Predation by foxes Vulpes vulpes on brown hares Lepus europaeus in central southern England, and its potential impact on annual population growth.

Abstract

A computer model was used to simulate processes of reproduction, growth and loss occurring during twelve months within a real-world brown hare Lepus europaeus L. population in a mixed farming area of central southern England. Model parameters representing hare density, and the density and diet of foxes Vulpes vulpes L., were derived from field studies, whereas likely values for other parameters were set on the basis of studies performed elsewhere. Simulations were created to represent a) the hare population on an area of 11 km² comprising several fox territories; and b) the hare population on individual fox territories. In the larger-scale simulations (a), the number of hares eaten by foxes easily exceeded their breeding density and amounted to 76-100% of annual production. The hare population could not have withstood more than a very low additional mortality without declining. When fox predation was set to zero, the final density of hares in the model was 3 to 6 times that produced when fox predation occurred. Simulations for individual fox territories (b) suggested that variation in territory size and social group composition of foxes introduced significant local variation within this overall picture. We conclude that the hares eaten by foxes were a substantial loss relative to productivity. This conclusion was robust in the face of estimation errors or changes in underlying assumptions of the model. This study describes the extent of fox predation on hares and its potential impact on hare population growth. Because the degree of compensation between mortality factors was unknown, the study does not show that fox predation per se limited the hare population. Nevertheless, our findings are a necessary adjunct to experimental evidence and population studies which suggest that red foxes play a major role in hare population dynamics in many environments.