Abrupt spatial and numerical responses of overabundant foxes to a reduction in anthropogenic resources

Abstract

Summary: 1. Carnivore overabundance that results from exploitation of human derived resources can have numerous detrimental effects on local human populations and ecological communities. Experimental studies on the responses of overabundant carnivores to reductions of such resources are necessary to understand the effectiveness and impacts of resource reduction. 2. We conducted controlled experiments in two villages in which we drastically reduced the availability of anthropogenic food sources in half of each village. Spatial and numerical responses of radio‐collared red foxes Vulpes vulpes were recorded and contrasted with those of radio‐collared foxes in three similar untreated villages and pristine areas in the region. In total, we looked at survival rates of 134 foxes. 3. Prior to the resource manipulation, home range sizes (0·47 and 0·56 km 2) and population densities (30 and 36 foxes km−2) in the two villages were comparable to documented low and high‐end values, respectively. 4. Fast and distinct spatial responses were observed in response to the resource manipulation, and were manifested in either increased home range size or home range shifts. In one village, foxes exposed to reduced resource availability more than doubled their home range size. 5. Survival rates of individuals in the treated areas were drastically reduced. Actual fox mortality in the two treated areas reached 100% and 64% within 12 months of the onset of resource manipulation. Estimated monthly survival in the two treated areas declined from 0·96–0·98 and 0·98–0·99 (∼0·69 and 0·78 derived annual survival) before treatment to 0·80–0·83 and 0·92–0·94 (∼<0·01 and 0·42 derived annual survival) after treatment, respectively. By contrast, average monthly survivorship in pristine areas was nearly 0·97 (∼0·69 annual survival) and in the untreated areas and other non‐treated villages was 0·95–0·99 (∼0·54–0·89 annual survival). 6. Synthesis and applications. This study demonstrates that sound waste disposal measures are very effective in controlling populations of overabundant carnivores. Contrary to common notion, the response of foxes to reduced resources was fast, manifested more by reduced survival than by successful dispersal into adjacent pristine areas. The results offer support to the Resource Dispersion Hypothesis regarding both home range size and density (suggested by the sharp decrease in survival) as a function of the spatial and temporal dispersion of resource.