Unique turtles, crocodiles are more vulnerable to extinction, threatening important ecological niches

Turtle and crocodile species that are uniquely adapted to their environment are most at risk of extinction, according to an Oxford University study.

The study adds to a growing body of work which outlines the links between animal species and how the demise of one can impact on others.

Extinction is not only bad news for the species dying out, but also has ramifications for entire ecosystems. This is particularly true for uniquely adapted animals which fill very specific ecological niches.

Approximately half of turtle and crocodile species worldwide are listed as threatened.

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Researchers modelled human-induced extinctions and assessed the impact on the ecosystem. They focused on species with different “life strategies” – how an organism divides its resources and energy between its own survival, reproduction, and growth.

Results from the Oxford-led research show that the most endangered species are those that have evolved highly specific ecological roles. These niches are, therefore, unlikely to be filled by other species if extinctions continue.

It finds if all species of turtle, tortoise and crocodile assessed by the International Union for Conservation of Nature (IUCN) as “Critically Endangered” became extinct, then 13 percent of unique life strategies would be lost.

“A key finding is that the threats do not affect all species equally; they tend to impact particular life history strategies,” says Professor Rob Salguero-Gómez. “For example, unsustainable consumption of turtles and crocodiles mainly affects the longest-lived species with the largest clutch sizes, such as sea turtles.”

Habitat loss was found by the researchers to be the main threat to all species of turtles, tortoises and crocodiles around the world.

This threat is twice as damaging as any other to overall biodiversity.

Climate change and global trade were also major threats to all species, while species with unique life strategies were most affected by unsustainable local consumption, disease and pollution.

The study also showed that species with slower reproductive cycles were particularly vulnerable to threats from invasive species and disease. Pollution most affects species with high reproductive output.

Many of the species at risk perform important ecological functions as seed dispersers, burrowers and predators which help maintain ecosystem balance.

“The main threat to the viability of these groups of reptiles is habitat loss and fragmentation, which is especially common in species inhabiting the Northern hemisphere,” says Oxford’s Dr Roberto Rodriguez.

“The disappearance of wetlands, increasing urbanisation, and the development of intensive agriculture, which already have tangible effects, will likely continue to negatively affect these species and their ability to persist in the mid- to long-term.”

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But other threats have more global effects.

“While sustainable use and trade of wildlife can sometimes benefit species conservation, unsustainable trade of live animals or their parts, threaten these reptiles throughout the world, regardless of their life history strategies,” says Dr Molly Grace, also at Oxford University.

“IUCN red lists of threatened species could incorporate information regarding the functional uniqueness to help managers make local decisions that would impact global conservation most efficiently,” adds Salguero- Gómez.

The research is published in Nature Communications.

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