Agriculture and species extinction
The Kangaroo Island assassin spider is quite possibly extinct, wiped out by the devastating Black Summer fires.
Ever since those fires, Dr Jess Marsh, an arachnologist, conservation ecologist and research fellow with Murdoch University, has been searching for the assassin spider, so far unsuccessfully.
“And I get asked a lot, ‘Why should we care?’ ” she says. “You know, if a spider goes extinct, what difference does it make?
“And to be completely honest, if one species goes extinct – say, the assassin spider – we may not notice any difference.”
But, she says, there are reasons to be concerned. “An extinction event is unlikely to just impact one species. There will be knock-on effects on the species that it eats and that eat it, and on its parasitoids.”
More broadly, she says, we should be concerned because the cause of the death of one type of animal may well be the cause of the deaths of others.
The 2019-20 bushfires, for example, were devastating for many more life forms than Marsh’s spider. More than 10 million hectares were burned, and enormous numbers of animals died. Many of these were invertebrates, although precision around exact numbers is hard.
There are about 100,000 “described” species of invertebrates in Australia, but these named ones probably comprise about only 30 per cent of the total. They make up an estimated 97 per cent of all animal species in this country yet we know precious little about them.
This is unfortunate, Marsh says, because “it’s really these small things that make the big things happen”.
Invertebrates are in trouble in this country, not just because of recent fires but because of intensive agriculture, land clearing, pesticides and climate change. This is a serious issue. Without these animals, ecosystems and economies will collapse.
Over recent years we’ve seen alarming reports from overseas. In 2017, an analysis of 27 years of data from Germany showed a 76 per cent decline in insect biomass. The following year researchers from Mexico reported a decline of 75 to 98 per cent in ground insects in an area of Puerto Rico over 35 years. Two years ago, an academic analysis of 73 other reports from various parts of the world concluded that more than 40 per cent of insect species – butterflies and moths, bees, wasps and ants, and beetles in particular – were in danger of extinction.
Dr Manu Saunders, lecturer in ecology and biology with the School of Environmental and Rural Science at the University of New England, advises to take such studies, and particularly the consequent media coverage of an “insect apocalypse”, with a large grain of salt.
As she wrote in a long piece for American Scientist magazine, and repeated to The Saturday Paper, these studies were localised and focused on a relatively small number of species. The one that predicted mass global extinctions, for example, incorporated data on about 2900 species of insects globally, out of an estimated five million.
That is not to deny there is serious cause for concern, however. It’s just that broad conclusions are hard to draw from narrow samples.
The reality, Saunders says, is that “we don’t know enough to actually know what we’re losing”.
All the factors that contribute to the more general crisis in biodiversity – habitat loss, destructive land use practices, environmental pollution and climate change – also are affecting insects. “And sometimes,” Saunders says, “it might be more critical because insects are smaller, they have small life cycles, they have very specific habitat requirements…
“For scientists who are actually working on this, it’s really frustrating because people want answers, and we can’t give answers.”
And so, even as they strive to get a better understanding of what is happening, many experts resort to anecdotal evidence of the kind that should be obvious to the lay person.
I have some to offer myself. As a kid, 50-plus years ago in Brisbane, I was a butterfly collector. Northern jezebels, painted ladies, tailed emperors and dozens of other species were everywhere in my suburban neighbourhood. One year there was a migratory swarm of caper whites so big it literally stopped traffic. Drivers reported trying to remove the butterflies with their wipers and having their windscreens rendered opaque with smeared carcasses. Now there seem to be far fewer.
When I tentatively share this observation about the apparent decline in butterfly abundance with Stephen Garnett, professor of conservation and sustainable livelihood at Charles Darwin University, he responds in kind.
What about grasshoppers, he says. It used to be that windscreens were similarly smeared by them.
“You used to have to put gauze over your radiators, to stop them filling up with grasshoppers,” he recalls. “It’s sad, really, that that’s the way we measure insects’ abundance.”
But, he says, it’s as “good a measure as we have” in many cases.
Butterflies, probably because they are a charismatic and obvious group of insects, are among those we know most about.
Only one Australian species, a prettily patterned, medium-sized brown, called the laced or Australian fritillary, seems to have become extinct, Garnett says. But several dozen are threatened.
One of these is the bulloak jewel, and its story illustrates a couple of aspects of the insect crisis.
“It’s a small, pretty blue butterfly that occurs in the Brigalow Belt in southern Queensland/northern New South Wales, and is only known now from a handful of locations,” says Chris Sanderson, a research officer at the ANU Research School of Biology.
The jewel’s larvae are attended by ants, he says: “a particular type of ant that lives on a particular kind of mistletoe that lives on a particular kind of tree.”
That tree, the bulloak, grows in areas with good soils for farming. Or grew, past tense – because 95 per cent has been cleared, and with the tress have gone the accompanying ecology, including the jewel.
Sanderson makes two points. First, that the bulloak jewel – like the spiders of Kangaroo Island and many other invertebrates – is vulnerable because it occupies an “extremely tight ecological niche”. Second, that the main cause of butterflies’ decline, “as with most things”, is habitat loss.
And Australia has an appalling record in that regard. Queensland is the worst, says Martine Maron, professor of environmental management at the University of Queensland.
According to the most recent official figures, for 2017-18, a total of 392,000 hectares were cleared in Queensland. Of this, 74,000 hectares was old-growth forest, and 318,000 was regrowth, she notes.
That was about the same as for the previous three years. In NSW, in contrast, deforestation has sharply increased following regulatory changes pushed by agribusiness and the National Party. Rates of tree clearing that had averaged a little over 30,000 hectares for seven years to 2015 suddenly doubled to more than 60,000.
The loss of old-growth forest, it is well established, is of particular concern for bird and mammal species that rely on holes in old trees for shelter and nesting. “But it may be that the loss of quite youngish regrowth vegetation is really important in affecting the insect fauna,” says Maron. “We just don’t know.”
Nor do we know much about the effects of climate change, except that they are many and complex.
Of the 5.3 million hectares of NSW that burned during the Black Summer, more than one-third was rainforest, including large areas of Gondwanan rainforest that is not a fire-adapted habitat, and which scientists reckon might have burned only once in 1000 years.
The rainforests are incredibly diverse. But, asks Maron, what happens when they dry out or burn, “which is going to happen more and more”?
“What about all the birds that live in the rainforests – like lyrebirds – that eat the insects in the leaf litter? They’ve got nothing to eat.”
Climate change has all sorts of impacts, including on the “choreography” of insects and their host plants, says Professor John Woinarski, of Charles Darwin University, and deputy director of the Threatened Species Recovery Hub of the National Environmental Science Program.
Many invertebrate species only come into maturity when the plants they eat are flowering or fruiting, he says. But climate change is altering that seasonal rhythm, with little-understood consequences.
Woinarski says many more invertebrate species are in trouble than we know, for the simple reason that “almost all of them don’t have good monitoring programs, or many of them don’t have any monitoring at all”.
“While we might be monitoring koalas relatively well, and many of the other charismatic vertebrates, far less attention has been given to the population trajectories of a whole lot of invertebrate species,” he says.
One we do know a bit about, he says, is the bogong moth. Historically, they were super-abundant. They were an important food source for Aboriginal people, and also a mainstay of the diet of many animal species, notably the critically endangered mountain pygmy possum.
Bogongs are migratory. They summer in the caves and boulder fields of Australia’s alpine areas, and disperse over large areas of NSW, Victoria and even southern Queensland in the cooler months.
But in recent years their numbers have crashed, to the point that Woinarski says he and other scientists are assessing them against the criteria for inclusion on the International Union for Conservation of Nature red list of endangered species.
This decline happened well before the fires. Drought may have been a factor, but land use changes and agricultural chemicals also are suspected.
Bogongs are one of a number of species farmers collectively refer to as “cut-moths” and are considered pests on a range of crops.
Australia’s regulatory regime for agricultural chemicals is very lax: we still use a number of pesticides that are widely banned elsewhere. The system of regulation of agricultural and veterinary chemicals is currently under review, and the worrying signs are that this will result in less “red tape” and more industry self-regulation. But that is a story for another day.
The uncertain future of the bogongs, says Woinarski, shows that what we do know about insect numbers and extinctions is not good. “That such a super-abundant, or formerly super abundant, species is being considered for listing as threatened is fairly indicative of something catastrophic going on.”
This article was first published in the print edition of The Saturday Paper on Mar 20, 2021 as "A bug in the system".
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