Microfauna relative abundance since the Late Pleistocene at Natural Trap Cave, Wyoming, U.S.A

Microvertebrate communities have shifted and adapted to a variety of climate extremes since the Late Pleistocene, which can inform us on how modern communities might respond to similar climatic changes. Here we evaluate the microvertebrate remains from Natural Trap Cave (NTC), Wyoming, in the Western US, as an initial evaluation of how these communities responded to changes in local climate throughout the Late Quaternary. We calculated the number of identified specimens (NISP) and the minimum number of individuals (MNI) to determine relative abundance, richness, and evenness across 3 layers at the site, from the Late Pleistocene, the Middle Holocene, and the Late Holocene. Community composition was largely affected by changes in the abundances of taxa rather than local extinctions or colonizations. Evenness was highest in the arid Late Pleistocene, 23,000 cal BP and Late Holocene, approximately 2,000 to 6,000 cal BP. Shifts in evenness were primarily driven by changes in abundance of Phrynosoma with abundances of Lagomorpha and Thomomys contributing to changes within the small mammal community. Raw richness was highest in the Middle Holocene when Cynomys and Perognathus appeared in the region while standardized richness was highest in the Late Pleistocene with these differences being caused by small Late Pleistocene sample sizes. We performed a principal coordinate analysis to compare the small mammal community of NTC to three other caves with well-represented small mammal fauna from the Late Quaternary. NTC grouped closest with Samwell Cave, in California, another cave where small mammal material is collected by packrats. Across all four caves, layers generally grouped based on cave affinity. However, Samwell and NTC layers were grouped by age rather than cave identity. Further comparison between these two caves found that evenness decreased similarly from the Late Pleistocene to the Holocene.