Effects of local habitat characteristics and landscape context on grassland butterfly diversity

Recent ecological studies suggest that the landscape context of native habitat remnants may significantly influence plant and animal abundance and distribution within those remnants. Other research has revealed a weak link between landscape context and native community composition. To understand the relative importance of local and regional habitat characteristics for grassland butterflies, we assessed butterfly community diversity in four types of grassland habitats surrounded by varying amounts of urban development near Boulder, Colorado (U.S.A.). We recorded butterfly species abundance and composition in 66 grassland study plots on five sampling dates in 1999 and 2000. Grasslands were of four types: native shortgrass, native mixed grass, native tallgrass, and planted hayfields. Grasslands also varied in quality, determined by the abundance of native versus exotic plant species. We observed highly significant effects of grassland type on butterfly species richness and composition. For example, tallgrass plots supported significantly higher butterfly species richness than shortgrass plots (p < 0.01). Habitat quality also affected butterfly species richness and composition. Low-quality plots generally supported fewer species than moderate- or high-quality plots (p < 0.05). Landscape context - the percentage of urbanization in the surrounding landscape - did not significantly predict butterfly species richness or composition. Our observations suggest that for the grassland butterfly communities in our study, (1) grassland type was the primary determinant of species richness and composition, (2) habitat quality secondarily affected butterfly community diversity, and (3) landscape context did not significantly predict butterfly species composition. Our findings emphasize the importance of maintaining high-quality grassland habitat to protect native butterfly diversity.