue vane traps were separated by approximately 200 m from their nearest neighbor, and were more than 2.5 km away from catchfly sites. Blue vane traps consist of a clear plastic container (15 cm diameter x 15 cm high) with a blue polypropylene screw funnel with two 24 x 13 cm semitransparent blue polypropylene cross vanes of 3 mm thickness (SpringStar™ LLC, Woodinville, WA, USA; Figure 3a; Stephen and Rao 2005). Traps were suspended approximately 1.2 m from the ground with wire hangers inserted into aluminum pipes. No liquids or other killing agents were used in traps. Bees collected in the traps were frozen, pinned, labeled, sexed, and identified to genus, and for bumble bees, species.

Additionally, bees caught on S. spaldingii were checked for pollen in their pile. Pollen was photographed using scanning electron microscopy (SEM) at OSU. We collected pollen samples from anthers of the only other species in (Dianthus armeria, S. scouleri, and S. douglasii) that were blooming at that time and examined them with SEM. All pollen was collected at the preserve except for that of D. armeria; insufficient collection at the preserve required the use of samples from plants in Corvallis, Oregon. We compared images of bee pollen with pollen from blooming species of Caryophyllaceae.

4 Taylor & Debano US FWS Agreement# F10AC00090 Spalding’s s catchfly pollination and predation

Density and Competition Studies To determine whether the frequency of visits by potential pollinators was related to the patch-scale density of S. spaldingii or other blooming forbs and shrubs, we monitored each of the 30 sites in Harsin Pasture four times, once within each of the following time periods: 0800-1000, 1000-1200, 1300-1530, and 1530-1800. Observation sessions lasted two minutes for a total of 60 minutes in each time period. During observation sessions, two people recorded and, if possible, captured, any visitors to flowers of S. spaldingii within view of the site’s center (an approximately 15 m radius).

Density of S. spaldingii was recorded by counting the stems of catchfly within the 10 m radius of the “focal” catchfly plant at the center of the site following the first observation period at each site. The density and richness of blooming, non-catchfly plants were estimated by counting stems and recording species of all non-catchfly blooming forbs or shrubs within 3 m of the focal plant. A blooming stem was defined as containing visible live anthers and/or stigmas on at least one open flower. When a pollinator visitation was observed at a S. spaldingii plant that was not the focal individual but that was within the 15 m radius site, the non-catchfly blooming density and richness was estimated within the 3 m radius surrounding that catchfly plant. Because surrounding blooming plant composition may have changed at the first sites we monitored between initial data collection and completion of all observation periods, we repeated stem-counts and species tallies at focal plants at sites for which observation periods were separated by more than three days. The scale of measurement for intra- and inter-specific densities differed because S. spaldingii density was much lower than all non-target blooming forbs and shrubs. Thus, meaningful variation in catchfly density occurred at a larger patch size than variation in all non-target bloom density.

To test predictions generated by the resource concentration, facilitation, and competition hypotheses, we summed all visits to each site, and divided this number by the total number of catchfly plants at the site to calculate a per capita visitation rate throughout the duration of the study. We used non-metric multidimensional scaling (NMS) ordination to characterize the blooming forb and shrub community at each site. NMS ordination is a robust technique that is based on ranked distances and performs well with data that are not normally distributed and contain numerous zero values (McCune and Grace 2002). NMS was run on the presence/absence data of plant species using Sorenson’s distance measure. We excluded all plant species that occurred at less than 10% of sites from the analyses to reduce noise (McCune and Grace 2002), resulting in a data set reduced from 21 to 13 species. The best solution was determined through 250 runs of randomized data and dimensionality was determined by evaluating the relationship between final stress and the number of dimensions. Ordinations were run using PC-ORD, version 5.19, set on “autopilot” mode (McCune and Mefford 2006). Microhabitat variables analyzed included NMS scores,

5 Taylor & Debano US FWS Agreement# F10AC00090 Spalding’s s catchfly pollination and predation abundance and species richness of blooming forbs and shrubs, and density of catchfly. Because most variables were not normally distributed, Spearman rank correlation was used to test whether microhabitat variables were significantly associated with per capita visitation rate. All univariate analyses were conducted with SYSTAT (1997).

Insect Predation and Fruit Production We studied insect predation at 6 sites in Harsin Pasture in 2010 and 2011 (Figure 2c). These study sites were established in 2007 as part of a long-term study of the demography and phenology of S. spaldingii (Dingeldein et al. 2009). Within these permanent plots we observed all catchfly plants weekly, beginning in May, prior to the plant’s emergence. As each plant emerged it was marked by pushing a steel nail into the soil a few centimeters from the stem. Each plant was then visited weekly until it senesced. During each visit all catchfly plants were observed and the following noted for each stem: phenological stage, number of flowers/fruits, and any sign of predation. Predation by insects was distinguished from that by ungulates, the latter of which sever the plant’s stem and leaving a distinct browse signature. Any plant which showed signs of damage to its floral parts by insects or insect larvae was considered “predated”. The final number of mature, seed-containing fruits (if any) was noted for each plant.

Seed Production and Viability We estimated the total number of seeds produced per fruit and determined rates of viability for seeds by collecting immature and mature fruits from 10 sites in Harsin, Main Gate, and Grader pastures (Figure 2c). To ensure that our sample included fruits resulting from early, mid-, and late-blooming plants, we collected fruits during 3 “bouts”: Aug 28-20, September 2, and September 8-9. During each bout we visited each site and collected one immature fruit and one mature fruit from up to 3 plants (up to 6 fruits / site / bout). At some sites during some bouts, however, we could not locate the desired number of fruits within a reasonable distance of the site center.

Immature fruits were dissected in the laboratory and seeds counted to provide an estimate of the average per fruit seed production. Only immature fruits were suitable for this as when fruits mature the capsule dehisces releasing the seeds. Seeds were collected from the mature fruits, stored in paper envelopes (one per site/bout) and stored at room temperature until shipped to Corvallis, Oregon for germination trials at OSU. There, a total of 58 seed germination trials (out of a possible 90) were conducted simultaneously beginning on December 23, 2010 using methods similar to (Lesica 1993).

Each trial evaluated the germination ability of 10 seeds randomly selected from a single fruit collected from a single plant on a given date. For each trial, seeds were placed into a Petri dish with distilled water and placed within a cold room at 4° C. The seeds were

6 Taylor & Debano US FWS Agreement# F10AC00090 Spalding’s s catchfly pollination and predation left there for eight weeks and checked every 2-4 days and watered if dry. During the eight weeks of cold stratification some seeds began to germinate. Any seed that germinated were removed, potted, and then placed in a greenhouse. After eight weeks from the start of the trial (February 18, 2011) any remaining seeds that had not germinated in the cold room were transferred to a green house under a grow light for 14 hours per day. As seeds germinated in the greenhouse they were removed from Petri dishes and potted. We terminated the experiment on March 11, 2011, after one week passed in which none of the remaining seeds germinated,

We tested for differences in mean number of seeds per immature fruit and germination rates among collection bouts using ANOVA; when an overall effect of bout was found, we examined differences among groups, pair-wise using the Tukey-Kramer method (JMP 9.0, SAS Institute).

Results

Pollinators of Spalding’s Catchfly on the Zumwalt Prairie We observed 78 visitation bouts in which a flying insect landed on one or more catchfly flowers. The only other insect found on flowers were caterpillars, which were feeding on the plant. All flying visitors were bumble bees (Bombus spp.). Bumble bee visitations were more frequent in the afternoon than the morning. Only 4% of visitors were observed in the 0800-1000 period, while 21% were observed between 1000 and 1200, 43% between 1300 and 1530, and 32% between 1530 and 1800. Fifty-five individuals were collected, of which 10% were B. appositus Cresson and 90% B. fervidus (Figures 3b, 4a). Percents of workers, queens, and males are shown in Table 1.

In contrast, blue vane traps in an adjacent grassland yielded 444 bees in 10 genera; 47% of bees collected were Bombus and 53% belonged to other genera. A total of nine species of Bombus were collected. B. fervidus made up 19% of Bombus individuals caught in traps and 9% of all bees, while B. appositus made up 25% of Bombus and 11% of all bees (Figure 3b). Percents of workers, queens, and males are shown in Table 1.

We followed 27 visitors to multiple plants. The average number of plants visited was seven, including both S. spaldingii and other species. Fifteen percent of bees visited only one catchfly plant within the bout, 52% visited 2-5 catchfly plants, 11% visited 6-10, 19% visited 11-15, and 4% visited more than 15 consecutively. Fifty-nine percent of bees visited only S. spaldingii flowers. These visitation bouts occurred in areas with flowers of many other species (listed in Table 2), and bees often flew over other blooming forbs as they traveled from one catchfly plant to another.

7 Taylor & Debano US FWS Agreement# F10AC00090 Spalding’s s catchfly pollination and predation

Attempts to take SEM photographs of pollen on bees that were caught on S. spaldingii resulted in one photograph with distinguishable pollen. The pollen was located on the face of one B. fervidus worker and its shape and external markings matched S. spaldingii pollen and did not match the pollen of the other three Caryophyllaceae species that were blooming at the study site during the study period (Figure 5). This provides anecdotal evidence that Bombus carries pollen of S. spaldingii.

Effect of catchfly density and other flowering plants on visitation rates Sites with higher densities of S. spaldingii were visited by more pollinators, and the number of visits per catchfly plant increased with catchfly density (rs = 0.51, P < 0.005, n = 30). Although sites varied in blooming plant composition (NMS ordination resulted in a two axis solution, with axis 1 explaining 45% of the variation and axis 2 explaining 29%), the number of visits per catchfly plant was not significantly correlated with axis 1

(rs = 0.34, P > 0.05, n = 30) or axis 2 (rs = 0.13, P > 0.05, n = 30). The number of pollinator visits per catchfly plant did not significantly increase with blooming forb and shrub species richness (rs = 0.34, P > 0.05, n = 30). However, patch-scale density of blooming non-catchfly forbs/shrubs showed a positive relationship with per capita pollinator visits (rs = 0.42, P < 0.05, n = 30). There was a significant positive correlation between the densities of catchfly and blooming plants at each site (rs = 0.39, P < 0.05).

Insect predation, ungulate browse, and reproductive success Predation by ungulates, insects, or other agents (i.e., plants were found pulled up or could not be located) was observed on 71% (32 of 45) of stems in 2010 and 69% 2011 (58 of 84). Rates of insect predation on floral structures in those years were 40% and 15% respectively (Figure 7; TNC unpublished data). Of the 15% of stems that produced mature fruits in 2010 most (5 out of 7) incurred damage from predatory insects at some point in the growing season. The likelihood that a stem with immature fruits bore mature fruits was lower when there was evidence of insect herbivory (42%, n=19) than when plants were unaffected (60%, n=5, 2010-2011). Despite higher overall stem numbers and lower rates of insect predation in 2011, fewer stems produced fruits. The low level of mature fruit production (5%) may be partly attributed to heavy ungulate browsing that year (52% of stems). Of the 44 stems that were browsed in 2010 only 4 (10%) went on to produce mature fruits.

The most common insect predator we observed was the larvae of Oregon gem moth (Noctuidae: Heliothis oregonica) which we identified by rearing a moth through metamorphosis into adulthood (Figure 6). Insect predators and evidence of their damage were found on plants at different phenological stages but was most commonly observed on plants having unopened buds, open flowers and immature fruits. Although the insect predation study sites were excluded from cattle grazing, both elk and deer

8 Taylor & Debano US FWS Agreement# F10AC00090 Spalding’s s catchfly pollination and predation inhabit the study area and were most likely responsible for the ungulate herbivory we observed.

Fecundity and viability We harvested a total of 90 immature and 58 mature fruits from the 10 collection sites. The number of seeds per immature fruit was approximately normally distributed and averaged 119 (±42 SD; Range 24-224). The date of harvest did not affect the number of seeds per fruit (F = 0.70, p = 0.50). Seeds from 58 mature fruits were used in the germination trials.

Of the 580 seeds used in the germination trials only 51 germinated, yielding an overall germination rate of 9% (Figure 8). Germination rates differed across collection bouts (F = 4.27, p = 0.02). Post-hoc pair-wise comparisons revealed that the mean germination rate for seeds collected during the last bout (15.6%) was significantly higher (nearly three times) than those collected in the first bout (5.7%; p = 0.01). There was no difference in germination rate between seeds collected during the second bout (8%) and those of the other two bouts.

Discussion

Bombus fervidus and B. appositus identified as principal pollinators This study suggests that the principal pollinators of S. spaldingii in the ZPP are bumble bees, a conclusion consistent with studies of this species in other locations (Lesica 1993, Lesica and Heidel 1996). However, although Lesica and Heidel (1996) identified B. fervidus as the sole bumble bee associated with catchfly throughout its range, we found that 10% of bees visiting the plant in the Zumwalt Prairie were B. appositus. In addition, they found non-bumble bee visitors; at one location, 17% of S. spaldingii visitors were halictid bees and at two other locations noctuid moths and vespid wasps were rare visitors (2% and 1%, respectively).

Several lines of evidence suggest that B. fervidus and B. appositus are providing pollination services for S. spaldingii at the Zumwalt Prairie. First, since recruitment of S. spaldingii is pollinator-limited (Lesica 1993) and size of the Zumwalt population is relatively large, some plants can be assumed to be receiving pollination services. The fact that no other invertebrates were found visiting the plant in over 90 person-hours of observation during the peak blooming season suggests that these two species of bumble bees are the most significant pollinators. Second, we observed Bombus individuals visit multiple catchfly plants consecutively. Only 15% of observed multiple- plant visitation bouts involved only one catchfly plant, while 34% included six or more. Over half of the bouts in which bees visited an average of seven plants consisted of

9 Taylor & Debano US FWS Agreement# F10AC00090 Spalding’s s catchfly pollination and predation visits exclusively to S. spaldingii. Inter-specific pollen transfer caused by pollinators frequently switching between plant species, or interference competition, significantly reduces seed set of plants (Waser 1978, Petit 2011). Therefore, high pollinator constancy is important for providing efficient pollination services. Our observations suggest that Bombus provides this necessary pollinator constancy. Third, our discovery of S. spaldingii pollen on the face of a Bombus worker caught on a catchfly flower suggests that bumble bees actually transport catchfly pollen.

Males accounted for 49% of Bombus individuals caught on S. spaldingii and 64% of those caught in blue vane traps. Though males generally visit fewer flowers than female workers, they may be more effective pollinators. Ostevik et al. (2010) found that males transfer more pollen between each flower, potentially because they have denser, longer pile, spend more time handling each flower, and do not remove pollen into corbiculae. Male bumble bee pollination may also facilitate long-distance pollen transfer and thus help prevent inbreeding depression. Unlike female bumble bees, males are not tied down to a colony and thus have larger foraging ranges (Kraus et al. 2009). They have also been shown to switch between patches of host plants more frequently than females (Ostevik et al. 2010).

B. fervidus and B. appositus may visit S. spaldingii more frequently than other bumble bees because they are long-tongued. Catchfly flowers have long narrow corollas that may require bumble bees with long tongues to reach the nectar and pollen (Figure 3b). The species found visiting catchfly were the two most common long-tongued bees present at the Zumwalt Prairie during the catchfly blooming period, making up 19% and 25% of all bumble bees captured in blue vane traps, respectively (Figure 4). Other bumble bees abundant in blue vane traps, such as B. bifarius (19%) and B. rufocinctus (21%), have intermediate or short tongues. Other long-tongued bees, such as B. flavifrons, B. centralis, and B. nevadensis, were relatively rare, making up 5% or less of bumble bees in blue vane traps.

More evidence for facilitation than competition Bees visited individual S. spaldingii plants more frequently when the plants were in more dense patches, which is consistent with other studies which have found higher pollination success and reproduction in more dense patches (Platt et al. 1974, Klinkhamer et al. 1989) as well as experimental results showing more visitors per plant in patches of plants placed closer together than those spaced farther apart (Kunin 1997). Previous work (Lesica and Heidel 1996) has suggested that other species of blooming plants may act as competitors of S. spaldingii for pollinators, however their study lacked actual measures of the abundance of other blooming plant species. Our results, which do include these measures, suggests that visitation of pollinators to

10 Taylor & Debano US FWS Agreement# F10AC00090 Spalding’s s catchfly pollination and predation catchfly plants is actually higher in areas where there is and abundance of other flowering plants, thus providing support for the “facilitation hypothesis” (Moeller 2004).

Low germination rates found While our observations of pollinator visitation strongly suggest that the required, insect- mediated pollination of catchfly is occurring to some extent, our measures of seed germination rates raise concerns as to whether pollination or some other factor might be significantly reducing total reproductive output and in doing so threatening the viability of the population. We discovered that rates of seed germination for catchfly plants on the ZPP averaged 8%, a figure substantially lower than rates reported for this species in other studies. In the late 1980s, Lesica (1993) found that 60% of seeds collected from S. spaldingii plants in Montana germinated using a protocol similar to that employed here (e.g., 8 weeks of cold stratification, Petri dishes, etc). In a 2009 study of seed germination from the Zumwalt population, rates were also low (<5%; J Graper, unpublished data). Whether the low germination rates found here were caused by lack of sufficient pollination is not known. In their study of S. spaldingii pollination ecology Lesica and Heidel (1996) found that pollination rates at Clear Lake Ridge (an area less than 10 miles from the ZPP and having similar habitat) were the highest of the five sites they studied. Clear Lake Ridge also had the lowest fruit abortion rates prompting the authors to conclude that “pollination limitation is not likely to be a problem for [this] site”. Other factors – e.g., inbreeding depression – could also reduce seed germination rates (Baldwin and Brunsfeld 1995). To clarify this we recommend further research into the pollination biology and reproductive success of S. spaldingii on the Zumwalt Prairie. Specifically, we believe a manipulative experiment in which a test group of flowers are hand-pollinated and germination rates compared to a control group would be helpful.

It is puzzling that germination success was higher for seeds collected 8-9 September than those collected just 9-10 days earlier is. While the design of this study does not allow us to answer that question, one possible explanation is that pollinators were scarce during the earlier part of catchfly’s flowering season. Studies of S. spaldingii phenology on the ZPP indicate that it takes approximately 27 days for an open flower to become a dehiscent fruit (TNC unpublished data). That would mean that the seed we collected in late August would have come from flowers blooming in mid- to late- July. In 2010 July temperatures were lower than average (15.5°C vs. 6 year average of 17.4°C (±2.2 SD; TNC unpublished data) and this may have reduced the activity of the Bombus spp. needed for successful pollination.

Ungulates and insects take heavy toll on fruit production The high levels of browse by ungulates and insect damage to flowers and fruits we observed on catchfly plants suggest that these factors may also be significantly limiting reproductive output of S. spaldingii on the ZPP. Predation by ungulates nearly always 11 Taylor & Debano US FWS Agreement# F10AC00090 Spalding’s s catchfly pollination and predation results in total reproductive failure as the flowers or developing fruits are consumed. Unpublished data from TNC show that of 92 plants studied only 3 that were browsed went on to produce mature fruits. The number of elk in the Zumwalt Prairie area has increased sharply in recent years – the current population is approximately 4000 individuals (Oregon Department of Fish and Wildlife, unpublished data) – and it is likely that populations of S. spaldingii are currently experiencing levels of herbivory unprecedented in recent decades. In fact, the ungulate browse rates observed in 2010- 11 (46%) was higher than that observed in the prior three years (17%, TNC unpublished data; Figure 7). In most catchfly populations on the Zumwalt Prairie, herbivory by cattle may be a compounding factor, although one study of browsing by cattle indicates that, at least under light to moderate stocking rates, herbivory by this domestic ungulate is not significant (Cullen and Taylor 2010).

Insect damage affected nearly half of all stems observed during this study and nearly three-quarters of the stems that did produce mature fruits suffered predation. Although we have identified one of the insect agents that prey on S. spaldingii flowers, there may be many others we have yet to discover. Interestingly, some insects, including noctuid moths (the family which includes the moth, Heliothis oregonica, which we report on here) both prey upon and pollinate their hosts (Kephart et al. 2006). This is also the family of moths which was observed to visit S. spaldingii plants at Clear Lake Ridge by Lesica and Heidel (1996). The only occasional mention of insect predators in previous studies of S. spaldingii makes us wonder if this ecological factor is less important in other catchfly populations. Incidence of insect predation is another area in which we suggest further inquiry.

Although population modeling is beyond the scope of this study, some simple arithmetic using available data suggests that reproductive rates of S. spaldingii may be insufficient to maintain the Zumwalt Prairie population. Of the 78 catchfly plants that TNC has followed since 2007, an average of 4 plants each year produced total of 12 fruits (TNC unpublished data). Given our observation that each fruit has an average of 119 seeds and each of those seeds has an 8% chance of germinating we calculate that each plant produces approximately 1.5 viable seeds each year. With an estimated seeding survival rate of less than 50% even in greenhouse environments (Lesica 1993), our data portend poorly for the plant. It may be that the conditions in which we did our study were in some way atypical and that in some years more higher rates of pollination, lower rates of predation, and higher seed fertility converge thus allowing for high rates of recruitment in S. spaldingii on the Zumwalt Prairie. Episodic recruitment has been observed in other studies of this species though the causes of this are not well understood (Lesica 1997). In 2011 we counted the highest number of seedling rosettes, 10 of 78 plants, since we began observing them in 2007 (TNC unpublished data), which is at least some indication that recruitment is occurring.

12 Taylor & Debano US FWS Agreement# F10AC00090 Spalding’s s catchfly pollination and predation

Understanding the ecology and population dynamics of any plant is challenged, but in the case of S. spaldingii it is further complicated by its long life-span, complex ecological interactions, and unique life history (Lesica and Steele 1994). Additional research will be necessary to better understand the conditions necessary to maintain the large population of catchfly on the Zumwalt Prairie. In addition to further investigations of insect predation, seed viability, and the role of pollinators, we also believe research into the effects of fire, which has been shown in other areas to increase recruitment (Lesica 1999), should be pursued.

Conclusions and Management Recommendations This study highlights the importance of protecting pollinators of S. spaldingii. Plants that require pollination by few species with specialized morphologies are more sensitive to land use change than plants that can be pollinated by a wide variety of generalist pollinators (Kremen et al. 2007). S. spaldingii appears to have only two major pollinators in the Zumwalt Prairie, of which one (B. fervidus) accounts for 90% of visits, and those pollinators appear to preferentially visit catchfly. It is therefore vital to prevent B. fervidus and B. appositus populations from declining. Bumble bees nest in abandoned nests of small animals or above ground in grass tussocks (Thorp et al. 1983, Kearns and Thomson 2001). Understanding how sensitive these habitats are to a variety of land use changes, including fire, livestock grazing, and pesticide use, is important for the continued recovery of S. spaldingii. One recent study showed that heavy cattle grazing led to reduced numbers of bumble bees thus having potentially harmful indirect effects on catchfly (Kimoto 2011).

Additionally, this study showed that dense patches of catchfly plants and plants in areas having a high abundance of other flowering forbs are disproportionately important for conservation, since they are visited more frequently by pollinators and thus probably have greater seed set and recruitment. Other work has found that dense floral patches also tend to have higher pollinator constancy, further improving pollination services (Kunin 1997). Pollinator abundance is also affected by many other factors, including those which extend beyond the site and which include land cover in the surrounding landscape (Kearns and Thomson 2001, Ries et al. 2001). Taken together these facts add further reason to focus protection efforts towards dense patches of S. spaldingii in areas of high ecological integrity (i.e., abundance of native forbs) and in areas unfragmented by other uses. Conservation of catchfly in these areas will be even more effective if management actions can be directed towards increasing catchfly numbers and increasing overall forb abundance. Even if the land upon which a small, sparse, isolated population of S. spaldingii were to be set aside, the abundance of catchfly there would likely decline if it failed to attract a sufficient number of bee pollinators. Decreased

13 Taylor & Debano US FWS Agreement# F10AC00090 Spalding’s s catchfly pollination and predation abundance of plants could in turn foster further declines, as a result of positive feedbacks.

Because we cannot speculate as to the cause of the high insect herbivory levels that we observed on catchfly plants on the ZPP compared to other locations, we can offer no management advice on this matter but rather encourage further investigation into this phenomenon. There may, however, be opportunities to address the high levels of wild ungulate herbivory that we observed. There is currently an effort by both TNC and other private landowners in the area to work with the Oregon Department of Fish and Wildlife to reduce the number of elk in this area. We believe such efforts would also yield benefits for S. spaldingii.

Acknowledgements We thank R. Halse and J. Dingeldein for help with plant identification, and W. P. Stephen and R. W. Thorp for confirming bumble bee species identification. We are infinitely grateful to C. Tubbesing, C. Strohm, N. Gonzalez, and C. Kimoto for their work on the pollinator portion of the study. We also thank H. Schmalz, J. Dingeldein, W. D. Blankenship, S. Bonner, S. Galbraith, C. Peyton, D. Snodgrass, and S. Thomas for their various contributions in the field and laboratory. Kelly Amsberry and Benjahmin Boschee kindly performed the seed germination trials. Part of this research was supported by the National Science Foundation under Grant No. 0755511.

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Jansen, V. S. and R. V. Taylor. 2009. Mapping and monitoring Spalding's Catchfly (Silene spaldingii) on the Zumwalt Prairie Preserve (2006-2009). The Nature Conservancy, Enterprise, OR.

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Tables

Table 1. Comparisons of percent male, workers, and queens for bumble bees visiting Silene spaldingii and collected in blue vane traps.

Blue Vane Trap S. spaldingii

Male 76% Male 100%

B. appositus Worker 18% Worker 0%

Queen 6% Queen 0%

n = 51 n = 5

Male 48% Male 44%

B. fervidus Worker 45% Worker 54%

Queen 8% Queen 2%

n = 40 n = 50

Male 64% Male 49%

Total Worker 29% Worker 51%

Queen 7% Queen 0%

n = 91 n = 55

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Table 2. Blooming plants observed through the course of the pollinator observation study and the number of sites (out of 30) in which the species was present.

Family Name Scientific name (common name) # sites Apiaceae Perideridia gairdneri (Hook. & Arn.) Mathias 10 (Gardner's yampah) Asteraceae Erigeron pumilus Nutt. 12 (shaggy fleabane) Cirsium brevifolium Nutt. 3 (Palouse thistle) Pyrrocoma carthamoides Hook var. cusickii (A. Gray) Kartesz 2 & Gandhi (largeflower goldenweed) Grindelia squarrosa (Pursh) Dunal 2 (curlycup gumweed) Symphyotrichum campestre (Nutt.) G.L. Nesom var. campestre 11 (western meadow aster) Solidago missouriensis Nutt. var. missouriensis 16 (Missouri goldenrod) Hieracium cynoglossoides Arv.-Touv. 8 (houndstongue hawkweed) Achillea millefolium L. var. occidentalis DC. 24 (western yarrow) Caprifoliaceae Symphoricarpos albus (L.) S.F. Blake 1 (common snowberry) Caryophyllaceae Silene scouleri Hook. 2 (simple campion) Dianthus armeria L. 7 (Deptford pink) Fabaceae Lupinus leucophyllus Douglas ex Lindl. 2 (velvet lupine) Gentianaceae Gentiana affinis Griseb. 1 (pleated gentian) Geraniaceae Geranium viscosissimum Fisch. & C.A. Mey. ex C.A. Mey. 1 (sticky purple geranium) Liliaceae Calochortus macrocarpus Douglas 5 (sagebrush mariposa lily) Onagraceae Clarkia pulchella Pursh 6 (pinkfairies) Epilobium brachycarpum C. Presl 9 (tall annual willowherb) Polygonaceae Eriogonum heracleoides Nutt. var. angustifolium (Nutt.) 3 Torr. & A. Gray (parsnipflower buckwheat) Scrophulariaceae Orthocarpus tenuifolius (Pursh) Benth. 10 (thinleaved owl's-clover) Castilleja oresbia Greenm. 1 (pale Wallowa Indian paintbrush)

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Figures

Figure 1. Distribution of Silene spaldingii (left) in North America and (right) in the Blue Mountain Basins ecoregion (from U.S. Fish and Wildlife Service, 2007).

19 Taylor & Debano US FWS Agreement# F10AC00090 Spalding’s s catchfly pollination and predation

Blue vane traps

Figure 2. a) Location of the Zumwalt Prairie in eastern Oregon; b) boundaries of the Zumwalt Prairie Preserve; and c) the location of the 30 pollinator observation sites, the 6 demography plots (indicated here by a single point), 10 fruit collection sites, and the four blue vane traps. 20 Taylor & Debano US FWS Agreement# F10AC00090 Spalding’s s catchfly pollination and predation

Figure 3. a) Blue vane trap in grassland adjacent to S. spaldingii observation sites and b) Bombus fervidus visiting S. spaldingii (Photograph by C. Strohm).

Figure 4. Comparison of a) Bombus species observed visiting S. spaldingii and b) Bombus collected in an adjacent grassland using blue vane traps.

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Figure 5. SEM photographs of pollen from a) the face of a Bombus fervidus worker caught visiting Silene spaldingii, b) S. spaldingii, c) S. scouleri, d) S. douglasii and e) Dianthus armeria.

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Figure 6. A common insect predator of Silene spaldingii, the larvae of the noctuid moth Heliothis oregonica is commonly observed feeding on the ovaries of catchfly plants on the Zumwalt Prairie. Shown here is the larvae (left) and the adult moth (right).

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25% 50 % 75 0% 10 % 0

0

100%

75%

Figure 7. Rates of predation by insects, ungulates, and other agents and frequency of fruit production (both immature [Im] and mature [M]) from 6 demography/phenology plots in Harsin Pasture on the Zumwalt Prairie Preserve. Also shown are rates of mature fruit production in conjunction with insect and ungulate predation. All rates are calculated as the number of stems divided by the total number of stems observed. Because categories are not mutually exclusive they may sum to greater than 100%.

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Figure 8. Germination rates of Spalding catchfly (Silene spaldingii) seeds collected on the Zumwalt Prairie Preserve from three collection bouts in 2010. Each germination trial tested germination success of 10 seeds from a single mature fruit. Bars indicate one standard error of the mean. Rates for bouts sharing the same lowercase letter were not significantly different (alpha = 0.05).

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