I’ve seen lots of headlines about this recently, but due to other things I’d read in the past, I was a little hesitant to believe it – and I thought I’d seen this come up before, and then get refuted in various ways. Also I tend to be distrustful of articles with EVERYTHING IS AWFUL FOREVER headlines (and journalism about science is often just . . . not good). There’s no doubt things are dire and getting more so, but to be on par with the other 5 extinction events, the extinction rate would have to be quite awful.
“Global Extinction Rates: Why Do Estimates Vary So Wildly?” talks about how the extinction rates have been arrived at. In short, it’s computer modeling, and extrapolating from what direct knowledge of documented losses we do have, and no one really knows how accurate it is. In addition,
. . . the documented losses may be only the tip of the iceberg. That’s because the criteria adopted by the IUCN and others for declaring species extinct are very stringent, requiring targeted research. It’s also because we often simply don’t know what is happening beyond the world of vertebrate animals that make up perhaps 1 percent of known species.
For more on that, check out this article on how invertebrates are so overlooked. (To say nothing of plant, fungi, and other species that we just don’t notice the way we notice vertebrates.) According to the article, we also really don’t have a good handle on how many different species exist in the world, especially among invertebrates.
Ecology is also a relative young science in many ways, and some of the methods used to calculate extinction rates were based on beliefs about ecological relationships that aren’t holding up to be true. The big estimates about extinction rates
. . . go back to the 1980s, when forest biologists proposed that extinctions were driven by the “species-area relationship.” This relationship holds that the number of species in a given habitat is determined by the area of that habitat. The biologists argued, therefore, that the massive loss and fragmentation of pristine tropical rainforests — which are thought to be home to around half of all land species — will inevitably lead to a pro-rata loss of forest species, with dozens, if not hundreds, of species being silently lost every day. The presumed relationship also underpins assessments that as much as a third of all species are at risk of extinction in the coming decades as a result of habitat loss, including from climate change.
But, as rainforest ecologist Nigel Stork, then at the University of Melbourne, pointed out in a groundbreaking paper in 2009, if the formula worked as predicted, up to half the planet’s species would have disappeared in the past 40 years. And they haven’t. “There are almost no empirical data to support estimates of current extinctions of 100, or even one, species a day,” he concluded.
. . . It seems that most species don’t simply die out if their usual habitats disappear. Instead they hunker down in their diminished refuges, or move to new habitats.
For some examples,
. . . El Salvador has lost 90 percent of its forests but only three of its 508 forest bird species. Meanwhile, the island of Puerto Rico has lost 99 percent of its forests but just seven native bird species, or 12 percent. [12% is NOT SMALL in my opinion but I see the point they’re making. -F]
Some ecologists believe that this is a temporary stay of execution, and that thousands of species are living on borrowed time as their habitat disappears. But with more than half the world’s former tropical forests removed, most of the species that once populated them live on. If nothing else, that gives time for ecological restoration to stave off the losses . . .
So, the reality looks not as dire as the headlines and the estimates present. Not that things are totally fine and we don’t have to worry; climate change is going to get worse, and other forms of habitat destruction likewise seem like they are going to get worse before they get better. And even if species don’t go completely extinct, losing one (or more) from specific areas can be very bad for that local ecosystem:
. . . Stork raises another issue. He warns that, by concentrating on global biodiversity, we may be missing a bigger and more immediate threat — the loss of local biodiversity. That may have a more immediate and profound effect on the survival of nature and the services it provides, he says.
Ecosystems are profoundly local, based on individual interactions of individual organisms. It may be debatable how much it matters to nature how many species there are on the planet as a whole. But it is clear that local biodiversity matters a very great deal.
Put too many holes in the local network, and it will no longer function like it used to – and the new system may be much impoverished.