Links between Microhabitat Preferences and Seed Predation by Small Mammals in Old Fields

Abstract

Recent studies indicate that seed predation by small mammals in old fields can be intense and, in conjunction with other herbivores, may influence the rate, composition and spatial pattern of tree invasion into these systems. Patterns of seed predation in old fields may be predictable, based on the preferences herbivores exhibit for particular microhabitats. Studies testing the strength of these linkages, however, are rare. The risk of predation for foraging animals can have a considerable impact on decisions about where to feed and what to consume in particular microhabitats. We examined how an experimentally created gradient of predation risk influenced the microhabitat use and foraging behavior a white-footed mice (Peromyscus leucopus) in an old field in central New Jersey, USA. Specifically, we monitored the removal of seeds from dishes placed in the center of replicated treatment plots in which we manipulated ground and canopy cover, as well as distance from the forest edge. We then determined the relative importance of these factors and their interactions in explaining patterns of seed predation by mice. In addition, the distribution and abundance of small mammals were monitored and the vegetation cover in the area immediately adjacent to our experimental plots was quantified to determine how these factors were related to patterns of seed removal. Other factors evaluated included seed species, nocturnal illumination, temperature, precipitation, and time of year. Ground cover, time of day, and distance from the forest edge explained the most variation in patterns of seed predation. Ground cover, particularly proximity to vines such as Rubus allegheniensis, appeared to take precedence over other microhabitat variables in the decisions seed predators made about where to forage. Significantly higher nocturnal rates of seed removal, trap data, feces and seed remains left around seed dishes, reinforced previous findings which suggest that white-footed mice are the dominant seed predators in the northeastern old fields. However, spatial patterns of seed removal did not correspond with the distribution and abundance of mice as indicated by the trapping data. These results suggest that the impact of P. leucopus on the spatial patterns of seed survival is more dependent on the behavioral responses of individual mice than the distributions of the populations they comprise. Overall. there was little variation from general patterns of seed predation for specific tree species, suggesting that in old fields dominated by mice. there may be relatively uniform regions of high and low seed predation based on the microhabitat preferences of this seed consumer. The consequences of the interaction between old field vegetation and patterns of seed predation by mice for tree invasion and establishment in old fields are discussed.