Optimal foraging theory states that an individual should seek to maximise its energetic gain from foraging effort. In doing so, both food abundance and predation risk must be considered. The study species used to test the importance of these two factors was the wood mouse, Apodemus sylvaticus, a common resident of mixed deciduous woodland. The study was carried out during winter. I consequently predicted that space use by A. sylvaticus would be related to patches of woodland containing habitat features which either increased food abundance or reduced predation pressure. A 1ha plot was selected and divided into 100 10m x 10m grid squares. Capture success and mouse diversity, the total number of different mice caught in each grid square throughout the study, were derived from a trapping effort of 1020 trapnights. Food abundance was estimated by measuring the abundance and size of seed-producing tree species. Predation risk was assessed by measuring logs, stumps, exposed roots, woody debris piles and total tree abundance.
Results/Conclusions
Models were produced for food abundance and predation risk and used to assess their relative importance in explaining capture success and mouse diversity. Patches of the invasive Rhododendron, the only evergreen and therefore foliated species at the study site, provided areas of reduced predation risk. Rhododendron was therefore used as a naturally occurring equivalent to an experimental treatment for lower and higher predation risk. The importance of food abundance and predation risk was then analysed for three patch types: mixed, open (low Rhododendron) and closed (high Rhododendron) patches. Predation risk was found to be more important overall, but the balance between predation risk and food abundance was found to shift more towards food abundance inside patches of Rhododendron. Outside of Rhododendron, predation risk variables such as logs and woody debris became stronger determinants of space use by mice.
