Mechanisms of competition between tadpoles of Australian frogs (Litoria spp.) and invasive cane toads (Rhinella marina)

Abstract

Summary Cane toads (Rhinella marina) have wrought considerable ecological damage during their invasion of tropical Australia, spurring the search for novel ways to reduce toad numbers. Previous laboratory and field studies have shown that the tadpoles of native frogs, which often co‐occur with toad tadpoles in temporary waterbodies, compete with the invaders and can suppress their survival, growth and development. Understanding the mechanisms responsible for that competitive suppression might suggest new ways to control toads: for example, a chemical produced by native tadpoles that disrupts toad development. Our laboratory experiments confirm that toad tadpoles are negatively affected by the presence of tadpoles of three native hylid frogs (Litoria caerulea, Litoria longipes and Litoria splendida) and identify direct exploitative competition for food as the primary mechanism. Manipulations of chemical cues and visual cues in the water had no significant effects on the viability of toads, whereas manipulations of direct physical contact and food supply relative to tadpole density had strong effects. The lack of chemically mediated interference competition may reflect the very short timescale of sympatry between the invader and native taxa, restricting opportunities for the evolution of such mechanisms. Re‐introducing native anurans to anthropogenically degraded sites (especially those where local frogs previously occurred, but have been lost) may provide a simple and effective way to reduce the recruitment rate of invasive cane toads.