Thursday, August 29, 2013

Diet overlap in aquatic snake assemblages

Competition for prey is thought to be important in structuring snake assemblages. However, given the secretive behavior and low detectability of many snake species, this generalization is based on a limited number of studies, most of which focus on a single study site. In a forthcoming paper in the Journal of Zoology Durso et al (2013) examined differences in diet composition, trophic niche overlap, site occupancy and detectability of five sympatric aquatic snake species [eastern mud snake, Farancia abacura; banded watersnake, Nerodia fasciata; Florida green water snakes, N. floridana; glossy crayfish snakes, Regina rigida; and black swamp snakes, Seminatrix pygaea] between two different habitat types in the southeastern US. They studies  permanent wetlands with fishes (n = 13) and isolated, often ephemeral wetlands without fishes (n = 10). More than 3700 prey items were collected from snakes and compared diet composition among snake species to examine niche breadth and overlap, correcting for relative availability of prey captured independently in the same wetlands. They also evaluated evidence for competitive exclusion by estimating the probability of co-occupancy for pairs of snake species in each habitat type using occupancy modeling. In wetlands with fishes, niche overlap was low, suggesting resource partitioning. Conversely, in wetlands without fishes, niche overlap was high, with most species feeding on larval or paedomorphic ambystomatid salamanders, but competitive exclusion did not occur. They suggest that high co-occupancy of aquatic snakes in wetlands without fishes, despite the apparent lack of resource partitioning, is due to a combination of seasonally high abundance of high quality amphibian prey, unique aspects of predator physiology and stochastic abiotic processes that prevent these systems from reaching equilibrium. The results demonstrate that snake diets can be highly context (e.g. habitat) specific.

Durso AM, Willson J D, & Winne CT. (2013)  Habitat influences diet overlap in aquatic snake assemblages. Journal of Zoology. DOI: 10.1111/jzo.12061

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