Why are island animals at risk of extinction?
Warm-blooded animals on islands tend to have slower metabolic rates than their mainland counterparts, making it harder for them to recover when stressed.
Desmarest hutia, a giant rodent that lives on the coast of Cuba, is an example of gigantism in island animals.
imageBROKER/Mathieu Foulquie/Alamy Stock Photo
Life for people who live on islands tends to move at a slower, more leisurely pace, and it turns out this same laid-back lifestyle also applies to the animals that live on islands. Scientific advances Many warm-blooded island species Metabolic rate slowed Compared to their mainland counterparts, they have characteristics that give them an advantage in resource-poor environments, but when humans are introduced to the environment, they are at increased risk of extinction.
“When the environment changes or invasive animals arrive on islands, island organisms are less able to defend themselves,” says co-lead author Yin Xiong, a zoologist at China’s Sichuan Agricultural University. “We discovered a general metabolic rule that helps explain this.”
The new discovery adds to what scientists know about island syndromes, the tendency for species that live on islands to evolve different physiology, ecology and behavior than their mainland counterparts. Several studies have identified metabolic differences as a hallmark of island syndromes, but previous studies have often been one-off, focusing on a single species or group, says co-lead author Roberto Rozzi, curator of paleontology at the Central Repository of Natural Science Collections at the Martin Luther University Halle-Wittenberg in Germany.
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The new study is the first to compile a “more or less comprehensive” dataset looking at the metabolic rates of island warm-blooded and cold-blooded species, according to Rozzi. Drawing on published papers and existing databases, Rozzi, Xiong and their colleagues compiled information on the metabolism and ecology of 2,118 warm-blooded species, including 193 island species, and 695 cold-blooded species, including 38 island species.
Through statistical analysis, the authors found that warm-blooded island species, a group that includes both birds and mammals, tend to have slower metabolic rates, but cold-blooded amphibians and reptiles do not. The authors compared these findings to the International Union for Conservation of Nature (IUCN) Red List of Conservation Status Lists and found a strong correlation between slower metabolism and increased extinction risk.
Many islands lack large predators, but also have fewer available resources than the mainland. In such environments, a slower metabolic rate is likely an advantage for a species’ survival, says Lozzi. They tend to expend less energy each day, reproduce slower, and live longer. But when conditions change, this metabolic advantage seems to turn into a disadvantage.
“At the same time, the shift to a slower pace of life slows recovery after disturbances and impacts the resilience of species,” Lozzi said. “Basically, it makes it harder for them to bounce back.”
From the Late Pleistocene to today, dramatic changes on islands tend to be caused by humans, who often hunt native animals, alter their habitats, and introduce harmful invasive species like rats and cats. In the case of island mammals and birds, a slowed metabolism, combined with other features of island syndrome—giantism and dwarfism in mammals and flightlessness in some birds—is likely to lead to species extinction, Lozzi says.
The new study “fits with previous expectations that island species are evolving slower life strategies, such as living longer or reproducing more slowly,” says Kevin Healy, a macroecologist at the University of Galway in Ireland, who was not involved in the study. But while the finding of increased extinction risk is “intriguing,” it should be treated with caution because the IUCN Red List data is “very incomplete,” Healy adds. Island species with slower metabolisms may actually be at lower or even higher risk of extinction than the authors found, Healy says.
