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The Effects of Experimental Subdivision on Flowering Plant Diversity in a California Annual Grassland

J. F. Quinn and G. R. Robinson
Journal of Ecology
Vol. 75, No. 3 (Sep., 1987), pp. 837-855
DOI: 10.2307/2260209
Stable URL: http://www.jstor.org/stable/2260209
Page Count: 19
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The Effects of Experimental Subdivision on Flowering Plant Diversity in a California Annual Grassland
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Abstract

(1) Numerous species-area studies indicate that diversity should be maximized in single contiguous areas, whereas patch models often predict regional coexistence and thus enhanced total diversity, resulting from spatial subdivision of habitat. We investigated this problem experimentally in a California annual grassland by isolating experimental areas of 64 m2, subdivided into 2, 8 and 32 subunits. The areas between plots were intensively grazed by sheep. Unfenced plots measured grazing effects. (2) Species richness and species evenness (J') of flowering plants increased with increasing subdivision, with approximately 40% more species in the most subdivided treatment than in the least. Mean species richness was highest in large plots; both grazed and ungrazed and species-area curves were similar to those derived from mainland habitat islands. (3) Above-ground interspecific competition appears to be an important causal mechanism. There is evidence of strong `priority effects' in which dominant species preempt particular plots and prevent the establishment of competitors. Late-emerging and low-growing species occur primarily on plot edges and the greater relative perimeter of the more subdivided treatments may contribute substantially to their greater diversity.

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