Mammal Community Structure through the Paleocene-Eocene Thermal Maximum

Abstract

Human-mediated species invasion and climate change are leading to global extinctions and are predicted to result in the loss of important axes of phylogenetic and functional diversity. However, the long-term robustness of modern communities to invasion is unknown, given the limited timescales over which they can be studied. Using the fossil record of the Paleocene-Eocene Thermal Maximum (PETM; ~ 56 Ma) in North America, we evaluate mammalian community-level response to a rapid global warming event (5° to 8°C) and invasion by three Eurasian mammalian orders and by species undergoing northward range shifts. We assembled a database of 144 species body sizes and created a time scaled composite phylogeny. We calculated the phylogenetic and functional diversity of all communities before, during, and after the PETM. Despite increases in the phylogenetic diversity of the regional species pool, phylogenetic diversity of mammalian communities remained relatively unchanged, a pattern that is invariant to the tree dating method, uncertainty in tree topology, and resolution. Similarly, body size dispersion and the degree of spatial taxonomic turnover of communities remained similar across the PETM. We suggest that invasion by new taxa had little impact on Paleocene-Eocene mammal communities because niches were not saturated. Our findings are consistent with the numerous studies of modern communities that record little change in community-scale richness despite turnover in taxonomic composition during invasion. What remains unknown is whether long-term robustness to biotic and abiotic perturbation are retained by modern communities given global anthropogenic landscape modification.

The interglenoid tubercle of the atlas is ancestral to lissamphibians

“…There is not a single formal hypothesized phylogeny that includes all the taxa of interest for this study. Thus, to analyze the evolution of the atlas‐axis complex in lissamphibians and their potential stem group, dissorophid temnospondyls, we constructed a semiformal supertree using optimum parsimony following the methods of Fraser and Lyons (2020) (R script kindly provided by D. Fraser). This supertree was constructed using source trees from the published literature (listed in supplemental Table , nexus files provided in the supplemental material).…”

Investigating Biotic Interactions in Deep Time

“…However, if interspecific and intraspecific interactions impact the ecological and reproductive success of individuals over large spatiotemporal scales, they can have effects on entire species and clades that are measurable on macroevolutionary and macroecological scales (Box 1 and Figure 1) [7,[11][12][13]. Such emergent patterns include, but are not limited to, shifts in species abundances, diversity, and spatial distributions (e.g., [14][15][16]), partitioning of trait and phylogenetic space (e.g., [17,18]), change in rates of diversification and morphological change (e.g., [19][20][21][22][23]), and the success or failure of biological invasion (e.g., [20,24,25]). Although a significant body of theory has been developed to address the cumulative effects of biotic interactions (Box 1; [7, 11,12,[26][27][28][29]), empirical tests of models that account for the complexity of paleontological data have lagged behind theory.…”

The preservation potential of terrestrial biogeographic patterns

“…In modern settings, changes in beta diversity have been shown to be a sensitive indicator of ecological stress [33], and, consequently, studies using beta diversity underpin much of conservation theory and practice [29,32]. Understanding how beta diversity changed over past biotic crises may therefore help to identify modern areas undergoing ecological stress, or ecosystems at risk of incipient collapse [11,33,34].…”