a community of plant and animal species that interact together along with their physical and chemical environment. (Source: IISD 2005) [ALSO] A community of organisms and their physiological environment interacting as an ecological unit (Source: DRobinson citing Lincoln et al. 1982). [ALSO] A dynamic system of interactions between all of the species inhabiting an area and the non-living, physical environment. Ecosystems vary spatially and change with time, and no ecosystem is closed with respect to exchanges of organisms, matter, and energy. Priority areas or sites for conservation exist within ecosystems. [fn]Source: (USAID 2005) from "USAID Biodiversity Primer"[/fn]. [ALSO] An ecosystem is a group of interconnected natural communities on land or in water that are linked together by ecological processes. Primary emphasis in portfolio design will be placed on conserving the highest quality examples of ecosystems and second, on viable populations of native species not captured within these ecosystems. Portfolio design and implementation is a dynamic and iterative process that will be periodically updated and refined. [fn]Source: (TNC 2005) from website; The Nature Conservacy (updated: Aug 2005)[/fn] . [ALSO] Dynamic assemblages of native plant and/or animal communities that 1) occur together on the landscape or in the water; and 2) are tied together by similar ecological processes (e.g., fire, hydrology), underlying environmental features (e.g., soils, geology) or environmental gradients (e.g., elevation). [fn]Source: (TNC 2005) from website; The Nature Conservacy (updated: Aug 2005)[/fn]