The ecological effects of providing resource subsidies to predators

Abstract

Aim: Predators often have important roles in structuring ecosystems via their effects on each other and on prey populations. However, these effects may be altered in the presence of anthropogenic food resources, fuelling debate about whether the availability of such resources could alter the ecological role of predators. Here, we review the extent to which human-provided foods are utilised by terrestrial mammalian predators (>1kg) across the globe. We also assess whether these resources have a direct impact on the ecology and behaviour of predators and an indirect impact on other co-occurring species. Location: Global. Methods: Data were derived from searches of the published literature. To summarise the data we grouped studies based on the direct and indirect effects of resource subsidies on predators and co-occurring species. We then compared the types of predators accessing these resources by grouping species taxonomically and into the following categories: (1) domesticated species, (2) mesopredators and (3) top predators. Results: Human-provided foods were reported to be utilised by 36 terrestrial predator species in 34 different countries. In the presence of these resources we found that: (1) predator abundance increased, (2) the dietary preferences of predators altered to include the food subsidy, (3) life-history parameters such as survival, reproduction and sociality shifted to the benefit or detriment of the predator, and (4) predators changed their home ranges, activity and movements. In some instances, these modifications indirectly affected co-occurring species via increased predation or competition. Main conclusions: The availability of human-provided food to predators often results in behavioural or population-induced changes to predators and trophic cascades. We conclude that there is an urgent need to reduce the access of predators to food subsidies to minimise human-wildlife conflicts and to preserve the integrity of ecosystem functioning in human-influenced landscapes world-wide.