We studied the demography of populations of the white-footed mouse, Peromyscus leucopus, inhabiting forest patches. Patch populations were characterized by high density, low rates of emigration and immigration, large temporal variance in density, low spatial variation in density, and high home-range overlap. There was no relationship between density and the distance from other forest patches. However, patches less than 2 ha in size had the highest mouse densities. Radiotelemetry, fluorescent-powder tracking, and trapping indicated that few mice disperse through grassland or agricultural fields surrounding patches. The recovery of a population from extinction was slower in more distant patches. We suggest that dispersal plays a key role in the demography of P. leucopus metapopulations that inhabit a landscape composed of a mosaic of large forest tracts, isolated forest patches, and agricultural fields.Résumé : Nous avons étudié la démographie des populations de Souris à pattes blanches, Peromyscus leucopus, dans des îlots de forêt. Les populations des îlots boisés sont caractérisées par une densité élevée, de faibles taux d'émigration et d'immigration, une variance temporelle importante mais une faible variation spatiale de la densité, un chevauchement important des domaines. Il n'y a pas de corrélation entre la densité des populations et la distance des autres îlots boisés. Cependant, ce sont les îlots de moins de 2 ha qui supportent les densités les plus élevées de souris. La radiotélémétrie, le repérage des pistes par utilisation d'une poudre fluorescente, et le piégeage ont démontré que peu de souris se dispersent à travers les zones herbeuses ou les terres agricoles qui entourent les îlots de forêt. Le retour à des îlots disparus se fait moins rapidement lorsque les îlots sont éloignés. Nous croyons que la dispersion joue un rôle capital dans la démographie des métapopulations de P. leucopus qui habitent les paysages constitués d'une mosaïque de grandes bandes de forêt, d'îlots de forêt et de terres agricoles.[Traduit par la Rédaction] 1253

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The patterns of spatial heterogeneity in density and demography were studied in a population of Peromyscus leucopus inhabiting a deciduous forest in west-central Indiana. A series of 9 live-trapping grids sampled densities from 3 spatial scales: 3 ha, 80 ha and 350 km. We found high levels of variation within all three spatial scales. There was as much variation within a single, large grid as within the entire Sugar Creek Valley (350 km). The patterns of density variation were not temporally stable and thus represent variation in demographic processes rather than simply differences in habitat quality. We suggest that the Sugar Creek Valley represents a metapopulation of Peromyscus leucopus composed of a number of temporally unstable subpopulations. This structure provides considerable demographic variation that dispersing animals can exploit.