The dynamics of habitat choice: alien predators stifle amphibian breeding

Posted on June 1, 2016

The way that animals select habitats reflects their need to balance the costs and benefits associated with factors such as food availability and predation risk. Therefore, habitat choices should vary in response to changes in these key factors. As an example, amphibians are expected to continually adjust the relative amounts of time that they spend on land and in the water. Although they need to spend weeks or months in the water in the breeding season to court and lay eggs, they also tend to avoid potential breeding sites occupied by predators such as fish. While the present global decline in amphibian populations is usually attributed to resource competition and predation, it’s possible that the behavioural avoidance of breeding habitats by amphibians in response to the presence of invasive fish also plays a part. To investigate this idea, researchers at the University of Liège in Belgium ran a controlled experiment in aquarium tanks to see how the presence and absence of alien predatory fish (goldfish, Carassius auratus) and a fish-excluding aquatic refuge affected the way that palmate newts (Lissotriton helveticus) used underwater and terrestrial habitats. The terrestrial habitat was a floating dock covered with natural moss. Neither newts or goldfish had previous experience of the other species. The experiment covered the two-month newt breeding season. When fish were present and when the aquatic shelter was absent, newts left the water more often, carried out significantly fewer courtship displays, and laid fewer eggs than newts in control treatments. The abandonment of reproduction, driven by the escape from fish habitats, helps to explain the commonly-observed negative association between introduced fish and amphibians. While amphibians tend to fare better in ponds with plenty of aquatic vegetation, which provides spawning substrate and shelter for both adults and larvae, the presence of suitable terrestrial habitat near breeding ponds invaded by alien fish helps newts to move freely between water and land to optimise the balance between reproduction and predator avoidance.

Reference: Winandy, L. et al. 2015.
Amphibians forgo aquatic life in response to alien fish introduction. Animal Behaviour 109, 209-216.