It has been hypothesized that tiger salamanders (Ambystoma tigrinum) in fishless aquatic habitats are functional equivalents of planktivorous fish. I tested this idea in a series of fishless prairie wetlands (“potholes”) in southwestern Manitoba by comparing macroinvertebrate community structure and phytoplankton standing crop across a gradient of gray tiger salamander (A. tigrinum diaboli Dunn) abundance, and in the presence and absence of tiger salamanders. Estimates of tiger salamander abundance included both adult and larval forms. Separate analyses yielded similar results. First, across a set of 45 potholes sampled over two years, I found that as tiger salamander abundance increased, aquatic insect abundance decreased and phytoplankton standing crop increased. Second, for a subset of seven potholes that had tiger salamanders one year but not the other, reverse trophic structure patterns were observed. For all analyses, abundances of mostly herbivorous and detritivorous macroinvertebrates (e.g., Gastropoda, zooplankton) were unrelated to tiger salamander abundance suggesting that either aquatic food web relationships in prairie potholes are complex or the link between tiger salamanders and phytoplankton standing crop may partly be a function of nutrient recycling rather than only direct predator-prey interaction. These results support the idea that effects of tiger salamanders on the trophic structure of prairie potholes mimic those of planktivorous fish.
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