Recently I happened to come across a book on biodiversity loss which stated, in the introduction, that much had been written about the crisis of biodiversity loss but little about what may be done about it. That book was written in 1975.
Matters, of course, are much worse now and there exists little sign that the tide will be reversed any time soon.
Ceballos, Ehrlich and Dinzo have just published a paper at The Proceedings of the National Academy of Sciences that underscores the sense of crisis, and the sense of urgency. The most interesting aspect of the paper is that it does not look at biodiversity loss with respect to species extinction rates, rather it looks at the extent of population decline among species.
Hitherto biodiversity loss has been measured as a function of extinction rates greater than the background rate of extinction. That rate of extinction is well above the background rate
For example, conservatively almost 200 species of vertebrates have gone extinct in the last 100 y. These represent the loss of about 2 species per year. Few realize, however, that if subjected to the estimated “background” or “normal” extinction rate prevailing in the last 2 million years, the 200 vertebrate species losses would have taken not a century, but up to 10,000 y to disappear, depending on the animal group analysed
The authors contend that placing greater attention to popular decline, both of individuals within populations of species and of the geographic range of populations, gives a more accurate, indeed more concerning, picture of the culling of life on Earth. They so argue on grounds that a thinning of populations is an important precursor to extinction, and serves a good metric by which to think about ecosystem fragility.
The picture the study paints is not a pretty one.
In our sample, comprising nearly half of known vertebrate species, 32% (8,851/27,600) are decreasing; that is, they have decreased in population size and range. In the 177 mammals for which we have detailed data, all have lost 30% or more of their geographic ranges and more than 40% of the species have experienced severe population declines (>80% range shrinkage)
The authors conclude
Given the recognized limitations of the use of SAR to estimate extinctions, our work provides an approach based on reduction of species range as a proxy of population extirpation. The most recent Living Planet Index (LPI) has estimated that wildlife abundance on the planet decreased by as much as 58% between 1970 and 2012
Australia has one of the worst records regarding mammals
Our most detailed data allow comparison of historic and present geographic range of a sample of 177 mammal species (Figs. 5 and 6). Most of the 177 mammal species we sampled have lost more than 40% of their geographic ranges in historic times, and almost half have lost more than 80% of their ranges in the period ∼1900–2015. At the continental and subcontinental level, some patterns become evident (Fig. 5). The predominant category of range contraction is ≥80% in Africa (56% of the sampled mammal species), Asia (75% of the species), Australia (60% of the species), and Europe (40% of the species)
The authors find that there has been significant population declines amongst species considered safe when viewed from the perspective of extinction alone.
Many doubtless would seize on the fact that Paul Ehrlich is one of the authors, whose long held ideas regarding a Malthusian type population crash have not borne fruit. One must be careful, however, to not commit logical fallacies here. The method the PNAS study employs is a good first step in drawing a picture of biodiversity loss through an examination of populations.
These findings remind one of a very good and thought provoking, anecdotal, article that not long ago appeared in The New York Review of Books on moths, bees and butterflies,
I wonder if the concept of “species” doesn’t sometimes get in the way of understanding the effect humans are having on the natural world. After all, a species endures even as the individuals that make it up come and go. But sometimes the word implies that the collective whole—the generality of goldfinches, say—matters more than the individual. Only when a species dwindles to its final numbers do the individuals seem to become, well, individual. Perhaps the only passenger pigeon ever to bear a name was Martha, the very last one
I have long regarded biodiversity as the leading ecological crisis of our times, not climate change, and it has since become an academic area of interest for me. To my mind there’s a connection to my usual areas of academic speciality, such as naturalism in philosophy and nuclear weapons in society.
The crisis of biodiversity challenges our relationship with nature, and our ideas regarding our place in nature, much more than climate change. The greenhouse effect we know is caused by the use of fossil fuels, a discrete, though of course central, concern whereas biodiversity encompasses the totality of our impacts upon nature. It is a point that the PNAS study also makes
In the last few decades, habitat loss, overexploitation, invasive organisms, pollution, toxification, and more recently climate disruption, as well as the interactions among these factors, have led to the catastrophic declines in both the numbers and sizes of populations of both common and rare vertebrate species
Of course, climate change is a contributor and its most forceful impacts on biodiversity are yet to come.
Notice that “the last few decades” encompasses precisely the neoliberal era, which has eroded, quite self consciously, bonds of solidarity, cooperation and sympathy among humans let alone that extendable to the wider organic world. By so doing neoliberalism has torn asunder the best means of arresting biodiversity loss precisely when the carnage has been at its greatest.
There is a flip side to this neither explored in the PNAS paper nor The New York Review of Books article of review. There exist some populations that are not declining; cows, pigs and so on. Imagine a world where most populations of Animalia are declining but those husbanded and herded for exclusively human use are rising.
You don’t have to imagine that world. You live in it.