Competing tadpoles: Australian native frogs affect invasive cane toads (Rhinella marina) in natural waterbodies

The cane toad (Rhinella marina) is one of the most successful invasive species worldwide, and has caused significant negative impacts on Australian fauna. Experimental work in the laboratory and in mesocosms has shown that tadpoles of native frogs can affect survival, size at metamorphosis and duration of larval period of cane toad tadpoles. To test if these effects occur in nature, we conducted a field experiment using two temporary ponds where we set up enclosures with tadpoles of native green tree frogs (Litoria caerulea) and cane toads in treatments with a range of densities and combinations. The presence of green tree frog tadpoles significantly decreased the growth rate of toad tadpoles and increased the duration of their larval period in both ponds; in one pond, frog tadpoles also significantly reduced the body length and mass of metamorph toads. Toad tadpoles did not have any significant negative effects on green tree frog tadpoles, but there was strong intraspecific competition within the latter species: increased frog tadpole density resulted in increased larval period and reduced survival, growth rate and size at metamorphosis for frogs at one or both ponds. Our results are encouraging for the possibility of using native frogs as one component of an integrated approach to the biological control of cane toads.