Interspecific Differences in the Direct and Indirect Effects of Two Neotropical Hylid Tadpoles on Primary Producers and Zooplankton

摘要

Herbivores can both consume and facilitate primary producers with important consequences for community structure. How differences in herbivore foraging ecology alter the relative importance of such effects is not well understood, especially in tropical lentic systems. To address this issue, we manipulated the density of two herbivores with different foraging strategies to evaluate their effects on primary producers and other consumers. Specifically, we examined the effects of the tadpoles of two common Neotropical hylid frogs at two densities on conspecific growth, periphyton and phytoplankton, and zooplankton. We found that the tadpoles of the pandess treefrog, Dendropsophus ebraccatus, reduced periphyton and increased phytoplankton abundances, whereas they had no affect on zooplankton. The red-eyed treefrog, Agalychnis callidryas, also reduced periphyton and increased phytoplankton, but to a greater extent, and they also had strong impacts on zooplankton by altering the composition, size structure, and total abundances of the zooplankton community. Differences between both species’ impacts on these food webs were independent of tadpole biomass, as size-selective filter feeding and nutrient cycling seems to drive the impacts of A. callidryas onphytoplankton and zooplankton, while the role of D. ebraccatus is more limited. Species level differences in the strength and direction of top-down and bottom-up effects on food webs suggest that the ecological roles of tadpoles may be diverse and important to aquatic communities.