Energy Flow and Ecosystems Alan P Covich, University of Georgia, Athens, GA, USA r 2013 Elsevier Inc All rights reserved Glossary Chemoautotrophs Species that use inorganic compounds as a source of carbon and energy, and function as primary producers Decomposition The biotic breakdown of dead organic matter (detritus) by bacteria and fungi that releases carbon dioxide and nutrients for recycling Ecosystems Composed of species assemblages (producers and consumers) that interact with each other and their associated abiotic environment within well-defined natural or conceptual boundaries Food chains Composed of species that are connected by the flow of energy and material from producers to consumers Food webs ‘‘Flow maps’’ that depict connections among multiple food chains Functional groups Aggregations of species that perform similar ecosystem processes, such as grazers, suspension or filter feeders, leaf shredders, predators, and decomposers Photoautotrophs These species, such as green plants and some bacteria, use solar energy and inorganic compounds to synthesize organic matter as primary producers Introduction Ecosystems are thermodynamically open, hierarchically organized communities of producers, consumers, and decomposers together with the abiotic factors that influence species growth, reproduction, and dispersal These abiotic factors include the flow of energy and the circulation of materials together with the geological, hydrological, and atmospheric forces that influence habitat quality, species distributions, and species abundances Energy flows through many species, and the way in which this flow affects the persistence of ecosystems is influenced by landuse changes, precipitation, soil erosion, and other physical constraints such as geomorphology Energy flow through ecosystems is essential for nutrients to cycle through food webs These food webs are often subwebs of more complex species assemblages and may be only partial descriptions of more complex hierarchies of energy flows The connections among species’ interactions in natural food webs typically result in some important feedback loops and recycling of nutrients and materials within the conceptually defined boundaries of an ecosystem Many species of producers are generalized in using solar energy (photoautotrophs) and form the basis of most food webs Certain species live in deep, ocean thermal vents and use inorganic chemical compounds as energy sources (chemoautotrophs) The connections among producers and consumers are often complex and change with species age and size during an individual’s life history These food webs are diagrams that can function as ‘‘flow maps’’ to Encyclopedia of Biodiversity, Volume Primary productivity The rate of synthesis of organic matter by plants (biomass per unit area of habitat per unit time or, in some cases, biomass per unit volume per unit time) Secondary productivity The rate of assimilation and growth by animals (biomass per unit area of habitat per unit time or, in some cases, biomass per unit volume per unit time) Trophic cascades These occur when changes in the presence or absence (or shifts in abundance) of a top predator alter the production at several lower trophic levels; primary and secondary production at lower levels are alternately constrained or unconstrained by the feeding activities of consumers at upper levels Trophic levels Groups of individuals classified as primary producers or primary or secondary consumers within food webs; individuals feeding both as primary and secondary consumers are omnivores A single species may be represented on more than one trophic level document which species interact with other species, either directly or indirectly, as energy flows through the community and determines the movement of nutrients and other materials This flow of energy is associated with the potential bioaccumulation of toxic chemicals that can be concentrated in predators who consume large amounts of prey that, in turn, have fed on large amounts of plants Different species have important functional values, such as for organic matter production (plant and animal growth) or organic matter breakdown (decomposition), oxygen production, nitrogen fixation, and nutrient cycling These species have intrinsic values as the unique end products of evolution, and native species are likely to have adapted specific ways to respond to local or regional environmental changes or other physical disturbances Conceptually, the loss of even a single native species, or the introduction of a nonnative species, could alter how the other remaining native species continue to perform different ecosystem functions Disruptions of ecosystem processes are known to have occurred after certain well-adapted, native species were lost through local extinction following intense (pulse) or prolonged (press) disturbances However, predicting species that are essential to ecosystem functions has generally remained difficult because information is lacking on many species interactions as well as on life history, adaptations to different disturbances, and dispersal abilities among key species Ecosystem studies can provide a broad perspective regarding species relationships and recycling of essential nutrients Species’ shifts in patterns http://dx.doi.org/10.1016/B978-0-12-384719-5.00045-9 237