Australia has been plagued by severe drought for two years and with January and February the two hottest summer months still ahead. In interviews with NU.nl, Australian experts stated that the forest fires probably cost the lives of at least 480 million wild mammals, birds and reptiles, including eight thousand koalas. And that is not the only risk factor for the marsupial.
The Australian Environment Minister previously reported that in New South Wales in the southeast of the country, 30 percent of the koala population must have died because 30 percent of their habitat has gone up in flames. While birds can fly away and kangaroos also have a chance to jump out of the fire, koalas on the ground are not fast enough.
"Koalas have always been vulnerable to forest fires by nature," says Valentina Mella, an ecologist specializing in koalas from the University of Sydney. "The problem now is that it has become a vulnerable species that is threatened in many ways at the same time."
Despite large numbers, koala has become a vulnerable species
The large numbers of victims among koalas are a blow to Australian conservationists, who are trying to reconnect isolated populations of marsupials. Koalas are found only along the east coast of Australia, from Queensland in the northeast to the states of New South Wales and Victoria in the southeast.
The total number of koalas in the country is not well known: estimates range from 300,000 (IUCN) to 80,000 (Australian Koala Foundation). Because the species is declining rapidly, IUCN has placed it on the Red List as 'vulnerable' in 2016. According to a 2017 study by the World Wide Fund for Nature, the koala population in New South Wales is more than a quarter smaller in every generation, while in Queensland it is even halved by every generation.
The habitat of the koalas has become much smaller and fragmented, Mella explains. For example, koalas are often hit by cars or attacked by dogs. There are also diseases and fragmented populations suffer from inbreeding.
In the early twentieth century, the original population declined sharply due to over-hunting for koala skins. In addition, 80 percent of the original habitat already disappeared due to the expansion of agriculture.
31Dehydrated koala drinks water from Australian cyclist
Eucalyptus leaves become toxic to koalas due to an increase in CO2
Koalas have an additional climate concern, which has to do with their strong specialization on a single food source: the leaf of the eucalyptus trees. This leaf naturally contains a balance between nutrients and toxins, so that few animals can live on it.
Koalas have developed genetic adaptations for this over millions of years, but nevertheless have to rest twenty hours a day to initiate detoxification processes that keep the animals healthy. The energy that this costs can only be supplied by the nutritional value of the leaves, says ecologist Elizabeth Neilson of the University of Copenhagen, who is researching the nutritional balance for koalas.
But the chemical composition of the leaves is changing due to the increase in the CO2 concentration in the atmosphere. The amount of nutrients becomes smaller, while the amount of toxic 'antinutrients' becomes higher. This was demonstrated in 2008 by laboratory research by the Australian Academy of Sciences.
If the CO2 concentration continues to increase, koalas have to eat more and more leaves to get enough nutrients, while the toxins concentration in their bodies threatens to rise. "A slight change in the chemical composition of eucalyptus leaves due to climate change can shift the balance between nutritional value and toxicity, and thus affect the chances of survival for the koala," said Neilson.
Is the koala 'functionally extinct'?
Due to the expected further decline, the Australian Koala Foundation recently went so far as to call the marsupial 'functionally extinct'. That is a confusing term. In this case it does not refer to a direct extinction risk for the koala as a species. What is meant is that koalas as their numbers per generation would continue to decline rapidly, are no longer able to fulfill their ecological role within Australian ecosystems.
Koalas should naturally be present in large numbers in eucalyptus forests, helping to maintain natural balance. For example, the droppings of koalas are important for the nutrient cycle in the forest.
Those Australian ecosystems are under great pressure anyway, says ecologist Dieter Hochuli of the University of Sydney at NU.nl. "In many reports it's about the effects of forest fires and climate change on iconic species, such as the koalas. But we also have to worry about how the whole of plants and animals is affected, and whether these ecosystems can still recover."
See also: Half koala population in Australian reserve eradicated by forest fires