Urban boundaries in a biodiversity hotspot: Declining butterfly diversity in California's modified Central Valley.
Anderson, Kayce*,1, Forister, Matthew2, Shapiro, Arthur1, O'Brien, J, Thorne, J, 1 University of California - Davis, Davis, CA, USA2 State University of New York - Stony Brook, Stony Brook, NY, USA
ABSTRACT- Long-term data sets are essential for documenting patterns of community change and in understanding interactions between organisms and their environment. Although butterflies have been the focus of much research and conservation, very few studies have spanned more than a few years. We used a thirty-year data set to analyze trends in species richness of butterflies observed along an approximately 150-mile transect running Northeast-Southwest through the California Floristic Province, a biodiversity hotspot. The Central Valley portion of the transect, which is largely composed of weed dependent species, showed a significant overall decline in butterfly species richness over the last 30 years. The decline has been detected at three of the four Central Valley sites and covers a range of habitats, disturbance levels, and species. We also analyzed similarities between species declines at a regional and local level. Additionally, to understand the influence of natural history and phonology on the patterns of decline, order of emergence, resident status, number of broods, weediness and overwintering state were considered at each site. Several natural history traits were associated with the decline within each site, but there was no single trait that was associated with the regional decline. Often regional scale synchrony among and between species can be attributed to weather, so we explored correlations between weather variables and the number of species observed per year at each site. Certain weather variables are highly correlated with species richness locally, but no single weather variable explained variation in species richness among all sites. These results demonstrate the importance of local factors in a regional decline. The dynamics of disturbance-tolerant organisms at urban boundaries is generally overlooked, but this study demonstrates that they, too, are vulnerable to a changing environment.
Key words: Butterflies, California, Species richness, Long-term trends
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