- Department of Wildlife and Fisheries Sciences, Texas A&M University, 77843-2258, College Station, TX, USA
Reproductive ecology, population structure, and diets of three common livebearing poeciliid fishes (Alfaro cultratus, Phallichthys amates, Poecilia gilli) from rainforest streams in Costa Rica were investigated over ten continuous months. The region experiences little annual temperature variation, and although monthly rainfall is continuous each year, two brief dry seasons typically occur. Monthly changes in indices of ovarian condition, percentages of females with developing embryos, and population size structure revealed that reproductive output by females of all three species varied seasonally. Based on testicular condition, males were reproductively active year-round, however the mean gonadal index for males of two algivorous species showed low levels of seasonal cycling that largely coincided with female variation in reproductive effort. All three species had seasonal differences in the female size-brood size relationship, whereby larger females tended to carry more embryos during the wet season. Several important adult and neonate food resources are more available in the flooded forest during the wet season, which is also the period when conspecifics and predators are at their lowest per-area densities. Three hypotheses are discussed: (1) brood size in relation to conspecific density-mating frequency, (2) reproductive allocation in response to variation in adult food resources, and (3) selection for greater reproductive effort during conditions optimal for juvenile growth and survival. Data for Alfaro were consistent with the latter two hypotheses. In Phallichthys and Poecilia, diets were poorer during wet seasons, indicating that reproductive effort does not coincide with availability of adult food resources, and that selection probably favors greater reproductive effort during periods optimal for juvenile growth and survival.
- 1 - sciences appliquees, technologies et medecines
- 2 - sciences biologiques et medicales
- 3 - sciences biologiques fondamentales et appliquees. psychologie
- 4 - agronomie. sciences du sol et productions vegetales
- 1 - Life Sciences ; 2 - Agricultural and Biological Sciences ; 3 - Ecology, Evolution, Behavior and Systematics