SPATIAL MODELS OF FORAGING IN CLONAL PLANT-SPECIES

Ramets of some clonal plant species alter their internode lengths or t heir frequency of lateral branching in response to their immediate mic roenvironment. Such ''plant foraging'' responses are thought to allow clones to concentrate in favorable portions of their environment. Desp ite widespread interest among ecologists in plant foraging, few realis tic models have been developed to examine conditions under which plant foraging responses are likely to provide clones with ecological benef it. In this paper we develop spatially explicit, stochastic simulation models to examine consequences of both empirical and hypothetical pla nt foraging responses. We construct a hierarchical series of models in which we incorporate effects of resource heterogeneity on spacer leng ths, angles of growth, and lateral branch production. We also vary the number, size, and arrangement of patches, and the presence or absence of ramet mortality. Simulations based on hypothetical data demonstrat ed the potential importance of shortening spacer lengths in favorable habitat. In these simulations, ramet crowding increased significantly, implying a potential cost to plant foraging responses whose magnitude is large enough to cause ramets to concentrate in favorable patches. Models calibrated with empirical data suggest that when clonal plants were able to concentrate in favorable habitat, this was usually caused by increased daughter ramet production in the favorable habitat. Vari ation in clonal growth angles had little impact on the ability of rame ts or clones to locate favorable patches, but did increase the ability of clones to remain in favorable patches once found. Alterations in t he number and size of patches strongly influenced the effectiveness of the foraging response. The spatial arrangement of patches also was im portant: clumped distributions of patches decreased the success with w hich plants located favorable patches, especially at the genet level a nd when the number of patches was low. Finally, when ramet mortality v aried with patch quality, there was an increase in the percentage of r amets located in favorable patches; differential ramet mortality also lessened the impact of other effects, such as the decreased success of clones when patches are clumped. Overall, our models indicate that th e effectiveness of plant foraging responses is variable and is likely to depend on a suite of environmental conditions.