The influence of density and ration level on cultured Physalaemus pustulosus tadpoles, and the mitigation of a crowding effect by soil substrate

Abstract

Tadpoles of Physalaemus pustulosus showed a marked crowding effect in cultures without soil substrate. Tadpoles fed ad libitum (high ration level) had slower growth and development at densities of 20 and 50 L −1 compared to 2, 5 and 10 L −1 , but there was little effect on mass at metamorphosis. The effect of extreme crowding (50 L −1 ) on a compound measure of tadpole performance was similar to that of a greatly reduced ration level (high/4), which lowered performance by about half at all rearing densities (2-50 L −1 ). Density and ration level interacted significantly in their effects on tadpole performance. A soil substrate, previously shown to promote growth and development of P. pustulosus tadpoles, largely mitigated the crowding effect, with little effect of density on performance between 2 and 50 L −1 and metamorph mass substantially greater than those reared without soil. Several measures of water quality in cultures were similar to values in field breeding pools of P. pustulosus . The exception was dissolved oxygen which was often lower than in field pools, although cultures with low values (with soil) were those showing greatest rates of growth and development and metamorph size. Factors that could be responsible for the mitigating effect of soil on crowding are discussed. The effect reduces the material and care time cost of rearing P. pustulosus to metamorphosis by 2-3 fold compared to the standard culture at 10 L −1 recommended previously.