CONSEQUENCES OF FORAGING IN CLONAL PLANT-SPECIES

Some clonal plant species decrease rhizome or stolen internode lengths and/or increase the frequency of branching when they grow in favorabl e environments. This ''foraging response'' is thought to be beneficial since it should allow ramets to concentrate in areas of favorable hab itat. However, there have been few critical tests of the effectiveness with which ramets are placed in favorable habitat as a result of the foraging response. In this paper, I use empirically calibrated stochas tic simulation and diffusion models to compare the growth of clones in favorable and unfavorable habitat. I ask whether observed changes in rhizome lengths and clonal branching patterns are likely to decrease s ignificantly the distance clones move, and thus, to enable ramets to r emain for longer periods of time in favorable habitat. For the empiric al data used in this study, results from the models indicate that the effectiveness of the foraging response is likely to be variable. In so me cases, such as results from models based on the response of Glechom a hederacea to nutrients, there is no significant difference in the di stance clones move in favorable and unfavorable habitat. Thus, even th ough rhizome lengths may be significantly shorter in favorable patches , this does not guarantee that clones disperse significantly less far and thereby remain longer in favorable habitat. The effectiveness of t he foraging response depends strongly on the distribution of clonal gr owth angles, the pattern of clonal branching, and the variance in rhiz ome or stolen internode length. These results, particularly the import ance of growth angles and the relatively limited effectiveness of the foraging response, differ from those in previously published models of foraging in clonal plant species. I conclude with a discussion of rea sons that may underlie these differences.