I was listening to some conservationists on the radio discussing the rate of loss of species and how this was a catastrophe in the making for biodiversity. It was an unsatisfactory talk mainly because they all made what I thought were quite unjustified assumptions. It was more about political advocacy rather than any attempt to argue based on evidence.
The “politically correct” view is that biodiversity (measured as the number of species in existence) is a “good thing” and that more species is “good” and fewer species is “bad”. Saving endangered species is also a “good” thing. That species are becoming extinct at an alarming rate means catastrophically that a 6th mass extinction is nigh. But I find this viewpoint lacking in substance. We have more species existing today than ever before. Probably too many. Mass extinctions have helped “clean out” the rubbish that evolution throws up. Extinction rates may be high but that is hardly surprising when the number of species is so high. A 6th mass extinction may, in fact, be necessary. More species and more biodiversity is not always a good thing.
The fossil record shows that biodiversity in the world has been increasing dramatically for 200 million years and is likely to continue. The two mass extinctions in that period (at 201 million and 66 million years ago) slowed the trend only temporarily. Genera are the next taxonomic level up from species and are easier to detect in fossils. The Phanerozoic is the 540-million-year period in which animal life has proliferated. Chart created by and courtesy of University of Chicago paleontologists J. John Sepkoski, Jr. and David M. Raup.
An endangered species is one whose population is low and dangerously in decline. If numbers of individuals of a species are that low, then that species has already become irrelevant in its contribution to the functioning of the biosphere. It may well be a matter of regret, just as there is always regret when a language becomes extinct from disuse. But apart from providing entertainment value for humans, the saving of a few members of a doomed species provides no real benefit for the functioning of the biosphere. I would be very sorry to see tigers becoming extinct, but the reality is that their numbers are so low that they play no significant part in the sustenance of the biosphere. The role of a predator species is primarily to control the population of its prey. From a biodiversity point of view they are already irrelevant. Saving the tiger has nothing to do with maintaining a healthy biodiversity and everything to do with human entertainment (including that of the conservationists) and “feeling good”.
(I am of the opinion that helping an endangered species to survive can be desirable but then “conservation” should be based on helping that species to adapt genetically rather than to freeze it into an artificial habitat – zoos and reserves – to which it is not suited).
At one time there was just a single species that all life derives from – perhaps even just one living cell. (And even for creationists, all the diversity of humankind has derived from a single mating pair – and the raging incest that that implies). There was no biodiversity to begin with. Genetic variation with each generation and genetic mutations then caused new species to come into being, first to fill up the spaces that the prevailing environment allowed and then to adapt to changing environments. If each generation of the first species had bred true there would, of course, be no biodiversity. Genetic variation and empty space in the environment led to growth of species. Overcrowding of a given space or drastic environment change cause the decline and extinction of species. The prevailing level of “biodiversity” at any time is not then some target to be achieved, but just the current balance between the birth and death of species.
It seems almost self-evident to me that, for any given environment there must be an optimum number of species, with particular combinations of characteristics, which allow the ecosystem or biosphere to be in a self-sustaining equilibrium (not growing or declining but self-sustaining). This optimum will vary depending upon the characteristics and interactions between the particular species existing and the available space in the prevailing environment. Then, having fewer than the optimum number of species in that environment would mean that all the complex interdependent, interactions between species that seem to be necessary for sustaining each of the participating species would not be fully developed. I say “seem” because it is not certain that all interdependencies are necessarily of benefit to individual species. “It is the entire ecosystem which benefits” I hear some say, but even that is more an assumption than a conclusion.
But what would happen in such a situation? If the interactions are truly necessary, then some of these sub-optimal number of species should logically be on the way to stagnation or to extinction. But it is not certain that some new equilibrium will not be reached. One species too few for a given environmental space will only lead to the space being occupied by an existing or a new species. One species too many for a given space will lead to the extinction of a redundant species or of a number of species existing under genetic stress, until genetic variation reduced the stress. The interactions between species in any environment are not planned in advance. They are just those that happen to prevail and survive because they succeed in the environmental space available. Too few species will give an increase of species until overcrowding reduces the number of species. A rapid change of environment and a reduction of the space available must give a decrease in the number of species making up the optimum for a self-sustaining biosphere.
Generally species of plant life have increased in the wake of human habitations.
For example, more than 4,000 plant species introduced into North America during the past 400 years grow naturally here and now constitute nearly 20 percent of the continent’s vascular plant biodiversity.
But then we try to eradicate “invasive” species even though that represents a decrease in biodiversity. Clearly some biodiversity “is not good”. We hunt down successful species as pests when they reach and thrive in new or empty environmental spaces. We protect and support unsuccessful (failed) species in the name of conservation and biodiversity. We have no qualms in trying to eradicate insects, microbes and bacteria which cause human disease even if biodiversity is consequently reduced. From the perspective of the biodiversity of the genetic pool, losing a species of some unknown bacteria may be just as significant as the extinction of the elephant.
The rate of growth of the human species has meant that other species have not been able to adapt fast enough – genetically – to their loss of habitat or the increase of competition. The environmental space available to them has drastically reduced. But that is reality. Creating artificially unsustainable habitats will not change that. The optimum level of biodiversity for the environmental space today is different to that of 100 years ago. Biodiversity cannot be considered independently of the environmental space available. Conservationism which seeks to maintain the wrong level of biodiversity for the available space seems to me to be both futile and stupid. Especially when conservationism has no idea what the “optimum” level of biodiversity is and whether the current level lies above or below the optimum level.
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