Testing mechanistic explanations for mammalian predator responses to habitat edges

Increased predator activity along habitat edges (the edge effect) is often documented in the temperate zone, but earlier studies have rarely been able to explicitly test the suggested mechanisms underlining this phenomenon. In this study, we measured the distribution of mammalian predators by scent stations and their main prey (rodents) in four types of landscape elements corresponding to an edge gradient between two habitat types; grassland and forest. We found a contrasting pattern in carnivore activities between years. Whereas carnivores did not exhibit a significant occurrence along the forest-grassland edge in the first year with low prey abundance, they were more likely to be detected along habitat edges in the subsequent year with high prey abundance. Our results do not suggest that the increased activity of carnivores at habitat edges arises as a consequence of predator overflow from higher quality habitat through the edge into lower quality habitat, but showed that most predator species focus their activity specifically to the edge structure. On the other hand, our data do not provide straightforward support for the hypothesis that predator edge preferences are caused by a spatial gradient in carnivores' main prey-rodents.