Are hedgerows the route to increased farmland small mammal density? Use of hedgerows in British pastoral habitats

Linear habitats are becoming increasingly common as a consequence of habitat fragmentation, and may provide the sole habitat for some species. Hedgerows are linear features that can vary substantially in structure and quality. Having surveyed 180 hedgerows, in four locations, and sampled their small mammal communities we examined the effect of physical hedgerow attributes on the abundance of small mammal species. Using three elements of landscape structure, we explored whether variation was best explained by the Random Sample Hypothesis (that small islands represent a random sample of those species populating larger areas), or by the Fragmentation Hypothesis (that species abundance will decrease with a loss of habitat area). We tested the relationship between the relative abundance of small mammals and 1. hedgerow connectivity; 2. total habitat availability and 3. local habitat complexity. We then explored the predictive power of combinations of these habitat variables. Connectivity was a positive predictor of wood mice Apodemus sylvaticus, and hedgerow gappiness was a negative predictor of bank voles Clethrionomys glareolus. The total amount of habitat available (hedgerow width, height and length) was a positive indicator of total small mammal biomass. These results support the Fragmentation Hypothesis that species abundance and distribution decrease with a loss of habitat area. The preservation of linear and associated habitats may therefore be important in maintaining metapopulations of the species we studied.