HOLOCENE SMALL MAMMALS OF THE GREAT BASIN: TRACKING RECENT RICHNESS DECLINES THROUGH LIVE/DEAD ANALYSIS OF RAPTOR-GENERATED FAUNAL REMAINS

Forecasting long-term biotic responses to anthropogenic environmental change necessitates unlocking the wealth of pre-settlement baseline information contained in the recent fossil record. Homestead Cave and Two-ledges Chamber, long-term owl roosts in the Great Basin of the western United States, contain stratified deposits of regurgitated raptor pellets rich in small-mammal skeletal remains. These deposits record shifts in local faunal composition through the Holocene. To successfully interpret the ecological information archived in these death-assemblages, however, the accuracy with which they record community composition must first be quantified to test the strength of the biological signals captured by such deposits.

Here I compare modern trapping surveys, modern “pellet rain”, and Holocene deposits from both caves to assess the ecological fidelity of Holocene small mammal fossil records. Preliminary results indicate high correspondence among modern and fossil death-assemblages and the living community in terms of presence/absence (Jaccard Similarity Index ~0.6-0.3), rank order abundance (Spearman Rho ~0.9-0.3), and relative abundance (Bray Curtis Index ~0.8-0.2). Agreement weakens as the amount of summed and elapsed time between samples increases. Additionally, modern and fossil death-assemblages are richer than snapshot trapping surveys, with 60-100% more taxa.

In contrast to Two-ledges Chamber, the Homestead Cave record reveals a striking decline in species richness and live-dead correspondence over the past century, suggesting a community in transition. By highlighting taxa with unexpected live-dead offsets, taphonomic analyses can reveal these transitions over decadal to multi-centennial timescales. Since this temporal scope is beyond that of direct human observation, this type of information provides a critical window into understanding longer-term biotic responses to fluctuating conditions, which in turn can better guide and inform long-term conservation efforts.