Predator-induced mortality does not explain variation in mayfly abundance in open systems.
Peckarsky, Barbara*,1, 1, McIntosh, Angus2, 2, Kerans, Billie, Taylor, Brad, 1 Cornell University, Ithaca, NY2 Rocky Mountain Biological Laboratory, Crested Butte, CO
ABSTRACT- Identifying factors affecting abundance is especially difficult in open systems where dispersal of organisms with complex life cycles may modify local population dynamics. We combined surveys and predation experiments to test whether trout or stonefly predation could explain observed abundance patterns of two mayfly species. In fish and fishless streams Baetis bicaudatus had similar abundances, loss rates, larval development times and probabilities of surviving the larval stage. Loss rates were high, but only a small proportion could potentially be attributed to predation. High stream flow during late larval development may increase mortality independent of predation. Surprisingly, Baetis sp. nov. was more abundant in fish than fishless streams despite high losses and a high proportion of total loss rates that could be potentially explained by trout predation. However, shorter development time compensated for higher losses in trout streams resulting in similar probabilities of surviving the larval stage in fish and fishless streams. Although stonefly densities were similar between fish and fishless streams, stonefly predation had minimal effects on Baetis losses in trout streams, possibly because of negative effects of trout on stonefly foraging behavior. However, the potential for stonefly-induced mortality in fishless streams was similar to that of trout predation in fish streams. Nonetheless, predation rates could not explain variation in mayfly abundance. A mathematical model predicted that high levels of recruitment by oviposition and accelerated larval development may enable vulnerable animals to maintain large populations in environments with high predation.
Key words: predation, mayflies, fish and fishless streams, recruitment
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