Date of Award
Doctor of Philosophy (PhD)
The geographic ranges of most plant and animal species are tied closely to climatic factors, including temperature, precipitation, and soil moisture. For this reason, recent changes in the global climate due to human activities are predicted to have profound effects on natural populations, communities and ecosystems over a relatively short period of time. Combined effects from global warming and other anthropogenic activities such as land-use changes, pollution, and habitat loss/fragmentation, are altering species' distributions faster than they can be documented. Recent climate change has also been shown to alter species' breeding behaviors and alter the synchrony and timing of species' phenologies. The Diana Fritillary (Speyeria diana Cramer 1777) is a North American butterfly that appears to have declined over the past century. This butterfly species once ranged from coastal Virginia westward to Missouri and Arkansas, southward to the northern tips of Georgia and Alabama, and northward through the Ohio River Valley. It has since disappeared from large portions of its once semi-continuous range, and persists now primarily in two geographically distinct regions separated by an 850 km disjunction. The North Carolina and Arkansas Heritage Programs currently list S. diana as an imperiled species of special concern (rank S2/S3) due to its rapid decline over the past two decades; it is also included on the Xerces Society Red List of Pollinator Insects. The conservation network, NatureServe, assigns S. diana a Global Status of G3/G4, which describes the species as very rare or local throughout its range, found locally in a restricted range (21 to 100 occurrences), and threatened throughout its range. Because of its rapid disappearance across portions of its former distribution, S. diana may soon become a candidate for listing under the Endangered Species Act of the United States (Federal Register 1991, Vol.56, no. 225, pp. 58, 831). Currently, S. diana is not protected through any special conservation status, despite its apparent decline. The Diana fritillary is univoltine, producing one generation per year. Adult males emerge and take flight in late May, typically several weeks before females. Males patrol along the edge of forest habitat, and have an active and mobile lifestyle. While males begin to die off in late July, females persist somewhat cryptically into early October. Females are believed to be longer lived than the males, and are often found resting quietly in the cover of forest for much of the day, nectaring or ovipositing on the forest floor. In general, S. diana inhabits moist cove forests and deep woodland areas near streams. Adult Diana fritillaries are often found in open areas feeding on tall, high-quality nectar sources such as milkweeds, butterfly bushes or large fall composites. Violets (Viola spp., Violaceae) are the only larval host plants used by Speyeria. Each female Diana fritillary can lay thousands of eggs singly on ground litter during the month of September in the vicinity of violets. The hatched larvae immediately burrow deep into the leaf litter of the forest floor where they overwinter until the following spring. This dissertation is a comprehensive study of this butterfly over time, which documents the species' changing distribution over time, and explores the causes for its decline. I have documented the pattern and timing of the range collapse, having compiled over 2,300 records of occurrence from the literature, my own field work, and public and private collections in the US and Europe. I show that the species has disappeared from lowland sites across its range, and now persists only at higher elevations in the southern Appalachian Mountains in the east and the Ozark and Ouachita Mountains in Arkansas, with no populations between. This first dissertation chapter, entitled Range Collapse in the Diana fritillary, was published in Insect Conservation and Diversity in 2013. Second, I have documented patterns in genetic variation using mitochondrial DNA of the cytochrome oxidase II (COII) gene from historical (museum) and field-collected specimens. There are clear differences between eastern and western populations, with the earliest split between east and west occurring around 20K years ago, long before the recent range collapse. An historical comparison suggests that lowland populations have disappeared, taking a unique haplotype with them. This second chapter is presently under review in the journal Conservation Genetics. Finally, I use bioclimate envelope modeling to predict the future distribution of S. diana under several climate change scenarios. I also explore alternative explanations for the range collapse, including changes in land use or fire management, recovery of white-tailed deer, and aerial spraying for gypsy moth. The Diana fritillary appears to be threatened by severe reduction and fragmentation of suitable habitat, especially in the southern Appalachian Mountains, by the year 2050.
Wells, Carrie, "RANGE COLLAPSE, GENETIC DIFFERENTIATION, AND CLIMATE CHANGE: AN ECOLOGICAL HISTORY OF THE DIANA FRITILLARY, SPEYERIA DIANA AND PROJECTIONS FOR ITS FUTURE" (2014). All Dissertations. 1382.