The Problem with Biodiversity

Hugh Pennington

Carolus Linnaeus, who was born almost exactly three hundred years ago, on 23 May 1707, was the founder of modern systematics and taxonomy, the sciences of classifying and naming living things. Science has no holy books, but Linnaeus’s Systema Naturae comes close. Its tenth edition, published in Stockholm in 1758, was the starting point of zoological classification, and the binomial system for naming – one for the genus, e.g. Homo, and one for the species, e.g. sapiens – is still the norm. Linnaeus was also a talented taxonomist in his own right; many of the species he described without the aid of modern microscopes and molecular methods still stand. He was, you might say, a founding father of biodiversity studies.

Declarations promoting biodiversity and calling for action to stop its diminution have been made over and over again during the last twenty years by the UN and many other international organisations, NGOs and biologists. The British government has a minister for it. The perception that it’s in decline is supported by history. There can be little doubt, for example, that at one time a good deal of mainland Scotland was covered by forest. But its Exchequer Rolls record the importation of Baltic pine from the 1320s onwards, and the first Act of Parliament ordaining the compulsory planting of trees was passed in 1503. The denudation continued nonetheless. Samuel Johnson lost his oak stick during his Scottish tour in 1773. Assured by Boswell that it hadn’t been stolen, he said: ‘No, no, my friend, it is not to be expected that any man in Mull, who has got it, will part with it. Consider, Sir, the value of such a piece of timber here!’ The Scots continue to legislate. The Nature Conservation (Scotland) Act 2004 gives all public bodies a biodiversity duty. It defines biodiversity as ‘simply the variety of life . . . all living things around us . . . in our forests and mountains, our rivers and seas, our gardens and parks. Biodiversity is the soaring eagle, the leaping salmon, the tiny ladybird, the lowly earthworm.’ Nice words.

But such an all-encompassing definition conceals too many complexities and exceptions. As a medical microbiologist, for example, I have spent my career fighting biodiversity: my ultimate aim has been to cause the extinction of harmful microbes, an objective shared by veterinary and plant pathologists. But despite more than a hundred years of concentrated effort, supported by solid science, smallpox has been the only success. Leprosy, cholera, typhus, plague and diphtheria no longer occur naturally in the UK, but their microbes are still active in other countries. Even these limited successes have been offset by the appearance of new pathogens. In evolutionary terms, HIV, influenza H5N1 and E. coli 0157 are brand new. When it comes to the life forms that are my business, it seems to me that biodiversity is increasing. Consider, too, the case of the hoverfly Eriozona syrphoides. This large, handsome bumblebee mimic occurs in northern continental Europe, north-west and Asiatic Russia, and Himalayan India. I was the first to find it in Britain, fifty years ago in Lancaster. It was undoubtedly new to Britain. Since then it has become widespread, from Sutherland in the north to Southampton in the south. So my perception of biodiversity has been determined by Miles’s Law, as stated in 1949 by Rufus E. Miles Jr, an official of the US Bureau of the Budget: ‘Where you stand depends on where you sit.’

It is traditional to blame the Vikings for much of the destruction of the Caledonian forest. But the written records of their doings in Scotland, such as the Orkneyinga saga and runic inscriptions, don’t say anything about trees. The view that species are currently dying out between a hundred and a thousand times faster than the natural rate is based on evidence no more substantial. The ‘Global 2000 Report to the President of the US’ published in 1980 predicted that between 15 and 20 per cent of all species would be extinct by 2000. There is no proof that this happened, but mass extermination is still said to be imminent. The calculations are extrapolations of guesses, based primarily on estimations of the number of species in tropical rainforests. It is certain that they contain many more species, hectare for hectare, than woods in cooler countries. How many more, nobody knows. The uncertainty is not about birds or monkeys, but about the vastly greater number of species of insects and microbes. The whole of the remaining forest would have to be scoured for years to make sure that the endangered species had really gone. This is so impractical as to make scientific analysis impossible. Alvin Weinberg defined trans-scientific questions as ones that have the same structure as scientific questions but cannot be answered by science. Environmentalists have been undeterred by the problem, and have embraced the Precautionary Principle. ‘Where there are threats of serious or irreversible damage,’ reads the form of this principle accepted by the UN Convention on Biological Diversity in Rio de Janeiro in 1992, ‘lack of full scientific certainty should not be used as a reason for postponing measures to prevent environmental degradation.’

In the face of such uncertainties, it is right to focus preservation work on habitats rather than species. But species help to create a habitat, so they cannot be ignored. And habitats are dynamic; the notion of an unvarying association of species in balance is theoretical. Only farmers and foresters come close to achieving it: it doesn’t occur in nature. Habitats also change and spread, sometimes with assistance from humans. More than 250 species of Red Sea fish swam into and stayed in the Mediterranean after the opening of the Suez Canal; competition with the natives led to one extinction.

Although, on balance, invasion of a habitat by foreign species increases local biodiversity, our attitude to the invaders is usually hostile. ‘Non-native’ is a pejorative term. Some time before 1829 the American salt-marsh grass Spartina alterniflora was introduced into Southampton Water, where it hybridised with the local Spartina maritima. The hybrid, Spartina x townsendii, is sterile, but in the 1880s its chromosomes doubled, leading to the creation of a new species, Spartina anglica. It grew faster than its parents and in more unstable areas of salt marsh than they could manage. It was planted extensively in Britain, Europe, Australia, New Zealand, China and the US to stabilise coastlines and assist the reclamation of intertidal land. Attitudes to it today are divided. For some its American ancestry and British origin still count against it. It has been nominated as one of the hundred ‘World’s Worst’ invaders. It is described as aggressive; it is said to diminish biodiversity because it produces a monoculture; waders and wildfowl don’t like it. Other scientists disagree. Studies carried out in Morecambe Bay since the 1940s – I took part in them in the 1950s – indicate that it has not been aggressive; it has helped the salt marsh to spread and it has provided bird cover; it has increased biodiversity.

Spartina also helps salt-marsh mosquitoes. Like midges in the Scottish Highlands, mosquitoes are excluded from the biodiversity canon. We are lucky in the UK in that no naturally occurring diseases are spread by them. But we still regard them as fit only for destruction. One of the most aggressive bloodsuckers we know is a mosquito first described in Egypt in 1775 by the Swedish entomologist Forskal. He called it Culex molestus and said that it was immensa copia, nocte incommodus dormientibus (‘extremely abundant, troublesome at night for sleepers’). It first came to public attention in Britain when London Underground stations were used as air-raid shelters in 1940 and those sleeping there were ravenously attacked. It is so closely related to an above-ground mosquito, Culex pipiens, which bites only birds, that their appearance is identical. Malariologists have an inordinate fondness for jargon, which has infected mosquito specialists, too. They describe the molestus breeding sites as hypogeous (underground), its mating as stenogamous (in confined spaces), its host preferences as mammophilic, its egg production as autogenous (lays fertile eggs without needing a blood meal) and its life cycle as homodynamic (not involving hibernation); pipiens is epigeous, eurygamous, ornithophilic, anautogenous and heterodynamic.

In Europe, pipiens and molestus do not interbreed: they behave like different species. It is different in the US. Culex pipens is a hybrid of the two. It bites both birds and humans, and is probably the most important vector of West Nile virus, which spread to North America in 1999. This increase in biodiversity has so far infected more than twenty thousand people and killed more than seven hundred of them. In summer, the mosquito feeds on and spreads the virus in the American robin. When the birds leave their breeding sites in the autumn the mosquito turns to humans. The London Underground molestus are not ornithophilic. We have nothing to fear from them. But even if they are Londoners born and bred that is unlikely to save them. We are all in favour of biodiversity – but especially favoured are large, colourful or rare species. Animals with a fixed smile like dolphins get special attention and mammals top the list, with birds not far behind. Native species do best of all.

In Scotland it is the red squirrel that gets all the favours. The American grey is being culled around Aberdeen to protect it. The grey’s first appearance was at Finnart on Loch Long in 1892. It is undoubtedly a foreigner. But so are most of the red squirrels. The destruction of the Caledonian forest led to their extinction around the middle of the 18th century. Animals from England were introduced by the Duchess of Buccleuch at Dalkeith in 1772, and on Loch Fyne in 1847. The Aberdeen reds are probably descended from those introduced from Scandinavia by the Duke of Atholl at Dunkeld in 1793. Animals introduced at Beaufort Castle on the Beauly Firth in 1844 did so well that the Highland Squirrel Club was formed to take them on, so great was the woodland destruction: it paid a bounty for tails.

Biodiversity is a new word, but scientists were studying it long before it was coined. In 1973, the UK Systematics Association organised a symposium on ‘The Changing Flora and Fauna of Britain’. It concluded that disproportionate attention was being paid to the conservation of rarities, and pointed out that this conclusion had also been reached at a meeting of the Linnaean Society in 1935. The preservation of habitats was emphasised (although there was disagreement on which ones); the importance of native flora and fauna was endorsed (although different speakers used different definitions of ‘native’). Much attention was paid to imported species. All these issues are still important. But there have been big changes since 1973. Then, it was concluded that global warming was a good thing, at least for butterflies, because the cooler climates of 1875-90 and 1950 onwards had led to their decline, and the warming between 1895 and 1950 had encouraged the northward movement of species from mainland Europe. There was pessimism then because the average summer temperature in central England between 1960 and 1969 was three-quarters of a degree below that of the previous thirty years, shortening the growing season by two weeks.

For biodiversity scientists, the biggest change has come from their adoption of molecular methods. Conservation genetics is a new discipline. The construction of molecular pedigrees enables the origins, migrations, increases and decreases of populations to be tracked. A particularly striking finding has been how much genetic variation there is between individuals of the same kind; biodiversity is vastly greater than the number of species, even though that is massive. The bacterium Escherichia coli is a good example. We all carry it in our intestines. It was chosen by the founders of molecular biology in the 1940s as a model organism and has become the most studied living entity. It doesn’t need sex to reproduce and so forms clones. It is certain that hundreds of different ones live in humans. Maybe thousands. Some cause disease. Eliminating them would be a good thing because they attack the bowels and the bladder. The signs and symptoms are bloody diarrhoea and painful urination. Again, where you stand on biodiversity depends on where you sit.