COS 263-5 - Impacts of the Invasive Burmese Python on the Everglades Food Web

Abstract: Non-native species introductions can result in biological invasions that have substantial impacts on native population abundances, community interactions, and ecosystem processes. Over the past twenty years, the establishment and subsequent invasion of the Burmese python (Python molurus bivittatus) in the Greater Everglades ecosystem has become a topic of concern amongst conservation and restoration efforts in South Florida. Substantial work has been done to assess at-risk biodiversity by understanding the breadth of the python’s diet within its invaded range. The objective of this study is to expand on this work by assessing community-wide impacts of the python on the native food-web as well as the function of the Greater Everglades Ecosystem by attempting to answer three central questions: 1) What niche space is the python occupying within the native community? 2) Is there a shift in overall food-web structure and/or function post-invasion? And 3) Are these effects different than we would expect from a random invader? Utilizing a food-web centered approach, we constructed two quantitative energy flow models (pre- and post-invasion) for the graminoid habitat within Everglades National Park (ENP). To address the first two questions, we use ecological network analysis (ENA) to quantify and compare ecosystem structure and function in each of the two network models. For our third question, we generated four randomization-based null models to test if the python’s trophic characteristics exhibited different effects than we would expect from a random invader. Here we show that the python exhibits a trophic cascade effect and occupies a novel niche space within the food web, with the snake compartment showing the highest similarity value of only 0.15. We found little to no shift in network level indices (e.g., Connectance, Finn Cycling Index, Ascendency) between the pre- and post-invaded networks, however, there was a consistent decrease in carbon flowing through higher trophic levels (2% from trophic levels 4 to 5, and 7.29% from trophic levels 5 to 6) indicating that the python is redirecting carbon flows through the higher trophic levels of the system. Additionally, results from the null model simulations indicate that python’s trophic impacts are different than we would expect from a random invader (p < 0.001 for majority of individual and network level indices). In conclusion, this study provides a holistic assessment of the Burmese python invasion on the native community and ecosystem function that can inform future management decisions as restoration of the Greater Everglades Ecosystem progresses.