Importance of consumptive and non-consumptive prey mortality in a coupled predator--prey system.

1. Laboratory experiments were completed to identify the mechanisms by which the predatory flatworm, Dugesia tigrina, imposes mortality on its Aedes aegypti and Daphnia magna prey. Feeding trials were completed in glass microcosms which contained one of three - nine densities of small or large individuals of each prey species. 2. Mortality by Dugesia on small and large Aedes followed a type II functional response, whereas the mortality of Daphnia resembled a type III functional response. Prey mortality imposed by Dugesia consisted of consumptive and non-consumptive elements. Non-consumptive mortality occurred when prey individuals trapped in mucus trails subsequently died but were not ingested. 3. Additional experiments were conducted to quantify consumptive (capture followed by ingestion) and non-consumptive mortality (death not followed by ingestion). 4. Consumptive mortality followed a type II functional response for small and large individuals of both prey species, whereas non-consumptive mortality increased with prey density, although the relationships differed with prey species and size. The nonconsumptive mortality of large Daphnia increased at an accelerating rate with prey density and exceeded consumptive mortality at intermediate prey abundances. In contrast, non-consumptive mortality of small Aedes and small Daphnia was lower than consumptive mortality and either increased with prey density at a decelerating (small Aedes) or accelerating (small Daphnia) rate. 5. These results suggest that the importance of consumptive and non-consumptive mortality to total prey mortality needs to be considered when modelling predator-prey dynamics. [ABSTRACT FROM AUTHOR]