The Birth and Spread of a Plant Population

Abstract

The establishment and increase over a 20-year period of a new plant population is reported. The European perennial, Silene paradoxa L. (Caryophyllaceae), was introduced as 27 transplants in 1964 to a serpentine barren in western Washington. In 1983 nearly 1000 plants were present in size classes ranging from seedlings to the original transplants. The new colony is still vigorous and locally expanding its numbers. The implications of a recorded introduction and spread of a population are discussed; inferences on demographic and microevolutionary consequences of this founder population are examined. INTRODUCTION Much of the heightened interest in plant population biology centers around the demography and ecology of established populations (Harper, 1977; Solbrig et al., 1979; Dirzo and Sarukhan, 1984). But the initial inoculum and the immediate fate of founder individuals should command our attention, too. All existing populations had to have a beginning, often beset with the uncertainties of establishment. It is useful to know how an initial colonization fares and to observe the reproductive success of the plants in their establishment phase and the status of the populations following establishment. While there are many recorded instances of population changes in introduced plants (weeds, escaped ornamentals, forest tree-farm species, land reclamation species, etc.), as well as population changes following natural disturbance (e.g, following vulcanism, flooding, fire, etc.), there are few instances of observations made from the time of deliberate introduction through assured establishment of a sexually reproducing popula-