The invasion epiphany

I have just read Ken Thompson's book Where Do Camels Belong for review, and it's one of those rare books that demands to be talked about. In the review I make the apparently outrageous claim that this book is to ecology what Darwin's Origin of Species is to evolution. By that I don't mean to minimise the importance of Origin - of course it's far more significant, because evolution is a much more fundamental part of biology. But just like Origin, Thompson's book points out an aspect of the science that is fundamentally obvious and crying out to be acknowledged, but that the experts of the time generally deny without even thinking about it.

In the case of Camels, the topic is invasive species. We spend large amounts of money trying to control foreign plants and animals that come to our country, terrified that these aliens are taking over the habitat of our natives (is this beginning to sound like a UKIP statement?), in a panic that the natural balance will be damaged. But as Thompson points out, almost all policy in this area is based on emotion and ignorance, rather than scientific fact.

Take a few of the points he makes.

We are very concerned about 'alien' species invading the UK - but it is almost impossible to make a sensible division between alien and native. Frankly, the decision is arbitrary. How do you tell the difference? What is a 'native' species? It's clearly not a species that has 'always' been here, because nothing currently living has 'always' been here, and most of it did not evolve in the UK. Take a familiar example - the rabbit. Is it native or alien? Rabbits were 'native' to the UK (though probably originally came from somewhere else) in previous interglacials, but were wiped out in the last encroachment of ice. So maybe they are native. But after the wipeout they were introduced by the Romans and Normans as food animals. So they're alien? But ecologists generally recognise anything introduced before 1500 has having been around long enough to be native. So native? Who knows? The division is entirely arbitrary because species have always moved from place to place to cope with variations in climate and land conditions. The concept of 'native' is a human one, not a part of nature.

Then there's the assumption that all invasive species are evil and take over, dominating the landscape. Of course they don't. If you look at the studies, they seem to show this - but this is because the studies are almost all of species like Japanese knotweed which are known to be aggressive. So the data is cherry-picked. There are also invasive native plants, like heather and bracken - but for some reason, we don't worry about them. Worse still, quite a lot of the handful of invasive species that are supposed to dominate, don't actually do so. In the US, there is panic about purple loosestrife taking over vast areas. Actually it doesn't, but because it is taller and has obvious flowers, it is more visible than the other plants around it, so appears to become a monoculture. In fact in the vast majority of cases, alien species increase diversity rather than decrease it.

Time and again, ecologists fall for that old science disaster that is confusing correlation and causality. Thompson gives a lovely example in the matter of magpies and sparrow hawks versus songbirds. It was discovered that magpies and sparrow hawks were invading the eastern parts of the UK, where they had previously been confined to the west. Songbird populations in the east plummeted. Damned predatory magpies and sparrow hawks, out of their natural environment and messing up the niche environment. Only no one thought to look at songbird populations in general. They were plummeting everywhere, not just in the areas the magpie and sparrow hawk numbers were increasing. There happened to be a correlation between the two, but the magpies and sparrow hawks weren't the cause (which was more likely to be the development of intensive agriculture).

The same kind of misunderstanding of statistics happened initially with otters and mink. When mink escaped into the wild, otter numbers went into the decline. Clearly it was competition from the evil alien. But there was, in fact, very little competition for food. Instead there was an unrelated cause reducing otter numbers. Since then, otter numbers are on the increase and they are proving very good at seeing off the much smaller mink.

A final consideration that seems to have escaped many of the ecologists is that they are not usually talking about a natural landscape, especially in the UK. Pretty well all of the UK has been changed by human intervention. Some of this is due to imports of alien food species. Bear in mind that, for instance, peas, potatoes, tomatoes, maize, pears, cabbages, apples, grapes, onions, garlic etc. etc. are not native, and all our cultivated food animals bear no resemblance to any natives (and some, like chickens, aren't native anyway). In the US around 98% of food species are alien. In the circumstance of an environment vastly changed by the hand of man, the classic ecological concept of niches where native species live in a balanced natural ecostructure is, frankly, baloney. Even pre-human there were vast numbers of species movements all the time, but we have also made huge changes to the environment which themselves influence the impact of aliens and the survivability of natives.

Thompson is not arguing for a free-for-all. We still need to control something like Japanese knotweed (just as we may need to control bracken in some circumstances). But the ridiculous levels of panic about alien invaders, and the large amounts of money spent trying to preserve things just as they were at a certain point in time is all about emotion and reaction to loaded words like 'alien', not about good science.

To see more on Thompson's book or to buy a copy, take a look at my review.

This has been a green heretic production