Editing Ecology Ecosystems (section)

== <span style="color: #FFFFFF;">Understanding</span> ==
Ecosystems are governed by the flow of energy and the cycling of matter.

'''The 10% Rule''': Energy enters an ecosystem via sunlight and is captured by producers. However, when a herbivore eats a plant, only about 10% of that energy is stored in the herbivore's body; the rest is lost as heat. This explains why food chains are usually short (rarely more than 4-5 levels) and why there are fewer lions than there are zebras.

'''Cycles of Life''': Unlike energy (which flows through and out), matter is recycled.
* '''The Carbon Cycle''': Photosynthesis takes CO2 out of the air; respiration and burning fossil fuels put it back.
* '''The Nitrogen Cycle''': Bacteria "fix" nitrogen from the air into a form plants can use to build proteins.

'''Interdependence''': No species lives in isolation.
* '''Mutualism''': Both benefit (e.g., bees and flowers).
* '''Parasitism''': One benefits, one is harmed (e.g., ticks on a deer).
* '''Competition''': Two species vying for the same niche; according to the '''Competitive Exclusion Principle''', two species cannot occupy the same niche indefinitely—one will always outcompete the other.
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