2. Five parameters measured to understand populations: size, natality, immigration, mortality, emigration.
3. Regulation of population growth can be density dependent (e.g., disease, predation) or density independent (e.g., weather, fire).
4. Interactions between organisms include mutualism (e.g., symbiosis), commensalism (e.g., epiphytic plants), competition (resource, interference, intraspecific, interspecific), predation, herbivory & parasitism.
5. Competition -- usually both organisms suffer; sometimes one wins. The competitive exclusion principle illustrated with species with same niche. The better competitor drives out the weaker competitor (e.g., barley & oats).
6. If the niches are different, species can coexist in an ecosystem. If all the niches are filled, the population either adapts to a different niche (evolves) or is excluded from the ecosystem (extinction).