Biodiversity is increasingly being destroyed by the many influences of humankind, of which a major aspect is biological invasion. Although there are plenty of studies indicating that invasive predators reduce the population size of native species, few studies have reported their effect on phenotypic features such as morphology and performance of native species. The island ecosystem in particular is very sensitive to invasive predators because powerful predators such as mammal predators are not in such an environment.
Researchers at the Tokyo University of Agriculture and Technology (TUAT) analyzed the effect of predators on frogs on a Japanese island and their findings are reported in Biological invasions On the third of January.
Ferrets have been introduced in many areas around the world and have seriously damaged the native ecosystem. In 1979, it was brought to Amami Island in Japan. As a result, the front-nosed frog, a relatively large forest species, is one that is in danger of extinction in the near future due to the invasive ferret.
“We hypothesized that the strong predation pressure of the ferret led to a rapid change in the shape and performance of the original frog,” said Hirotaka Komine, the paper’s first author and associate professor (upon conducting this research) at TUAT.
“We recorded hind limb length and two types of performance characteristics: blast motion ability (evaluated based on jump distance) and endurance (assessed based on number of hops),” Komen said. As for jump distance, the researchers measured the distance of the first jump after the frog was released. For the number of hops, they analyzed the number of hops in the net upon capture until the frog was exhausted (i.e. stops jumping). “We then estimated the relationship between hind limb length and explanatory variables (ferret effect agent, gender, and year), and the relationship between performance traits and explanatory variables using a spatial regression model,” Kumin explains.
Interestingly, the results showed that the hind limb length of the frog was longer under the influence of strong ferret predation, which may act as a selective factor to induce rapid morphological responses. The frog’s stamina, but not the ability to move, was higher under the strong influence of predation by the mongoose. “Our results indicate that endurance was a specific target of natural selection and that local prey performance changed in response to the new predation type,” Kumin said.
When their research was conducted, it was at least 7 years after the ferret had mostly been removed and the original frog population size had recovered due to an eradication project run by Japan’s Ministry of Environment. Therefore, their results clearly indicated that the effect of the invading ferret on the phenotypic features of the native frog remained mostly even after the invasive predator was removed.
An island’s ecosystem is often unique in terms of behavior, morphology, and performance, which reflects its evolutionary uniqueness. Hence, restoration of traits in native species after the removal of invasive species may be a useful measure of the success of eradication projects, ”Comin concludes.
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Komine, H. *, Iwai, N. & Kaji, K. Rapid responses in morphology and performance of domestic frogs resulting from predation pressure from an invasive ferret. Biol invasions (2021).
*: The corresponding author
Hirotaka Comin, PhD.[email protected]