Indirect effects of invasive Burmese pythons on ecosystems in southern Florida

Invasive predators can dramatically alter ecosystems through both direct predation and indirect effects such as tropic cascades. However, most examples of top-down effects of invasive predators in terrestrial systems stem from islands or similar low-diversity ecosystems. Snakes are an emerging guild of damaging invasive predators, but demonstration of ecosystem-level impacts of invasive snakes are limited to the single case of the brown treesnake on Guam. Invasive Burmese pythons are firmly established in southern Florida and have been linked to severe (80-100%) declines of several previously common mammal species (e.g. raccoons, opossums and rabbits). Specifically, spatiotemporal patterns of mammal declines in the Everglades mirror the spread of pythons and experimental reintroductions of rabbits to areas where they had been extirpated failed due to high (77% of mortalities) rates of predation by pythons. I evaluated the potential indirect effects of pythons on the nesting success of oviparous species by monitoring artificial turtle nests (N=183) at 13 sites across the expanding range of the python population. I documented few mammals and low rates of nest predation (average score=15 on a 1-5 scale) in the southern Everglades where pythons have been established the longest, intermediate (average score=23) rates of nest predation at recently invaded sites, and very high (average score=46) rates of nest predation at sites with few or no pythons. These findings represent the first documentation of potential indirect effects of pythons on non-prey species, and suggest that loss or decline of mammals is resulting in trophic cascades that threaten the Everglades ecosystem.Synthesis and applications. My results suggest that an introduction of non-native apex predators can result in trophic cascades that alter even complex, continental ecosystems. The Burmese python invasion of South Florida shows remarkable parallels with the catastrophic case of the brown treesnake in Guam, but in some ways is even more worrisome. Documentation of both strong direct impacts on prey and potential indirect effects on Everglades' ecosystems within 15years after being recognized as established emphasizes the need to integrate python management into restoration of the Greater Everglades Ecosystem. More broadly, non-native snakes warrant significant attention for their potential to become damaging invasive species.