1) Ecosystem degradation occurs when environmental problems diminish species' ability to survive and is caused by deforestation, mining, habitat change, overexploitation, pollution, and climate change.
2) Ecological succession refers to predictable changes in community composition, such as hardwood trees replacing pine forests by outcompeting them for sunlight. Primary succession occurs on new areas without soil, while secondary succession occurs where soil is present.
3) A food chain represents the transfer of energy between trophic levels from producers to primary, secondary and tertiary consumers, and decomposers. Food webs show the complex interconnected food chains in an ecosystem.