THE MISSING PIECES: CHANGES IN THE ECOLOGICAL NICHE OF A MAMMAL COMMUNITY IN NORTH AMERICA OVER THE LATE QUATERNARY

The conservation status of large-bodied mammals is dire. Their decline has serious consequences because they have unique ecological roles, which are not replicated by smaller-bodied animals. Here, we use the fossil record of the megafauna extinction at the terminal Pleistocene to explore the consequences of past biodiversity loss. We characterize the isotopic and body-size niche of a mammal community in Texas before and after the event to assess the influence on the ecology and ecological interactions of surviving species (>1kg). Pre-extinction, a variety of C₄-grazers, C₃-browsers, and mixed-feeders existed, similar to modern African savannas, with likely specialization among the two sabertooth cats for juvenile grazers. Post-extinction, body size and isotopic niche space were lost, and the δ¹³C and δ¹⁵N values of some survivors shifted. We see mesocarnivore release within the Felidae: the jaguar, now an apex carnivore, moved into the specialized isotopic niche previously occupied by extinct cats. Puma, previously absent, became common and lynx shifted towards consuming more C₄-based resources. Lagomorphs were the only herbivores to shift towards C₄ resources. Body size changes from the Pleistocene to Holocene were species-specific, with some animals (deer, hare) becoming significantly larger, and others smaller (bison, rabbits) or exhibiting no change to either climate shifts or biodiversity loss. Overall, the Holocene body size-isotopic niche was drastically reduced and considerable ecological complexity was lost. We conclude biodiversity loss led to reorganization of survivors and many ‘missing pieces’ within our community; without intervention, the loss of Earth’s remaining ecosystems that support megafauna will likely suffer the same fate.