An introduction to the first of four sections of an intended series on the infinitely complex issue of biodiversity. By Colin Tudge
What, first of all, do we mean by “biodiversity”? Most obviously it is taken to mean the number of species in a given habitat. But this immediately raises a whole raft of issues. What, for starters, is a species? The concept is not as straightforward as it may seem. And, of course, diversity doesn’t just mean number of species. Just as important is the genetic diversity within each species (many modern populations of animals in particular are dangerously inbred). We should also consider the variety of ecotypes in any one ecosystem or area –“ecotype” in effect meaning a way of life, as in flying, arboreal, fossorial (burrowing), aquatic, littoral, carnivorous, herbivorous, scavenging, etc.
Crucially, too we need a variety of habitats. So it is for example that cities and suburbs may be very rich in species partly because they provide so many intricate niches, and so tend to combine creatures from different wild habitats including woodland, grassland, cliffs and some wetland (as in all those garden ponds); partly because they provide easy pickings from bird tables and half-eaten pizzas; and partly because suburbanites (apart from their liberal use of pesticide) are often more welcoming than country folk.
Hundreds of creatures worldwide take advantage of this seeming benison including versatile generalists like pigeons and foxes but many others too including some that seem most unlikely. Thus turnstones fossick for titbits in the carparks of Scarborough; peregrine falcons in many great cities the world over treat tall buildings as cliffs from which to swoop down on the pigeons; and in their native countries the world over animals as diverse as hermit crabs, hill sheep, polar bears and orang-utans supplement their diet by raids on dustbins (alongside of course the usual generalists like foxes, crows, gulls and cranes which flock to feed on spoil heaps). Asian water monitors, second in size among lizards only to the Komodo dragon, flourish in rivers and sewers and parks in many a South-East Asian city, feeding on rodents and crabs and whatever they can get their jaws around, and also on carrion including, in Sri Lanka, human corpses. Spotted hyaenas have made themselves at home in the ancient Ethiopian city of Harar, while Mumbai harbours the world’s greatest concentration of leopards. Strangest of all perhaps are the hippos that in and around their habitual rivers and lakes are the most dangerous mammals in Africa and yet in the twilight hours wander peaceably enough around the suburbs of St Lucia, in South Africa.
Some of the creatures on that list can injure or even kill people but as long as they are left alone they usually rub along well enough with their human neighbours and some, like Harar’s hyaenas, may become positively companionable when treated kindly. (Does anywild animal ever attack human beings simply out of viciousness?) Suburbs and cities also harbour a great many exotics including some that have escaped from gardens or menageries to become minor or major pests, which in Britain range from rhododendrons to ring-necked parakeets to Mexican fleabane, a pretty garden escape which seems these days to be everywhere. But suburbs rarely for example include representatives from specialist habitats such as dunes.
A country that was all suburb, as southern England seems in danger of becoming, might seem impressively species-rich but in truth would be a pastiche of what a flourishing ecosystem should be: a transient, arbitrary and sometimes bizarre assemblage of creatures squeezed out of their natural habitats or introduced for their decorative value, cashing in as best they can on human enterprise and profligacy. In short, mere diversity – at least when measured simply by number of species – can be very deceptive. The legislators framing the law on BNG include ecologists who obviously are aware of all this and more. But they and the lawyers and politicians have got their work cut out to frame legislation that truly reflects reality and is truly of value. Clearly, too:
Diversity isn’t all that matters
Abundance matters too: not too many of any one creature in any one place – and not too few. A very big population is no guarantee of long-term safety (vide the rapid collapse of America’s passenger pigeons, the American chestnut, and bison at the end of the 19th century and the start of the 20th – and of all the subspecies of tigers and both species of elephant over the past 100 years or so). But there is some safety in numbers. Big populations are less likely to be wiped out overnight by some random storm or whatever and are less likely to become dangerously inbred. (The matter of abundance warrants more discussion in future articles. I wrote a book about it in the early 1990s called Last Animals at the Zoo, published first by Hutchinson and then by OUP).
Then there’s the matter of triage. More and more species of many kinds are being pulled from the brink by heroic measures including captive breeding in various forms; but heroic rescue is not always possible and far too many creatures are in danger to provide intensive care for all of them and so we are obliged to choose what to focus on. In practice, various criteria are employed to help us decide which to choose and often the wrong decisions are made. Notably, would-be captive breeders who seek to make a serious contribution to conservation should contrive to maximize the genetic diversity within the inevitably small populations that they are able to accommodate. But until recent decades curators of zoos, and private collectors even today, were and are wont instead to breed their captive animals as if for the show-bench – the tallest giraffe, the handsomest lion or whatever – or else focus on the rarities, like collectors of antiques. Thus, various maharajahs have sought to multiply white tigers. But pale-skinned tigers are simply strains of mainstream tigers that just happen to harbour particular mutant genes. In the wild they are less viable than the more usual types because they are more conspicuous and find it even harder than the standard ones do to creep up on their prey.
More broadly, it is very difficult indeed to see which creatures in any ecosystem make the most positive contribution to the wellbeing of the whole, and it is all too easy to get it wrong with disastrous results – as discussed in Section III. Perhaps the greatest single lesson of the past few decades is the absolute importance in all ecosystems of microorganisms. Notably, the microbes that live in the guts of all animals, were until recently seen simply as freeloaders with an eye to mischief. Now they are seen as essential players in digestion, absorption, and detoxification – so much so that nutrition as a whole is increasingly perceived as an exercise in ecology. All of us depend upon our uninvited cargo of microbes and must seek to maintain a harmonious relationship with them. Indeed, all organisms above a certain size should be seen as ecosystems in their own right, each providing board and lodging sometimes to thousands of other species, which in turn interact with far more.
Most strikingly, perhaps, viruses are now emerging not simply as nature’s spivs and villains as they have generally been viewed since they were first described in the late 19th century, but as key players in evolution. They transmit genes between unrelated organisms – not only between unrelated species but even between kingdoms and indeed between domains (see section II). It becomes more and more obvious that without such “horizontal transmission” life on Earth would be sadly impoverished. Creatures like oak trees, say, or indeed ourselves, would not have come into being if viruses hadn’t been on hand to nudge our evolution. Many a medic must have thought how sweet it would be to eliminate all viruses and all the foul diseases they bring with them but the lesson here, as so often, is that we must be careful what we wish for. As folk wisdom has it — “Nature knows best!”, and it is harder than is often supposed to improve on Nature (or indeed on folk wisdom).
Finally, in addition to diversity and abundance, there’s the crucial matter of what might be called Interactiveness. (I can’t find a suitable more formal term for this. If anyone knows one, please let me know).
By interactiveness I mean the sum of all the relationships between the various players in a given ecosystem: the dynamism of the whole thing. After all, the inventory of species is just the cast list, and what really matters is how the cast members interact with each other, and the cast as a whole affects and is affected by the rest of the world. As Hamlet said (Act 2 Scene 2): “The play’s the thing!” The cast list in any one ecosystem may be very large but it is always finite and theoretically should be countable – but the number of possible interactions between all the players in a mature ecosystem is potentially infinite. Indeed, the relationships of any one creature with others of its own and very different kinds may boggle the mind. All trees for example depend on soil fertility which one way or another is mostly laid on by bacteria and archaea. Trees like acacias and other legumes, and many non-legumes too including the alder, harbour bacteria in their roots that convert atmospheric nitrogen into soluble ions that for plants are nutrients; and all macroscopic plants it seems exude sugars from their roots specifically to nurture the micro-organisms in their immediate surroundings.
Most plants too including all trees (are there exceptions?) are assisted by mycorrhizal fungi – sometimes up to 150 species of fungi on and in a single tree. In a mature wood the mycorrhizal hyphae link all the trees of all species into a single super-organism. Many trees too (including the vast majority in the tropics, which has the most tree species) have enormously complex relationships with a host of insects, birds, bats, lemurs or whatever, who effect pollination and disperse their seeds. Most intriguing of all perhaps is the relationship between the 700-plus species of figs and the corresponding suite of fig-wasps that pollinate them (which I describe at length in The Secret Life of Trees (Penguin 2006).) As I have commented often on this website, nature all in all is more cooperative than it is competitive, and if it were not so life would be impossible. The neoliberal claim that it is “natural” to compete with everyone else for material advantage is wrong headed at every level, and may indeed be the most damaging idea in the modern Zeitgeist.,
All ecological relationships take decades to unravel, and are still being unravelled. If all the biologists in the world spent their whole lives describing the intricacies of all the world’s ecosystems they still would need more time than is left in the life of the Earth to get to grips. Yet we sweep entire ecosystems aside while seeking at the same time to protect them with ad hoc and formulaic legislation. The legislation may well be necessary, but it clearly is not sufficient. Jesus said in a somewhat different context “Forgive them, for they know not what they do”. When the living world is being devastated it is not obvious that post hoc forgiveness quite meets the case, whoever does the forgiving.
All in all it’s clear that our knowledge of what goes on in the natural world must always fall very far short of the reality – and that the metrics by which scientists aspire to get to grips with ecological reality must always be crude. Diversity is part of what’s needed to keep the biosphere in good heart but only a part. Of all the relevant factors it seems the easiest to quantify – but even here, quantification is far harder than it may seem.
Abundance too is quantifiable – but again it is very difficult to judge its significance. To what extent, for example, does the abundance or rarity, or the changing fortunes of any one species over time, affect the wellbeing of the ecosystem as a whole?
Interactiveness, the thing that matters most, simply cannot be captured with statistics. In the end (as I discuss in The Great Re-Think, Pari 2021) it seems we can best appreciate the intricacy and subtlety of ecosystems by employing the language of the music critic — invoking ideas of tone and harmony and rhythm and counterpoint and all the rest. Beyond doubt, science is essential and quantification as far as it can be achieved is essential too if we are to continue to survive on this Earth in such large numbers and achieve some harmony with or fellow creatures. But understanding requires us to move beyond quantifiable science and into the realms of aesthetics and spirituality.
Action without certainty and the absolute need for humility
Crucially, too, we need to acknowledge that however much we discover about the natural world, our knowledge will always be just a fragment of what there is to know. Scientists above all need to be humble, at least intellectually, as indeed the best ones are: Newton, John Ray, Darwin, Einstein, Bohr, all stressed as Socrates did their own ignorance. Some scientists though are anything but humble, and evidently think that they already know enough to control the world, if only governments and the rest of us would follow their instructions..
For physicians qua physicians humility comes with the territory. Every true physician knows that the outcome of his or her ministrations can never be certain. Only quacks and purveyors of snake-oil offer certainty. But physicians are obliged to act in the absence of perfect knowledge. Decisiveness is forced upon them. Some politicians are humble too, like physicians – but politicians are always pressured by public opinion to take action even when the outcome is extremely uncertain. And in truth, some politicians, like some scientists, are supremely arrogant, keen to impose their will on the rest of us and on the world whatever the likely outcome. To invade another country for example is arrogance writ large, but it happens all the time.
For all our science the natural world in the end is beyond our ken and all attempts to influence its machinations must be essayed with extreme caution. But political and economic reality, and the ticking clock, oblige us, and in particular oblige governments, to act, and in a desperate and decaying world inaction does not seem to be an option. Concerted and effective action requires clear guidelines – which is what the BNG legislation is intended to provide.
Well, it could be a step in the right direction. Whatever benefits it may bring, however, the concept of BNG clearly is not enough. It is at best an attempt to solve or at least to ameliorate a huge and urgent problem using the political and technical tools and ideas that are now available to us, without unduly upsetting the status quo. But the status quo won’t do. If we really do take the world’s biggest problems seriously then we really do need to re-think everything from first principles, from the practicalities of everyday life to the highest reaches of science, morality and metaphysics, and everything between.
And that, of course, is not happening.
An intro to Section II of this series –“How diverse is biodiversity? — will follow as soon as I can get my act together.
Share this article:
Leave a Reply