Submitted to: Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 11/4/2011
Publication Date: 11/14/2011
Citation: Espeland, E.K., Rice, K.J. 2011. Survivorship and plant-plant interactions: maintaining the evolutionary potential of restored populations. In: Willoughby, J.W., Orr, B.K., Schierenbeck, K.A., and Jensen, N.J. [eds.], Proceedings of the CNPS Conservation Conference: Strategies and Solutions. California Native Plant Society, January 17-19, 2009, Sacramento, CA. pp. 42-48. Interpretive Summary: When plant populations are small and isolated, genetic drift can cause loss of genes from populations, genes that could be useful in adaptation to environmental change. Genetic drift can prevent a population from adapting to the environment because the population has little genetic diversity and does not contain the types that may do well in a new environment. This study demonstrates how plant neighbors (competing for resources) and soil type (stressful serpentine vs. nonstressful nonserpentine) affect genetic drift in populations. While we often think of specialized, adapted plant communities occurring on harsh soil types, I found a large amount of death on serpentine, and that the populations of plants growing on these stressful soils have more genetic drift. Thus, adaptation in non-stressful environments actually can occur more quickly and easily than adaptation in stressful environments. I also found that more plant neighbors decreased death rates. Normally we think plant-plant interactions are competitive, as resources are contested. While I did find that plants growing with other plants were smaller, I also found that they were more likely to survive and produce a few seeds when they grew with other plants, compared to growing alone. This means that fifty small plants growing in a dense population actually may experience less genetic drift compared to fifty large plants growing without competition from other plants.
Technical Abstract: Ecological models of plant competition predict both low growth rate variance when below-ground competition occurs and high growth rate variance in above-ground competition. Reproductive output in annual plants is highly correlated with plant size, therefore models of plant competition also predict reproductive variance and variance in effective population size (Ne). In this experiment, we manipulated inter- and intra-specific competition in Plantago erecta populations growing on low nutrient (serpentine) and high nutrient (non-serpentine) soils. Competition produced low plant size variance on both soil types, and intraspecific facilitation occurred at the survivorship stage. Serpentine populations had reproductive variance three times higher than non-serpentine populations, due to high mortality on serpentine soil. High reproductive variance means lower Ne for populations on serpentine soils. Soil environments act as selective forces, and here we demonstrate that soil can also alter the importance of genetic drift in annual plant populations.