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Abundance-Range Size Relationships in Stream Vegetation in Denmark

Tenna Riis and Kaj Sand-Jensen
Plant Ecology
Vol. 161, No. 2 (2002), pp. 175-183
Published by: Springer
Stable URL: http://www.jstor.org/stable/20051268
Page Count: 9
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Abundance-Range Size Relationships in Stream Vegetation in Denmark
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Abstract

Streams experience a constant redistribution of species and in-stream plant stands due to the extensive disturbance caused by flow variation, high continuity of habitats and efficient dispersal in the stream network. These conditions increase the homogeneity of environmental conditions and composition of vegetation among stream localities and are likely to promote a positive interspecific relationship between abundance and range size through mechanisms of metapopulation dynamics and use of common widely distributed resources. Using data from 206 localities in 29 stream systems distributed throughout the cultivated lowlands of Denmark, we examined the overall relationship between local abundance and geographical range size of the vascular flora. We found a significant positive relationship for all species at all stream localities and an even stronger relationship for ecologically similar species such as obligatory submerged or amphibious species. The amphibious species, which can easily disperse by seeds between stream systems and by vegetative growth from permanent bank populations to the open streambed, had a significantly stronger abundance-range relationship than obligatory submerged species probably due to more effective dispersal. The importance of metapopulation dynamics was also supported by the fact that species in seven of the ten stream systems with multiple localities showed a stronger positive relationship than the overall relationship for all streams, while the relationship for distinct stream habitat types of the same width and lengthwise locations in different stream systems did not show a stronger positive relationship than the overall relationship. The few obligatory submerged species having a high local abundance and low range size could not be regarded as specialist species on narrowly distributed resources. Their occurrence is probably a temporal phenomenon due to the profound habitat destruction during the last 100 years, restricting to a few localities the species that were previously widely distributed. Many species presently survive in a marginal position of low range size and low local abundance. They face a double jeopardy of extinction and may have difficulty benefitting from environmental improvements.

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