Interspecific differences in antipredator strategies determine the strength of non-consumptive predator effects on stream detritivores

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Animal species differ considerably in their response to predation risks. Interspecific variability in prey behaviour and morphology can alter cascading effects of predators on ecosystem structure and functioning. We tested whether species-specific morphological defenses may affect responses of leaf litter consuming invertebrate prey to sit-and-wait predators, the odonate Cordulegaster boltonii larvae, in aquatic food webs. Partly or completely blocking the predator mouthparts (mandibles and/or extensible labium), thus eliminating consumptive (i.e. lethal) predator effects, we created a gradient of predator-prey interaction intensities (no predator < predator – no attack < predator – non-lethal attacks < lethal predator). A field experiment was first used to assess both consumptive and non-consumptive predator effects on leaf litter decomposition and prey abundances. Laboratory microcosms were then used to examine behavioural responses of armored and non-armored prey to predation risk and their consequences on litter decomposition. Results show that armored and non-armored prey responded to both acute (predator – non-lethal attacks) and chronic (predator – no attack) predation risks. Acute predation risk had stronger effects on litter decomposition, prey feeding rate and prey habitat use than predator presence alone (chronic predation risk). Predator presence induced a reduction in feeding activity (i.e. resource consumption) of both prey types but a shift to predator-free habitat patches in non-armored detritivores only. Non-consumptive predator effects on prey subsequently decreased litter decomposition rate. Species-specific prey morphological defenses and behaviour should thus be considered when studying non-consumptive predator effects on prey community structure and ecosystem functioning.

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