Colonization-extinction and patch dynamics of the perennial riparian plant, Silene tatarica

Although the concept of metapopulation is central to modern conservation biology, plant population biologists have divergent views concerning the importance of metapopulation dynamics. We studied the patch structure and colonization-extinction dynamics of Silene tatarica by mapping its distribution along a 43-km stretch of riverside subjected to annual flood disturbances. Plants were grouped into patches that were surveyed annually. The effect of spatial scale on dynamics was evaluated by varying the interplant separation used to determine grouping from 5 to 200 m. Using the 5-m criterion, the number of patches varied from 703 to 854 over the 5 years of the study. New patches were colonized by a few individuals and located on average 50 m away from the closest old patch. Recolonization of extinct patches was very rare. Small patches had the highest risk of extinction (5%) and, although floods can destroy even large populations, no large patches with flowering individuals became extinct. Elasticity analysis indicated that the survival of patches made a much greater contribution to patch dynamics than the production of new patches. Increasing patch scale decreased the rates of colonization and extinction as well as the projected finite rates of increase in patch number, but elasticities remained invariant. The river dynamics both create space for colonization and cause local extinctions, especially of small patches. The short-term dynamics of S. tatarica depend primarily on local dynamics but, in the long run, the species will track the availability of habitat, and its persistence will depend on a positive balance between colonization and extinction. This species from a transient environment does not exhibit the extinction-recolonization dynamics predicted for metapopulations at equilibrium. The rate of the dynamics of plant species in relation to the rate of habitat changes may be one of the key determinants of their regional dynamics.