Patch selection and tree‐seedling predation by resident vs. immigrant meadow voles

Many small mammal species may exhibit source–sink dynamics, in which some patches (sources) are occupied mainly by residents, while others (sinks) are occupied mainly by recent immigrants. Residents and immigrants are expected to differ in their degree of familiarity with their surroundings, which could affect resource use. Small mammals are known to inhibit the establishment of tree seedlings, especially when population densities are high, and habitat quality, especially the availability of cover and food, has been found to affect local densities. In addition, availability of food can affect the use of other food items, especially those of lower quality. Our goals were to study how population status (residents vs. immigrants) affects use of habitat patches differing in cover and food availability, and how the quality of habitats and individuals interact and affect tree‐seedling predation by meadow voles (Microtus pennsylvanicus). We conducted a field experiment in six 40 m × 40 m enclosures in an old field. The enclosed populations were randomized into resident vs. immigrant treatments and exposed to a habitat manipulation treatment (cover vs. food) using a 2 × 2 factorial design within the enclosures. We planted seedlings of red maple (Acer rubrum) and black birch (Betula lenta) in each habitat patch and censused them for three weeks. Seedling predation was lower in food‐supplemented than in non‐supplemented patches. Voles were attracted by cover and killed more seedlings within it than in open patches. Immigrants moved more between habitat patches than residents. When controlling for the number of visitors to patches, the immigrants killed fewer seedlings than did the residents. This study demonstrates that spatial dynamics of animal consumers, such as source–sink movements between habitat patches, can influence community dynamics of plants, such as the invasion of old fields by trees, in ways beyond those predicted by simple numerical relationships between consumers and resources.