LOCAL COMMUNITY REORGANIZATION AFTER THE TERMINAL PLEISTOCENE MEGAFAUNAL EXTINCTION

Recent studies connecting the decline of large predators and other apex consumers with the ‘unraveling’ of ecosystems overlook that this natural experiment already occurred in the recent past; most of the modern large-bodied consumers were meso-consumers at the terminal Pleistocene. As recently as 14 ka, millions of large-bodied mammals including mammoth, camels, llamas, saber-tooth cats and short-faced bear were widespread across the Americas. Within 1,000 years of the arrival of humans, ~80% of these large-bodied mammals were extinct, including all over 600 kg. While the cause of the extinction remains somewhat contentious, humans likely played a crucial role through a combination of hunting and habitat alteration. What has been largely overlooked in this debate, however, is the consequence on ecosystems of the loss of millions of large-bodied animals. Our work focuses on Hall’s Cave in the southern Great Plains of Texas; a site with an exemplary temporal record with continuous representation over the past 20ka. Here, we examine the community level response to the catastrophic loss of 80% (12/15 species) of the local large-bodied herbivores, and 20% (3/15 species) of the apex predators in the ecosystem. Using 8 tightly constrained temporal windows, which span from the full glacial to the modern, and site-specific faunal lists, we reconstruct the local mammal body size distribution. We analyze both the shape and composition of the distribution, as well as species associations, to assess the influence the megafauna extinction had on the remaining mammals in the community. Overall, we see a pattern of consistency: species diversity and the statistical moments do not vary substantially across time. Although all metrics of body size are greater at the Full Glacial and a drop in maximum size is seen in the early Holocene, the median and mean size are roughly constant across most the past 20ka. Pairs analysis yields no significant pattern of association or disassociation across these temporal windows, suggesting that mammals responded individualistically to the loss of megafauna and climate shifts over this time period.