Extrapolating from individual movement behaviour to population spacing patterns in a ranging mammal

Abstract

A model was developed in which patterns of home range area and overlap are an emergent property of individual forager movements over short time scales. Forager movements were simulated as responding to energy requirements, a memory map of food availability and the distribution of nests. Interaction between foragers occurred predominantly as a result of food depletion and the occupation of nests; territorial or mutual avoidance interactions were not included. The model was parameterised for the red squirrel ( Sciurus vulgaris) and used to investigate the effect of changing food density on the spacing pattern of a fixed number of individuals (10) within a fixed area (25 ha) of initially uniform food availability. Forager positions were sampled and used to generate estimates of home range area and overlap. The space use patterns generated varied from small, similarly sized, non overlapping ranges at high food densities to large, different sized, overlapping ranges at low food densities. This was a combined result of the change in food density itself, the resultant change in the ratio of population density to carrying capacity and the random positioning of nests. An uncertainty analysis indicated that the results were robust to changing parameter values. The predictions emerged from just one set of relatively simple movement rules. This approach offers the ability to simulate other plausible movement rules (based on food availability and conspecific interactions) to generate further quantitative, testable, predictions regarding the mechanisms causing mammal spacing patterns.