Suspension feeding dynamics of anuran larvae related to their functional morphology

Abstract

The tadpoles of two anuran species, Rana sylvatica and Xenopus laevis, were fed various concentrations of two algae, Anabaena sphaerica (large filaments) and Chlorella pyrenoidosa (small unicells). Filtering rates were measured indirectly with a Coulter Counter system; buccal pumping rates were observed directly.Experimental measurements of buccal volume (volume cleared with each pump stroke) agreed closely with independent predictions from a descriptive model based on tadpole morphology. The Xenopus larvae had a larger buccal volume than Rana larvae of comparable size.The R. sylvatica tadpoles demonstrated: a lower (threshold) and an upper limit on the food concentration for filtering and ingestion, a peak in filtering rate at an intermediate (critical) concentration, a probable higher filtering efficiency on larger particles, and an asymptotic relationship between ingestion rate and concentration.Tadpoles maintained a maximum ingestion rate over a wide concentration range (above the critical concentration for filtering) by species-specific patterns of adjustment in pumping rate and buccal volume. Maximum ingestion rates, expressed as volume (but not number) ingested per unit time, were similar for tadpoles fed both Anabaena and Chlorella.Several anatomical features may limit the maximum ingestion rate, the maximum filtering rate, the maximum particle size ingested, the maximum volume of food that can be removed without clogging the gill filters, and other components of tadpole feeding dynamics.Data on tadpole feeding may be used to evaluate general suspension feeding models.The behavior of Rana tadpoles at various algal concentration in the field was consistent with predictions from these experimental studies. sediments when concentrations fell near or below a "critical" concentration. These field observations indicate that laboratory experiments and morphological studies can predict certain aspects of tadpole feeding activities in the field.Three general conclusions concerning the feeding dynamics of tadpoles follow from the data and discussion just presented: (i) they are similar in several respects to those of invertebrate suspension feeders, (ii) they apparently are regulated as functions of biovolume not of particle number, (iii) they can be predicted, in part, from morphological measurements on the tadpole's buccal pump. In addition, these data on tadpole feeding may be used to evaluate general models of suspension feeding dynamics.