Size-dependent foraging efficiency,cannibalism and zooplankton community structure |
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Authors: | E Wahlström L Persson S Diehl P Byström |
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Institution: | (1) Department of Biology, Wheaton College, Norton, MA 02766, USA e-mail: scott_shumway@wheatonma.edu Fax: +1-508-2858278, US |
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Abstract: | Only recently has the importance of positive interactions among plant species in structuring natural communities been supported
by experimental evidence. Most studies have focused on interactions between a pair of species at a single life-history stage.
In this study positive interactions between a woody nitrogen-fixing shrub (Myrica pensylvanica) and two herbaceous sand dune species (Solidago sempervirens, Ammophila breviligulata) which frequently grow beneath shrub canopies are examined throughout the life cycles of the herbaceous species. Comparisons
of S. sempervirens and A. breviligulata growing beneath and outside M. pensylvanica shrubs show that plants growing in association with shrubs are larger, are more likely to flower, produce greater numbers
of flowers and seeds, have higher midday xylem water potentials, have higher tissue nitrogen concentrations, and have higher
photosynthetic efficiencies. Measurements of environmental conditions show that areas beneath shrubs are more shaded, have
lower soil temperatures, and have higher soil nitrogen levels. The results from experimental manipulations designed to test
the effects of Myrica shrubs on understory species suggest that the observed differences in plant performance are strongly influenced by canopy
shading and soil nutrient enrichment associated with the shrubs. The results demonstrate that M. pensylvanica facilitates growth, reproduction, and recruitment of S. sempervirens and A. breviligulata growing beneath it. This study, one of the few to examine positive interactions at different life-history stages, supports
previous predictions that positive interactions may be particularly important in plant communities characterized by physiologically
stressful conditions.
Received: 21 July 1999 / Accepted: 18 January 2000 |
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Keywords: | Ammophila breviligulata Facilitation Myrica pensylvanica Sand dune ecology Solidago sempervirens |
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