Why study plant populations?
In this book we have thus far focussed on introduced plant species and their impacts on and relationships to native plant communities. We are interested in the patterns of spread, the stability of established populations, and the impact of control procedures particularly biological control. For all of these considerations environmental and biological heterogeneity are major perturbing factors. Land managers are confronted with serious questions about interactions among populations of plant species, particularly those between native and introduced species. Therefore it becomes imperative to measure, predict and interpret changes in populations.
When plant species move into new communities their dynamics create challenges for population ecologists. That introduced species are able to establish and invade a new plant community indicates either: 1) the presence of empty niches in the native community, 2) that the introduced species itself creates a new niche, or 3) that the introduced species is a superior competitor able to respond to disturbance or utilize resources better than existing species. The introduced plant species will probably also differ from species in the native community by having less herbivore and disease pressure (Chapter 3). During establishment and spread, the introduced species will increase in density and distribution. Following the invasion, the dynamics of the invader may not be very different from those of the native species other than that densities will be higher and therefore intraspecific competition will be strong.