Consequences of the Megafauna Extinction: Changes in Food Web Networks on the Edwards Plateau Across the Pleistocene-Holocene Transition

Authors

Quentin A. Smith Jr., University of Nebraska-LincolnFollow

First Advisor

S. Kathleen Lyons

Second Advisor

Daizaburo Shizuka

Date of this Version

5-2024

Citation

A thesis presented to the faculty of the Graduate College at the University of Nebraska in partial fulfillment of requirements for the degree of Master of Science

Major: Biological Sciences

Under the Supervision of Professors S. Kathleen Lyons and Daizaburo Shizuka

Lincoln, Nebraska, May 2024

Comments

Copyright © 2024, Quentin A. Smith, Jr. Used by permission

Abstract

We are experiencing biodiversity loss due to climate change and human impacts, which is not only harmful to the environment but can also alter the composition of communities and interactions among species. The late Pleistocene experienced a loss of large-bodied mammals which resulted in significant changes in community structure due to changes in body size, diet, and species associations. The impact of these changes on species interactions and community structure across the Pleistocene-Holocene transition remains poorly understood. Using a robust data set of species composition, stable isotopes, body size, and climate variables, we constructed and compared ecological networks of mammal paleocommunities on the Edwards Plateau, Texas. One site, Hall’s Cave, has a temporal resolution that allows an in-depth analysis by separating the last 22,000 years into 16 time intervals. We measured the structure of food webs using modularity, and species contributions to modularity. Additionally for Hall’s Cave, we measured an index of node overlap and segregation for each time interval. We find consistent decreases in modularity across all sites with food webs shifting from having multiple clusters in the Pleistocene to fewer clusters in the Holocene. The less complex network post extinction is largely attributed to the loss of particular species interactions. In Hall’s Cave, we find node overlap increases and modularity decreases over time. Spearman-Rank correlation analyses indicate that changes in modularity were not driven by changes in species richness or climate change. The degree of node overlap shifted across the Pleistocene-Holocene transition and was significantly different from null model expectations in the Holocene but not in the Pleistocene. These results suggest that the transition from a modular network to a network of less complexity with an overlap of interacting species may have been driven by other factors that changed the food web, such as species composition. Thus, the change in mammal food web structure of Hall’s Cave was mainly a consequence of the megafauna extinctions.

Advisors: S. Kathleen Lyons and Daizaburo Shizuka