<descriptor thcode="2"><thesaurus thcode="2" name="USGS Thesaurus" scope="Topics and methods of scientific study carried out by USGS, with product types, scientific disciplines, geologic time, and types of institutional structure and activities.  Broad and shallow, used to help people find scientific information." creator="U.S. Geological Survey" rights="Public domain" edition="2.0" date="2020-01-09" codetype="number" prefix="topic" uri="https://www2.usgs.gov/science/USGSThesaurus" tblname="term" nonpref="nonpref" relterm="relterm" root_code="1" contact="pschweitzer"><category><term thcode="25" code="29" name="distinct labels" parent="26" scope="Preferred labels (descriptor texts) are distinct within the thesaurus. A concept can be specified either by its unique identifier (code) or by the text of its descriptor."/><term thcode="25" code="16" name="hierarchical" parent="11" scope="Substantive broader-narrower relationships exist among the terms."/><term thcode="25" code="13" name="transitive" parent="12" scope="Narrower terms have an &quot;is a&quot; relationship with their broader terms, and generally can be described as part-of, type-of, or instance-of the broader term."/><term thcode="25" code="21" name="disciplines" parent="2" scope="Broad categories of human inquiry or activity, such as scientific disciplines."/><term thcode="25" code="20" name="methods" parent="2" scope="Actions taken to obtain or analyze information"/><term thcode="25" code="19" name="organizational functions" parent="2" scope="Things that organizations do, typically including various types of programs, projects, and services."/><term thcode="25" code="7" name="temporal" parent="2" scope="Terms indicate periods of time, such as chronostratigraphic units, named historical periods or intervals surrounding known historical events, or seasons."/><term thcode="25" code="5" name="theme" parent="2" scope="Terms indicate domains of human concern, such as scientific discipline, societal problems, or characteristics of earth, space, oceans, and living things."/><term thcode="25" code="29" name="distinct labels" parent="26" scope="Preferred labels (descriptor texts) are distinct within the thesaurus. A concept can be specified either by its unique identifier (code) or by the text of its descriptor."/><term thcode="25" code="16" name="hierarchical" parent="11" scope="Substantive broader-narrower relationships exist among the terms."/><term thcode="25" code="13" name="transitive" parent="12" scope="Narrower terms have an &quot;is a&quot; relationship with their broader terms, and generally can be described as part-of, type-of, or instance-of the broader term."/><term thcode="25" code="21" name="disciplines" parent="2" scope="Broad categories of human inquiry or activity, such as scientific disciplines."/><term thcode="25" code="20" name="methods" parent="2" scope="Actions taken to obtain or analyze information"/><term thcode="25" code="19" name="organizational functions" parent="2" scope="Things that organizations do, typically including various types of programs, projects, and services."/><term thcode="25" code="7" name="temporal" parent="2" scope="Terms indicate periods of time, such as chronostratigraphic units, named historical periods or intervals surrounding known historical events, or seasons."/><term thcode="25" code="5" name="theme" parent="2" scope="Terms indicate domains of human concern, such as scientific discipline, societal problems, or characteristics of earth, space, oceans, and living things."/></category><altlabel><altlabel>USGSThesaurus</altlabel><altlabel>USGSThesaurus</altlabel></altlabel></thesaurus><term thcode="2" code="310" name="ecological processes" parent="101" scope="Dynamic biogeochemical interactions that occur among and between biotic and abiotic components of the biosphere."/><uf><usefor name="ecological models"/><usefor name="environmental processes"/></uf><bt><term thcode="2" code="101" name="biological and physical processes" parent="1174" scope="All continuing activities, functions, and phenomena associated with organisms and non-living matter."/><term thcode="2" code="1174" name="topics" parent="1" scope="Themes, subjects, and concerns for which USGS information resources are relevant."/><term thcode="2" code="1" name="Categories" scope="Thematic terms for categorizing information resources.  This thesaurus is intended to support finding and understanding scientific information."/></bt><nt><term thcode="2" code="30" name="algal blooms" parent="310" scope="Exceptional growth of algae and cyanobacteria in lakes, rivers or oceans due to excessive nutrients or climatic conditions."/><term thcode="2" code="88" name="bioaccumulation" parent="310" scope="The biological sequestering of a substance at a higher concentration than that at which it occurs in the surrounding environment or medium.  Also, the process whereby a substance enters an organism through the gills, epithelial tissues, dietary, or other sources."/><term thcode="2" code="93" name="biogeochemical cycling" parent="310" scope="The cycling of chemical constituents through a biological system."/><term thcode="2" code="108" name="biological productivity" parent="310" scope="The rate at which primary producers in the ecosystem utilize solar energy to produce food for consumption by other organisms. Do not use this term for productivity of organisms related to studies of the reproduction rates of a species."/><term thcode="2" code="2277" name="carbon flux" parent="310" scope="The rate and amount of carbon exchanged between the oceans, atmosphere, land, and living things."/><term thcode="2" code="196" name="contaminant transport" parent="310" scope="Processes involved in the movement of impurities through air, water, and soil."/><term thcode="2" code="268" name="dispersal (organisms)" parent="310" scope="The dissemination or geographic spread of individuals of a plant or animal population."/><term thcode="2" code="308" name="ecological competition" parent="310" scope="The struggle between members of two or more species for scarce environmental resources."/><term thcode="2" code="315" name="ecosystem functions" parent="310" scope="The total life activities of organisms in habitats and the effects of those activities on the nonliving components of the environment."/><term thcode="2" code="2281" name="ecosystem resilience" parent="310" scope="Measure of the persistence of systems and of their ability to absorb change and disturbance and still maintain the same relationships between populations or state variables. (Holling, 1973)"/><term thcode="2" code="359" name="eutrophication" parent="310" scope="The process by which water becomes enriched with plant nutrients, most commonly phosphorus and nitrogen."/><term thcode="2" code="365" name="extinction and extirpation" parent="310" scope="Extinction is the complete disappearance of a species from the earth.  Extirpation is the complete disappearance (elimination) of a species from a given region, island, or area."/><term thcode="2" code="522" name="habitat alteration and disturbance" parent="310" scope="Changes in the environments where plants and animals live.  Includes natural changes as well as results of human actions, deliberate or accidental."/><term thcode="2" code="743" name="migration (organisms)" parent="310" scope="The movement of animals, often periodical, from one area to another due to seasonal changes, availability of food, or climatic conditions."/><term thcode="2" code="915" name="pollination" parent="310" scope="Wind, bees, or other agents transfer plant pollen from flower anthers or cones to stigmas, thereby fertilizing plants for reproduction."/><term thcode="2" code="1123" name="succession (biological)" parent="310" scope="Gradual replacement of one species in an area by another."/><term thcode="2" code="1356" name="transpiration" parent="310" scope="Evaporation of water from plants."/></nt><rt><term thcode="2" code="311" name="ecology" parent="650" scope="Study of the relations between living plants and animals and their environment."/><term thcode="2" code="921" name="population and community ecology" parent="1174" scope="Interactions of a single species (population) or an association of different species (community) occupying a particular region, including their biotic and abiotic environments."/><term thcode="2" code="1710" name="soil formation" parent="451" scope="Geological, geochemical, and ecological processes that work together to produce soils."/><term thcode="2" code="2289" name="state and transition modeling" parent="2286" scope="Modeling of systems such as ecosystems to predict the consequences of natural events and management actions by describing how specified events and actions may change the components and relationships in the system."/></rt></descriptor>