The Comparative Ability of Anuran Larvae (Genera: Hyla, Bufo and Rana) to Ingest Suspended Blue-Green Algae

Abstract

feeders that do not reject blue-green algae at the time of ingestion. The filtering and ingestion rates of North Temperate tadpoles were measured with a Coulter counter system. Tadpoles of five species of anurans (Rana catesbeiana, R. sylvatica, Hyla crucifer, Bufo americanus and B. woodhousei fowleri) all ingested Anabaena sphaerica about the same maximum rates. Maximum ingestion rates were similar for tadpoles of Rana catesbeiana when fed unialgal cultures of blue-green algae of varying size and morphology. All these pond tadpoles apparently regulate food intake as a function of volume or biomass. Patterns of change in filtering and ingestion rates in response to changes in the concentration of A. sphaerica were measured for H. crucifer, B. w. fowleri and R. catesbeiana tadpoles. The patterns were consistent for all three species in that: 1) the ingestion rate was maximum and constant over a wide range of concentrations but declined continuously at lowered concentrations; 2) the filtering rate peaked at an intermediate concentration; 3) measuable filtering and ingestion ceased at a lower concentration. This hyperbolic relationship between ingestion rate and concentration fit a modified Michaelis-Menten model (with a threshold), and parameter values were estimated for each species. The critical and the threshold concentrations for Rana and Bufo were nearly one order of magnitude lower than those for Hyla. The differences in feeding capability of the tadpoles can account for some, but not all, of their relative competitive ability and survivorship in the field.