Australia's mammal megafauna face long-term decline from extinctions and invasive species

Australia's mammal megafauna face long-term decline from extinctions and invasive species
by Simon Mansfield
Sydney, Australia (SPX) Jul 24, 2025

Over the last 100,000 years, Australia's largest animals have undergone dramatic shifts due to waves of extinction and the arrival of invasive species, according to new research from Flinders University. The study reveals mammals have been disproportionately affected compared to birds and reptiles, reshaping ecosystems across Australia and New Guinea.

The research team focused on large-bodied animals over 10 kilograms, assessing extinction and introduction trends before and after European colonization in the 18th century. They found that the decline of Australia's iconic megafauna-such as the rhino-sized Diprotodon and the six-meter Megalania-was followed by an influx of non-native species like goats, pigs, and deer.

"Mammals and herbivores have suffered the most significant losses, while reptiles and birds have remained relatively stable," said Dr John Llewelyn, Research Fellow in Ecological Modelling at Flinders. He noted that these patterns suggest targeted impacts, rather than random declines.

Evolutionary isolation may partly explain the vulnerability of Australian mammals, yet the study indicates that this alone does not account for the disparity. "Reptiles and birds have fared better despite the same isolation," Llewelyn said. "Mammals' susceptibility appears linked to a combination of dietary specialization and the kinds of species introduced."

The analysis also revealed that diet plays a critical role. Carnivory among large reptiles and omnivory in large birds may have bolstered their resilience, whereas mammalian herbivores have struggled with changes in vegetation caused by both natural events and human activity.

Professor Corey Bradshaw, Matthew Flinders Professor of Global Ecology, added, "Most of the large animals introduced post-colonization have also been mammals. This compounded pressure likely exacerbated the decline of native mammal populations."

The study underscores the growing ecological impact of invasive species, which are not filling ecological voids but instead intensifying competition and habitat stress. "We're seeing a net negative effect from introduced species, which are displacing rather than replacing extinct animals," Bradshaw said.

Research Report:Big changes to Australia's largest animals over 100,000 years reveal mammals are most vulnerable