DO WE HAVE TO KEEP DOING THIS? (INSECT EDITION)

Seems every news and information source is offering that we are on the cusp of a global insect mass-extinctions threatening all life on earth. The Guardian reported "The world’s insects are hurtling down the path to extinction, threatening a 'catastrophic collapse of nature’s ecosystems', according to the first global scientific review." But where is the justification for talking about 40% of insect populations being in decline (or inevitable catastrophe)?

Yes, that study, Worldwide decline of the entomofauna, by Sánchez-Bayo and Wyckhuys, highlights "the dreadful state of insect biodiversity in the world" and concludes that "almost half of the species are rapidly declining and a third are being threatened with extinction." Bold.

OKAY, BUT IS THAT TRUE?

The first thing I notice when I go read the above report is that their survey of studies excludes effectively all of Africa, Asia, Australia, Central and South America, as well as Mexico and Canada. That's right, this assessment of the global state of insect populations looked at data almost entirely in the northern hemisphere and overwhelmingly from Europe and the United States. That's curious on its face but also makes sense because that's where the data is.

From this very limited vantage, of the many studies these researchers found, only a tiny minority of insect population evaluations were long-term in nature and thus useful at all for the meta-assessment they conducted. Narrower still, those studies almost entirely look at a period in which major land use changes occurred and industrial agriculture and the worst pesticide use was at its most intense. And then paired with those severe limitations, most commonly the long-term studies out of America and the EU also look at a single species or genus; so nothing like a comprehensive regional insect population evaluation. This is likely the best data we have but, doubtless, is more of a problem than an illuminating and clarifying vision of the state of the world.

From this footing, what are the kind of assessments made within the survey? One section notes things like:

A comprehensive report on the status of 576 species of butterflies in Europe found that 71 were threatened and declined over a 25-year period (van Swaay et al., 2006). The largest declines occurred among specialist butterflies of grassland biotopes (19% species), wetlands and bogs (15%) and woodlands/forests (14%), due to habitat conversion into crops and the adoption of intensive agricultural practices, e.g. fertilisers and pesticides negatively affected 80% species.

How does that look to you? First I notice that 71 of 576 species is 12% of European butterflies showing any evidence of decline. That figure seems shockingly low (rather than staggeringly high, as implied.) Why? Consider the population explosion and as a result the level of development and urban sprawl experienced by the nations of the EU at the end of the 20th century. Then notice that we're looking at numbers from 1980 to 2005 (with the bulk of the research therein looking at previous decades and getting published between 1990 and 1996), and thus ignoring all the tremendous recent efforts over the last twenty years to prevent and reverse habitat degradation and loss, transform agriculture and forestry, limit pollution and pesticide use, establish and expand protected areas, and revive threatened populations all across Europe. All of that has been huge and makes this survey feel more blinding than otherwise. But those are just some surface observations.

From there I go and look at the cited research paper, van Swaay et al., 2006. There I find that the authors everyone is referencing, Sánchez-Bayo and Wyckhuys, carefully edited out the actual findings of the research they cite and offer only the most dire bits. Serious red flag. The paper notes, "The distributions of the 25 most 'generalist' species are declining only slowly (−1%) compared to specialist butterflies of grassland (−19%), wetlands (−15%), and forests (−14%)." Why skip that bit? 25 species is 35% of the noted 71 species labelled "threatened and declined." And those 25 generalists are not experiencing a concerning population collapse. Problem, problem, problem, problem. But all this is from just looking at the abstract of the paper as I can't evaluate it any further without purchasing the article. Still, I think we can safely suggest we're getting something other than the goods.

WHAT DO OTHER SOURCES SAY?

When I look for more info, knowing the EU does collect a ton of data, I find more conflict. The European Red List, a comprehensive review of the conservation status of 6,000 animal and plant species in Europe, tells me "there are 482 species of butterflies" in Europe, with only 142 of those species being endemic. So what are the 576 species noted earlier? Who knows. It seems that, other than me, someone is very confused.

Reading the Red List's conclusion, coming four years after the van Swaay paper above, further reveals a series of critical caveats that confirm my earlier assumptions and assessments:

Despite a lack of good trend data from many countries, the results show that about a third of European butterflies species experienced a decline in their populations over the last 10 years and 9% are threatened.

It should be noted that both the distribution and population size of numerous species have declined severely during the 20th century (but not in the time frame of 10 years or three generations taken into consideration by IUCN methodology), especially in Western Europe. In some cases the few remaining populations in these countries are nowadays stable as a result of conservation measures, which means these species do not occur in the list of threatened species.

"A lack of good trend data", "declined severely during the 20th century", and "stable as a result of conservation measures" sounds closer to the apparent state of things.

A BROADER PICTURE?

The IUCN Red List is currently the leading summary of available knowledge on global population trends, including that of insects. What does a study of the IUCN Red List reveal? Well, there's no global population data of any kind on 99% of insect species. At last count, only around 8,131 species of insects have had their global populations formally assessed. That represents 0.8% of all known insect species. There are roughly one million known and five million estimated unknown species. Of these known species, only 10% of those have been assessed as declining in population (or 0.08% of all known insect species.) What of the rest of the 0.8% that we have some data on? Well, obviously, they're increasing or stable (15%) or the population trend is totally unknown (75%).

Yes, there are solid indicator species, assessments of whom can provide a reliable barometer of ecosystem health and suggest to us how other species may be faring. Fact. And insects can be particularly sensitive organisms, highly specialized and easily impacted by perturbations of all sorts. Fact. But pretending that a very vague and limited look, and some decades ago, at effectively no species of insects doesn't give us a especially excellent test of the global insect situation. it certainly doesn't give us amazing predictive capacity. Sorry. If this new global insect survey reveals anything it's that we need both more and better data collection and that conservation is effective, and as such essential.

More than that, the IUCN has estimated that 0.8% of the 112,432 plant and animal species within its data set have gone extinct over the last five centuries. Yes, extinction is forever and the ripple effects can be huge. Also, that’s an average rate of fewer than two species per year, for an infinitesimal annual extinction rate. And, of course, not only do we have no idea how many species there are but the tremendous increase in biodiversity arriving in the last 100 million years, according to the fossil record, very significantly outweighs those species lost to all those naturally occurring mass-extinctions. So pretending that everything is simple and obvious (and the present is maximally catastrophic) helps nothing.