3~ \\ INVESTIGATING SEED DISPERSAL AND SEED PREDATION IN A HAWAllAN DRY FOREST COMMUNITY IMPLICATIONS FOR CONSERVATION AND MANAGEMENT A THESIS SUBMITTED TO THE GRADUATE DIVISION OF THE UNIVERSITY OF HAWAI'I IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE IN BOTANICAL SCIENCES (BOTANY - ECOLOGY, EVOLUTION, AND CONSERVATION BIOLOGY) DECEMBER 2004 By Charles G. Chimera Thesis Committee: Donald Drake, Chairperson Gerald Carr David Duffy Lloyd L. Loope ACKNOWLEDGEMENTS I would like to thank the EECB Program, the Hawai'i Audubon Society, the Dai Ho Chun Fellowship, and the Charles H. Lamoureux Fellowship in Plant Conservation for providing funding for my research. I would like to thank Sumner Erdman and Tony Durso ofUlupalakua Ranch for facilitating access to my study site through ranch lands. I would like to thank the staffofthe Natural Area Reserve System, particularly Betsy Gagne, Bill Evanson and Bryon Stevens, for providing access to the Kanaio Natural Area Reserve as well as for logistical support. Lloyd Loope and Art Medeiros were extremely generous with their knowledge and guidance, factors that greatly influenced my decision to conduct research in Hawaiian dry forests. Lloyd Loope also provided vehicle support during the initial stages ofmy research. I thank my thesis committee chair, Don Drake, and my committee members, Gerry Carr, Dave Duffy and Lloyd Loope for providing me with guidance and assistance during all stages ofmy thesis research. Finally, I would especially like to thank my wife, Melissa, for providing me with unlimited patience and support during my entire graduate experience. 111 TABLE OF CONTENTS ACKNOWLEDGEMENTS .111 LIST OF TABLES VI LIST OF FIGURES VIII CHAPTER 1. INTRODUCTION 1 Loss ofNative Seed Dispersers 4 Rodents and Seed Predation 5 Influence ofVegetation on Seed Dispersal and Predation 6 Hypotheses 8 CHAPTER 2. PATTERNS OF SEED DISPERSAL: VEGETATION STRUCTURE, FRUGIVORY AND SIZE EFFECTS 10 Introduction 10 Loss ofNative Seed Dispersers 12 Influence ofVegetation on Seed Dispersal 13 Methods 15 Study Site 15 Measurement ofSeed Rain Under Trees Versus in Exposed Areas 16 Seed Dispersal Analysis 19 Bird Observations 20 Seed Size Measurements 21 Characterization ofthe vegetation 22 Results 22 Seed Rain 22 Bird Observations 33 Seed Size and Bird Dispersal 35 Discussion 36 CHAPTER 3: POST-DISPERSAL SEED PREDATION: LOCATION AND EFFECT ON SPECIES 46 Introduction 46 Methods 49 Study Site 49 Measuring Seed Predation Levels 50 Treatments 51 Analysis 53 Results 54 Discussion 62 IV CHAPTER 4: CONCLUSION 68 APPENDIX A. TREE DIMENSIONS (BASAL DIAMETER, HEIGHT, CROWN DIAMETER) OF STUDY SPECIES AND DEAD TREES 73 APPENDIX B. PHENOLOGY OF STUDY TREES AND COMMON FLESHY- FRUITED SHRUBS OF THE KANAIO NATURAL AREA RESERVE 75 Methods 75 APPENDIX C. RELATIVE FREQUENCY AND ABUNDANCE OF NON-NATIVE BIRDS IN KNAR STUDY SITE 82 Methods 82 APPENDIX D. CHARACTERIZATION OF THE VEGETATION OF KNAR STUDY SITE 87 Methods 87 LITERATURE CITED 91 v LIST OF TABLES Table 2.1. Mean seed density by dispersal vector and location at KNAR from April 2003 to March 2004 23 Table 2.2. Mean density under trees and in exposed sites, and percentage oftotal seed rain for all species collected in 180 seed traps in KNAR from April 2003 to March 2004 24 Table 2.3. Mean species richness per trap offleshy-fruited seed rain under trees and in exposed sites for six dry forest trees 25 Table 2.4. Mean density ofseeds dispersed by birds and fleshy-fruited seed rain under trees and in associated exposed sites for six dry forest trees in KNAR. 27 Table 2.5. Mean density ofseeds dispersed by birds for 11 species under six dry forest trees in KNAR 28 Table 2.6. Relative frequency offleshy-fruited species in the seed rain under six dry forest trees and all exposed seed traps at KNAR 29 Table 2.7. Frequency ofseedlings offleshy-fruited species under six dry forest trees at KNAR 33 Table 2.8. Mean visits per hour and mean fruits consumed per foraging visit by seven non-native bird species to five dry forest trees at KNAR. 35 Table 2.9. Mean seed length and width of 14 seeds collected in the seed rain at KNAR.. ................................................................................................................................... 36 Table 3.1. Means ofseed length and width and mean removal rate under trees and in exposed sites for species used in the seed predation trials 55 Table 3.2. General linear models for number ofseeds and/or fruits remaining versus block, treatment, location, and the interaction oftreatment and location after 15 days for four dry forest trees in KNAR 56 Table 3.3. Two-way ANOVA results for the effects oftreatment and location on removal rates for Pleomele auwahiensis 60 Table A.I. Tree dimensions ofstudy species used in sampling offleshy-fruited seeds and seed removal trials 73 Table B.1. Monthly percentage offleshy-fruited trees and shrubs with mature fruit.. ..... 76 VI Table B.2. Mean monthly percentage ofstems with immature fruits by tree species...... 76 Table B.3. Mean monthly percentage ofstems with mature fruits by tree species 77 Table B.4. Mean monthly number ofimmature fruits and mature fruits on branches by shrub species 77 Table C.l. Relative frequency and abundance ofbird species recorded at 10 sampling stations over a l2-month period in KNAR. 83 Table D.l. Abundance ofground vegetation at KNAR study site 88 Table D.l (Continued) Abundance ofground vegetation at KNAR study site 89 Table D.2. Abundance ofcanopy vegetation at KNAR study site 89 Table D.3. Abundance ofnative and non-native vegetation, dead trees, bare ground, and open sky at KNAR study site 90 Vll LIST OF FIGURES Figure 1.1. Remnant dry forests ofthe Hawaiian Islands 3 Figure 2.1. Study area within Kanaio Natural Area Reserve 16 Figure 2.2. Mean density ofseeds dispersed by birds under six dry forest tree species... 30 Figure 2.3. Mean density ofconspecific seeds under five dry forest trees at KNAR....... 31 Figure 2.4. Mean density ofBocconia seeds versus conspecific seeds under four dry forest trees at KNAR 32 Figure 3.1. Removal rates ofseeds and fruits from the KNAR 57 Figure 3.2. Removal rates for Bocconiafrutescens and Diospyros sandwicensis seeds and fruits under trees and in exposed sites 58 Figure 3.3. Removal rates for Pleomele auwahiensis seeds and fruits under trees and in exposed sites 59 Figure 3.4. Removal rates for Pleomele auwahiensis seeds and fruits on the open ground under trees and in exposed sites 60 Figure 3.5. Removal rates for Reynoldsia sandwicensis and Santalum ellipticum seeds under trees and in exposed sites 61 Figure A.1. Tree dimensions for study species and used in sampling offleshy-fruited seeds 74 Figure B.1 Monthly percentage offleshy-fruited trees with mature fruit.. 78 Figure B.2. Monthly percentage offleshy-fruited shrubs with mature fruit.. 79 Figure B.3. Mean monthly percentage ofstems with immature and mature fruits by tree species 80 Figure B.4. Mean monthly number ofimmature and mature fruits on branches by shrub species 81 Figure C.1. Relative frequency ofbird species recorded at 10 sampling stations over a 12- month period in KNAR 84 V111 Figure C.2. Relative abundance ofbird species recorded at 10 sampling stations over a 12-month period in KNAR 85 Figure C.3. Mean number ofthree important non-native frugivores at 10 sampling stations over a 12-month period in KNAR. 86 IX CHAPTER 1. INTRODUCTION BACKGROUND Tropical dry forests are among the most diverse, yet imperiled, natural communities worldwide (Janzen 1988; Lerdau et al. 1991), and those ofthe Hawaiian Islands are no exception (Loope 1998). Tropical dry forests, which are found from Mexico to South America, Africa, Australia, Southeast Asia, and many ofthe world's tropical islands, are characterized by a mean annual rainfall of250 to 2000 mm, mean annual temperatures higher than 17°C, and one to two dry periods per year (Murphy and Lugo 1986). Unlike other tropical dry forests, which generally contain fewer tree species than neighboring rain forest does (Murphy and Lugo 1986; Janzen 1988), Hawaiian dry forests are richer in tree diversity than comparable areas ofwet forest (Rock 1913; Carlquist 1980; Sohmer and Gustafson 1987). Like their global counterparts, which have experienced a rapid and significant loss ofarea throughout the world (Murphy and Lugo 1986; Janzen 1988; Bullock et at. 1995), these unique Hawaiian communities have now been reduced to approximately 10% oftheir former extent (Bruegmann 1996; Mehrhoff 1998). Extensive impacts on and alterations ofthese Hawaiian ecosystems began with the agricultural and hunting practices ofthe early Polynesians, their use offire for land clearing, and the introduction ofnon-native animals such as the Polynesian rat, (Rattus exutans) (Kirch 1982; Sadler 1999; Burney et at. 2001; Athens et at. 2002). This deterioration and loss accelerated after the arrival ofEuropeans. As has occurred in dry forests throughout the world (Murphy and Lugo 1986; Janzen 1988), the introduction of ungulates such as cattle and goats, further land clearing for agriculture and development, 1 accidental and intentional anthropogenic fires, and the introduction ofaggressive weeds, a particularly fire-carrying grasses such as fountain grass (Pennisetum setaceum ), all contributed to the rapid decline ofthe Hawaiian dry forests (Stone 1989; Cuddihy and Stone 1990; Loope 1998). Despite these losses, however, biologically diverse areas ofdry forest still remain on several ofthe Hawaiian Islands. Notable remnant forests can be found at Pu'u Wa'a Wa'a on the island ofHawai'i, on the southern slopes ofMaui at Auwahi, Kanaio and Pu'u-o-kali, on Lanai at Kanepu'u, on Molokai at Kauhako Crater, and at Mokuleia on Oahu (Figure 1.1; Medeiros et al. 1984; Medeiros et al. 1986; Cuddihy 1989; Medeiros et al.1996; Loope 1998; Mueller-Dombois and Fosberg 1998).