“Inheritors of the Earth” – A provocative treatise argues that, for many species, the era of extinction may be all right. What are your thoughts on this book?

This book offers a radically different perspective on the current ecological processes in the anthropocene.

I’ll quote something here to give an idea of what the author is getting at:

In reference to the effect of invasives:

More remarkable than the losses, however, is quite how few foreign species have caused any others to go extinct at all.

Only a few dozen out of thousands of foreign species that humans have transported across the constellation of Oceania’s islands have driven any native species extinct. Even fewer have caused other species to become extinct on the world’s largest continents.18 With notable exceptions, including the chytrid diseases of amphibians and chestnut blight in North America,19 foreign species hardly ever cause native species to become extinct from entire continents. This is not surprising. Researchers who study the interactions between different organisms long ago demonstrated that a small number of species have a major effect on other species, but that most do not. This was first appreciated in 1969 by North American ecologist Robert Paine, who spent his days scrabbling around on rocky shores near the University of Washington, where he worked. He discovered that one species, which was a relatively rare starfish, had a huge effect on almost all the other species on the shore.20 He christened it a ‘keystone species’. When he experimentally removed this mussel-guzzling starfish, beds of mussels grew in great abundance, crowding out other rock-encrusting animals and plants that used to grow there. The entire biological community changed. However, although Paine is deservedly remembered for the keystone concept, it is worth recognizing that most of the other species he experimentally manipulated had very little effect–otherwise, the starfish would not have seemed remarkable.

The ever ebullient Dave Raffaelli, enthused by this research, set out to test Paine’s ideas in the estuary muds of the Ythan River, north of Aberdeen in Scotland–a landscape so bleak and windswept that it perhaps accounts for his decision to grow a wind-cheating protection of dense facial hair. Disappointed not to find a keystone species in his initial work, he hit on a plan: to add and remove as many species as he could, in turn. He reckoned that persistence would pay; eventually, he would find the keystone species. After a decade or more of experimentally adding and subtracting species in search of the elusive keystone species, he gave up. There wasn’t one. Lots of species had relatively small effects, a conclusion that is critical to our understanding of ecosystems. Sometimes there are one or two species in a particular place that have large and disproportionate impacts on all the others, like Paine’s starfish, and sometimes there are not. Most species that are added to or subtracted from an ecosystem have little impact on the others. This is equally true of foreign species, caricatured by York biologist Mark Williamson’s ‘tens rule’,21 whereby only about one in ten species that arrive in a new part of the world escape from captivity or gardens, only about one in ten of these then become fully established in the wild, and only about one in ten of the established species go on to be regarded as pests or weeds. A tenth of a tenth of a tenth. This ratio varies quite a bit from place to place, but roughly one in a thousand species that arrives causes a real issue for the native animals and plants, consistent with Paine’s keystone ideas in community ecology and Raffaelli’s failure to find any such species.

And when people say that these species become pests or weeds, this usually just means that they become common, without actually endangering other species with extinction. Foreign species are acting like any other species: a few have major impacts, but most don’t.22 Because a large majority of them have such limited impacts, the importation of lots of new species almost always increases the numbers of species in any given location, just as we saw in the forests and waters of Lake Maggiore. When lots of new arrivals establish breeding populations, hardly any ‘natives’ die out as a consequence. This is true even in New Zealand, one of the world’s hotspots of extinction. When my wife, Helen, and I accompanied invasion biologist Jacqueline Beggs for a jet-lagged view over New Zealand’s largest city, Auckland, we could almost have been at home. Species-rich meadows now cover the tip of the old volcanic cone of Mount Eden–Maungawhau, to give it its Maori name–that protrudes above the city, forming a vegetation comprised largely of European plants. Meadow plantains, wild cranesbills, sorrels and European grasses generated the scents of our own hay meadow. But walk into the remaining areas of forest near Auckland, and hardly a foreign plant species can be seen. A few introduced plants do live in the forest: Kahili ginger from the Himalayas, check; wandering Willie, or Tradescantia, from South America, check; Plectranthus blue spur flowers from South Africa, check. But even though these plants grow in the forest, the forest is still dominated by native New Zealand trees, shrubs and ferns, and there is no indication that they will cause native species to disappear.23

This story is told and retold. On average, for every new species that arrives, less than one of the species that was originally there dies out.24 The arrival of foreign plants has not only approximately doubled the diversity of New Zealand’s flora,25 it has also done so in the Hawaiian islands and elsewhere in the Pacific. The botanical diversity of these islands seems to just go up and up and up as new species arrive, with no obvious limit in sight.26 This is also true of vertebrates. Despite the extinction of many native birds from the Hawaiian archipelago, the islands are now home to many different introduced mammals, lizards, frogs and freshwater-fish species, as well as to imported birds.27 This all leads to an increase in the diversity of each region. Take Britain, which now has six species of wild deer, rather than the original two. Some 1,875 foreign species of plants and animals have established wild populations in Britain in the last two thousand years, and mostly in the last two hundred; yet, as far as we know, no native species has died out as a consequence (although some have died out for other reasons).28 This pattern repeats itself across the world’s continents.29 American states have experienced approximately 20 per cent increases in plant diversity through imports, and a similar level of increase has taken place for fish in American river catchments.

It is worth reflecting on the British ratio of 1,875 arrivals to zero extinctions caused by invasive species. With odds that low, I might cease to worry so much about legislating against new arrivals. Of course, some of the new arrivals do engender ecological changes–the replacement of one introduced crayfish by another, for example–that fall short of the extinction of native species, but change is how the biological world works.30

%d bloggers like this: