Habitat-mediated predation and selective consumption of spawning salmon by bears

Predator–prey interactions are key elements of ecosystem functioning and can be mediated by physical characteristics of the environment. To examine this, I studied interactions between bears and spawning salmon on the Central Coast of British Columbia, Canada. I first show how size-biased predation is mediated by stream characteristics that provide refuge for prey, with implications for size-selective pressures acting on salmon in different streams. I then demonstrate that bears feed selectively on energy-rich parts of salmon, depending on characteristics of the stream, with consequences for terrestrial nutrient transfer via uneaten salmon biomass. Overall, I found that bears captured larger salmon in streams with less wood and fewer undercut banks and fed more selectively in narrower, shallower streams with less pool volume. This suggests that habitat characteristics play a role in mediating predator behaviour and, therefore, have implications for the selective pressures faced by salmon, and nutrient subsidies to surrounding habitats.