The study of the combination of plant species that inhabit a particular locality became a scientific discipline toward the end of the nineteenth century. A. Areas that are recovering from serious disturbances like volcanic eruptions and heavy floods provide special opportunities to observe the development of plant communities. B. Whether a given species will be found in a given ecosystem strongly depends on what other species it would interact with in that ecosystem. C. Computer-aided studies of entire system of associated organisms together with their environment provide a solid basis for current studies of specific ecological problems. D. According to the earliest theories of ecology, the development of plant communities proceeds in lawlike fashion and results in stable climax communities. E. The idea of associations of plants and animals that function as "superorganisms" was later rejected by biologists who saw no strong evidence in support of that idea. F. The once popular idea of communities as integrated ecosystems has been largely rejected by modern ecologists, who are more interested in problems involving behavior and adaptations.