Density-dependent foraging effort of Deer Mice (Peromyscus maniculatus)

Summary

• 1
   Little is known about how population density affects the foraging behaviour of individuals. Simple models are developed to predict the net effect of density on the quitting-harvest rates of optimal foragers. The theory was tested with experiments that measured the foraging behaviour of free-ranging Deer Mice under control and reduced densities.
• 2
   An increased density of conspecifics may (a) reduce the costs of foraging by increasing competition for resources (reduces the energetic state of the forager; competition hypothesis) or (b) increase the costs of foraging by increasing the value of time spent on social activities (social benefits hypothesis).
• 3
   A reduction in the costs of foraging caused by competition will reduce the quitting-harvest rate of an optimal forager, whereas an increase in the value of alternative activities will increase the quitting-harvest rate. Both hypotheses predict a reduction in optimal foraging time with increased density.
• 4
   The hypothesis that applies to Deer Mice (Peromyscus maniculatus, Wagner) was assessed by measuring their foraging activity and quitting-harvest rates at control and reduced population densities on four study plots located in boreal forest in north-western Ontario, Canada.
• 5
   Deer Mice increased their per capita foraging activity and their quitting-harvest rates when population densities were reduced. The results confirm the very important role of competition in the behaviour of optimal foragers.