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Species/area relationship
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Outline:
1. Discussion of the ubiquitous relationship between species richness and area
A. Patterns associated with k and z
2. Four possible explanations for this pattern
3. How loss of A may unexpectedly affect S via supersaturation
4. How universal is the S/A relationship?
Terms/people:
S=kAz
passive sampling hypothesis
area per se
Preston
Darlington’s Rule
supersaturated
habitat heterogeneity hypothesis
Arrhenius
extinction debt (Tilman et al.)
faunal relaxation (Diamond)
As area increases, richness increases: one of the few “laws” in ecology, according to Schoener
(1976).
First attributed to H.C. Watson (1859).
Lots of empirical evidence for S/A relationship e.g. Darlington’s Rule
Formalization of the S/A relationship - Arrhenius 1921, Preston 1962:
S = kAz
where k = y-intercept, z = slope, S=number of species, A=area
To linearize: log(S) = zlog(A) + log (k)
See Scheiner (2003) for a discussion of 6 types of species-area curves, based on various aspects
of sampling.
Properties of k and z can provide insights about isolation, extinction risk, etc.
In general, data are plotted and a curve is then fitted retroactively, which allows calculation of k
and z.
Explanations for species-area relationship:
1) area per se with respect to colonization and extinction
2) habitat heterogeneity hypothesis (see Fig. 2.14 in Mittelbach text)
3) passive sampling phenomenon
4) disturbance
BUT...
The species-area relationship is not as straightforward as it first appears…
Habitat loss, supersaturation, extinction debt, and faunal relaxation
What are we to conclude about species/area relationships? S is related to A because of a
variety of factors that vary with A, including habitat, sampling, and other properties. There is
considerable scatter about the S/A regression line (supersaturation). Nonetheless, the S/A
relationship is a reasonably robust pattern––it is the process behind it that is unclear.
Next time: the relationship between biodiversity and environmental productivity.
References:
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Arrhenius, O. 1921. Species and area. J. Ecol. 9:95-99.
Becker, P. 1992. Colonization of islands by carnivorous and herbivorous Heteroptera and
Coleoptera: effects of island area, plant species richness, and ‘extinction’ rates. J. Biogeogr.
19:163-171.
Boecklen, W.J. 1986. Effects of habitat heterogeneity on the species-area relationships of forest
birds. J. Biogeogr. 13:59-68.
Connor, E.F., and E.D. McCoy. 1979. The statistics and biology of the species-area relationship.
Am. Nat. 113:791-833.
Darlington, P.J. 1957. Zoogeography: The Geographical Distribution of Animals. Wiley, New
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den Boer, P.J. 1968. Spreading of risk and stabilization of animal numbers. Acta Biotheor.
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