Global Threat to Life’s Diversity
In a simplified perception, the existing biosphere is the aggregate of all organic species living on this planet. Systematic biologists assume that between 10 and 100 million species of various organisms exist on Earth, ranging from primitive microscopic viruses to complex and gigantic organisms, such as a giant sequoia tree a hundred metres tall or a blue whale, the biggest mammal weighing tens of tonnes. The estimated number of species is so inaccurate mainly because scientists have only described some 1.8 million species up to now. The remainder is believed to be ten times (or maybe more) that number.
The diversity of species on Earth tends to be referred to by the term biological diversity, or shortly, biodiversity. However, this term does not only cover the differences among species (interspecific variability). Biological diversity is also understood as variability among the individual members of a particular population (intraspecific variability) as well as differences at levels above the species – among society types, ecosystem types, various ecological formations, etc. To date, biology has described the species that are either conspicuous or important to man. We know very little about species that are small, unattractive, or lead hidden lives; therefore we know very few of them. The well-studied families include vertebrates and flowering plants. The little-known ones are, for example, viruses, bacteria, fungi, and nematodes.
Following the sober estimate, which assumes that about 15 million organic species live on Earth currently, it is certain that we have very little knowledge of the species that compose Earth’s biosphere. We only know and name somewhere over 10% of the total number of species; insects make up the majority of that figure.
Species Evolution and Extinction
Throughout the long evolutionary history of planet Earth, its biosphere has been evolving progressively. Minute and simple species have evolved into others, exerting a large influence on the development of the atmosphere and rocks, for example. The present-day atmospheric concentration of oxygen may serve as an example: but for the work of green plants, the air would scarcely contain one or two per cent of oxygen.
Species evolution has always been directed by two contrary evolutionary forces: speciation – evolution of new species – and extinction, the dying out of species. New species have evolved or seceded from parent species based on their changed genetic information. Species unable to adapt to changing conditions have died out. Progressively, perhaps more than a billion species are estimated to have ‘taken turns’ on this planet since geological prehistory.
Whereas families of organisms were mostly threatened by various changes in their natural environment due to climatic, geological and cosmic factors (temperature changes, landmass shifts, earthquakes, meteorite and asteroid impacts) in the past, human beings have been the major factor causing species extinction for the last several thousand years. Even when considering the great extinctions of the geological past, exemplified by the dinosaur extinction 65 million years ago, the natural speed of extinction is estimated at 1-3 species a year. The present speed of species disappearance, however, is a hundred times to ten thousand times faster than that. For example, it has been calculated that one mammal species may go extinct every two hundred years. But we have recorded the disappearance of 58 mammal species since 1600, which is more than 25 times the natural rate of extinction. Admittedly, these are estimates, based moreover on the knowledge of only some families of organisms. Still, the current rate of species disappearance is alarming.
The fastest rate of extinction occurs in one of the most species-rich ecosystems: the tropical rainforest. It is estimated that between 1/2 and 2/3 of all species live at that latitude. If logging continues at the current rate, the vast forests will be reduced to ruins by 2025. If this ecosystem disappears, with it will probably go the majority of the (several million) species currently living in it; all this within a few decades. Unique island biotopes with endemic species are in similar danger. It has been established that humans and the animals that accompanied them during their expansion across the Pacific tropical islands (dogs, cats, pigs, rats) brought about the extinction of up to one-quarter of the world’s bird populations 1,000-2,000 years ago.
The principal causes of the present-day species disappearance are suitable habitat reduction and alteration. Man has imprinted an entirely unnatural character on both the interior and coastal areas in various parts of the world, and such disrupted areas keep growing. Further influences include hunting and gathering of organisms for food and their destruction as pests and competitors. The latter half of the twentieth century also saw a spread in illegal trade in exotic plant and animal species, most of which are critically endangered. Every one rare specimen delivered alive to the passionate keeper means the death of many more of its kind. Numerous species, particularly the less conspicuous soil and aquatic organisms, are threatened by the growing use of chemicals in agriculture and increasing numbers of industrial accidents. Paradoxically, it is the human being that threatens Earth’s biological diversity on the one hand and exploits the biosphere by the armful as a source of food and industrial materials on the other hand. Growing numbers of tourists are also headed to former protected areas seeking recreation and relaxation.
Few of us realise that it is the biosphere itself that can reduce or even halt the current threat of global warming: the green plants, which are the only things capable of retaining one of the major greenhouse gases – carbon dioxide – during photosynthesis.
The forthcoming century will probably be a critical stage, particularly in respect of the expected global population growth. The most sober estimates are around eight billion at least; the pessimist ones reckon with twelve billion people (see above). Adequate nutrition can therefore only be obtained via improvement to the existing varieties of domesticated crop plants and animals, or additional discoveries of highly nourishing and productive plants, which may be hiding somewhere in the unexplored regions of this planet. There are few places in the world that offer humans zero benefit in terms of food acquisition.
Nevertheless, nature is not only the source of food, building materials, medicines, decorative plants and interesting animals. It is a huge factory that maintains favourable living conditions, secures clean air, soil fertility and stability, neutralises pollutants, retains greenhouse gases, etc. At the same time, it is a giant library – database in modern terminology – of all successful and failing survival strategies. Besides, the biosphere is also a source of aesthetic experiences. To ditch all this essential information, sources of material wealth and beauty irresponsibly and so quickly would probably entail the rapid demise of humanity.