Millennial-scale ecomorphological shifts in a mesocarnivore community in southern California

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Mairin Balisi, Natural History Museum of Los Angeles County

Background/Question/Methods
Major disturbances may precipitate the rise of novel communities, as was seen after the last Ice Age ~11,700 years ago following a combination of megafaunal extinctions, climatic change, and human impacts. As large carnivores and large prey disappeared, so did the interactions that had exerted cascading trophic effects. Most of the Anthropocene’s remaining carnivores are of small to medium body size: mesocarnivores.
North American mesocarnivores from Pleistocene to Recent present a natural laboratory to track the effects of large-scale biotic and abiotic disturbance on a faunal community. Here, I quantify the ecomorphology of mesocarnivores from the Rancho La Brea (RLB) asphalt seeps in Los Angeles, southern California. While RLB is known for having abundantly trapped megafauna over the last ~55,000 years, the asphalt also ensnared smaller carnivores, systematically evaluated here for the first time.
Results/Conclusions
Excluding coyotes, RLB preserves five mesocarnivore species having sample sizes >=10 individuals: badger (Taxidea taxus), bobcat (Lynx rufus), grey fox (Urocyon cinereoargenteus), striped skunk (Mephitis mephitis), and long-tailed weasel (Mustela frenata). These species were found in 33 separate deposits spanning 44,650–5,270 radiocarbon years before present and continue to inhabit Los Angeles today. In various linear ecomorphological traits, most RLB specimens differ significantly from historic representatives of the same species. Using dental and postcranial body-size proxies, I estimated mesocarnivores to have been generally larger in the late Pleistocene and Holocene, undergoing as much as a 27% reduction in body size into the Anthropocene. RLB mesocarnivores also exhibit greater tendencies for carnivory, as quantified by the slicing and grinding areas of the teeth, perhaps in response to greater levels of competition presented by megafaunal carnivores. Further, species-specific differences in postcranial morphology highlight shifts in mesocarnivore locomotor ability, potentially reflecting environmental changes. These results highlight the utility of a deep-time approach to studies of ecosystem resilience, particularly given ongoing anthropogenic change. As different mesocarnivore species likely responded to different stressors, future analyses will refine radiocarbon chronology to pinpoint potential causes for these shifts.