Patchy indirect effects: predators contribute to landscape heterogeneity and
ecosystem function via localized pathways
Predators are widely recognized for their irreplaceable roles regulating the abundance and altering the traits of lower trophic levels. Predators also have irreplaceable roles in shaping community interactions and ecological processes via highly localized pathways, irrespective of their influence on prey density or behavior. We synthesized empirical and theoretical research describing how predators have indirect ecological effects confined to discrete patches on the landscape, processes we have termed patchy indirect effects of predation. Predators generate patchy indirect effects via three main pathways: generating and distributing prey carcasses, creating biogeochemical hotspots by concentrating nutrients derived from prey, and killing ecosystem engineers that create patches. In each pathway, the indirect ecological effects are limited to discrete areas with measurable spatial and temporal boundaries (i.e., patches). Our synthesis reveals the diverse and complex ways that predators indirectly affect other species via discrete patches, ranging from mediating scavenger interactions to interspecific parasite/disease transmission risk, and from altering ecosystem biogeochemistry to facilitating local species biodiversity. We also show how existing multi-scale ecological frameworks (metapopulation, meta-ecosystem, and patch dynamics concepts) offer insight into the mechanisms underlying the formation of these patches within ecosystems. We then provide basic guidelines on how these effects can be quantified at both the patch and landscape scales, and discuss how these predator-mediated patches ultimately increase landscape heterogeneity and contribute to ecosystem functioning. Whereas density- and trait-mediated indirect effects of predation generally occur through population-scale changes, patchy indirect effects of predation occur through individual- and patch-level pathways. Our synthesis provides a more holistic view of the functional role of predation in ecosystems by addressing how predators create patchy landscapes via localized pathways, in addition to influencing the abundance and behavior of lower trophic levels.