Date of this Version
Ecological Applications, 14(5), 2004, pp. 1306–1320
Habitat loss and fragmentation currently threaten ecosystems worldwide, yet remain difficult to quantify because within-fragment habitat and landscape-scale influences often interact in unique ways. Although individual species respond to fragmentation differently, large-scale conservation planning must unavoidably target multiple species. Although information on a population’s response to fragmentation is critical, and measurements of species richness provide useful insights, exclusive reliance on these responses may mask important information about the taxonomic composition of assemblages in response to fragmentation. The North American tallgrass prairie ecosystem is one of the most threatened and fragmented ecosystems in the world, and insects are significant contributors to its biodiversity. In remaining grassland fragments, we evaluated within-fragment influences in conjunction with landscape-scale responses of representative insect communities from four feeding guilds: generalists, specialists, multiple life stage habitat use, and predators. Fragment-specific attributes capable of influencing insect diversity include plant species composition, plant biomass, abundance of blooming flowers, and vertical habitat heterogeneity created by the vegetation. Landscape-scale factors expected to influence patterns of insect species diversity include fragment size and shape as well as the spatial configuration of fragments. Ordination techniques were used to summarize composition of each feeding guild assemblage of each fragment, and structural equation modeling was used to examine the direct and indirect effects of fragmentation with influences from local habitats. Generalists (Orthoptera), mixed-modality feeding that changes with life stage (Lepidoptera), and specialist herbivores (Curculionidae) all responded directly to withinsite characterizations of the plant community. Site management from large ungulate grazing or mowing for hay production consistently had an indirect effect on the insect community through influences on plant community composition. The predator assemblage (Coccinellidae) was influenced directly by fragment shape. To maintain insect biodiversity in tallgrass prairie fragments, these results indicate that conservation practices should focus on communities in order to maintain insect biodiversity in tallgrass prairie fragments. Landscapescale factors must also be considered when making conservation decisions, primarily because predators (top trophic level organisms) are more likely to respond to regional changes.