Quantifying the roles of larval amphibians in nutrient cycling in neotropical headwater streams

Amphibians play important roles as primary consumers in aquatic ecosystems.  However, the ecological roles of tadpoles are poorly studied, particularly in neotropical headwaters where abundance and diversity are high. As amphibian populations continue to decline precipitously around the world, understanding their ecological roles is becoming increasingly important.  As part of the Tropical Amphibian Declines in Streams (TADS) project, we are quantifying the degrees to which stream-dwelling tadpoles mediate nutrient cycling and influence consumer-resource stoichiometry.  We measured ammonium excretion rates of 5 tadpole species in 3 streams in eastern Panama that have not yet experienced massive declines.  Mass-specific ammonium excretion rates ranged from 0.02 μgNH₄/mg hr^-1 for centrolenid tadpoles that burrow in detrital accumulations to 2.4 μgNH₄/mg hr^-1 for Hyla tadpoles, which feed on periphyton and sediments on substrata. These rates suggest that high densities of tadpoles have a strong influence on nutrient recycling in headwater streams, and the large differences among species suggest that some may be more influential than others.  These rates will be incorporated into consumer nutrient recycling (CNR) stoichiometry analyses and compared to post-decline streams, thus furthering our understanding of the ecological consequences of amphibian declines.