FELID GUILD ECOLOGICAL NICHE DYNAMICS PRE- AND POST-PLEISTOCENE MEGAFAUNAL EXTINCTION

During the Pleistocene, megafelids such as the saber-toothed cats Smilodonand Homotherium dominated North American ecosystems, potentially suppressing smaller-bodied felids such as the cougar (Puma concolor) and bobcat (Lynx rufus). The terminal Pleistocene megafaunal extinction (~ 13ka) resulted in the loss of these more massive hypercarnivores, yielding vacant habitat/niche space. Here, we use Ecological Niche Modelling (ENM) to evaluate whether cougars and bobcats began to occupy unfilled niche-space following the megafelid extinctions. Our approach utilizes fossil felid occurrences from the Neotoma Database and paleo-climactic reconstructions from the PaleoClim Database. We use the R package ecospat to produce ENMs of felids in environmental space for multiple time periods pre- and post-megafaunal extinction, testing for cougar/bobcat niche expansion into previously occupied megafelid niches. We also evaluate the sensitivity of ecospat’s extrapolation methods, especially as applied to the fossil record and explore model thresholding schema that align environmental space-based ENMs with geographic space-based species distribution models (e.g., MaxEnt). Preliminary results suggest that cougar/bobcat niches expanded somewhat post-megafaunal extinction, but this is primarily attributed to warming climates. Contrary to our expectations, neither cougars nor bobcats appeared to fill in vacant megafelid niche space post-extinction. Moreover, these analyses revealed that the disappearance of acutely cold non-analog habitats from the Pleistocene likely contributed to the extinction of Homotherium, but not any other megafelid. Ultimately, our findings suggest that the niches of modern felids were not significantly constrained by interactions with larger megafelids in the Pleistocene. Specifically, warmer/colder habitat availability appears to have most strongly influenced felid niche occupancy during the late Quaternary. Sensitivity analyses of ecospat extrapolations suggest that users must vet environmental space hulls to avoid predictions in physiologically impossible conditions (e.g., negative precipitation regimes).