Demographic processes in a local population: seasonal dynamics of the Sinai Baton Blue butterfly

Abstract

Quantifying abundance and determining the factors affecting it are critical to understanding and conserving small animal populations. The seasonal dynamics of a local population of butterflies Pseudophilotes sinaicus (Lycaenidae) occupying a discrete patch of habitat were investigated using data from a capture-recapture study that sampled the local population every day during the adult flight season in 2002 and 2003. Throughout the study (re)capture rates were extremely high,
meaning that intra-seasonal changes in demographic parameters could be accurately assessed. ‘Survival’ rates were not related to the age of adult butterflies, but were lower early in the season compared with later on. This is probably due to emigration of butterflies early in the season, rather than within-patch mortality. Lower survival rates in females compared with males were probablybecause females have both higher within-patch mortality and a higher  emigration rate. This
confirms results from another study (see James 2007d) that suggested migration in the Sinai Baton Blue was linked to the phenology of its hostplant, Thymus decussatus. Daily variation in the sex ratio is a consequence of between-sex differences in daily recruitment and within-patch survival rates. Males were most abundant relative to females early in the season, indicating protandry. Total adult population size was small and showed dramatic variation between the two years,
indicating how vulnerable the local population is to demographic extinction.