A mechanism for Passive Range Exclusion: Evidence from the European badger (Meles meles)

The Passive Range Exclusion (PRE) Hypothesis provides a mechanism whereby species that rest or breed in communal residences, but forage independently on dispersed food items, may avoid entering the core home ranges of neighbouring groups. A stochastic simulation shows that as the occupants of a communal residence travel outwards to feed, their activities create a gradient in food availability. Food closest to the point of origin tends to be discovered first and at the highest rate. As the foraging period continues, the probability of encountering unexploited food increases with distance from the residence. Areas of relatively high food availability persist as ridges between neighbouring communal residences. The simulation predicts that once such a gradient is established, a strategy of preferential feeding in these areas optimizes food intake. Feeding excursions deep into neighbouring ranges are disadvantageous because areas of lower food availability are encountered and travel times back to the home residence become longer. The observed reluctance of individuals to forage close to neighbouring residences can therefore be explained partly or wholly as a result of exploitation competition and feeding optimization, without necessarily invoking territorial arguments about interference competition and conflict avoidance. At lower forager and food patch densities the simulation indicates that the gradient is insufficient to award significant benefit to border feeding. Hence border feeding strategies and the range exclusion that results should diminish as food or forager densities decrease. We use the European badger (Meles meles L.) as a test case for the hypothesis and show that exploitation competition between groups may be an important factor in shaping this species' home ranges.