Survival and competition of clonal plant populations in spatially and temporally heterogeneous habitats

Clonal populations are hierarchically organized: genetic individuals (genets) can consist of many physiological individuals (ramets). Each ramet takes up resources from its local environment, but the resource pattern can be reorganized within the clone by transport between ramets. Thus, an integrated clone is not directly subject to the pattern of resource availability in its habitat. Local shortages can be compensated, hence, the clone can ‘buffer’ itself against spatio-temporal heterogeneity in the habitat. We modelled a series of habitat types, assuming that one limiting resource was patchily distributed in space, and could fluctuate over time. Habitat types differed in the density, size and persistence of resource patches, and in the contrast between resource-rich patches and the resource-poor background. We applied an individual-based, spatially explicit population dynamic model to compare the performance of two plant strategies in these habitat types. In the Integrator, ramets that were interconnected distributed the resource evenly. In the Splitter, no resource translocation occurred. First we observed population growth of the two strategies separately, then in competition. We found a range of habitat types, where none of the strategies was viable, because of the scarcity of resource patches. As the density of resource patches was increased, first only the Integrator could persist. Then, at intermediate densities of resource patches, the Splitter became viable, and, being a stronger competitor, excluded the Integrator. Finally, at high resource-patch densities, the Integrator occupied the area again. Since the Splitter was viable at high density of resource patches when growing alone, its disappearance is more due to spontaneous extinction, due to competitive exclusion by the Integrator. We predict, therefore, the dominance of integrated clones both in extremely unproductive and productive environments, but for different reasons. It is important to note that this trend was observable only at high spatial and temporal variation in resource availability. Less contrast between patches of different quality, smaller patch sizes, or longer persistence of patches facilitated the dominance of the Splitter. Thus, buffering is advantageous in many but not all habitat types.