A recent study which analysed over 250 tropical and subtropical islands has pointed out that being isolated does not protect islands from alien species. Rather, remote islands are more susceptible to alien invasion, be it from plants or mammals, the study found.
“What really surprised us was to see that the isolation of an island had the opposite effects on native and non-native species richness. Native species declined whereas non-native species numbers increased,” says Dr. Dietmar Moser from the University of Vienna in a release.
Anthropogenic causes
With the increase in anthropogenic activities like trade and transport, the biogeographical borders are broken down and the human-aided introduction of alien species has been on the rise. The international team of researchers analysed large datasets of alien and native plants, ants, reptiles, mammals and birds on 257 tropical and subtropical islands, including India’s Andaman and Nicobar Islands and Lakshadweep. They used different statistical tools and assessed the relationship between alien species richness and island isolation.
The report says that alien species richness increased with isolation for all five groups. They also note that with increasing geographical isolation there was a decrease in the resistance of the resident species. “In the absence of competitor species from the mainland, these [island] species do not need to sustain their defence mechanisms and can reallocate the energy into other characteristics that they benefit from. Hence, many island species lose their defence mechanisms or become less competitive,” explains Bernd Lenzner from the University of Vienna in an email to The Hindu. He is the corresponding author of the paper published in Proceedings of the National Academy of Sciences.
Alien species bring in traits that native species lack. “They [alien species] have advantages compared to native island species due to their evolutionary history and the fact that they have evolved in a context where competition for resources is stronger and where other threats are more prominent,” Lenzner adds. The report states that alien species have markedly changed fundamental biogeographical patterns of species richness on islands around the world.
Bernd Lenzer urges that new nature conservation measures be enforced to strengthen alien species management strategies and monitor potential introduction pathways. There is also an urgent need to keep track of the already introduced alien species to save our islands, which are hotspots of biodiversity.
