Reproduction, foraging and the negative density–area relationship of a generalist rodent

Abstract

While many species show positive relationships between population density and habitat patch area, some species consistently show higher densities in smaller patches. Few studies have examined mechanisms that may cause species to have negative density-area relationships. We tested the hypothesis that greater reproduction in edge versus interior habitats and small versus large fragments contributes to higher densities of white-footed mice (Peromyscus leucopus) in small versus large forest fragments. We also examined vegetation structure and foraging tray utilization to evaluate if greater reproduction was a result of higher food availability. There were greater number of litters and proportion of females producing litters in the edge versus interior of forest fragments, which may have contributed to greater population growth rates and higher densities in edge versus interior and small versus large fragments. Data on vegetation structure and giving-up densities of seeds in artificial patches suggest that food availability may be higher in edge versus interior habitats and small versus large fragments. These results, in an area with few or no long-tailed weasels, provide a distinct contrast to the findings of Morris and Davidson (Ecology 81:2061, 2000) who observed lower reproduction in forest edge habitat as a result of high weasel predation, suggesting that specialist predators may be important in affecting the quality of edge habitat. While we cannot exclude the potential contributions of immigration, emigration, and mortality, our data suggest that greater reproduction in edge versus interior habitat is an important factor contributing to higher densities of P. leucopus in small fragments.

Genetic estimates of immigration and emigration rates in relation to population density and forest patch area in Peromyscus leucopus

“…Relative abundance of P. leucopus in our 12 study patches ranged from 50.8 to 121.1 individuals/500 trap-nights for small forest patches and only 11.7-76.2 individuals/500 trap-nights for large forest patches and a significant negative density-area relationship has been reported previously (Anderson et al 2003;Wilder and Meikle 2005;Anderson and Meikle 2006). These values are similar to values reported by other investigators (e.g., Cummings and Vessey 1994).…”

“…either producing their first litters at an earlier age or having fewer failed breeding attempts (Duquette and Millar 1995). Wilder and Meikle (2005) found that nest boxes in forest edge habitats in most of the same forest patches as the current study had the vast majority of litters as well as a greater proportion of adult females reproducing than in forest interior habitats. Their results suggest that reproductive rates were higher in smaller patches since small patches have a greater proportion of structurally complex edge habitat than large patches.…”

“…In contrast, investigators have found a consistent negative relationship for population densities of the forest habitat generalist Peromyscus leucopus and forest patch area, suggesting that densities of white-footed mice are enhanced by forest fragmentation (Yahner 1992;Swihart 1996, 1998;Krohne and Hoch 1999;Mossman and Waser 2001;Schmid-Holmes and Drickamer 2001;Anderson et al 2003;Wilder and Meikle 2005;Anderson and Meikle 2006). The underlying mechanisms to explain this negative density-area relationship in P. leucopus, (also found in other rodents such as Apodemus sylvaticus, P. gossypinus, Sigmodon hispidus, and Oryzomys palustris; see Bowers and Matter 1997), are a matter of debate.…”

“…The goal of this study was to estimate migration among populations of P. leucopus using microsatellite-DNA to test the inhibited dispersal hypothesis and the immigration hypothesis as alternative explanations for the negative density-area relationship. The role of reproduction in maintaining patterns of density and gene flow is also considered (Wilder and Meikle 2005). To our knowledge, this is the first study utilizing Bayesian and maximum-likelihood coalescent-based methods for estimating migration rates to explain relationships between population density and forest patch area.…”

Edges: Where Landscape Elements Meet

“…It is reasonable to expect habitat generalists to adapt readily to edges because, by definition, these species exploit a range of patch types (e.g. Wilder & Meikle 2005), although Imbeau et al (2003) found that 28 out of 30 edge-using birds were considered specialists of early successional habitat, which just happened to occur most commonly at patch edges. Species that require multiple patch types are favoured by edges between these types because this represents the optimum location for access to the spatially separated resources.…”