PS 36-33 - Non-lethal effects of dragonfly predators on interactions between the tadpoles of two Neotropical hylid frogs

Wednesday, August 10, 2011
Exhibit Hall 3, Austin Convention Center
Zacharia J. Costa, Biology, Virginia Commonwealth University, Richmond, VA and James R. Vonesh, Department of Biology, Virginia Commonwealth University, Richmond, VA

Prey frequently alter their phenotype in response to perceived predation risk in order to reduce vulnerability. Differences in the costs and benefits of such plastic responses to predators can lead to differences in non-consumptive predator effects. Such differences can occur between taxa or through ontogeny for a given species, and may alter interactions between prey and other species in the food web. Less vulnerable prey may respond less to predator cues compared to vulnerable prey and thus may have higher performance in risky environments. Here we build upon previous research on the tadpoles of two hylid treefrogs, Agalychnis callidryas and Dendropsophus ebraccatus, and predaceous dragonfly nymphs, Anax amazili. Agalychnis callidryas appears to be the more effective competitor, A. amazili consumes both species, but A. callidryas is more vulnerable. Here we examine whether there are differences between the two species in their responses to A. amazili cues, whether these responses change through ontogeny, and how their responses to predator cues alter interactions with each other and their resources.

We conducted a 2 x 4 factorial experiment in 400 L mesocosms in which the presence or absence of a caged predator was crossed with no tadpoles, 25 tadpoles of each species alone, or 25 tadpoles of each species combined. Mesocosms were given standardized aliquots of filtered inoculate collected from a nearby pond and left for 3 weeks to allow the establishment of primary producers and microorganisms before tadpole additions. Tadpole growth, periphyton and phytoplankton were sampled at intervals though the experiment. Our study was conducted in October 2010 at the Smithsonian Tropical Research Institute in Gamboa, Panama.


Tadpoles differed in their response to predator cues as A. callidryas reduced their growth, but D. ebraccatus did not. Furthermore, A. callidryas’ response changed through ontogeny, reducing early growth relative to no predator treatments, but increasing growth later in development such that their were no size difference between treatments at the end of the experiment. Consistent with previous studies, A. callidryas reduced D. ebraccatus final size, but only in the absence of predators. Both predators and tadpoles altered algal standing biomass, but these effects were independent of each other. Tadpoles decreased periphyton and increased phytoplankton, while predators increased both. Our results suggest that differences in early responses to predators may have altered competitive interactions between these species, but non-consumptive effects did not have strong cascading effects to resources.

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