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Competition Among Old-Field Perennials at Different Levels of Soil Fertility and Available Space

Jessica Gurevitch, Paul Wilson, Judy L. Stone, Paul Teese and Robert J. Stoutenburgh
Journal of Ecology
Vol. 78, No. 3 (Sep., 1990), pp. 727-744
DOI: 10.2307/2260895
Stable URL: http://www.jstor.org/stable/2260895
Page Count: 18
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Competition Among Old-Field Perennials at Different Levels of Soil Fertility and Available Space
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Abstract

(1) Competitive effects and responses to neighbours were examined by growing plants of three species (Achillea millefolium, Dactylis glomerata and Vicia cracca) singly and in intra- and interspecific pairs at low and at moderate substrate fertility. The effects of neighbours were distinguished from the effects of a reduction in available space by growing plants across a range of pot sizes. (2) Focal plants were affected by a simple reduction in available space differently than by the presence of competing neighbours. The effects of neighbours were complex, and depended on the species that were competing and on how the effect was measured. (3) Competition did not generally have greater negative effects on plant performance (using several measures of performance) at higher fertility levels and when more space was available. Nor was there a tendency for greater competitive effects at lower soil fertility and when space was more restricted. There were no apparent trade-offs in competitive abilities at different resource levels. (4) The negative effects of competition on an individual plant's growth, for the poorer competitor of a pair, was greater if the neighbour was of a different species than if the neighbour was a conspecific. (5) There was a generally consistent hierarchy of competitive effects and responses among species that reflected the hierarchy of initial seed sizes. (6) Root: shoot ratios differed among species and were altered by available space (pot size), fertility level and neighbour identity. Root: shoot ratios were most variable in response to neighbour identity in Achillea, the poorest competitor, and least responsive in Vicia, generally the best competitor.

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