An Introduction To Species-Environment Interactions: The Importance Of Scale
Robert K. Swihart, Department of Forestry and Natural Resources, Purdue University, 715 West State St., West Lafayette, IN 47907; (765) 494-3590; rswihart@purdue.edu
An ongoing challenge for fisheries and wildlife biologists is how to estimate the potential impact of environmental variables on populations of a focal species. A closely related issue is to understand the spatial scale over which environmental forces might exert their effects. We know that vertebrates differ in their responses to environmental factors. Do they also differ in the spatial scale of their population responses? The answer to this question has important practical implications. If organisms are sensitive only to local environmental variables, then traditional methods of habitat management may be used. However, if organisms are more sensitive to environmental factors operating at larger (e.g., landscape) scales, then an emphasis on local management of habitat may do little to address the real issues affecting population vitality. To address questions of species-environment interactions and spatial scale, the Upper Wabash Ecosystem Project was undertaken during 2001-2004. The upper Wabash River basin covers 2 million hectares and drains approximately 20% of Indiana. A spatially hierarchical sampling design was used in which local sampling units were nested within local habitat patches which in turn were nested within 23-km2 landscapes. Sampling of mammals, birds, and reptiles relied on methods to enable estimation of detection probability for species. Data were collected from 2,278 bird point counts, 933 small mammal trapping grids, and 227 turtle hoop-trap sites. I explain the utility of this sampling design for addressing commonly encountered problems associated with species-environment modeling, especially related to issues of scale.