Capture-recapture studies of a Heliconius ethilla colony occupying a ridge in northern Trinidad were carried out over a 27-month period. Individuals had limited home ranges based primarily on the distribution of pollen sources which were visited in the course of daily activity. These ranges fell into two virtually discrete sets, dividing the colony into two populations which rarely exchanged individuals. The size of the two populations, and thus of the colony, remained remarkably stable over the entire course of the study, which covered about 27 generations. This constancy appears to result from a combination of high preadult mortality, long adult life, and limited adult resources which in turn limit total egg production. STABILITY OF tropical climate is thought to allow more species to occupy a given amount of habitat space since each can survive at lower, more constant population sizes than would be possible in less stable temperate climates (Pianka 1966). While some data have been gathered to support the resulting prediction that tropical communities have lower mean niche breadths than similar temperate communities (Colwell 1970), the above assumptions about size and stability of tropical populations (insect populations in particular) have not been tested. Many of the long-term population studies of temperate-zone insect populations have been carried out on the Lepidoptera (Fisher and Ford 1947, Sheppard 1951, Ehrlich 1965, Brussard and Ehrlich 1970). Similar studies on the biology of tropical butterfly populations (e.g., Turner 1971) are not of sufficient length to allow conclusions about the stability of population sizes and structures. In many tropical areas adult populations are present in both dry and wet seasons of the year. Therefore any direct comparsion with temperate-zone populations involves investigations extending over at least one year, a criterion which no prior study of tropical insects has fulfilled. A major objective of this work was to provide basic information concerning population structure and dynamics of a tropical insect over a long period of time. A study was initiated on Trinidad populations of the tropical butterfly Heliconius ethilla Godart (Nymphalinae: Heliconiini) in December 1969 and continued until May 1971. Additional observations were made in March 1972. H. ethilla ranges from eastern Panama to coastal southern Brazil. It belongs to the most taxonomically difficult part of Helicorims known as species. Previous workers have erroneously referred to this species as H. numata (Turner 1968), but recent work on the systematics of H. ethilla and other silvaniform species (Brown, unpublished) has largely cleared up the previous confusion. Benson (1971) summarizes information on the races of H. ethilla. In Trinidad this species (race ethilla) is restricted to the forested ridges of the northern range where it is the primary model in the tiger stripe mimicry complex (Moulton 1909). The Trinidad populations have been of particular interest in that they show a color polymorphism (Sheppard 1963, Turner 1968) now known to be characteristic of some mainland populations (Brown, pers. comm.). The selection of this species for study was based on the easy access of forest reserves where the species is found, and the proximity of these areas to the excellent butterfly research facilities of the William Beebe Tropical Research Station at Simla, Arima Valley. The general biology of the genus Heliconius has been intensively studied (Alexander 1961, Beebe et al. 1960, Brower et al. 1963, Crane 1957, Emsley 1963, 1965, Swihart 1967, Turner and Crane 1962) which was also significant in the choice of H. ethilla. The H. ethilla populations under study for the past one and one-half years live in the vicinity of ridge top traces (narrow roads) on opposite sides of the Arima Valley (fig. 1). Andrew's Trace, which runs south from Arima Pass (figs. 1; 2), is the primary study area while La Laja Trace on the other side of Arima Valley is periodically sampled for comparative purposes. BIOTROPICA 5(2): 69-82 1973 69 This content downloaded from 207.46.13.120 on Wed, 14 Sep 2016 05:09:13 UTC All use subject to http://about.jstor.org/terms