Factors Affecting the Distribution and Abundance of Tadpoles in a Lowland Tropical Stream.

Factors affecting the distribution and abundance of the tadpoles of Bufo marinus, Colostethus nubicola, Hyla boans, and Smilisca sila were studied in a tropical stream. Both observational and experimental approaches were utilized in understanding community organization and population heterogeneity. The research was done during two consecutive dry seasons, November-June, 1977-1979, in the Frijoles River, Panama Canal Zone, Panama. Variation in spatial distribution of tadpoles was related to both abiotic and biotic factors. Abiotic factors investigated include habitat, weather, current velocity, exposure, substrate, and depth. Biotic factors included interactions among and between tadpole species, predation, food abundance, and distance from oviposition site. All species found during the dry season were generally limited to shallow shorelines by both predator pressure in deep water and greater food abundance. Habitat selection was demonstrated in Hyla boans. This most common species was found in shallow water throughout various habitats. Small H. boans tadpoles dispersed from oviposition sites only to the nearest shallow shore. After attaining greater size, they dispersed again, actively selecting the "preferred" habitat, which is characterized by open canopy, gravel substrate, and fast current. The other species inhabited the areas where they hatched, and thus habitat was selected predominantly by parental behavior. Competition may have occurred in this system at the highest natural tadpole densities. In stream enclosures, high densities of Hyla boans and Smilisca sila resulted in a lower growth rate among H. boans. Poor food quality was inferred in microhabitats that H. boans deserted, and when high density of H. boans was correlated with a shift in tadpoles to deeper water.Ph.D.EcologyUniversity of Michiganhttp://deepblue.lib.umich.edu/bitstream/2027.42/159016/1/8224975.pd