The Ecology and Metapopulation Dynamics of the Endangered Miami Blue Butterfly Emily V. Saarinen* and Jaret C. Daniels University of Florida, Department of Entomology and Nematology; McGuire Center for Lepidoptera and Biodiversity, Florida Museum of Natural History *
[email protected] Results
Abstract
Ecology Our field data show that female butterflies are significantly larger and longer lived than males. Both sexes are poor dispersers but females disperse farther than males (Table 1). Dispersal data is poor owing to the low absolute number of recaptures in the field. Field data and observations of the captive colony show an equal sex ratio and synchronous emergence time of males and females. Butterflies are multiple-brooded, but suggest that there is a short winter diapause. Metapopulation dynamics Three years of surveying show that butterflies are found throughout Bahia Honda State Park in areas that support both adequate adult nectar sources and patches of their sole larval host, gray nickerbean (Caesalpinia bonduc: Fabaceae). Recaptures only occurred in the southwestern portion of the island (large map), where the population density of butterflies is higher. There is considerable movement of adults within patches, but recapture data indicate limited movement between patches over 30m apart. Data show that butterflies have colonized suitable habitat by Florida Bay as well as new areas by the southern beach in 2004-2005. The overall population size decreases in the winter and is highest in the summer with yearly fluctuations and a general trend of increase in size over the years, despite regular disturbances by hurricanes (Table 2).
The Miami blue butterfly Cyclargus thomasi bethunebakeri (Lepidoptera: Lycaenidae) has been listed as a state of Florida endangered species since 2003. This once common butterfly previously existed in 16 coastal Florida counties but can now only be found on one of the lower Florida Keys in Bahia Honda State Park. Field studies have shown that the butterflies exist as a metapopulation, with 13 subpopulations occurring on Bahia Honda. Individual subpopulations may disappear and reappear over time and preliminary data show a population range of 20-115 adult butterflies. Studies have also demonstrated that these are highly sedentary butterflies with poor dispersal abilities and a short winter diapause. Females live significantly longer than males in the field (4.32 days versus 2.27 days) but there is a highly equal sex ratio and a synchronous emergence time. A captive colony of Miami blue butterflies has been produced from Bahia Honda stock to safeguard the remaining population and to repopulate appropriate areas within two south Florida national parks. Our preliminary life history, population structure, and spatial ecology data are being used to develop a comprehensive species reintroduction and management strategy.
Female (dorsal)
Male (dorsal)
Female (ventral)
Table 1
Sex Males
Introduction
11.24 ± 0.667 N=116
Adult dispersal distance (m) 9.375 ± 2.86* N=24
Females 11.93 ± 0.686 N=93
A metapopulation structure consists of several relatively discrete populations that interact through migration and gene flow (Hanski and Gaggiotti, 2004). The individual population level is of critical importance to such organisms, especially when extinction at this level may mean the end of the species. The Miami blue butterfly exists as a metapopulation with patches of individuals interbreeding to varying extents and several populations acting as sources of individuals for new populations. In considering this species, the question quickly arises, how could a once common species now be found only on one small island in a matter of 40 years? Furthermore, what is it about this one small colony that allows it to persist after all others have vanished? A metapopulation approach, one encompassing ecological variables in a spatial context, may shed light on these questions and assist in management efforts. Lack of life history and ecological data has hindered many conservation projects (Szymanski et al., 2004). Aspects of the butterfly’s biology and metapopulation dynamics in its last natural environment in Bahia Honda are critical to the success of reintroduction efforts into Everglades and Biscayne National Parks.
12.3 ± 2.83 N=20
Adult longevity (days)
2.27 ± 1.796 N=110 4.32 ± 5.197 N=130
All values are significant at p
