Oecologia

, Volume 158, Issue 3, pp 473–483

Switching from negative to positive density-dependence among populations of a cobble beach plant

  • William M. Goldenheim
  • Andrew D. Irving
  • Mark D. Bertness
Population Ecology - Original Paper

DOI: 10.1007/s00442-008-1157-0

Cite this article as:
Goldenheim, W.M., Irving, A.D. & Bertness, M.D. Oecologia (2008) 158: 473. doi:10.1007/s00442-008-1157-0

Abstract

Interactions among species occur across a continuum from negative to positive and can have a critical role in shaping population and community dynamics. Growing evidence suggests that inter- and intra-specific interactions can vary in strength or even switch direction (i.e., negative to positive) depending on environmental conditions, consumer pressure, and also among life-history stages. We tested the hypothesis that seedlings and adults of the intertidal annual forb Suaeda linearis growing on New England shores exhibit positive density-dependence under physically stressful conditions high on the shore (i.e., greater temperatures, evaporative stress), but negative density-dependence under physically milder conditions low on the shore. Among experimental treatments of plant density (dense versus sparse) at each shore height, plant biomass, length, and number of leaves/branches were greater in dense stands high on the shore (positive density-dependence), but greater in sparse stands low on the shore (negative density-dependence). Such responses were consistent among life-history stages and generally consistent between sites. As a more direct measure of fitness, per capita seed production was also positively density-dependent high on the shore, but negatively density-dependent low on the shore. These results support the current theory predicting an increase in the frequency of positive interactions with increasing environmental stress and further emphasize the previously understated role of positive interactions in shaping and maintaining populations and communities.

Keywords

FacilitationPhysical stressSpartina alternifloraStress gradient hypothesisSuaeda linearis

Copyright information

© Springer-Verlag 2008

Authors and Affiliations

  • William M. Goldenheim
    • 1
    • 2
  • Andrew D. Irving
    • 1
    • 3
  • Mark D. Bertness
    • 1
  1. 1.Department of Ecology and Evolutionary BiologyBrown UniversityProvidenceUSA
  2. 2.Department of BiologyCalifornia State UniversityNorthridgeUSA
  3. 3.Scienze AmbientaliUniversità di BolognaRavennaItaly