Factors driving distribution limits in an annual plant community


  • Nancy C. Emery,

    1. Center for Population Biology and Department of Evolution and Ecology;
    2. Present address: Department of Biological Sciences and Department of Botany and Plant Pathology, Purdue University, 915 West State Street, West Lafayette, IN 47907-2054, USA
    Search for more papers by this author
  • Maureen L. Stanton,

    1. Center for Population Biology and Department of Evolution and Ecology;
    Search for more papers by this author
  • Kevin J. Rice

    1. Department of Plant Sciences and Center for Population Biology, University of California, Davis, CA 95616 USA;
    Search for more papers by this author

Author for correspondence:
Nancy C. Emery
Tel: +1 765 496 6931
Fax:+1 765 494 0876
Email: nemery@purdue.edu


  • • Studies examining plant distribution patterns across environmental gradients have generally focused on perennial-dominated systems, and we know relatively little about the processes structuring annual communities. Here, the ecological factors determining local distribution patterns of five dominant annual species distributed across micro-topographic gradients in ephemeral California wetlands are examined.
  • • Over two growing seasons in three vernal pools, patterns of inundation and above-ground biomass were characterized across the microtopographic gradient, population boundaries for five dominant species were documented and a reciprocal transplant experiment and neighbor removal treatment were conducted to test the relative effects of within-pool elevation, competition and seed dispersal on plant performance.
  • • Despite large differences in inundation time between growing seasons, above-ground biomass and the elevation of population boundaries remained consistent. The predicted ‘optimal’ depth for each species shifted between years, but competition and recruitment limitation restricted species’ abilities to track these conditions.
  • • The distributions of the focal taxa are primarily driven by differential responses to environmental conditions associated with different microtopographic positions along pool inundation gradients, and are reinforced by competition and dispersal constraints. The relative importance of competition, other environmental factors and dispersal patterns appear to contrast with results obtained in systems dominated by perennial plants.