Size isn’t everything – ScienceDaily

Ancient clues, in the form of fossils and archaeological evidence of varying quality scattered across Australia, have formed the basis of several hypotheses about the fate of the megafauna that disappeared around 42,000 years ago from the ancient continent. of Sahul, comprising mainland Australia, Tasmania, New Guinea and neighboring islands.

There is a growing consensus that multiple factors were at play, including climate change, the impact of people on the environment, and access to freshwater sources.

Now, research by Professor Corey Bradshaw of Flinders University and the Australian Biodiversity and Heritage Research Council’s Center of Excellence (CABAH) has used sophisticated mathematical modeling to assess the vulnerability of different species. to extinction – and what that means for survival. creatures today.

Using various characteristics such as body size, weight, lifespan, survival rate and fertility, they created population simulation models to predict the likelihood of survival of these species under different types of environmental disturbances. .

The simulations included everything from increasing droughts to increasing hunting pressure to see which species of 13 extinct megafauna, as well as 8 comparative species still alive today, had the greatest chance of surviving.

Published in the newspaper eLife, Bradshaw and his team compared the results to what we know about the time of extinction for different megafauna species derived from dated fossil records. They expected to confirm that the species most prone to extinction were the first to go extinct – but that wasn’t necessarily the case.

Although they found that slower-growing species with lower fertility, like the rhino-sized wombat diprotodon, were generally more likely to go extinct than more fertile species like the thylacine marsupial. ” tiger ”, the relative sensitivity rank between species did not match. the time of their extinctions recorded in the fossil record.

“We found no clear relationship between a species’ inherent vulnerability to extinction – such as being slower and heavier and / or slower to reproduce – and the time of its extinction in fossil record, ”explained Professor Bradshaw.

“In fact, we found that most of the living species used for comparison – such as short-billed echidnas, emus, bush turkeys, and common wombats – were on average more susceptible than their counterparts today. hui missing. “

The researchers concluded that the true extinction cascade was likely the result of complex and localized scenarios, including the impacts of regional climate variations and the different pressures exerted by people from region to region.

Associate Professor Vera Weisbecker of Flinders University and co-author of the study said: “The relative speed of different species to escape hunters, as well as whether or not a species has dug protective burrows, has probably also contributed to the mismatch between vulnerability and the time of extinction.

“For example, the fast-leaping red kangaroos still alive today might have had an escape advantage over some of the slower, short-faced kangaroos that went extinct. Smaller burrowing wombats would also have been more difficult. to hunt for people that bigger and not terrifying megafauna. “

Co-author Dr Frédérik Saltré, Flinders University, added: “We determined that kangaroo species were the least susceptible to extinction based on their biology, followed by monotremes (echidnas) and of the giant species ‘wombat.’ Interestingly, the large, flightless birds, such as the emu and the giant ‘thunderbird’ mihirung Genyornis, had the highest susceptibilities.

“Our results support the notion that the risk of extinction may be high for all body sizes depending on the particular ecology of a species, meaning that predicting future extinctions due to climate change and human impacts n It’s not always simple based on the first principles of biology, ”concluded Professor Bradshaw.

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