title: Population responses of small mammals to food supply and predators: a global meta-analysis.
abstract: 1. The relative importance of food supply and predation as determinants of animal population density is a topic of enduring debate among ecologists. To address it, many studies have tested the potential effects of food on population density by experimentally supplementing natural populations, with much focus on terrestrial vertebrates, especially small mammals. 2. Here we perform a meta-analysis of such experiments, testing two complementary hypotheses: (i) small mammal populations are bottom-up limited and (ii) population increases in response to food supplementation are constrained by predation, a top-down limitation. 3. In the 148 experiments recorded, food supplementation had an overall positive and significant effect, increasing population densities by 1.5-fold. Larger population increases occurred when predation was reduced and populations were open to immigration. Predation appeared to be unimportant when populations were closed to immigration. Immigration was the major mechanism underlying increases in abundance by increasing local population density and crowding. Contributions of increased reproductive rate could be detected, but were minor compared to immigration, and no effects were detected from survival. 4. Our analyses support the view that animal population density is determined by both bottom-up and top-down forces. They also suggest the possibility that food supplementation experiments might unintentionally create ecological traps by aggregating both prey and predators in small areas of the landscape. We suggest an alternative experimental design to increase the contribution that food supplementation experiments can make in future.
authors.affiliation: Depto de Ecologia, Universidade Federal do Rio de Janeiro, CP 68020, Rio de Janeiro, RJ, 21941-590, Brazil.
authors.forename: Jayme A
authors.initials: JA
authors.lastname: Prevedello
authors.forename: Chris R
authors.initials: CR
authors.lastname: Dickman
authors.forename: Marcus V
authors.initials: MV
authors.lastname: Vieira
authors.forename: Emerson M
authors.initials: EM
authors.lastname: Vieira
mesh_terms: D025041:Animal Migration; D000818:Animals; D001835:Body Weight / Q000502:physiology; D005247:Feeding Behavior / Q000502:physiology*; D020387:Food Chain; D060434:Herbivory / Q000502:physiology*; D008322:Mammals / Q000502:physiology*; D009026:Mortality; D011156:Population Density; D011157:Population Dynamics / Q000639:trends*; D012107:Research Design
keywords: pantry effect; population limitation; population regulation; predator‐prey interactions; resources