CHANGES IN THE STRUCTURE OF HALL'S CAVE FOOD WEB NETWORKS OVER THE LAST 22,000 ARE ASSOCIATED WITH CLIMATE CHANGE

We are experiencing rapid biodiversity loss due to climate change and human impacts. Such biodiversity loss is not only harmful to the environment but can also alter the composition of communities and the interactions of their members. The Late Pleistocene megafauna extinction demonstrated a drastic loss of large-bodied mammals which resulted in significant changes in community structure due to changes in body size, diet, and species associations. However, the effect of climate change on species interactions and community structure across the Pleistocene-Holocene transition remains poorly understood. The interactions between species within a community can be represented by an ecological network (food web) which can be used to measure how communities are partitioned into clusters of interacting species (modularity), and how much overlap in ‘neighbors’ there are between any pair of species nodes called node overlap and segregation index (NOS). Using a robust data set of species composition, stable isotopes, body size, and multiple climate variables, we constructed and compared ecological networks of mammal paleocommunities across the last 22,000 years at Hall’s Cave, TX. We find node overlap increases and modularity decreases over time. Partial correlation analyses indicate that changes in modularity is significantly correlated with increases in temperature and decreases in precipitation. We used a null model that randomized the species composition within a time bin while keeping species richness constant to determine whether changes in NOS were different than expected by chance. Changes in NOS were significantly different from null model expectations in the Holocene but not in the Pleistocene except for two time bins at the start of deglaciation. These results suggest that the transition from a diverse and modular network to a network of less complexity with an overlap of interacting species had a significant correlation with climate change during the period of the megafauna extinction.