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The Species-Area Curve

Stanley A. Cain
The American Midland Naturalist
Vol. 19, No. 3 (May, 1938), pp. 573-581
DOI: 10.2307/2420468
Stable URL: http://www.jstor.org/stable/2420468
Page Count: 9
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The Species-Area Curve
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Abstract

1. The so-called species-area curve expresses the relationship between areas of different sizes and the number of species found on those areas. Curves of this sort have been constructed in different ways and used for the following purposes: a) To determine the minimal area of a community. Whole stands (community individuals) are employed. b) To determine the minimum quadrat area in the single-plot method, i.e. to determine the least size of quadrat (equivalent to minimal area for the community) to be used in obtaining constancy data. c) To determine the minimum quadrat area in the multiple-plot method, i.e. to determine the least size of quadrat to be used in obtaining frequency (local frequency) data. d) To determine the least number of quadrats, of minimal size, which will give an adequate sample of a community: to be used in obtaining either constancy or frequency data. 2. The shape of the species-area curve has been used to indicate the minimal area in the above cases. The point on the curve at which the curve flattens strongly and tends to become asymptote with the x axis (on which area is plotted) is taken to indicate the minimal area. It is shown that the shape of the species-area curve depends on the ratio between the y and x axes which is used in plotting the data. Hence, the shape cannot be used to indicate minimal area, a point overlooked in the literature. The suggestion is made that a better procedure would be to locate the region of the curve where 1/10 increase in area gives 1/10 increase in species. A mechanical method of finding this point on the curve is described. Its location on the curve is independent of the ratio between x and y axes which is used.

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