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Ecosystem structure and function

Ecosystem structure and function



Ecosystem structure and function

Ecosystem structure and function



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    Ecosystem structure and function Ecosystem structure and function Presentation Transcript

    • 2.1 History of the Ecosystem Concept The term “ecosystem” was first coined by Roy Clapham in in 1930, but it was ecologist Arthur Tansley who fully defined the ecosystem concept. In his classic article of 1935, Tansley defined ecosystem as “The whole system…including not only the organism-complex, but also the whole complex of physical factors forming what we call the environment.” Eugene Odum, a major figure in advancing the science of ecology, developed the ecosystem concept in a central role in his seminal textbook on ecology, defining ecosystem as: ”Any unit that includes all of the organisms (i.e.: “the community”)in given area interacting with the physical environment so that a flow of energy leads to clearly defined trophic structure, biotic diversity, and material cycles (i.e.: exchange of materials between living and nonliving parts within the system is san ecosystem.”
    • An ecosystem is a very complex entity with many interactive components. It can be defined as “ a system of complex interactions of population between themselves and with their environment” or as “the joint functioning and interaction of these two compartments (populations and environment in a functional unit of variable size” in a functional unit of variable size” (Odum, 1975, Ellenberg,1973; Nybakken, 1992; Scialabba, 1998).
    • Ecosystem maybe considered at different geographical scales from a grain of sand with its rich micro fauna, to a whole beach, a coastal area or estuary, a semi-enclosed sea and eventually, the whole Earth. As stated by Lackey (1999), ecosystems are defined at a wide range of scales of observation “from a drop of morning dew to an ocean,. From a pebble to a planet” Ecosystems defined at a given geographical and functional scale are therefore nested within larger ones and contain smaller ones with within they exchange matter and information.
    • Ecosystem are dynamic, composites entities within which large quantities of matter, energy and information flow, within and between components, in a way that is not yet completely understood. These flows are controlled primarily by: 1.top predator’s feeding behavior (top down control); 2.Primary procedures (bottom up control); 3.Some numerically abundant species somewhere in the middle of the food chain (wasp-waist control); or 4. Some combination of some or all of these, depending on system and their possible states ( Cury et al., 2003).
    • The functioning of an ecosystem results from the organization of its species communities, consisting of species populations having their own dynamics in terms of abundance, survival, growth, production, reproductive and other strategies. The community's resilience depends on its capacity to adapt to the physical environment and on its relations with the other communities, e.g. through competition or predation. Communities are interdependent and interconnected as trophic networks (resulting from predator-prey relationships) depending on environmental variables. Food-web analysis and estimates of consumption are essential for understanding possible reactions of the ecosystem to exploitation regimes as well as rebuilding strategies and, during the last decade, the information on this matter has greatly improved (Trites, 2003).
    • Fig. 1 Levels of organization in specific illustration
    • Ecosystems may be observed in many possible ways, so there is no one set of components that make up ecosystem. However, all ecosystem must include both biotic and abiotic components, their interactions, and some source of energy. The simplest (and least representative) of ecosystems might therefore contain just a single living plant ( biotic component) within a small terrarium exposed to light to which a water solution containing essential nutrients for plant for plant growth has been added (abiotic environment) The other extreme would be the biosphere, which comprises the totality of Earth’s organism and their interactions with each other and the earth systems (abiotic environment). At a basic functional level, ecosystem generally contain primary producers capable of harvesting energy from the sun by photosynthesis and of using this energy to convert carbon dioxide and other inorganic chemicals into the organic building blocks of life. Consumers feed on this captured energy, and decomposers not only feed on this energy, but also break organic matter back into its inorganic constituents, which can be used again by producers. These interactions among producers and the organism that consume and decompose them are called trophic interactions, and are composed of trophic levels in an energy pyramid, with most energy and mass in the primary procedures at the base, and higher levels of feeding on the top of this, starting with primary procedures consumers feeding on primary procedures, secondary consumers feeding on these and so on. Trophic interactions are also described in more detailed form as a food chain, which organizes specific organism by their trophic distances from primary procedures, and by food webs, which detail the feeding interactions among all organism in an ecosystem. Together, these processes of energy transfer and matter cycling are essential in determining ecosystem structure and function and in defining the types of interactions determining ecosystem structure and function and in defining the types of interactions between organisms their environment. It must also be noted that most ecosystem contain a wide diversity of species, and that this diversity should be considered part of ecosystem structure.
    • Fig 2. illustration of the flow of matter and energy in ecosystem.
    • 1. Productivity plant specific leaf area Plant gas exchange structures Plant root to shoot ratio Plant leaf/stem architecture canopy structures/leaf area index nutrient use efficiency Decomposition plant tissue chemistry soil biota 2. Energy transfer  Loss food web length/complexity/connectivity  Nutrient/water cycling  Soil chemistry  Soil density/composition 3. Balance  Stability/resiliency/homeostasis  Niche breath/overlap  Species competitive hierarchies  Self-organization/regulation/entropy
    • Food web and food chain- a food web is a graphical description of feeding relationships among species in an ecological community, that is, of who eats whom (fig.1). It is also a means of showing how energy and materials (e.g., carbon) flow through a community of species as a result of these feeding relationships. Typically, species are connected by lines or arrows called species are connected by lines or arrows called “links”, and the species are sometimes referred to as “nodes” in food web diagrams.
    • Energy input to ecosystem drives the flow of matter between organism and the environment in a process known as biogeochemical cycling. The biosphere provides a good example of this, as it interacts with and exchanges matter with the lithosphere, hydrosphere, and atmosphere, driving the global biogeochemical cycles of carbon, nitrogen, phosphorus, sulfur and other elements. Ecosystem processes are dynamic, undergoing strong seasonal cycles in response to changes in solar irradiation, causing fluctuation in primary productivity and varying the influx of energy from photosynthesis and fixation of carbon dioxide into organic materials over the year, driving remarkable annual variability in the carbon cycle-the largest of the global biogeochemical cycles. Fixed organic carbon in plants then becomes food for consumers and decomposers, who degrade the carbon to forms with lower energy, and ultimately releasing the carbon fixed by photosynthesis back into carbon dioxide in the atmosphere, producing the global carbon cycle. The biogeochemical cycling of nitrogen also uses energy, as bacteria fix nitrogen gas from the atmosphere into reactive forms useful for living organism using energy obtained from organic materials and ultimately from plants and sun. Ecosystems also cycle phosphorus, sulfur and other elements. As biogeochemical cycles are defined by the exchange of matter between organisms and their environment, they are classic examples of ecosystem-level processes.