Modelling the combined effect of chemical interference and resource competition on the individual growth of two herbaceous populations
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Resource competition and chemical interference are mechanisms of interaction among plants that may occur simultaneously. However, both mechanisms are rarely considered together when modelling plant growth. We propose a new empirical model that estimates biologically significant parameters on both plant competition and chemical interference. The model is tested with data sets from different density-dependent experiments done with two species (the grass Lolium rigidum Gaud. and the legume Glycine max soya L.) subjected to a noxious chemical environment when growing (allelochemicals and herbicides, respectively). Hypotheses on the effect of allelochemicals and its interaction with density are tested using maximum likelihood ratio tests in order to ask, for these species, whether chemical interference is playing a significant role in the interactions among plants or on the contrary, whether interactions among plants are sufficiently explained by the resource competition. In all cases a significant interaction between chemicals and density is observed. This interaction is inconsistent with the hypothesis of only resource competition having an influence of plant biomass and suggests a significant density-dependent effect of chemicals on plant growth.
KeywordsAllelopathy Lolium rigidum Gaud. Neighbour effects Size-density response function
We thank Jacob Weiner, and other anonymous reviewers for valuable comments and Birgit Nielsen for helping on the writing process. Part of the research was done in the National Environmental Research Institute of Silkeborg, Denmark. The research was funded by the Navarra Council for Education and Culture (2002–2003), and the Public University of Navarra defrayed the costs of a first author’s stay in Denmark.
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