Species-area curve

Species-area curve
The species-area relationship for a contiguous habitat

In ecology, a species-area curve is a relationship between the area of a habitat, or of part of a habitat, and the number of species found within that area. Larger areas tend to contain larger numbers of species, and empirically, the relative numbers seem to follow systematic mathematical relationships.[1] The species-area relationship is usually constructed for a single type of organism, such as all vascular plants or all species of a specific trophic level within a particular site. It is rarely, if ever, constructed for all types of organisms if simply because of the prodigious data requirements. It is related to, but not identical with, the species discovery curve.

Ecologists have proposed a wide range of factors determining the slope and elevation of the species-area relationship.[2] These factors include the relative balance between immigration and extinction,[3] rate and magnitude of disturbance on small vs. large areas,[3] predator-prey dynamics,[4] and clustering of individuals of the same species as a result of dispersal limitation or habitat heterogeneity.[5] The species-area relationship has been reputed to follow from the 2nd law of thermodynamics.[6] In contrast to these "mechanistic" explanations, others assert the need to test whether the pattern is simply the result of a random sampling process.[7]

Authors have classified the species-area relationship according to the type of habitats being sampled and the census design used. Frank Preston, an early investigator of the theory of the species-area relationship, divided it into two types: samples (a census of a contiguous habitat that grows in census area, also called "mainland" species-area relationships), and isolates (a census of discontiguous habitats, such as islands, also called "island" species-area relationships).[1] Michael Rosenzweig also notes that species-area relationships for very large areas—those collecting different biogeographic provinces or continents—behave differently from species-area relationships from islands or smaller contiguous areas.[2] It has been presumed that "island"-like species-area relationships have higher slopes (in log-log space) than "mainland" relationships,[2] but a recent metaanalysis of almost 700 species-area relationships found the former had lower slopes than the latter.[8]

Regardless of census design and habitat type, species-area relationships are often fit with a simple function. Frank Preston advocated the power function based on his investigation of the lognormal species-abundance distribution.[1] If S is the number of species, A is area, c is a constant (number of species in the smallest sampling area) and z is the slope of the species area relationship in log-log space, then the power function species-area relationship goes as:

S = cAz

which looks like a straight line on log-log axes. In contrast, Henry Gleason championed the semilog model:

S = c + zlog(A)

which looks like a straight line on semilog axes, where area is logged and the number of species is arithmetic. In either case, the species-area relationship is almost always decelerating (has a negative second derivative) when plotted arithmetically.[9]

Species-area relationships are often graphed for islands (or habitats that are otherwise isolated from one another, such as woodlots in an agricultural landscape) of different sizes.[3] Although larger islands tend to have more species, it is possible that a smaller island will have more than a larger one. In contrast, species-area relationships for contiguous habitats will always rise as areas increases, provided that the sample plots are nested within one another.

The species-area relationship for mainland areas (contiguous habitats) will differ according to the census design used to construct it.[10] A common method is to use quadrats of successively larger size, so that the area enclosed by each one includes the area enclosed by the smaller one (i.e. areas are nested).

In the first part of the 20th century plant ecologists often used the species-area curve to estimate the minimum size of a quadrat necessary to adequately characterize a community. This is done by plotting the curve (usually on arithmetic axes, not log-log or semilog axes), and estimating the area after which using larger quadrats results in the addition of only a few more species. This is called the minimal area. A quadrat that encloses the minimal area is called a relevé, and using species-area curves in this way is called the relevé method. It was largely developed by the Swiss ecologist Josias Braun-Blanquet.[11]

Estimation of the minimal area from the curve is necessarily subjective, so some authors prefer to define minimal area as the area enclosing at least 95 percent (or some other large proportion) of the total species found. The problem with this is that the species area curve does not usually approach an asymptote, so it is not obvious what should be taken as the total.[11] In fact, the number of species always increases with area up to the point where the area of the entire world has been accumulated.[12]

See also


  1. ^ a b c Preston, F.W. 1962. The canonical distribution of commonness and rarity: Part I. Ecology 43:185-215 and 431-432.
  2. ^ a b c Rosenzweig, M.L. 1995. Species Diversity in Space and Time. Cambridge University Press, Cambridge.
  3. ^ a b c MacArthur and Wilson. 1967. The Theory of Island Biogeography. Princeton University Press: Princeton, NJ.
  4. ^ Brose, U., A. Ostling, K. Harrison, and N.D. Martinez. 2004. Unified spatial scaling of species and their trophic interactions. Nature 428:167-171.
  5. ^ Green, J.L. and A. Ostling. 2003. Endemics-area relationships: The influence of species dominance and spatial aggregation. Ecology 84:3090-3097.
  6. ^ Würtz, P. and Annila, A. (2008). "Roots of diversity relations". J. Biophys 2008: 1–8. doi:10.1155/2008/654672. http://www.hindawi.com/journals/jbp/2008/654672.html. 
  7. ^ Connor, E.F. and E.D. McCoy. 1979. The statistics and biology of the species-area relationship. American Naturalist 113:791-833.
  8. ^ Drakare S, Lennon J.L., Hillebrand H., 2006 The imprint of the geographical, evolutionary and ecological context on species-area relationships Ecology Letters 9 (2), 215–227
  9. ^ Arrhenius, O. 1921. "Species and Area" J. Ecol. 9: 95-99
  10. ^ Scheiner, S.M. 2003. Six types of species-area curves. Global Ecology and Biogeography 12:441-447.
  11. ^ a b Barbour, M. G., Burk, J. H., & Pitts, W. D. (1980). Terrestrial plant ecology. Menlo Park CA: Benjamin/Cummings. Pp. 158-160.
  12. ^ Williamson, M., K.J. Gaston, and W.M. Lonsdale. 2001. The species-area relationship does not have any asymptote! Journal of Biogeography 28:827-830.

External links

Wikimedia Foundation. 2010.

Игры ⚽ Нужен реферат?

Look at other dictionaries:

  • Species discovery curve — In ecology, the species Discovery Curve is a graph recording the cumulative number of species of living things recorded in a particular environment as a function of the cumulative effort expended searching for them (usually measured in person… …   Wikipedia

  • Species richness — is the number of species in a given area. It is represented in equation form as S.Typically, species richness is used in conservation studies to determine the sensitivity of ecosystems and their resident species. The actual number of species… …   Wikipedia

  • Species distribution — A species range maps represents the geographical region where individuals of a species can be found. This is a range map of Juniperus communis, the common juniper. Species distribution is the manner in which a biological taxon is spatially… …   Wikipedia

  • Curve-billed Thrasher — Conservation status Least Concern ( …   Wikipedia

  • Invasive species — See also: List of invasive species, Introduced species, Pest (organism), and Weed North American beavers constitute an invasive species in Tierra del Fuego, where they have a substantial impact on landscape and local ecology through their… …   Wikipedia

  • Endangered species — An endangered species is a population of an organism which is at risk of becoming extinct because it is either few in numbers, or threatened by changing environmental or predation parameters. An endangered species is usually a taxonomic species,… …   Wikipedia

  • Introduced species — Alien species redirects here. For life on planets other than Earth, see Extraterrestrial life. For a list of extraterrestrials in fiction, see List of alien species. Sweet clover (Melilotus sp.), introduced and naturalized to the U.S. from… …   Wikipedia

  • Generalist and specialist species — With its eucalyptus only diet, the koala can be considered a specialist species. A generalist species is able to thrive in a wide variety of environmental conditions and can make use of a variety of different resources (for example, a heterotroph …   Wikipedia

  • Species of Psittacosaurus — Seventeen species have been assigned to the extinct ceratopsian dinosaur genus Psittacosaurus , although only nine to eleven are considered valid.Xu Xing Zhao Xijin. (1999). Psittacosaur fossils and their stratigraphical implications. In: Wang Y …   Wikipedia

  • Atlanta metropolitan area — Metro Atlanta redirects here. For the transit agency, see Metropolitan Atlanta Rapid Transit Authority. Metro Atlanta Atlanta Sandy Springs Marietta, Georgia MSA   CSA   …   Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”