PARENT SESSION
Oral Session #87: Ecosystem Ecology.
Presiding: B. Currie
Thursday, August 8. 1:00 PM to 3:45 PM. Graham Meeting Room, TCC.
Do discontinuous body mass distributions of species within landscapes provide evidence of hierarchical landscape structure?
Skillen, Jennifer*,1, Maurer, Brian1, Kahl, Katherine1, 1 Michigan State University, East Lansing, MI
ABSTRACT- It has been conjectured that ecosystems are structured by relatively few physical and biotic processes operating at different spatial and temporal scales. These processes are thought to create landscapes that are hierarchically structured, with resources that can be used by species of different sizes existing on different scales. If such resource structure exists, then the distribution of body masses of species using those resources should exhibit discontinuities or "gaps" between species of different sizes that use resources on different scales. When human activities change the environment, the hierarchical structure of landscapes should also change. If this is true, then the discontinuities in body mass distributions should change to reflect human induced changes in landscapes. If discontinuities in body mass distributions indicate a paucity or high degree of variability of resources for species of particular body sizes, then species that are sensitive to human alteration of landscapes should have body masses that place them in or near gaps in the body mass distribution. Using Breeding Bird Survey data, we examined 13 species assemblages of birds occupying mutually exclusive physiographic regions of the North American continent. We tested the hypothesis that avian body masses within a landscape are discontinuously distributed, using several different methods to recognize the discontinuities. We then tested the hypothesis that species with highly variable, declining, weedy, or exotic populations in a region are found significantly more often near large discontinuities in the size spectrum than species with stable populations within that region. The results of these qualitative and quantitative tests have important implications for the understanding of the formation and maintenance of species assemblages within the landscape.
KEY WORDS: body size, Breeding Bird Survey, species assemblage