Living on the edge: trophic ecology of Alligator mississippiensis (American alligator) with access to a shallow estuarine impoundment

I used a combination of stomach content and stable isotope analyses to examine intrapopulation and temporal variation in use of estuarine prey resources by Alligator mississippiensis (American Alligator) with access to a shallow estuarine impoundment located on the northeast Atlantic coast of Florida. I used a multi-tissue stable isotope approach to examine temporal trends in trophic interactions. This study took place within the Guana River Wildlife Management Area located in Ponte Vedra, Florida. From 2010 to 2012, I collected stomach contents from 44 A. mississippiensis and stable isotope samples from a total of 127 individuals. Stomach contents indicated the principal prey taxa consumed on a short-term basis were invertebrates (i.e., insects and crustaceans) and small baitfish. Individuals of all sizes used estuarine, as well as freshwater prey resources; however, the importance of estuarine prey to the diet increased through ontogeny. Juvenile and sub-adult stomach contents predominantly contained freshwater insects, while adult diets mainly contained estuarine baitfish and crustaceans. I used stable carbon and nitrogen isotope ratios (δ13C and δ15N) measured in three tissues (blood plasma, red blood cells, scute keratin) differing in turnover rates to assess overlap and temporal variation in the isotopic niche and inferred trophic interactions of A. mississippiensis sub-populations. Isotopic niche and inferred trophic interactions of A. mississippiensis varied among size classes, sexes, years, and capture habitats. Overlap in isotopic niches of sub-populations was highest between sexes of similar body size and for individuals captured in similar habitats within the same years. Temporal shifts in trophic interactions were most prevalent for juveniles and sub-adults, while adults demonstrated a higher degree of temporal stability in trophic interactions and niche specialization. These findings represent one of the few studies to examine intrapopulation variation in use of estuarine prey resources by A. mississippiensis. Results of this study should be useful to habitat managers designing and implementing conservation programs for coastal ecosystems in the southeastern United States, especially in light of the expected alterations in coastal habitat structure due to sea level rise and global climate change.