Over the last two decades, water frogs have been increasing in Central Europe and now, University of Basel researchers have used a statistical model to provide evidence that local native species, such as the yellow-bellied toad and the common midwife toad, are suffering due to the presence of the Eurasian marsh frog, a dominant and invasive water frog species.
When it comes to ecosystem communities, it is not uncommon to see population compositions change over time. Although these changes can sometimes lead to the decline of certain species, some species benefit from these changes. These invasive species reap the benefits by hunting other species or replacing them in their native habitat, and in the marshes of Europe many of them belong to the water frog species complex.
Most are in agreement that humans are to blame for the dominance of the water frog, and the recent study uses data from more than 1,000 bodies of water in the Swiss Canton Aargau as well as observational data obtained from the cantonal Amphibian Monitoring Aargau to study the impacts that water frogs are having on native amphibians in the area.
The results from the statistical model, which takes into account the different detection probabilities of species as well as various environmental factors, found that yellow-bellied toads and common nidwife toads have smaller communities when they live alongside water frogs in the same body of water.
"Based on our analysis we estimate that the populations of both species would be up to five times bigger without the water frogs' presence," Christoph Bühler, co-author of the study, said in a press release.
The situation presents conservationists with the question of whether or not they should intervene. However, due to the fact that Eurasian marsh frogs have been crossing with other native amphibians, leading to genetically mixed species, it is hard to label some of them as as an invasive water frog.
"What is clear, however, is that the changes in the landscape currently favor water frogs," said Valentin Amrhein, another co-author on the study. "Small waters that dry out quickly and are being avoided by water frogs but sought after from other species have become rare these days. The spread of invasive species is often supported, consciously or unconsciously, by the actions of humans and cannot easily be undone."
The findings were published in the Feb. 26 issue of The American Naturalist.
