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

Abstract

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.

Increasing density of rare species of intertidal gastropods: tests of competitive ability compared with common species

“…rare grasses in American prairies, Rabinowitz et al 1984) is a general explanation for rarity (see review by Lyons et al 2005). In contrast, our results are consistent with those of Angel et al (2006), who found no evidence that spatial distribution or abundance of the rare limpet Siphonaria compressa and the common gastropod Assiminea globulus were determined by interspecific competition.…”

The value of structuring rarity: the seven types and links to reproductive ecology

“…LA may instead be driven by competitive dynamics or other density-dependent processes unrelated to reproductive ecology, for example by a strong negative relationship with soil biota (Klironomos 2002). Locally sparse prairie grasses have been found to tolerate interspecific competition better than intraspecific competition (Rabinowitz et al 1984;Rabinowitz and Rapp 1985). Thus, locally sparse species may be sparse due to negative density dependence (strong intraspecific competition) and thus may persist in the landscape (Chesson 2000).…”

“…While plant species distributions may reflect basic demographic processes of seed production, dispersal, and establishment, the distribution of species may also in itself be a selective force and affect evolutionary trajectories. For example, species that grow in locally abundant populations may evolve to tolerate intraspecific competition better than interspecific competition (Rabinowitz et al 1984;Rabinowitz and Rapp 1985). Species of locally sparse populations may be highly dependent on pollinators to ensure reproduction when non-autogamous.…”

Competitive responses of the rare Viola elatior and the common Viola mirabilis

“…Experimental studies of competitive abilities, however, give contrasting results. Rare species can be inferior competitors (Walck et al 1999;Binney and Bradfield 2000;Lavergne et al 2003;Moora et al 2003), roughly equivalent competitors (Snyder et al 1994;Ru¨nk et al 2004) or even superior competitors (Rabinowitz et al 1984). Lloyd et al (2002) investigated experimentally the largest species sample so far and received mixed results.…”