Namaqua Dwarf Adders are generalist predators

Abstract

Prey items vary greatly in the total amount of energy they provide and the costs associated with their location, capture, consumption and assimilation. As a result not all prey types are of equal value, and the relative frequency with which different prey types are consumed can strongly influence an organism's fitness. In order to understand foraging behaviour of an organism adequately, one needs to know not only what constitutes suitable prey, but also the relative frequency with which different prey types are encountered by a foraging individual. In this article we investigate the foraging ecology of the Namaqua Dwarf Adder, Bitis schneideri. We use field observations of feeding snakes and records of stomach contents to describe the diet of the species at our study site and compare these measures to measures of prey abundance, collected using passive trapping, to assess whether the species is a selective or generalist feeder. We recorded four species of lizard and one species of frog in the diet of our study population. Our data show that Namaqua Dwarf Adders are generalist predators, feeding year-round, and feeding on prey in proportion to the frequency at which they are encountered. Moreover, we show that large Namaqua Dwarf Adders do not exclude small prey items from their diet. The capacity for Namaqua Dwarf Adders to feed on a wide variety of prey species in proportion to the rate at which they are encountered suggests that future changes in prey species composition are unlikely to influence rates of energy uptake by foraging snakes.

Key words:

• dietary specialisation
• pitfall trap
• prey community
• Bitis schneideri

Acknowledgements

We thank E. Oppenheimer and Son, the Rufford Small Grants Foundation and the South African National Biodiversity Institute for financial support. Ditsong National Museum of Natural History (Transvaal Museum) is thanked for access to specimens. All work was cleared under Northern Cape Province Department of Tourism, Environment and Conservation (0914/07 and FAUNA 698/2009) and University of the Witwatersrand Animal Ethics Screening Committee (2007/68/1 and 2007/69/3) permits. Rose Sephton-Poultney commented on an earlier draft of this manuscript.