Canal structure influences watersnake assemblage structure in an urban environment

Abstract

Abstract The precise manner in which vertebrate species utilize urban environments remains to be explored in a variety of taxa, with snakes in particular being poorly studied. Watersnakes (Genus: Nerodia) are semiaquatic snakes found throughout the eastern United States and are known to occur in urban systems. Four species of watersnake are commonly found in freshwater environments in southeastern Louisiana: Mississippi Green Watersnake, Plain-bellied Watersnake, Southern Watersnake, and Diamond-backed Watersnake. Plain-bellied Watersnake and Southern Watersnake preferentially feed on anurans, while Mississippi Green Watersnake and Diamond-backed Watersnake tend to be more piscivorous in their feeding habits. Water depth is important in structuring anuran and fish community structure, with shallower water bodies typically supporting higher anuran abundance and richness, and deeper waters supporting more fishes. We examined watersnakes in canal transects of varying depth in Kenner, Louisiana to test the hypotheses that species that feed on anurans would be more abundant in shallower canals, while species that preferentially feed on fishes would be more abundant in deeper canals. We found significant correlation between watersnake assemblage and anuran/fish community structure, with the Plain-bellied Watersnake most abundant in the shallowest canal transects, Mississippi Green Watersnake most abundant in transects of intermediate depth, and Diamond-backed Watersnake most abundant in the shallow transects. The former two species largely followed the hypothesized trends, while the Diamond-backed Watersnake did not.