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Live Long and Falter: Spry Population Linked to Endangered Species

If a country's human population is long-lived, it's bad news for the local critters—almost as bad as being a native bird in New Zealand.
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Thousands of kakapos have been collected for museums across the world. (PHOTO: BS THURNER HOF/WIKIMEDIA COMMONS)

Thousands of kakapos have been collected for museums across the world. (PHOTO: BS THURNER HOF/WIKIMEDIA COMMONS)

When it comes to protecting endangered species, the debate is usually presented in the stark terms of a zero-sum game—every extra tick in the ledger for some struggling critter is matched by one on the deficit side for humanity. While the answers hammered out usually involve some trade-offs on both sides, the flags flying over the battles lines often read  "People or fish?" or "Jobs or owls?" as if we can’t possibly have both.

Except that new research looking into predictors of a species’ demise finds that the longer a country’s human population is likely to live, the greater percentage of endangered species it will have.

Writing in the newest edition of the open access journal Ecology and Society, ecologists Aaron Lotz and Craig R. Allen examined the “social-ecological” factors that underlay both the influx of invasive species and the status of potentially endangered ones.

While there’s an obvious connection between some social metrics—think economic or population growth—and some natural ones, Lotz and Allen tried out a number that aren’t usually applied to this arena. All told they examined 15 different variables: economic ones such as per capital GDP, export-import ratio, tourism, undernourishment, and energy efficiency; ecological ones like agricultural intensity, rainfall, water stress, wilderness protection, and total biodiversity; and social indicators like life expectancy, adult literacy, pesticide regulation, political stability, and female participation in national government. Their analysis also included the latitude, total land area, and yes, population.

If you’re a policy geek, it’s almost fun to consider the role a woman head of state or universal literacy would have on conservation issues. But after looking at 100 countries representing 87 percent of the world’s population, the one variable the pair’s analysis ID’d as being the biggest predictor of a nation's endangered and invading animals was life expectancy. "Out of all this data, that one factor -- human life expectancy -- was the determining factor for endangered and invasive birds and mammals," Lotz was quoted in a release from the University of California-Davis. (It’s worth noting that other scholars’ work on humanity’s footprint did not implicate a long life as a leading problem but did identify affluence and population as factors.)

As explained in the Ecology and Society paper:

Increased life expectancy means that people live longer and affect the planet longer; each year is another year of carbon footprint, ecological footprint, use of natural resources, etc. The magnitude of this impact is increased as more people live longer.

Take Africa, with some of the lowest life expectancies on the planet—and the lowest percentage of invasive and endangered birds and mammals. Lotz and Allen noted there are few—in absolute numbers—invasive (29 bird and 39 mammal) species or endangered species. Looking at invasives, the authors put the blame on trade, or lack of it. African countries as a group are weak players in international trade. On the other hand, Britain, for centuries the trading capital of the world, is positively awash in invasive species.

I might also argue that African countries are less picked over by researchers, and so we might not have full grasp on the real state of the animal kingdom. Sometimes being the focus of lots of investigations has its drawbacks, which is part of the reason that I believe the U.S. and New Zealand (along with the Philippines) have the highest percentages of endangered and invasive birds—'cause we have a great handle on what’s to be found there.

Let’s look closer at New Zealand, the land that eco-tourism embraced. NZ has a hyperactive sensitivity to protecting what’s left of its unique and endangered fauna (i.e. kiwis, kakapos, and tuataras) and flora (from kauri to kaka beak). It also has a long-lived (if small) population. While the authors repeatedly caution that New Zealand is an “extreme outlier,” and not just geographically, it sounds like a mess:

New Zealand has the highest percentage of endangered birds, invasive birds, and invasive mammals, and also has the highest percentage of all endangered and invasive species combined. New Zealand’s complete lack of native terrestrial mammals [they do have thumb-sized bats] is a key factor in its outlier position relative to the rest of the countries analyzed. New Zealand has had a massive invasion by nonindigenous species since its human colonization in the past 700 to 800 years, and this has resulted in catastrophic biodiversity loss. New Zealand’s invasive species crisis may be due in large part to its isolation, high endemism, and recent human colonization.

If that makes New Zealand seem like hell on Earth, well, you probably haven’t been there. But knowing that New Zealand is both a hotbed of species problems and a hell of a nice place points to the call to action that concludes Lotz and Allen’s paper: People and their habitats are not mutually exclusive, and the sooner we accept, and act on, the realization that this isn’t a zero-sum game of man vs. bird, the better for all.