Closed+Systems+vs+Open+Systems


 * Closed Ecosystems**
 * self reliant
 * resources are reused through varies natural cycles
 * water cycle
 * precipitation > transpiration, runoff, infiltration, groundwater > evaporation > condensation (clouds)
 * nitrogen cycle
 * []
 * carbon cycle
 * []
 * plants develop natural defenses to threats


 * Open Ecosystems**
 * rely on constant external supply of resources
 * most resources are not recycled
 * managed agricultural ecosystems are closed systems
 * fertilizer is required to supply nutrients to plants - main source of nitrogen
 * pesticides, insecticides, herbicides are used to control pests
 * water is often supplied through irrigation - not enough natural rainfall to support crop growth
 * threats are controlled