How many invertebrates go extinct in Australia each week?

There’s an important mantra in conservation biology that, if you don’t understand a species you have no hope of saving it. But, in Australia, as Jess Marsh at the University of Adelaide and John Woinarski at Charles Darwin University point out, the problem isn’t just one of known unknowns, it’s also unknown unknowns: there are thought to be hundreds of thousands of invertebrate species across the continent, but only a fraction have been scientifically documented; so if they went extinct, who would know? And, moreover, how many are going extinct? Thanks to this new study, we now think an alarming number. To reach this conclusion they’ve taken the approach of using extinction rates of animals we do know more about and applying those to the invertebrates we don’t yet know about. The answer will alarm you…

Jess - In Australia, there are an estimated 320-odd thousand invertebrate species. Invertebrates include slugs, snails, insects, spiders—basically, animals without backbones. However, only around a third of them have been described. So, for many, we actually don’t know much about them at all. We don’t know where they are. We don’t know what’s threatening them. Currently, only 10 invertebrate species are officially recognised as having gone extinct. This seems far too small compared to the huge number of species we have and the threats we know are impacting them. So, in this study, we set out to try and work out how many invertebrate species have likely gone extinct in Australia.

Chris - It’s a huge country, John. That’s not a small undertaking. How have you tried to do it?

John - It’s challenging, of course, because there’s so little data for many of these species. We took two approaches. One was to get the proportion of extinct species in well-known taxonomic groups like mammals, birds, reptiles and the like, and then apply that proportion to the number of invertebrate species in Australia. The second approach, which complemented the first, was to look at the proportion of extinct invertebrate species globally and then apply that to Australia as well. They yielded much the same result—that about 9,000 invertebrate species have become extinct in Australia since 1788. Clearly, this means we’ve had a far greater impact on Australian environments than previously recognised. We also calculated the current rate of extinction. Our calculation showed that between one and three invertebrate species are becoming extinct every week.

Chris - And what do you think the drivers of those extinctions are?

Jess - There are a number of threats impacting invertebrates. Many are interacting and cumulative, which amplifies the effects. One of the key threats is habitat loss and clearance, forcing species into smaller and smaller areas and reducing movement between habitats. Additionally, there’s large-scale pesticide use, the introduction of feral animals and weed species—all of which degrade habitat, break it down, and make it less suitable for animals to survive in. Then, of course, there’s climate change. Many invertebrate species are at high risk from climate change because they require high humidity and lower temperatures. All of these threats, which have intensified with increasing human population sizes, are impacting fauna.

John - In many cases, invertebrates are far more prone to extinction because, more so than birds, mammals or reptiles, they often have really small ranges—sometimes just a few hectares. So even a small amount of land clearing can potentially wipe out an entire species.

Chris - There’s presumably also, John, this tendency for humans to obsess over the big, visible and cuddly things. We tend to overlook smaller species—especially ones we may have an aversion to, like the spiders I know Jess loves. As a result, we overlook some really important elephants in the room.

John - Well, not elephants in this case—slugs. There are major biases in our treatment of nature. We care far more about charismatic mammals—pandas, koalas and the like—than we do about invertebrates. There’s far more knowledge and conservation management focused on mammals, birds and reptiles than there is for invertebrates. There’s a whole series of neglect-related issues affecting invertebrate conservation. We believe we should be more egalitarian in our approach to nature. Invertebrates really do matter. Our lives depend on them—more so than on koalas. We’re trying to redress the balance and eliminate some of the biases in conservation thinking, planning and public awareness.

Chris - The thing you've stated - that species are disappearing on a weekly basis - is A, very alarming, and, B, seems to fly in the face of the Australian government’s pledge to stop all extinctions. Is that just rhetoric to win elections, or have they made meaningful efforts and simply failed?

John - It’s an admirable and egalitarian pledge to prevent further extinctions. The trouble is, with invertebrates, we don’t really know which species are most imperilled and most in need of conservation. There’s a huge amount of ignorance about invertebrate fauna in Australia and globally. We don’t really know where we should be focusing our efforts. But there are some clues. Many invertebrate species are narrowly endemic, and lots of them co-occur in centres of endemism. If we can identify where those places are and protect them, that will go a long way towards conserving our most imperilled invertebrates.

Chris - Have you got a strategy for that, Jess? The old saying goes: if you want to conserve something, you’ve got to know about it and understand it. If we don’t know about a lot of these things, we can’t draw up policies to protect them.

Jess - Absolutely. It’s a key problem in Australia. We need to address the knowledge gaps. We almost need to look at invertebrates differently from how we treat mammals, reptiles and other better-known taxa. As John mentioned, centres of endemism are important—but we don’t yet know where many of them are. We need to work that out. We need to understand what’s threatening them and how to protect them. From the general public right up to government and conservation decision-makers, there’s a general ignorance about invertebrates—their lives, their threats, and their importance to us. It’s a double-edged issue. We need to find out more, protect key areas, and also change this widespread lack of awareness of invertebrates and their value. They are essential to our natural world, agriculture and ways of life. Losing one to three species a week should be a wake-up call that we need a new approach.