Tansley, Arthur G. (1871 – 1951) British Botanist

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Arthur G. Tansley (1871 – 1951)
British botanist

Arthur G. Tansley was a highly influential British botanist and ecologist. He was educated at University College, London, and Trinity College of Cambridge University. He taught at University College until 1906, and then moved to Cambridge. In 1927, He became a Professor of Botany at Oxford, and he retired as a Professor Emeritus in 1937. Much of his retirement was spent working for the conservation of nature in Britain, largely by public advocacy and by working with the Nature Conservancy , of which he was the first Chairman.

In 1902, Tansley founded the influential botanical journal, New Phytologist, and was its editor for thirty years. He was a founder of the British Ecological Society in 1913, and was the editor of its key periodical, the Journal of Ecology, for twenty years. Tansley's classic book, The British Islands and Their Vegetation, was published in 1939.

Tansley was highly influential in the development of the field of ecology. He was the first person to use the word "ecosystem" to describe a basic unit of nature. He coined the word as a reduction of the phrase "ecological system" (the word "system" was borrowed from its prevalent use at the time in the field of physics). The new word was initially used at a conference at Ithaca, New York, in 1929. It was first published in 1935 in a highly influential paper in which Tansley discussed and clarified key terms and concepts in ecology. His ideas about "systems" were important in helping ecologists to understand that organisms and their communities are profoundly influenced by many non-living environmental factors, and vice versa (i.e., organisms and their communities also influence environmental factors). Much of the power of the ecosystem concept is inherent in its consideration of the complex, often unpredictable behavior of systems. The subsequent emergence of the field of systems ecology drew heavily on physics, mathematics, and computer science, as well as the more traditional ecological disciplines of plant and animal ecology. Prior to Tansley's ideas about ecosystems, ecologists mostly studied populations of plant and animal species ,or their communities, but with relatively little regard for the influence of and interaction with environmental factors.

Modern ecologists now consider ecosystems as consisting of all of the biotic (plants, animals, and microorganisms ) and abiotic (climate , soil , and other non-living environmental factors) elements of a specified area or volume. As such, an ecosystem can be relatively small (e.g., contained within a clod of earth or an aquarium) or as large as the entire biosphere of the Earth. Moreover, the state of an ecosystem at any point in time (for example, during succession following disturbance) represents the present balance between biological and abiotic influences.

Many ecologists also believe that ecosystems do not just consist of the sum of the qualities of their individual parts. Rather, there are also "emergent" properties that cannot be easily predicted, but may nevertheless be extremely important in the stability and resilience of the ecosystem. For example, some particularly important species, known as keystone species , may have a highly disproportionate influence on the integrity of their ecosystem, which could not be predicted based only on their relative contribution of biomass or productivity. Some top predators, for instance, play a key role in setting the structure of their entire food web, while certain microorganisms (such as nitrogen fixers) have an inordinate influence on overall productivity. Interestingly, in his 1935 paper, Tansley objected to some of the original, emerging ideas about holism in ecology; nevertheless, as evidence of emergent properties has accumulated, holistic ideas have taken root in the theory and practice of ecology.

Tansley is also known for his criticisms of the views of the influential American ecologist, Frederic Clements (1874-1945). Clements believed that plant communities were highly integrated and "organismic" in their qualities, and not merely a sum of their individual species. He also suggested that succession, or the process of development of plant communities after disturbance, should proceed to a highly predictable and stable climax community determined by regional conditions, particularly climate. This view was heavily criticized by another American ecologist, Henry Gleason (1882-1975), who argued that plant species respond to succession and environmental gradients in an individualistic manner, rather than in a strongly integrated, or organismic way. Tansley played an important role in this debate, and favored the individualistic hypothesis as being most realistic.

Tansley also performed important research that showed that plant species are capable of growing over a wider range of environmental conditions than they actually manage to exploit in nature. His experiments showed that competition is the key factor restricting species to a relatively narrow range of habitat conditions. This work influenced the development of the ecological concept of the niche . Modern textbooks define the fundamental niche as the inherent tolerance of a species to environmental extremes (such as high and low temperatures), and the realized niche as the range of environmental conditions that a species actually exploits in nature, being mediated by competition.

[Bill Freedman Ph.D. ]