Lewis/Life - Review of Key Concepts

Review of Key Concepts - Chapter 42

Biotic communities are made up of coexisting species that are specialized in where, when, and how they live. Communities are most diverse near the equator.
As species interact with each other and their physical habitats, they change the community, a process called biotic succession. Primary succession occurs in a previously unoccupied habitat; secondary succession occurs after a disturbance. Succession leads toward a stable climax community, but complete stability is rare---most communities continue to change.
An ecosystem is the biotic community and its physical habitat. An ecosystem can range from a very small area to the entire biosphere. Ecosystems interact and change. Related ecosystems form biomes, which can be terrestrial or aquatic.
A food chain begins when primary producers harness energy from the sun or earth, forming the first trophic level. The total amount of energy converted to chemical energy in food is gross primary production. The energy remaining after metabolism is net primary production.
At the next trophic level, primary consumers (herbivores) eat the primary producers. A secondary consumer may eat the primary consumer, and a tertiary consumer may eat the secondary consumer. Decomposers break down nonliving organic material into recyclable nutrients. Food chains rarely extend beyond four trophic levels because only about 10% of the energy one trophic level takes in transfers to the next level. Ecological pyramids measure energy, numbers of organisms, or biomass in a food chain. Stable isotope tracing measures 13C/12C ratios to identify primary producers.
Biogeochemical cycles are geological and chemical processes that recycle chemicals essential to life. Water cycles from the atmosphere as precipitation, into the ground, and into organisms that release water in metabolism. Photosynthesis uses atmospheric carbon in CO2 to manufacture carbohydrates. Cellular respiration and burning fossil fuels release CO2. Decomposers release carbon from once-living tissues. Bacteria convert atmospheric nitrogen to ammonia and then to usable nitrates. Decomposers convert the nitrogen in dead organisms to ammonia. Nitrifying bacteria convert the ammonia to nitrites, and other bacteria convert nitrites to nitrates. Denitrifying bacteria convert nitrates and nitrites to nitrogen gas. As rain falls over land, rocks release phosphorus as useable phosphates. Decomposers return phosphorus to the soil.
Bioaccumulation concentrates chemicals in cells compared to the surroundings. Biomagnification concentrates chemicals to a greater degree at successive trophic levels because the chemical passes to the next consumer rather than being metabolized or excreted.