Relationship between plant and butterfly community composition on upland prairies of the Willamette Valley, Oregon

Graduation date: 2003Small remnants of 'natural' habitats exist today throughout much of the world. Upland\ud prairies in the Willamette Valley, Oregon have been nearly eliminated by conversion to\ud agriculture and other uses. As a result, very few prairies remain and at least four butterfly\ud species that require this habitat appear to be locally uncommon. To better understand\ud requirements for conservation and management of upland prairies and the species that\ud depend on them, I investigated plant abundance and species richness, butterfly abundance\ud and species richness, and prairie integrity on 17 prairie remnants. To evaluate the\ud relationship between prairie integrity and butterfly community composition, integrity was\ud defined by abundance and species richness of native, prairie plant species. Because little\ud is known about the habitat requirements of prairie-dwelling organisms, I also investigated\ud juvenile and adult food resource use and spatial patterns associated with resource use by\ud four locally uncommon butterfly species: common checkered-skipper, Fender's blue, Anise\ud swallowtail, and field crescent. Plant species used and not used for nectaring and\ud oviposition and spatial relationships between the two were explored for each butterfly\ud species. My study provides evidence that remnants, including small, degraded sites, serve\ud as refuges for locally uncommon butterfly species. The greatest mean number of butterfly\ud species was detected on sites of high integrity, but total butterfly abundance at all but one unique site was similar to that of low and medium integrity sites. Butterfly species\ud richness appeared to be positively associated with remnant integrity while factors other\ud than remnant integrity as defined here may be influential on butterfly abundance.\ud Furthermore, I suggest that the locally uncommon butterflies studied here have specific\ud habitat requirements and this likely contributed to their sparse distribution. Although host\ud plant abundance did not appear to limit butterfly distributions within either site, I lacked\ud sufficient sample sizes necessary to make strong inferences. Factors other than, or in\ud combination, with host plant occurrence, such as presence of Composite nectar species and\ud native plant abundance, may be important in determining their distribution within a site.\ud Lack of large areas of habitat and incidence of uncommon species on remnants makes it\ud imperative that we conserve biodiversity by the maintenance, improvement, and protection\ud of some very small areas