PREDATOR-INDUCED BEHAVIORAL INDIRECT EFFECTS - CONSEQUENCES TO COMPETITIVE INTERACTIONS IN ANURAN LARVAE

This study examines the non-lethal effects of an odonate predator (Ana x junius) on the competitive interactions among several size classes o f anuran larvae, In an outdoor experiment using cattle watering tanks, we estimated the effects of both large and small bullfrogs (Rana cate sbeiana) on themselves, on each other, and on small green frogs (R. cl amitans) in the absence and non-lethal (caged) presence of Anax. The p resence of Anax depressed both growth and survivorship of small bullfr ogs and green frogs. In contrast, the presence of Anax had positive ef fects on growth rates and size at metamorphosis of the large bullfrogs . Increasing density of competitors also decreased survivorship of sma ll classes, and growth rates of all classes. The per-unit-biomass comp etitive effects of the small bullfrogs on target classes were much gre ater than those of large bullfrogs. The presence of Anax significantly altered the per-unit-biomass competitive effects of small bullfrogs b ut not large bullfrogs, presumably because individuals in the small cl ass reduced their activity rates in the presence of Anax. Overall prod uction of new tadpole biomass was quite similar across experimental un its, with decreases in production of small size classes in the presenc e of Anax compensated for by increases in production of the large size class. Thus the non-lethal presence of Anax had substantial effects o n the nature of competitive interactions in this system, and we discus s the implications of such behavioral indirect effects in the study of ecological communities; Our results also illustrate the futility of a ttempting to partition the effects of competitors and predators, as bo th competitors and the non-lethal presence of predators significantly affected growth rates and death by starvation of small larvae. Finally , our results illustrate how individual behavioral responses may be tr anslated to community and ecosystem properties.