Small Biological Preserves and Smaller Mammals: Can Protected Areas in Our Most Populous Regions Conserve Historic Community Composition?

The multi-faceted impacts of the Anthropocene are increasingly modifying natural ecosystems and threatening biodiversity. Protected spaces in and adjacent to urban landscapes may be critical in protecting species in human-modified systems. Can small, protected spaces act as reservoirs for biodiversity across dynamic spatial and temporal gradients of human impact? To address this question, we identified small mammal remains from modern raptor pellets and Holocene archaeological sites along a human modification gradient in the San Francisco Bay Area, CA. We assessed small mammal alpha and beta diversity for both modern and Holocene sites. We tested for significant differences between sites and time bins using permutational multivariate analysis of variance (PERMANOVA) and visualized these differences using non-metric multidimensional scaling (NMDS). We found that alpha diversity decreased with increasing human modification in Anthropocene sites, with no corresponding change between Holocene sites. Additionally, the alpha diversity of modern sites with moderate/high levels of human modification was significantly lower than that of protected modern sites and all Holocene sites, driven by the dominance of human-commensal and disturbance-tolerant species. On the other hand, the small mammal communities from a small, protected area (Jasper Ridge Biological Preserve) retained Holocene levels of alpha diversity. Jasper Ridge has also changed less over time in terms of overall community composition than more modified sites. Despite this, both PERMANOVA and NMDS show that Holocene and Anthropocene communities are significantly distinct regardless of collection site and level of anthropogenic modification. Our results suggest that even relatively small, protected spaces within an urbanized matrix conserve native faunal communities, highlighting their important role in urban conservation.