The spatial ecology of small mammals in old fields: A study of movement, demography and community structure in a fragmented landscape

Habitat fragmentation is a ubiquitous form of habitat degradation and a major cause in the global decline of biodiversity. Habitat fragmentation changes spatial relationships among organisms and their resources, and thus should dramatically affect all aspects of a species' ecology. Habitat fragmentation can be used as a means to study how, and to what extent, changes in the spatial context of landscapes modify ecological dynamics. I compared 7.7 years of mark-recapture data from two sites--a continuous old-field, and an experimentally fragmented landscape--to study the influence of habitat fragmentation (and hence space) on individual movements, population demography, and community structure in three species of old-field small mammals--cotton rats (Sigmodon hispidus), prairie voles (Microtus ochrogaster) and deer mice (Peromyscus maniculatus). Changes in the spatial configuration of the landscape due to habitat fragmentation influenced all aspects of small mammal biology from individual movements, to demographic and community level processes. Habitat fragmentation changed shorter-scale behaviors: animals moved farther distances, and less frequently, as fragmentation increased. Furthermore, different species showed different responses in movements to the same pattern of fragmentation. The net direction of individual movements between blocks indicated source-sink dynamics were not occurring in the fragmented site. Population-level analyses indicated fragmentation changed the amounts of available habitat to dominant competitors, likely decreasing their competitive influence on subordinate species. Additional analyses at the community level indicated the continuous site had higher diversity by several measures than the fragmented site. There was greater temporal variation in abundances on the fragmented site, and more stable rank abundances on the continuous site. Finally, the landscape surrounding the two sites affected species richness presumably by defining the source pool of potential community members. Analyses of individual movements indicate the spatial scale influencing local short-term dynamics in this small mammal community is relatively small, on the order of 100 m, and that movements have larger impacts when populations are small. Thus, the spatial scale of fragmentation created in the field experiment is appropriate for studying population level and community level responses by small mammals to fragmentation.