PATCH DYNAMICS OF GLAUCOPSYCHE LYGDAMUS (LYCAENIDAE) - CORRELATIONS BETWEEN BUTTERFLY DENSITY AND HOST SPECIES-DIVERSITY

Glaucopsyche lygdamus egg densities were surveyed over a 2000-m section of Cold Creek and at 30 different isolated patches in the Gold Basin drainage in Colorado. Host plant numbers and diversity were quanti fled, as well as other variables potentially influencing butterfly population size, such as patch size and isolation. Egg densities correlated significantly only with measures of host species diversity. Patches consisting of a single host species, no matter how large, did not support high butterfly densities, but patches of multiple, equitably distributed host species did. The most likely explanation, in light of oviposition preference and larval performance data accumulated for this butterfly species, is that host species diversity is necessary for the persistence of G. lygdamus populations, because alternative host species buffer population losses during poor or unusual years. The dependence of both ovipositing butterflies acid developing larvae on the ephemeral, young, host plant flowers make the butterfly especially vulnerable to year-to-year variation in host plant availability and quality.