What is rarity? Image of a black Jaguar and a spotted Jaguar (same species, different morphs) courtesy of www.shutterstock.com
The Kingdom of Rarities
Edgar Vaid reviews Eric Dinerstein's latest book, and whilst reflecting on our apparent obsession with seeking out the 'rare', discovers that it's all rather relative.......
In 1859, long before the IUCN was born, or started compiling its famed "Red List of Threatened Species", a scientist wrote: "Rarity is the attribute of a vast number of species of all classes, in all countries". A clue to the source of this key insight is of course the year - yes, Charles Darwin writing in "On the Origin of Species".
That this eminent Victorian was one of the first people to draw attention to the significance of biological rarity is acknowledged by Eric Dinerstein in "The Kingdom of Rarities" which, if written by Darwin in say 1867, might have been called "On the Origin and Ubiquity of Rare Species", or some such title with a similarly sonorous ring to 21st Century ears.
"Kingdom" is not used here in the sense of one defined geographical part of the Earth's biosphere, but rather a collective noun for all our planet's rarities. The tacit impetus behind Dinerstein's book suggests we might pose a fundamental question: "Is the human species hard-wired to seek out, collect, and treasure what we believe, or know, to be rare?" This instinct (if we may call it that), is found more strongly in some individuals than others, and manifested in a huge range of collecting categories, whether of natural objects (eg fossils) or man-made artefacts (eg vintage cars).
Just as the naturalist may be spurred on to seek out charismatic rarities such as the snow leopard, or the more humble (but possibly as rare) violet click beetle, so this behavioural pattern is replicated in completely different spheres - the philatelist, for example, coveting a specimen of the almost legendary British Guiana 1856 one cent black on magenta postage stamp, or the numismatist dreaming of a 1344 gold florin.
But is the naturalist's desire for encounters with rare species any different from the acquisitive drive of the rare coin seeker? Well, in one respect we may discern a crucial difference. The gold florin's proud owner might easily suffer some chagrin on learning of a metal detectorist unearthing a hoard of 150 examples - because of his own coin's potential loss in market value. Conversely, on hearing about the discovery of a previously unknown population of 150 Javan rhinos, all naturalists would be thrilled and delighted.
However, florins and rhinos apart, there arises also the question of how we define ‘rare', and this is not simply a semantic exercise. Thus you could easily regard your local Home Counties English bluebell wood as something rather commonplace, whereas in an international context it's not only relatively rare, but with a future possibly threatened by hybridisation with Spanish bluebells. On the other hand, exotic species such as the Bloody Bay poison frog of Trinidad or Cuba's Fernandinas flicker bird are also locally rare in their own restricted ecological niches.
Categorising a living thing as ‘rare' is often a response to comparing its numbers with that of a relatively common species which shares its ecosystem or taxonomic group. But the question of ‘rarity' may also be considered in other ways. For example, with only 3,000 greater one-horned rhinos existing globally, it's quite reasonable to view them as rare. However, they are relatively common compared to the Javan rhino, of which an estimated fewer than 50 remain.
Aside from wrestling with definitions, Dinerstein makes the arrestingly counter-intuitive suggestion that owing to their narrow ranges or low densities, or both, the majority of Earth's species are in fact rare. With thousands of potential species to choose for inclusion in his "Kingdom", he explains his selection process as picking "species that best illustrated the various conditions of rarity that I knew something about .......... and also that conservation groups like my own, WWF, have devoted a great deal of effort to preserving".
This serves his central purpose of trying to answer the perennial conundrum of why some species are naturally rare, and others so abundant, matters which are considered when the study of rarity is treated as a science itself; eg "Are all rare species, by definition on the verge of extinction? Have all species that are currently rare been historically rare? Which species common now are likely to become rare?"
Questions such as these have led some scientists to dub Earth's current epoch (traditionally called the Holocene) as the Anthropocene or the Homogenocene. The former, perhaps more widely recognised term, is encapsulated by the view that "the human footprint extends everywhere in nature". The latter refers to the human introduction of plants and animals far beyond their original ranges, potentially resulting in the biological homogenisation of the Earth's eco-systems, as each fills up with invasive species.
Their two most pre-eminent representatives in the English context are usually sighted as Japanese knotweed and the grey squirrel. Indeed, I was conscious of the irony (and slight dysphoria) when viewing the ‘red squirrels of Formby' - yes, solemnly making a 300 mile round trip to visit a nature reserve devoted to the conservation of our native Sciurus vulgaris which, only a century ago was so widespread in most parts of the country that it was taken for granted.
Setting aside the familiar story of greys' larger size, more flexible diet, and squirrel parapoxvirus they carry which is fatal to reds but not themselves, one sobering statistic stands out - today we have countless millions of Sciurus carolinensis - reputedly descended from just one pair introduced to our shores as a novelty show-creature in 1876.
That our native reds have not succumbed completely to the introduced greys may be of some comfort when we compare the effects of introduced species on the native fauna of islands smaller than Britain. Particularly vulnerable are places such as Hawaii, where the lowlands' dense native forests have been replaced by introduced trees such as Indian banyans, Australian eucalypts, and Brazilian jacarandas - leading to the inexorable decline of honeycreepers.
Hawaii's roadsides include plants from Bermuda or the Seychelles, which display large, showy flowers, but are ignored by the native birds - a classic example of imported human aesthetics inadvertently winning out over the habitat requirements of local fauna. In fact the Hawaiian Islands provide a case study of human intervention's malign effects, starting perhaps a thousand years ago when the Polynesian autochthons accidentally introduced stowaway rats - resulting in the early predation and extinction of many bird species.
However, a finding of chorology suggests that not all rarity may be ascribed to human activity - either historic or recent. For example, the pristine and uninhabited Foja uplands of New Guinea's rain forests are species-rich, but because population densities are naturally low - whether the species in question is the pale-billed sicklebill or golden-mantled tree kangaroo - individuals are rare.
Dinerstein speculates that "there may be something about the very nature of rain forests that prevents some species from becoming super-abundant ...... the sheer number of species in the eco-system leads to a novel mechanism at work - a kind of diffuse competition in which the interactions of many species keep others in a limited range or at low density". This implies that even in a region with no history of human habitation, rarity amongst species may be the norm.
An intriguing historical question is posed about the species of New Guinea: How can the extinction times of rare birds and mammals be predicted from the arrival dates of Christian missionaries? Before they came, strict hunting taboos were held by mountain clans, either in areas where they believed spirits dwelt, or during some animals' breeding seasons. Whatever the reasons for honouring such traditions, the incidental ecological effects were beneficial, especially to species which reproduced slowly. When priests successfully urged ‘converts' to drop their pagan beliefs, one malign result was over-hunting.
Conversely, in Bhutan, the dominant religion of Tibetan Buddhism means that "humans coexist peacefully with wildlife and treat rare species with respect and compassion". Fortunately this translates into monarchical-influenced Government policy, Bhutan's king using "gross national happiness" as a measure of his subjects' well-being. Eudemonic motivated laws protect the full range of Himalayan eco-systems - from lowland jungles to snow-covered peaks, export logging is banned, and there is a commitment to keep 60 percent of the country under native forest cover.
Thus our superficial western image of Bhutan as essentially a colourful medieval relic of a society is quite wrong in one respect. In the sphere of nature conservation it's ahead of all industrialised nations, even if this does extend to designating Sakteng as a wildlife sanctuary because it's the preferred habitat of the mythical yeti!
Large cats such as the jaguars of Peru's Tambopata region are very real, but almost match the yeti's elusiveness. They are rare to encounter because of a naturally low density, itself a reflection of their position at the food pyramid's apex. Large carnivores require a sizeable population of prey species - preferably the white-lipped peccary in our Peruvian example. Transposing this ecological structure to India, researchers found that tiger density can be predicted for a given habitat based on its density of prey species - in this case deer, boar, and bison.
Such nuggets tumble from almost every page and, with few exceptions, Dinerstein's text is admirably accessible to the non-scientist. Indeed, stylistically it might be characterised as a euphonious fusion of Gerald Durrell and David Attenborough. Besides the passing nods to ethnography, the book is also enlivened by occasional poetic touches, and an unexpectedly numinous regard for the aesthetics of the flora and fauna encountered. An extra bonus is the inclusion of Trudy Nicholson's dozen or so elegant illustrations.
Edgar Vaid is a freelance book reviewer and writes the readers highlights for each bimonthly edition of Resurgence & Ecologist magazine. He can be contacted at firstname.lastname@example.org.
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