Viewpoint: Diversity Crisis

by Lorna Salzman

Extinction is the fate of all species. If you don't believe that, all you need to do is some reading in paleontology to find out that over 98 percent of the species that have ever existed are gone.

While the fact of extinction for all species sounds dire, it really makes a statement about something positive: evolution, which means the transmutation of one species into another. Evolution is really just another way of saying speciation. Evolution, speciation and biological diversity are all about the same thing: the disappearance of the old and the appearance of the new.

This is not to say that one species always replaces or extinguishes another. Often similar species with a common ancestor co-exist without conflict because they exploit different niches. Sometimes there is competition which can lead to extinction of one species. Modern humans seem incapable of co-existing with anything but themselves and barely that, considering the inter-ethnic inter-racial and inter-religious violence we see everywhere.

Over the long haul, however, if Nature has her way, more new species evolve to exploit new niches than go extinct. The result since life began has been increased diversification of life forms. When we speak of biological diversity, we generally mean the number of different species that live in proximity in biotic communities or ecosystems. Diversity has many advantages but it is only one measure of the ecological value of a landscape or ecosystem. Traditional ecological wisdom has claimed that species diversity is a stabilizing factor in ecosystems and makes them more resilient and able to recover from environmental adversity.

This is not true under all conditions, however. It is probably true for intact ecosystems free of human interference. In tropical forests, old age, disease and weather constantly uproot large trees which fall, taking other trees and plants with them and opening up the ground to sunlight, which enables other plants to gain a foothold otherwise denied them by the absence of sunlight. But enough previously cleared areas have already grown up elsewhere to shade out opportunistic invaders so they never really gain overall.

But human-induced change, whether by bulldozers, burning or chemicals, is always on a larger scale, creating such changes in many more places over a wider area and at an accelerated rate, with regional and global implications. While evolution can repair local ecological upheavals, human-induced change can outpace evolution easily, creating artificial conditions for so long a period and over such a wide area that in effect indigenous plant and animal populations disappear.

The tropical jungle is often pointed to as the pinnacle of natural diversity and therefore of stability. Unlike northern boreal regions, which have many individuals of a very few species, tropical forests have very few individuals of a great many species. A collapse in a boreal food chain may kill off many individuals; destruction of a large piece of jungle kills off a few individuals from hundreds and hundreds of species of plants and animals in a small area and therefore has a greater impact.

This is where another level of diversity comes in: genetic diversity, which also has great ecological implications. Although we all share part of the primal gene pool from which life evolved, no two individuals are identical (even identical twins can mutate in the womb). This genetic diversity provides a species with the latent ability to adapt to environmental change, which facilitates speciation. We have learned to our sorrow, as we spray insects with pesticides, that we are actually acting as agents of evolution because the spraying is selecting for survival those insects whose genes make them resistant to the chemical. This kind of genetic variability is a prerequisite for a species' continued existence.

But genetic diversity can only be maintained through large enough numbers of individuals, that is, populations, which in turn require large enough areas of appropriate habitat. Since all populations suffer mortality, there needs to be a source for new influxes of individuals to maintain both the number and the genetic diversity. If a species falls below a certain number, it is threatened by things like hereditary physiological weaknesses, which become magnified by inbreeding. This is what apparently is threatening the cheetahs in Africa now. Once widespread across Asia, there were three species of cheetahs; now there is only one in Africa. They are particularly vulnerable to feline infectious peritonitis (FIP) and studies of infected animals show extreme genetic uniformity, due to the shrunken restricted habitat of the remaining population.

The key to all this, which you may have already surmised, is preserving species by preserving component populations, and preserving populations by preserving habitat— not in small pieces like suburban gardens but in large contiguous tracts of undisturbed undegraded habitat to maintain large numbers and therefore genetic diversity. Individuals preserved or bred in zoos, or genes stored in gene banks, are not functioning members of evolving biotic communities; deprived of their habitat and neighbors, they are really artifacts. And releasing zoo-bred species into a degraded or altered habitat dooms them because they no longer have the appropriate conditions that nurtured their appearance as new species. Because all life forms are the result of interaction between genes and environment, it is impossible to recreate a species once it has become extinct because the precise environmental conditions under which it evolved and adapted cannot be reproduced.

Diversity of species is also an indicator of general planetary health; the more species there are, the more different habitats we know exist. If species disappear, it means that the planet's ecosystems and natural resources are being destroyed and that the earth is becoming more homogeneous. The loss of genetic diversity within species means the loss of the ability to adapt to a changing environment; the loss of biological diversity means the loss of planetary life support systems.

The threats to species diversity continue to be overwhelming: overharvesting of fisheries and forests, poisoning and pollution by chemicals, heavy metals and acid rain; predator control, monocrop agriculture, ranching, desertification, and general abuse of lands. But the most definitive irreversible means is by destruction of habitat. While animal rightists deplore, not without justification, mistreatment of animals in laboratories, they seem unaware that every time a marsh is filled or a woodland bulldozed or a coral reef killed by pollution or runoff, or a tropical forest burned, hundreds, perhaps thousands, of individuals, and often whole populations, are threatened with extinction.

Habitat destruction is not recent, only its scale. The ancient Greeks and Romans deforested the Mediterranean basin by logging and goats. Yet today, when we permanently have the knowledge they lacked to preserve the environment, we lack the will and the ethics. There are innumerable reasons to preserve biological diversity: utilitarian, aesthetic, educational, medical, scientific, economic, ethical, environmental. But there are two that in my opinion stand out: the fact that ecosystems are in effect earth's life-support systems and provide basic services indispensable to all life on earth; and the fact that humans may well have an innate need to live in proximity to plants and animals.

Natural ecosystems are the products of evolution, of living and non-living things that have interacted over billions of years, and we are as much part of this as any other species and equally dependent on them. Our modern technology and machinery and agribusiness and power plants have not freed us from ultimate dependence on specific climatic and atmospheric conditions, biological cycles involving soils and the recycling of nutrients, the need for decomposition of organic matter, an abundance of genetic and species diversity for food and other needs, minerals for construction, the need for healthy balances between predator and prey, between grasslands and herbivores, the need for pure fresh water, the control of pests and blights, and of course pollination of flowers, trees and crops. All of this leads to a sort of tautology: life on earth wouldn't be the way it is if it weren't for life on earth, or to put it another way: the richness, complexity and variety of life on earth are not here by accident or by design; they and we are products of the miracle of evolution, all descendants of that first metabolizing, self-replicating organism.

To undo this web, to lop off branches of the evolutionary tree is to defile the greatest cosmic achievement, and it may well be that if we lop off one branch too many, we may discover too late that we are sitting on the wrong side of the branch. Without the diversity of Nature we would forever be trapped in the universe of our own making, of industrialism, and of urbanization, and worst of all, of uniformity, the antithesis of evolution. We are already alienated by technology, fragmented, forced into reliance on artifice and machines, into mass living and mass production. To allow this trend to continue at the expense of the rest of Nature will irrevocably burn our evolutionary bridges and make construction of new ones impossible. Treasuring biological diversity in its smallest or least appetizing details is the only means we have of preserving our own humanity.

Source: Southampton Press, July 26, 1990.

© 2002 Lorna Salzman. All rights reserved. Material may be quoted with permission.