Evidence for the induction of interference competition between anuran larvae in plastic pond cages

We recently showed that growth inhibition of Bufo bufo larvae by those of Rana temporaria in garden ponds only occurred when the larvae were confined in plastic cages. We therefore carried out further experiments to investigate the mechanism of this growth inhibition. Bufo bufo larvae were raised in mesh cages, plastic cages or plastic cages with supplementary food either alone or in the presence of R. temporaria. Three lines of evidence suggested that competition in the plastic cages had an interference component: firstly, growth inhibition of B. bufo by R. temporaria was only seen in plastic cages despite the fact that these cages supported normal growth rates of B. bufo in the absence of R. temporaria; secondly, food supplementation in plastic cages did not reduce the extent of B. bufo growth inhibition; and thirdly Anurofeca (= Prototheca) richardsi production was high in plastic cages but not in other treatments and correlated negatively with subsequent B. bufo larval growth. Plastic cages supported a different trophic web from other treatments and biotic factors seem the most likely regulators of A. richardsi abundance in these pools.