Abstract: Experiments with tadpoles have been used to distinguish between intra- and inter-specific interactions and between interactions that arise through direct physical contact or indirectly through water-born movement of chemicals or micro-organisms. In the case of two Australian frog species, the Green and Golden Bell Frog Litoria aurea and the Striped Marsh Frog Limnodynastes peronii, it has been suspected that there are negative chemical interactions between the tadpoles of these two species, and that management of the former species, which is considered ‘threatened’ with extinction, may have to consider such interactions. We therefore sought to evaluate the nature of any interactions between tadpoles of these two species using three experimental treatments in which each tadpole species occurred on its own (i.e., “separate”), in the same water as the other species but separated by a mesh partition (i.e., “adjacent”), and intermingling together in the same water (i.e., “mixed”). We minimized any effects of coprophagy through the use of a mesh that was below the tadpoles and through which the faeces settled and became unavailable.
We found that: (a) L. aurea tadpoles grew faster but developed more slowly than Lim. peronii tadpoles; (b) for both frog species, tadpoles grew more slowly in the “adjacent” treatment than in the “mixed” or “separate” treatments, but there was no significant difference between these latter two treatments; and (c) treatment had no apparent effect on tadpole survival or development for either species. These results indicate that there were no differences between the effects of intra- and inter-specific interactions on either growth or development when tadpoles were allowed to intermingle. It is difficult to explain why our “adjacent” treatment was significantly outside the range exhibited by the other two treatments in terms of tadpole growth and there was no clear evidence of any indirect chemically-based interactions between tadpoles of the two species. As this study has provided no indication that there may be inter-specific interactions between tadpoles of L. aurea and Lim. peronii that are any different from intra-specific interactions, it does not support suggestions that L. aurea breeding habitat might be enhanced through modifications that make it less suitable for tadpoles of Lim. peronii.