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Competitive Abilities of Sparse Grass Species: Means of Persistence or Cause of Abundance

Rabinowitz, Deborah, Rapp, Jody K., Dixon, Philip M.
Ecology 1984 v.65 no.4 pp. 1144-1154
grasses, greenhouses, habitats, planting, population size, seedlings, tillers
Sparse species have chronically small local population sizes, even though they occur in several habitats over a wide geographic range. Greenhouse de Wit replacement series with seven species of sparse and common perennial grasses of tallgrass prairie were performed with seedlings and tiller fragments for 5, 10, and 15, mo. As younger and older seedlings, sparse grasses overyielded and were advantaged by the interaction with common grasses. The common grasses underyielded and were disadvantaged in mixture with sparse grasses. As tillers, the interaction was less antagonistic, and both common and sparse grasses either overyielded or were unaffected by the interaction. Seedlings of sparse species were largest when planted in low proportion, surrounded by individuals of a common grass. Because the sparse species are not disadvantaged by interactions with their common neighbors, their competitive abilities are not implicated as a cause of their local rarity. Rather, the good competitive abilities of these sparse grasses are best viewed as a mechanism that offsets the hazards of low density and makes local persistence more likely.