RESOURCE-BASED MODELS OF COMPETITIVE INTERACTIONS - I - INTRASPECIFICCOMPETITION IN RATIBIDA-COLUMNIFERA (ASTERACEAE)

We constructed and rested a series of regression models of intraspecif ic competition in Ratibida columnifera (Asteraceae), based on the grow th and water use of individual plants. Models were constructed From a set of plants (''model'') grown without competition under three wateri ng regimes. Each model was then tested on another set of plants (''tes t'') grown, singly or in pairs, under two watering regimes, one of the m different than those of the ''model'' plants. Both sets of plants we re grown simultaneously. Models that used only estimates of plant dry mass (ISON [interval by interval size only], and SON [size only]) were outperformed (i.e., the difference between predicted values of final dry mass and their true values were larger on average) by models that incorporated direct measures of water uptake and usage (ISAW [interval by interval size and water], WON [water only], SAW [size and water]). Harvest biomass predictions given by these three last models deviated from values of true biomass by an average of only 6.1%.