Feeding performance in the Western Ribbon Snake (Thamnophis proximus): ontogeny and the effects of prey type and size

Abstract

It has been suggested that juveniles have exaggerated morphologies or improved performance to compensate for the disadvantages of being small. As gape-limited predators, juvenile snakes are at a particular disadvantage in terms of prey availability, capture, and ingestion. Prey preference often changes with snake size yet previous studies generally compare only one prey type or relative prey size among age classes. Using Western Ribbon Snakes ( Thamnophis proximus (Say in James, 1823)), I investigated the ontogeny of head dimensions and feeding performance on frogs and fish using a range of relative prey sizes. Comparison among snake sizes indicated that smaller individuals had larger relative head sizes than larger conspecifics; however, larger individuals had larger heads. Initial bite position differed between juveniles and adults fed fish but not frogs. Both frogs and fish were generally consumed headfirst by adults and juveniles. Head length did not influence feeding performance in terms of time or pterygoid protractions for snakes fed either fish or frogs. In general, this study suggests that allometry of trophic morphology does not improve feeding performance.

Allometry of cranial morphology, gape size and ingestion performance in the banded watersnake (Nerodia fasciata) feeding on two types of prey

“…This pattern does not seem to hold true for snakes when performance is a measure of the effort required to consume a prey item (Vincent et al, 2007;Hampton, 2011a) (this study). While studies have shown that relative prey size affects the time and functional effort required for ingestion (Pough and Groves, 1983;Hampton, 2011a), ingestion performance does not explain the allometry of trophic morphology when corrected for prey size. Large snakes typically consume a disproportionately high number of small prey, which is thought to be a consequence of prey availability (Voris and Moffett, 1981).…”

“…The heads of snakes play many functional roles, and various ecological pressures may constrain which bones are modified and to what limit. While the number of jaw protractions required to ingest prey varies among snake species (Pough and Groves, 1983), head size has not been shown to influence ingestion time or jaw protractions within a species (Vincent et al, 2007;Hampton, 2011a). This suggests that other factors are influencing head size and shape.…”

“…Most commonly, gape is estimated from a single linear dimension, such as head length, head width or mandible length (Pough and Groves, 1983;Hampton, 2011a). Although such measurements are effective for making comparisons, they are limited by a single dimension.…”

“…While evidence suggests that the negative allometry of trophic morphology improves feeding performance in juveniles in some species (Van Wassenbergh et al, 2005), an explanation for the scaling pattern remains inconclusive for some taxa (Reilly, 1995;Hampton, 2011a). For many snake species, juveniles exhibit relatively large heads compared with larger conspecifics (Vincent et al, 2006;Hampton, 2011a;Hampton and Moon, 2013).…”

“…For many snake species, juveniles exhibit relatively large heads compared with larger conspecifics (Vincent et al, 2006;Hampton, 2011a;Hampton and Moon, 2013). At least two studies have tested whether negative allometry of head size lowers feeding effort (time and mechanical effort) in snakes, yet ingestion performance has not been shown to vary with body size within a species (Vincent et al, 2006;Hampton, 2011a), suggesting that alternative phenomena are driving negative allometry of head size. For instance, in many species that consume their prey whole, juveniles consume larger prey relative to body size than the adult conspecifics (Miller and Mushinsky, 1990;Scharf et al, 2000;Ford and Hampton, 2009).…”