DYNAMICS OF A SUBTROPICAL POPULATION OF THE ZEBRA LONGWING BUTTERFLY HELICONIUS CHARITHONIA (NYMPHALIDAE)

Abstract

We studied the population dynamics of the zebra longwing butterfly, Heliconius charithonia (Nymphalidae), in a 0.05 ha garden in Miami, Florida, for 2 years to answer the following questions: (1) How stable is a suburban, subtropical population of this widespread neotropical butterfly? (2) What are the major factors influencing its population dynamics? (3) What are the implications of adult mobility regarding gene flow within and between fragmented urban populations of this species? A mark-recapture study indicated that adult population size averaged 59 individuals (range: 9-115 individuals). Peak numbers occurred in mid-wet season (September) in 1996 and in the late dry and early wet seasons (April through June) in 1997. Fluctuations in size of the adult population paralleled changes in biomass of the larval food plant, Passiflora incense. Population sex ratio was consistently male-biased (68% males). Reproduction occurred year-round, and parasitism by a trichogrammatid wasp killed about 50% of Heliconius eggs throughout the year. Recruitment of adults from chrysalises produced in the garden and deaths, rather than immigration and emigration, accounted for most numerical changes. Both males and females apparently adjust their home range locations in response to changes in the biomass of Passiflora plants. Females search these plants for suitable oviposition sites, and males search them for female pupae (mates). In addition to relatively high mortality from egg parasitism, fluctuations in the number of suitable oviposition sites and amount of larval food limited recruitment into the adult butterfly population. High adult mobility probably results in substantial gene flow within and between populations of this butterfly in urban south Florida.