This section emphasizes one of the three main branches of ecology—population, community, and ecosystem. Extensive, real-life examples of how ecological concepts and principles can be applied to problems with invasive species are included. It also introduces invasion ecology protocols—techniques or methods scientists use in research—and beyond protocols—conducting interactive research. It is important to understand the protocols and, in many cases, to practice them before embarking on an independent research project. Students also can design their own research project using the protocols in this section.