IMMIGRATION AND LOCAL COMPETITION IN HERBACEOUS PLANT COMMUNITIES: A THREE-YEAR SEED-SOWING EXPERIMENT

Mouquet N., Leadley P., Meriget J. and Loreau M. (2004).

Oikos, 104, 77-90, doi:10.1111/j.0030-1299.2004.12644.x

Key message : We tested the influence of immigration on species diversity dynamics in a three-year experiment using herbaceous plant communities. We manipulated the intensity of seed rain (i.e., immigration) and the relative contribution of each species to the seed rain. For each of three levels of intensity of immigration (seed rain), we considered three cases, in which immigration was either negatively correlated, positively correlated, or uncorrelated with local competitive ability. Our experiment illustrates how both immigration and local competition contribute to explaining species diversity in herbaceous plant communities. Communities were more diverse when they received more seeds and when immigration was inversely correlated or uncorrelated with local competitive ability. Only species of intermediate or low competitive ability responded positively to the seed addition treatment. Community level functional properties were not strongly modified by immigration: immigration treatments did not differ in total above-ground biomass and plant cover, soil surface occupation was higher at high immigration intensities. A comparison of our results with theoretical models of plant community structure suggests that the mechanisms underlying the species dynamics in our communities were probably a mixture of colonization-extinction and competitive weighted lottery.