Species richness

Species richnessis the number of different species represented in anecological community,landscape or region.^[1]Speciesrichness is simply a count of species, and it does not take into account theabundancesof the species or theirrelative abundance distributions.Species richness is sometimes considered synonymous with species diversity, but the formal metricspecies diversitytakes into account both species richness andspecies evenness.

Sampling considerations[edit]

Depending on the purposes of quantifying species richness, the individuals can beselected in different ways.They can be, for example, trees found in aninventory plot,birds observed from a monitoring point, or beetles collected in apitfall trap.Once the set of individuals has been defined, its species richness can be exactly quantified, provided the species-leveltaxonomyof the organisms of interest is well enough known. Applying differentspecies delimitationswill lead to different species richness values for the same set of individuals.

In practice, people are usually interested in the species richness of areas so large that not all individuals in them can be observed and identified to species. Then applying differentsampling methodswill lead to different sets of individuals being observed for the same area of interest, and the species richness of each set may be different. When a new individual is added to a set, it may introduce a species that was not yet represented in the set, and thereby increase the species richness of the set. For this reason, sets with many individuals can be expected to contain more species than sets with fewer individuals.

If species richness of the obtained sample is taken to represent species richness of the underlyinghabitator other larger unit, values are only comparable if sampling efforts are standardised in an appropriate way.Resampling methodscan be used to bring samples of different sizes to a common footing.^[2]Properties of the sample, especially the number of species only represented by one or a few individuals, can be used to help estimating the species richness in the population from which the sample was drawn.^[3]^[4]^[5]

Trends in species richness[edit]

The observed species richness is affected not only by the number of individuals but also by the heterogeneity of the sample. If individuals are drawn from different environmental conditions (or differenthabitats), the species richness of the resulting set can be expected to be higher than if all individuals are drawn from similar environments. The accumulation of new species with increasing sampling effort can be visualised with aspecies accumulation curve.Such curves can be constructed in different ways.^[6]Increasing the area sampled increases observed species richness both because more individuals get included in the sample and because large areas are environmentally more heterogeneous than small areas.

Many organism groups have most species in the tropics, which leads tolatitudinal gradients in species richness.There has been much discussion about the relationship between productivity and species richness. Results have varied among studies, such that no global consensus on either the pattern or its possible causes has emerged.^[7]

Applications[edit]

Species richness is often used as a criterion when assessing the relativeconservationvalues ofhabitatsorlandscapes.However, species richness is blind to the identity of the species. An area with manyendemicor rare species is generally considered to have higher conservation value than another area where species richness is similar, but all the species are common and widespread.

References[edit]

^Colwell, Robert K. (2009). "Biodiversity: Concepts, Patterns and Measurement". InSimon A. Levin(ed.).The Princeton Guide to Ecology.Princeton:Princeton University Press.pp.257–263.
^Colwell, R. K. and Coddington, J. A. (1994) Estimating terrestrial biodiversity through extrapolation. Philosophical Transactions: Biological Sciences, 345, 101–118.
^Chao, A.(1984) Non-parametric estimation of the number of classes in a population. Scandinavian Journal of Statistics, 11, 265–270.
^Chao, A.(2005) Species richness estimation. Pages 7909–7916 in N. Balakrishnan, C. B. Read, and B. Vidakovic, eds. Encyclopedia of Statistical Sciences. New York, Wiley.
^Webb, L. J.;Tracey, J. G.;Williams, W. T.;Lance, G. N. (1969),Studies in the Numerical Analysis of Complex Rain-Forest Communities: II. The Problem of Species-Sampling. Journal of Ecology, Vol. 55, No. 2, Jul., 1967, pp. 525-538,Journal of Ecology, British Ecological Society,JSTOR 2257891
^Scheiner, Samuel M. (October 17, 2003). "Six types of species-area curves".Global Ecology and Biogeography.12(6). Wiley: 441–447.Bibcode:2003GloEB..12..441S.doi:10.1046/j.1466-822x.2003.00061.x.ISSN 1466-822X.
^Waide, R. B. et al (1999) The relationship between productivity and species richness. Annual Review of Ecology and Systematics, 30, 257–300.

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Species richness

Sampling considerations[edit]

Trends in species richness[edit]

Applications[edit]

See also[edit]

References[edit]

Further reading[edit]