MICROENVIRONMENTAL EFFECTS ON COMPETITION BETWEEN RANA AND BUFO LARVAE, AND ON THE ABUNDANCE OF PROTOTHECA-RICHARDSI, IN SMALL FISHPONDS

Previous laboratory and replicated pond experiments have implicated Pr ototheca richardsi, a unicellular alga, in interference competition wi thin larval anuran assemblages. We investigated the extent of interspe cific competition between Rana temporaria and Bufo bufo larvae, and th e occurrence of P. richardsi, in small fish-ponds where initial tadpol e densities were high. Mortality of both R. temporaria and B. bufo lar vae was high during the early stages of development, and interspecific competition was negligible in these ponds and in mesh cages suspended in them. However, growth of B. bufo larvae was reduced when they were raised with R. temporaria larvae at natural densities in plastic cage s within the ponds. P. richardsi was positively associated with the pl astic cage treatments, but was much less frequent in the ponds outside or in the mesh cage treatments. Predation appears to be a much more i mportant structuring force than either resource competition or Prototh eca-mediated interference competition in the anuran communities inhabi ting these fish-ponds.