SYNCHRONIZATION OF SEXUAL REPRODUCTION OF TREES WITHIN THE DRY SEASON IN CENTRAL AMERICA

This paper discusses the following hypothesis: many tree species in lowland Central America have evolved the timing of their flowering and fruiting period with the dry season to maximize vegetative competitive ability of individuals, and to maximize use of pollinating and dispersal agents.The physiological stimuli for dry season flowering and fruiting are not of concern (see discussions and included references in Schimper, 1903;Simon, 1914;Coster, 1925 Coster, , 1926;;Baker, 1947;Richards, 1952;Holttum, 1953), but rather the selective forces that brought about the use of these stimuli to induce reproductive activity during the dry season.The focus is shifted to the advantages and disadvantages of sexual reproduction during the dry season (ultimate causes), instead of mechanisms of sychronization of reproduction by many species (proximate causes).Virtually all of Central America below 1000 m elevation, and much of that above, experiences a dry season.By "dry season" is meant a consistently timed annually recurrent period of several weeks or more when rainfall is distinctly reduced to the point where animals and plants show behavioral reactions to the lack of rainfall and its byproducts.The discussion in Schulz (1960) would lead one to choose a month with less than 65 nun of rain as a dry month.However, in lowland Costa Rica, Guatemala, and southern Mexico, plants and animals react to months with as much as 150 mm of rainfall as if they were Contribution No. 1319 from the Department of Entomology, The University of Kansas, Lawrence.This study is a result of research and teaching activities for the Organization for Tropical Studies in Costa Rica during 1965 and 1966.* Producing fruit and flower during the rainy season as well as the dry.** Few flowers and/or fruit present now, but major period later in the dry season.