Ecological Significance of Flight Activity in Colias Butterflies: Implications for Reproductive Strategy and Population Structure

Abstract

This study documents the ecological significance of flight activity in relation to thermoregulation in Colias butterflies. Observations of behavior, flight movements, and basking temperatures were made on tethered and free—flying butterflies to evaluate individual components of the elevational patterns of population flight activity reported elsewhere (Kingsolver 1983). The relationship of flight activity to reproductive strategies and population structure in Colias is emphasized. Male Colias spend more time in flight and make flights of longer duration when they can achieve basking temperatures within the 30°—40°C flight activity range. Male Colias at all elevations fly 50—90% of the time when the required body temperatures are attainable. Males fly for short durations during nectaring and longer during mate location and courtship activities. Females spend less time in flight and make flights of shorter duration than males. These differences are discussed in terms of the different reproductive strategies of males and females. The significantly longer duration of flight for Colias at mid— and high—elevation sites may explain the longer dispersal distances observed in population structure studies at these sites. The observed differences in catchability between sexes is also correlated with the sexual differences in flight behavior reported here. The time spent in flight, short life expectancies, and time budgets of Colias suggest that the time available for flight activity during an individual's lifetime may be limited. Calculations indicate that egg production during the lifetime of females is usually below the physiological maximum due to the limitations in flight activity time; because of elevational differences in available flight time, egg production at higher elevations may be less than half of that at lower elevations.