Broadening the ecology of fear: non-lethal effects arise from diverse responses to predation and parasitism

The ecology of fear demonstrates how prey responses to avoid predation
cause non-lethal effects at all ecological scales. Parasites also elicit
defensive responses in hosts with associated non-lethal effects, which
raises the longstanding, yet unresolved question of how non-lethal effects
of parasites compare with those of predators. We developed a framework for
systematically answering this question for all types of predator and
parasite systems. Our framework predicts that trait responses and their
non-lethal effects should be strongest from predators and parasites that
do not kill individuals to feed on them, but which nevertheless damage
fitness. Analysing trait response data on amphibians, which have been
well-studied for this area of research, showed that individuals generally
responded more directly to short-term predation risks than to parasitism.
Apart from studies using amphibians, there have been few direct
comparisons of responses to predation and parasitism, and none have
incorporated responses to micropredators, parasitoids, or parasitic
castrators, or examined their long-term consequences. Addressing these and
other data gaps highlighted by our general framework can advance the field
toward understanding how non-lethal effects shape real food webs, which
contain multiple predator and parasite species.