The Late Pleistocene is characterized by the Last Glacial Maximum, the Younger Dryas (a period of climate change marked by brief cooling and then rapid warming), and the loss of megafauna on most continents. While these rapid changes affected mammal body size distributions and co-occurrence networks, small mammal alpha diversity remains largely unaffected. Most studies on small mammals of the Late Quaternary, however, focus on taxonomic diversity, and few studies have explored other dimensions of diversity such as functional and trait diversity, which allow for more mechanistic interpretations of diversity change through time. Additionally, comparative studies spanning two or more continents are non-existent. We tested if functional and trait diversity of small mammals were similarly affected by Late Pleistocene ecological change in both North America and Europe for the first time using data from two sites: Samwell Cave (SC) in Northern California and El Mirón Cave (EMC) in Northern Spain. We quantified functional diversity for subsampled communities using body size, dietary, activity time, and locomotor data and regressed the resultant values against median radiocarbon dates for each stratigraphic layer.
Results/Conclusions
We find that small mammal communities of Europe and North America responded differently to changing environmental and biotic conditions. The small mammal community at EMC (Spain) experienced significant increases in functional richness and functional dispersion, suggesting that more specialist niches became occupied during the Holocene. These changes were underpinned by increases in the proportion of species that are arboreal, diurnal, and granivorous and decreases in the proportion of ground-dwelling species that eat leafy plant material in the community. Conversely, the community at SC (North America) underwent a significant decrease in functional dispersion indicating a relative decline in more specialist species. There, ground-dwelling species that eat leafy plant material increased in relative abundance while arboreal, nocturnal, and insectivorous species decreased in proportion. These results suggest small mammal communities in Europe grew to occupy a greater extent of niche space with trait values evenly distributed throughout this space, whereas in North America, species characterized by more extreme trait values became less abundant. Our research suggests that small mammal responses to Late Quaternary environmental change may differ between sites or entire continents and highlights the advantages of trait-based approaches for reconstructing dimensions of biodiversity in the past.