Consequences of Foraging in Clonal Plant Species

Abstract

Some clonal plant species decrease rhizome or stolon internode lengths and/or increase the frequency of branching when they grow in favorable environments. This foraging response is thought to be beneficial since it should allow ramets to concentrate in areas of favorable habitat. 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 stochastic 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 significantly the distance clones move, and thus, to enable mets to remain for longer periods of time in favorable habitat. For the empirical data used in this study, results from the models indicate that the effectiveness of the foraging response is likely to be variable. In some cases, such as results from models based on the response of Glechoma hederacea to nutrients, there is no significant difference in the distance clones move in favorable and unfavorable habitat. Thus, even through 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 the foraging response depends strongly on the distribution of clonal growth angles, the pattern of clonal branching, and the variance in rhizome or stolon internode length. These results, particularly the importance 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 reasons that may underlie these differences.

Clonal development of Maianthemum dilatatum in forests of differing age and structure

“…However, we did not observe increased allocation to roots or rhizomes, which would be expected if plants were actively "foraging" for microsites with greater resource levels. Thus, our observations are more consistent with a model of "passive growth response", in which growth or production show a simple relationship to resource availability, than with a model of "active foraging", in which lateral growth increases in locally unfavorable microsites (Cain 1994;Cain et al 1996;Stoll et al 1998). Although allocation to foraging organs did not increase in young, closed-canopy forests, allocation related to clonal growth and storage was affected.…”

On the evolution of clonal plant life histories

“…Mathematical models showed fitness effects of sexual vs. vegetative recruitment, which depended on the scale of disturbances and on growth form, where phalanx species had an advantage at small disturbances and guerilla at large ones (Winkler and Schmid, 1995;. In further models, fitness effects were found for foraging (Sutherland and Stillman, 1988;Cain, 1994;Oborny, 1994;Cain et al, 1996), and for integration (Oborny et al, 2000), which also depended on the scale of spatial heterogeneity. Experiments showed fitness effects of growth form which depended on ramet density (Schmid and Harper, 1985;Humphrey and Pyke, 1998), and fitness benefits of foraging [347] in a spatially heterogeneous competitive environment (va n Kleunen a nd Fischer, 2001).…”

Morphological plasticity in the rhizome system of Solidago gigantea (Asteraceae): Comparison of populations in a wet and a dry habitat

“…By this division, relatively tall and suppressed, relatively short shoots were compared in each site disregarding the average shoot size of sites (A = dry site, B = wet site) experiments: there is plasticity in the geometry of Solidago's rhizome system in natural conditions. Cain (1991Cain ( , 1994 pointed out that the long-term consequence of different rhizome lengths in terms of net displacement of the clone strongly depends on the distribution of branching angles. In our case, however, the distribution of branching angles proved to be constant.…”