Biological Conservation 46 (1988) 183-200 Ecological Studies and the Conservation of the Bay Checkerspot Butterfly, Euph ydryas editha ba yensis Dennis D. Murphy & Stuart B. Weiss Center for Conservation Biology,Department of Biological Sciences, Stanford University, Stanford, California 94305, USA (Received 13 November 1987; revised version received 4 February 1988; accepted 10 March 1988) ABSTRACT The historical decline of the bay checkerspot butterfly Euphydryas editha bayensis is discussed and pertinent ecological information presented. The distribution of the butterfly has become highly restricted as its habitat has been destroyed by development and its numbers reduced by severe drought. Habitat loss and fragmentation disrupts the ability of habitat patches to support populations as key topographic features are eliminated. The continued survival of the butterfly is dependent on a reservoir population which provides colonists for smaller habitat patches in the vicinity. The political struggle to gain federal protection for the butterfly is reviewed. INTRODUCTION Butterflies are showy, conspicuous, taxonomically well-known, and frequently collected by amateurs, making them an almost ideal group for field studies in population biology. Information has been accumulated on their distributions, natural histories and population dynamics, thus opening a window through which we may view both the status of butterfly populations themselves, and the health of the ecological communities of which they are a part. Many published biological studies provide substantial information pertaining to the conservation of endangered butterfly taxa (Arnold, 1983; J. A. Thomas, 1983, 1984; Gall, 1984; Warren et al., 1984; C. D. Thomas, 1985; Warren, 1987a,b,c). We think, however, that 183 Biol. Conserv. 0006-3207/88/$03"50 © 1988ElsevierSciencePublishersLtd, England.Printed in Great Britain