The document discusses key concepts in ecosystems, including: 1) An ecosystem is defined as a community of interdependent organisms (biotic factors) and the physical environment (abiotic factors) they inhabit. 2) Key biotic factors include populations, communities, and species. Abiotic factors include physical and chemical components of the environment like climate, soil, and water. 3) Limiting factors are those that prevent or restrict growth of populations and can include biotic factors like predation as well as abiotic factors such as nutrient availability.