If frogs return to breed at the place where they hatched, how do they spread across the country?
Hugo Cayuela, University of Lyon, France
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For a long time, naturalists thought that amphibians (such as frogs, toads, salamanders and newts) were philopatric animals. This means that, if a frog began life in a given pond, it will always come back to breed in this pond when it is old enough to do so.
However, this view suffers from obvious contradictions.
First, the populations of some species of amphibians occupy large geographical areas, which implies movement between ponds to colonise these vast spaces.
Second, studies have shown that some invasive amphibian species have colonised wide parts of Europe and Australia within a few decades, with negative effects on native species and ecosystems. This indicates low fidelity to their natal pond and high movement propensity/capacity.
Third, the absence of flow of individuals between ponds would lead to extinction of populations and less genetic variation.
So, amphibians aren’t as pond faithful as we imagined. In fact, dispersal, that is the movement of an individual between its birth and breeding ponds or between successive breeding ponds, is an essential mechanism in the life cycle of amphibians.
Studies show that in some populations, nearly 30 per cent of individuals change breeding sites at least once in their life. Moving depends both on individual characteristics (physical condition, behaviour), but also on environmental conditions (water level, predation risk).
More than 40 per cent of amphibian species are threatened, according to the International Union for Conservation of Nature. Dispersal plays a critical role in their viability and conservation. By modifying landscapes, human activities limit the dispersal capacities of amphibians, thus contributing to the isolation and decline of their populations.
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