ADULT MOVEMENTS AND POPULATION STRUCTURE IN EUPHYDRYAS EDITHA.

Abstract

In recent years it has become increasingly apparent that many natural populations are subdivided into smaller units with an effective breeding size well below that at which drift and inbreeding begin to play a major role in determining gene frequencies (Petras, 1967; Reimer and Petras, 1967; Selander, 1970). Evidence from several of these studies indicates that subdivision is achieved in part by various behavioral devices which limit movement between these units and result in very small home ranges (Selander, 1970). This study was undertaken to discover whether subdivisions such as these exist within local populations of the checkerspot butterfly, Euphydryas editha. The biology of E. editha has been under constant study by Ehrlich and his coworkers at Stanford since 1960. Although this work has recently been expanded into a broad ecological comparison of numerous populations of this insect (see, for example, Singer, 1971; Gilbert and Singer, 1973), the most intensively studied colony is located at Stanford University's Jasper Ridge Biological Experimental Area, San Mateo County, California. Here it occupies an island of grassland at the top of a ridge in the Santa Cruz Mountains at an altitude of about 600 feet. The grassland is surrounded by an essentially continuous band of chaparral and oak woodland. A concentrated capture-mark-releaserecapture program has been conducted at