530 Glossary Reaction center A bacteriochlorophyll–protein complex that performs the primary photochemical reactions of photosynthesis Reaction norm The relationship between the phenotypic expression of a single genotype and the environmental conditions under which the phenotype is shaped Reactive nitrogen All forms of nitrogen except atmospheric dinitrogen gas, including all radiatively, photochemically, and biologically active inorganic forms (e.g., NH3, NH4ỵ , NOx, HNO3, N2O) and organic molecules (e.g., proteins, urea, etc.) Realm See BIOGEOGRAPHIC REALM Rear edge A stable margin of a species’ range where population size is declining Recalcitrant Describing seeds that have high moisture content and lose viability if moisture drops below a critical amount limiting their storage for long periods Recipient control A situation in which consumers substantially depress populations of their resources Reciprocal selection Evolutionary change as a result of species acting as selective agents on each other through interspecific interactions Reclamation A revegetation or land management goal that includes a lower diversity of species and may include substitutions by introduced species The conversion of an area of the ocean, a lake, a riverbed, or a wetland to dry land The restoration of depleted or desert land to productive agricultural land The cleansing of wastewater for return to the natural environment Recolonization The reappearance of a species in an area where it has earlier been present, then disappeared Recombinant DNA (rDNA) A DNA sequence obtained by artificially combining two or more different DNA strands, thus creating a sequence that would not be found in nature Recombinant DNA is widely used in biotechnology, biomedicine, and research; e.g., comparative phylogenetic studies Reconstructed evolutionary tree A phylogeny linking contemporary species, and thus containing no information about lineages that have gone extinct Recruitment The arrival of new juvenile animals or plants into a habitat or an older stage of the population; e.g., the entry of juvenile fish into the adult stock Recruits A term for young fish that are first caught by a fishery Recycling The process of reusing industrial materials (e.g., aluminum, glass, plastic, paper) after the initial use, to preserve useful materials and reduce the need for manufacturing new materials (as well as for other benefits) The transpiration and evaporation of water from the land surface, followed by reprecipitation elsewhere within the continent REDD Reduced emissions from deforestation and forest degradation; a form of payment for ecosystem services in which the carbon storage value of forests threatened by degradation or clearance is financially recognized through payments to forest owners (usually, but not exclusively, nation-states) to conserve the forest Redfield ratio The ratio of carbon, nitrogen, phosphorus, and oxygen for normal ocean plankton and deep-ocean nitrate and phosphate pools, on the basis of time-averaging for a large-area Also, Redfield stoichiometry [Described by the U.S oceanographer Alfred C Redfield.] Red list See IUCN RED LIST Red tide The popular name for a harmful algal bloom (HAB) having a reddish or brownish coloration See ALGAL BLOOM Reference area An undisturbed or natural area chosen to compare with a restored site to determine the success of restoration Reflective beach A narrow, steep beach; so called because it reflects a major part of the incoming waves Reforestation The re-establishment of trees and understory plants at a site previously occupied by forest cover This can occur by natural means or by some form of human intervention, including planting seedlings or sowing seeds Refugia Arctic land areas that were not covered by ice sheets or glaciers during the last glaciation Consequently, some biota could survive there and recolonize adjacent areas when the ice retreated Therefore, these areas are associated with high biodiversity and endemism Refugia usually occurred in coastal areas (now continental shelves) and ice-free mountain tops or ‘‘nunataks.’’ Regenerated production Primary production in the ocean derived from recycling of nutrients within the euphotic zone such as by uptake of ammonia (NH4ỵ ) or dissolved organic nitrogen Compare NEW PRODUCTION Regeneration The ability of organisms to regrow lost or destroyed tissue or body parts See FOREST REGENERATION Regime The specific, relatively stable structural and functional state of a given ecosystem Regime shift A large, persistent, often abrupt change in the structure and function of an ecosystem, associated with a change in dominant feedback processes Regime shifts are abrupt and often difficult to reverse Region A large geographic area that contains more than one landscape Regional pool Species occurring within a defined geographical area or in a collection of samples from within such an area Regulating services The ecosystem services (see) obtained from the regulation of environmental processes, including flood protection, climate regulation, human disease regulation, water purification, air quality maintenance, pollination, and pest control Rehabilitation The process of re-establishing the productivity and some, but not necessarily all, of the plant and animal species thought to be originally present at a site For ecological or economic reasons, the new ecosystem might also include species not originally present at the site The protective function and many of the ecological services of the original system may be re-established Reintroduction The placement of individual organisms by humans into a habitat for the purpose of establishing a population where a previous population has gone locally extinct Relative abundance distribution A frequency distribution depicting the number of species in a community as a function of the number of individuals comprising each species Relay intercropping See INTERCROPPING