Seasonality in Tropical Hermit Crab Reproduction in the Bay of Panama

Abstract

Seasonal components in the reproduction of three sympatric hermit crab species in the Bay of Panama are examined. All three species reveal reproductive patterns mediated by their supply of shells, which are in limited supply. Crabs with shells large enough to allow growth put effort into growth, while crabs in shells too small to permit growth allocate more time and effort to reproduction. This resource-regulated trade-off between growth and reproduction accounts for seasonal components in hermit crab reproduction. Dry-season upwelling increases the food supply to these hermit crabs and results in increased hermit crab growth rates. The increased size of dry-season crabs in the same suite of shells as the smaller rainy-season crabs triggers increased reproductive activity during the dry season. IT IS A COMMONLY HELD VIEW that temperate animal and plant population processes are more seasonal than their tropical counterparts. In temperate latitudes, harsh climatic conditions in winter months can preclude successful growth and reproduction; while in the tropics, mild climatic conditions prevail and do not appear to influence populations as strongly. For marine invertebrates, Thorson (1950) stated that tropical planktonic larvae are equally dense throughout the year as opposed to the highly seasonal occurrence of larvae in temperate seas, and Pearse (1974) suggested that reproductive cycles become more markedly seasonal with increased latitude. In spite of this generalization, numerous seasonal patterns in the processes of tropical organisms have been documented, and a number of explanations for the patterns have been offered (Glynn 1970, Lee 1978, Reese 1968, Wolda 1978, Lessios 1979). In order to understand temporal patterns in tropical organisms, an understanding of the biology and ecology of the organisms under consideration is nec-