What Being Functionally Extinct Means, Why Koalas Aren’t, and Why Things Are Still Pretty Dire

Image Credit: Swallowtail Grass Seeds, Public Domain Mark 1.0, Image Cropped

There has been a lot of recent (and well deserved) press surrounding the bush fires in Australia. Because of these fires countless animal and plant life has been lost, and the most visible example of that are the koalas. You probably saw the video of a woman running into a burning area to save a koala from the fire*. Unfortunately, most of the koalas didn’t have people around to save them and over 1,000 are estimated to have died. Because of this a group has claimed that koalas are now “functionally extinct”, and the press has run with this claim. While it is unfortunate that this misinformation spread so quickly and so widely, the good news is that koalas are in fact NOT functionally extinct. Great! But what does being “functionally extinct” mean? 

Functional Extinction in Ecology

There are a few different definitions of functional extinction. Usually it occurs when a population undergoes some cataclysmic event (like a bushfire) that kills off most of the organisms in the population. In ecology, a species can be functionally extinct when its population is so low that it ceases to fulfill its ecological function, which then affects other species. Another definition, and the one that is relevant to the koalas, is when a species has declined to the point that whilst it isn’t totally gone yet, it has crossed a threshold from which it cannot recover. Although there are still some organisms alive, there are so few of them that the lack of genetic diversity will make it next to impossible for the population to survive long-term.

Species can also become functionally extinct when the resources they need are no longer available. To bring it back to the bushfire example, about 1 million hectares of forest have been lost to the fires. Organisms like the koala depend on these forests for their habitat and food, so when the forest is gone the animals can no longer survive and will eventually go extinct.

So, why aren’t the koalas functionally extinct?

The bushfires are obviously terrible. Over 1 million hectares of forest have burned, and over 1,000 koalas are estimated to have died. But we have to keep in mind that these fires are happening in Eastern Australia, not across the entire country. Australia is a BIG place, so while 1 million hectares have burned, that still leaves plenty of eucalyptus forest (eucalyptus leaves being their exclusive food source).

But 1,000 gone is a pretty big chunk right? Well, yes, but in 2016 researchers estimated that about 300,000 koalas live in the eastern and southeastern parts of the country. Many of those are in areas not currently affected by the wildfire, including some areas where they actually suffer from overpopulation (see more about those problems in this interview with Australian wildlife guru Kath Handasyde). Some koala populations might die out in parts of Eastern Australia, rendering them “locally extinct”, but there are still hundreds of thousands of them in other areas. The koalas are in no danger of going functionally extinct (on a national level anyway).

So Everything’s Okay?

What? No! Those local extinctions are still devastating. When we lose entire regional populations, we lose a huge pool of behavioural and genetic diversity. The eastern Australian koalas aren’t officially classed as a different subspecies (we’ve talked about subspecies before on EcoMass, you can read more at this link), but they look and behave very differently from koalas in southern Australia. Because of this, we can’t simply repopulate the affected areas. Koalas have irritatingly specific dietary requirements, and many populations can only survive in areas with the specific eucalypt species that surround them.

More importantly, whilst not gone yet, koala populations are on the decline, due to extensive habitat loss, climate change and disease. Extreme heat waves and drought, the likes of which Australia has seen a worrying increase of lately, are not something koalas can handle. Yet they may be able to survive extreme weather if enough eucalyptus forest remains. And whilst bushfires obviously reduce that habitat, Australia has one of the worst land clearance rates in the world, fuelled by a logging industry which isn’t exactly prioritising sustainability and a government unwilling to act on unauthorised clearing. And lastly, while chlamydia in koalas may have been reduced to a Jon Oliver punchline, the disease (most likely spread by European cattle) is the second biggest killer of koalas in Australia.

But most of all, while the koalas might not have gone functionally extinct as a result of the bushfires, they’re far from the only species affected by the fires. Thanks again to that unchecked land clearance rate, several species have been whittled down to dangerously low numbers. Many of them are just as vulnerable to fires as koalas are, and many don’t have other populations in the rest of the country.

I do want to reassure you that koalas are not in danger of going extinct anytime soon. Yet if Australians don’t act on the causes that are driving their populations down, these regional extinctions will continue. And if that happens, the threat of extinction will become very real.

*Unfortunately, that koala would have died soon after. If they don’t burn to death, the smoke intoxicates them.

We’d like to thank Katrin Hohwieler from the University of the Sunshine Coast for her help getting some of our facts straight. Check out Katrin’s research at the Celine Frere lab at this link.

Adam Hasik an evolutionary ecologist interested in the ecological and evolutionary dynamics of host-parasite interactions. You can read more about his research and the rest of the Ecology for the Masses writers here, see more of his work at Ecology for the Masses here, or follow him on Twitter here.


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