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Relationship between Size and Foraging in Dusky Salamanders (Genus Desmognathus)

Abstract

Foraging is important ecologically because it determines an animal’s ability to maintain a positive energy budget, which is necessary for growth and reproduction. Biologists have traditionally categorized foraging mode in animals as active hunting or lying in ambush. Salamanders in the genus Desmognathus forage at night when humidity is high. Large species often remain in refugia with their heads protruding while waiting to ambush approaching prey. Small species commonly forage outside of refugia, presumably as active hunters. We tested the hypothesis that foraging mode in these salamanders depends on body size rather than species. We collected large samples of four species that span most of the range of adult body size within the genus including the small D. ocoee, the moderately large D. monticola and D. folkertsi, and the large D. quadramaculatus. We collected all specimens at night along two streams in the Georgia Piedmont and two streams in the Blue Ridge. We categorized salamanders with heads sticking out of refugia versus those out wandering. Mean body size of refuge-inhabiting individuals of all four species was significantly larger than in wandering individuals. Moreover, as maximum size of the population increased, the proportion of individuals that hunted from refugia also increased. We concluded that larger desmognathans more commonly ambush prey from refugia, and small salamanders appear to be active hunters. This pattern of foraging may be a consequence of variation in metabolic rate. Small animals including amphibians have a higher metabolic rate than large ones. If small salamanders require more food per gram of body weight than do large ones, they may need to seek out prey in order to meet nutritional requirements.

Acknowledgements

Piedmont Univesity, Department of Biology

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