Effects of habitat and fish type and diet on the behavior of Daphnia

Abstract

ABSTRACT Infochemical landscapes, also referred to as landscapes of fear, can strongly influence the distribution of organisms. Planktivore infochemicals alter zooplankton distribution; zooplankton avoid macrophytes in the absence of planktivorous fish and associate with macrophytes when planktivorous fish are present. It is unclear, however, how zooplankton respond to fish with different diets in the presence and absence of habitat. In a laboratory experiment, we evaluated avoidance of Daphnia pulex to 4 fish treatments including a fishless control, a piscivore (muskellunge [Esox musquinongy]) with a diet of planktivores, and a planktivore (bluegill [Lepomis macrochirus]) with either a diet of conspecific zooplankton or a diet of heterospecifics: terrestrial invertebrates (crickets [Acheta domesticus]). These treatments used presence and absence of macrophytes to evaluate whether macrophytes alter responses to these fish treatments. Relative to control treatments, D. pulex avoided bluegill fed D. pulex and did not avoid muskellunge or bluegill fed A. domsesticus. Macrophytes were avoided in all fish treatments. Consumption of D. pulex, which was concurrently evaluated for the 2 bluegill diet treatments, was higher in bluegill fed A. domesticus treatments than in treatments of bluegill fed D. pulex, suggesting differences in behavior based on the presence of different infochemicals. A conceptual model based on results from the present study and the broader literature suggests that infochemical landscapes may cause high association for Daphnia, planktivores, and piscivores with macrophytes, ultimately influencing food web structure through higher encounter rates among taxa.