Although anuran larvae with generalist feeding morphology have traditionally been treated as lower-level consumers, emerging studies indicate that the larvae of many species are intraguild predators of other anurans. We conducted two experiments to examine priority effects of the Wood Frog (Rana sylvatica) on the Upland Chorus Frog (Pseudacris feriarum). Wood frogs hatch before upland chorus frogs and could potentially function both as intraguild predators and competitors of the latter. In a laboratory experiment, R. sylvatica did not prey on P. feriarum hatchlings that were greater than 1-day old. In a mesocosm experiment in which food level and the density of R. sylvatica hatchlings were manipulated, R. sylvatica engaged in stage-structured intraguild predation on egg masses of P. feriarum. The number of P. feriarum embryos surviving to hatching was inversely related to the initial density of R. sylvatica, but was independent of food level. Growth rates of P. feriarum hatchlings were inversely related to R. sylvatica density, suggesting strong interspecific competition. Collectively, these results illustrate that the density of an intraguild predator may mediate the strength of both stage-specific intraguild predation and interspecific competition. Our findings suggest that food webs in many seasonal pond communities are more complex than previously thought and need to be revised to incorporate intraguild predation by anurans.
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Vol. 2007 • No. 1