Evaluating the functional importance of secretive species: A case study of aquatic snake predators in isolated wetlands

Abstract

AbstractAlthough the need to prioritize limited conservation resources has prompted increased interest in understanding the functional importance of species within ecosystems, species that are infrequently observed are often written off as being unimportant. In this study, we use aquatic snakes as a case study for examining the importance of secretive predators. Most snakes are extremely cryptic and secretive, traits that not only lead to the perception that they are rare, and of minor importance, but also impede attempts to quantify densities. We used high sampling effort and robust‐design capture–recapture analyses to estimate density of aquatic snakes inhabiting an isolated 5.4‐ha wetland in South Carolina, USA. We assessed snake diets and coupled field measurements of growth rates with laboratory‐derived data on mass conversion efficiency to estimate prey consumption by snakes over a 1‐year period. We found a peak density 171 snakes ha−1 of wetland habitat, corresponding to a standing biomass of 7.77 kg ha−1. We calculated that snakes within the wetland consumed a total of over 200 kg (>55 000 individuals) of amphibian prey annually, translating into >150 000 kJ ha−1 of energy flow from secondary to tertiary consumers within the wetland food web. Further, because many amphibians are primarily terrestrial as adults and are consumed by aquatic snakes only when they return to wetlands to breed, snakes can be responsible for substantial transfer of energy and biomass between terrestrial and aquatic habitats. Our study is one of the first comprehensive evaluations of the importance of snakes as predators and underscores the need to consider snakes in initiatives aimed at preserving overall ecosystem integrity.