Small Mammal Faunal Stasis in Natural Trap Cave (Pleistocene– Holocene), Bighorn Mountains, Wyoming
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SMALL MAMMAL FAUNAL STASIS IN NATURAL TRAP CAVE (PLEISTOCENE– HOLOCENE), BIGHORN MOUNTAINS, WYOMING BY C2009 Daniel R. Williams Submitted to the graduate degree program in Ecology and Evolutionary Biology and the Graduate Faculty of the University of Kansas in partial fulfillment of the requirements for the degree of Doctor of Philosophy. ______________________ Larry D. Martin/Chairperson Committee members* _____________________* Bruce S. Lieberman _____________________* Robert M. Timm _____________________* Bryan L. Foster _____________________* William C. Johnson Date defended: April 21, 2009 ii The Dissertation Committee for Daniel Williams certifies that this is the approved version of the following dissertation: SMALL MAMMAL FAUNAL STASIS IN NATURAL TRAP CAVE (PLEISTOCENE– HOLOCENE), BIGHORN MOUNTAINS, WYOMING Commmittee: ____________________________________ Larry D. Martin/Chairperson* ____________________________________ Bruce S. Lieberman ____________________________________ Robert M. Timm ____________________________________ Bryan L. Foster ____________________________________ William C. Johnson Date approved: April, 29, 2009 iii ABSTRACT Paleocommunity behavior through time is a topic of fierce debate in paleoecology, one with ramifications for the general study of macroevolution. The predominant viewpoint is that communities are ephemeral objects during the Quaternary that easily fall apart, but evidence exists that suggests geography and spatial scale plays a role. Natural Trap Cave is a prime testing ground for observing how paleocommunities react to large-scale climate change. Natural Trap Cave has a continuous faunal record (100 ka–recent) that spans the last glacial cycle, large portions of which are replicated in local rockshelters, which is used here to test for local causes of stasis. The Quaternary fauna of North America is relatively well sampled and dated, so the influence of spatial scale and biogeography on local community change can also be tested for. Here I use the herbivorous and omnivorous small mammal fauna (<5 kg) of Natural Trap Cave, which are more likely to be members of a local paleocommunity than more mobile large mammals and carnivores. A significant proportion of the fauna is present throughout the record and these are primarily arid and open-habitat adapted, or generalist, taxa that are predicted to find the full-glacial environment of northern Wyoming suitable in any case. An invasion of arctic and alpine tundra taxa occurred during the Last Glacial Maximum, but these were extirpated locally following the deglaciation. The regional ecosystem surrounding Natural Trap Cave also had significant faunal carryover (>50%). The likely cause for the local stasis in Natural Trap Cave is distance from the modern northern and southern edges of the member taxa distributions, a reflection of their broad range of adaptation. North–south oriented mountain barriers preserve the integrity of the regional fauna by allowing habitat-tracking down-elevation. These mountain barriers also limit east–west dispersal from neighboring faunal provinces. iv Acknowledgments I wish to thank L. D. Martin for making the Natural Trap Cave collection available for study, critical input, and manuscript review. S. A. Chomko, B. M. Gilbert, and J. Chorn for answering questions regarding excavation of Natural Trap Cave and the rockshelters, R. M. Timm for KUM collections use and manuscript review, J. Bradley and J. Kenagy of UWBM for specimen loans; B. Lieberman, B. Foster, and W. Johnson for manuscript review, S. Klopfenstein and S. Maher for GIS help, N. Slade for discussions on nonparametric statistics, financial support from the KUNHM/BRC Panorama Grant program, C. Baxter for comments on leporid identification, S. Hasiotis for IchnoBioGeoScience Lab equipment use, and Liz for life support. v TABLE OF CONTENTS ABSTRACT iii ACKNOWLEDGMENTS iv TABLE OF CONTENTS v FIGURES AND TABLES vi CHAPTER 1: INTRODUCTION 1 CHAPTER 2: SYSTEMATIC DESCRIPTION AND ADDITIONS TO THE 19 NATURAL TRAP CAVE SMALL MAMMAL FAUNA CHAPTER 3: SMALL MAMMAL TAPHONOMY OF NATURAL TRAP 61 CAVE CHAPTER 4: TESTING FOR PALEOCOMMUNITY STASIS IN 106 NATURAL TRAP CAVE CHAPTER 5: THE GEOGRAPHIC SCALE OF FAUNAL CHANGE 141 DURINGTHE LAST GLACIAL CYCLE IN THE CENTRAL ROCKY MOUNTAINS SUMMARY OF CONCLUSIONS 161 REFERENCES 163 APPENDICES APPENDIX 1.1. HETEROMYIDAE AND CRICETIDAE 192 APPENDIX 1.2. GEOMYIDAE 218 APPENDIX 1.3. LEPORIDAE 222 APPENDIX 1.4. SCIURIDAE 233 vi FIGURES AND TABLES Figures Figure 1. Topography of the area surrounding Natural Trap Cave (NTC). 8 Figure 2. Plan view of the main floor of Natural Trap Cave and stratigraphic 11 column. Figure 3. Plan view of the main floor of Natural Trap Cave. 13 Figure 4. Occlusal view of p3's referred to Lepus californicus. 30 Figure 5. Histogram of dentary and maxilla occlusal length measurements 32 from Natural Trap Cave Tamias and from three modern Tamias species from NW Wyoming. Figure 6. p4 analysis of Natural Trap Cave Urocitellus. 36 Figure 7. Arvicoline right m1s from Natural Trap Cave. 44 Figure 8. Natural Trap Cave faunal list showing the stratigraphic distribution of 49 small mammals. Figure 9. Relationship of Natural Trap Cave to Bighorn Mountain glaciers of 56 Pinedale age. Figure 10. Mandible fragmentation classification. 69 Figure 11. Regression of log taxon abundance on log median weight 71 for each stratigraphic unit. Figure 12. Rodent, lagomorph, and soricid bone wear and Rodent mandible 73 fragmentation. Figure 13. Proportion per taxon without ascending ramus, Proportion without 75 incisors. Figure 14. Lagomorpha %NISP of select cranial and postcranial elements. 76 Figure 15. Bone distribution within example quadrat, NISP/quadrat within Unit 1. 82 Figure 16. NISP/weight histograms for Natural Trap Cave stratigraphic units. 86 Figure 17. Rarefaction curve for pooled NTC data. 114 vii Figure 18. Taxonomic diversity/sample size comparisons for major taxonomic 115 groups. Figure 19. UPGMA clustering for taxa and localities. 118 Figure 20. GNMDS scaling of Little Mountain samples in three dimensions. 119 Figure 21. Combined Q and R mode clustering for the Little Mountain samples. 120 Figure 22. Modern Little Mountain taxa distributions. 131 Figure 23. Modern mammal provinces for central western North America. 145 Figure 24. Number of samples (X-axis) and taxonomic occurrences (Y-axis) 147 for each time bin. Figure 25. Geographic extent of 35% similar clustered faunas for each time 149 interval. Tables Table 1. Radiocarbon dating chronology for Natural Trap Cave and Hole-in-the-Wall 14 Shelter. Table 2. Comparison of KUVP 123030 with Cynomys leucurus and Cynomys 38 niobrarius. Table 3. Comparison of Natural Trap Cave Perognathus sp. to modern 40 Perognathus fasciatus. Table 4. Comparison of NTC small cricetid with Peromyscus and 41 Reithrodontomys. Table 5. Comparison of the Natural Trap Cave IEG fauna with 51 the closest IEG faunas. Table 6. Leporid prey remains collected from modern coyote scat and a 64 Golden Eagle nest. Table 7. Late Pleistocene–Holocene Natural Trap Cave mammal assemblage. 68 Table 8. Lagomorph fragmentation patterns in the pelvis and selected long bones 76 by stratigraphic unit. Table 9. Common modern predators of NTC rodents and lagomorphs. 89 viii Table 10. Taxonomic list for all Little Mountain Samples. 113 Table 11. Results of repeated Kruskal–Wallis nonparametric tests for spatial 121 and temporal differences among temporally grouped Little Mountain samples. Table 12. Comparison of expected modern taxa and Little Mountain Holocene 127 taxa. Table 13. Number and type of biomes inhabited by Natural Trap Cave taxa. 133 Table 14. Taxa from the first province used in this study organized into 149 age bins. 1 CHAPTER 1 Introduction The nature of communities in neoecology is a long running debate that can be traced to the works of Elton and Gleason (Gleason, 1926; Elton, 1966), which were diametrically opposed on this level: Elton (1966) argued that communities were stable super-organisms held together by interactions between species, whereas Gleason (1926) thought that communities were loose agglomerations of species occupying a single space at any given time. Both models have consequences for paleocommunities, also known as biofacies, in geological time. Communities that perform under the model of Elton (1966) would result in biofacies that are stable in membership through time until being overwhelmed by environmental change. Conversely, biofacies that operates under Gleason’s (1926) model would be expected to change rapidly as species constantly invaded and abandoned a community. The property of community stability has import for the study of evolution in the fossil record as well. Observed cases of paleocommunity stasis correlate with periods of limited speciation and extinction, so stasis may be an explanation for observed cases of punctuated equilibria in many taxa (Lieberman and Dudgeon, 1996). The data used by paleoecologists is often different from the data of neoecology, but has the valuable attribute of long temporal spans. Ecologists can sample organisms from an environment and document interactions among avatars (local economic populations of a taxon) that are members of a community, but only over the course of decades at most. Paleoecologists can only infer interactions between avatars through spatial proximity of remains in a single outcrop, but they can trace change over time scales of millions of years. Paleoecological data has obvious limitation pertinent to