Geoscience Reference
In-Depth Information
KEY POINTS
1
Diversity is measured by the Shannon index, which takes into account the number of species and the
evenness of distribution of species. Several indices are available to measure stability, depending on the
aims and nature of the investigation.
2
The relation between diversity and stability has come under close scrutiny, as serious doubts have arisen
concerning the old adage 'more diversity means more stability'. Hence it is important to define carefully
a priori what particular property of stability is being studied. Diversity and stability are both relative
concepts; they need to be defined in terms of geographical space, community and time.
3
The latitudinal gradient of biodiversity, with fewer species the higher the latitude, has exercised the minds
of biogeographers for many years. There are many probable contributory causes, with the true explanations
likely to vary from biome to biome, and from taxon to taxon.
4
Fragility of ecosystems is an important index. Advances in understanding are coming from field, laboratory
and computer studies. The concept of 'keystone species' is promising in offering new insights.
5
The upsurge of interest in biodiversity at an international level has been brought about by the increasing
concern for the diversity of species, especially in a number of tropical locations. What is certain is that
many more species on Earth have yet to be discovered than are at present known. Only by the scientific
study of diversity and stability, according to the principles and methods discussed in this chapter, will it
be possible for effective policies to be formulated at the international and national levels, and for those
policies to be translated into action programmes at a more local level.
FURTHER READING
Gaston, K. J. and Spicer, J. (1998) Biodiversity: an introduction, Oxford: Blackwell. A readable and approachable introduction
to the many strands of the biodiversity debate.
Groombridge, B. (ed.) (1992) Global Biodiversity: the status of the Earth's living resources, London: Chapman & Hall.
A detailed study of the current situation regarding threats to species and to ecosystems of high diversity.
Tudge, C. (2005) The Secret Life of Trees, London: Allen Lane. A readable and comprehensive account of tree species,
their distribution, evolution and uses. Devotes much space to the debate on tropical tree biodiversity, and the many
hypotheses proposed in explaining global gradients of tree diversity.
UN Environment Programme (1995)
Global Biodiversity Assessment, Cambridge: Cambridge University Press. The official
and detailed study coming out of the Rio conference on global biodiversity. Packed with useful discussion and examples.
Wilson, E. O. (1992) The Diversity of Life, London: Penguin. This is perhaps the most scholarly and up-to-date account
of the nature and causes of diversity. Very readable and full of examples.
WEB RESOURCES
http://www.unep-wcmc.org T
he World Conservation Monitoring Centre (WCMC) at Cambridge is managed by the United
Nations Environment Programme (UNEP). It produces policy documents on biodiversity, and is a source of many data
on biodiversity and conservation across the globe.
http://www.iucnredlist.org T
he International Union for the Conservation of Nature (IUCN) (also known as the World
Conservation Union) maintains lists of threatened species giving rise to concern. It publishes Red Data topics for the
different classes of organisms whose future is threatened.
