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<br />(: <br />'< <br /> <br />f <br /> <br />~> <br />\ <br />\ <br /> <br />68 <br /> <br />carbohydr~tes', "and (3) climatic regime such as precipitation, temperature <br />and photoperiod. The biotic components include (1) ~Iducers or <br />autotroeh!S"on~an~sms largely characterized by photosynthetic greea plants, <br />(2) macroconsumers such as heterotrophic or~;anisms which ingest other <br />organisms or particulate organic matter, and (3) microc:onsumers cOllsisti;1g <br />chiefly of bacteria and fungi. <br /> <br />Although not generally recognized" stre,am ecosystE:ms are diffE!rent <br />from other ecosystems in several ways (Webst.er and Wallace 1974). ThE! <br />functional food chain/food web, nutrient cycles and eaergy circuits are <br />distinctly different from those of terrestrial and other ecosystems. For <br />example, the food chain concept has not been very useful in theoretical <br />approaches to stream ecology and has been largely replaced by the <br />functional group concept. The energy circuit of some stream ecosystems may <br />, <br />! not be dependent on the instream autotrophic: component as in most <br />\ terrestrial systems, but on energy produced from outside of the system <br />, (i.e., allochthonous). Nutrient cycles, as commonly visualized for ot:,er <br />l. types of systems, are essentially nonexistent within st.ream ecosystems. <br />i The linear configuration of streams and wate:r flow results in a do,mstream <br />! displacement of nutrients. Cycling still oc:curs, but the longitudinal <br />~ spacial dimension resul ts in partially open cycles called spirals. <br /> <br />The Biotic Communit~ Concept <br /> <br />(The three maj or biotic components of all ecosystems (producers, <br />macroconsumers, microconsumers) compose the biotic community. Bv <br />definition. a biotic community is any assemblage of populations living in a <br />prescribed*1\abitat, forming an organized unH to the e>:tent that il: has <br />characteriStics additional to its individual and popuhtion cOmpOnl!nts and <br />functioning as a unit through coupled mutual interactions and coupled <br />dependence (Odum 1971). Communities not only have a de:Unite func1:ional <br />unity witn characteristic trophic structures and patterns of energy flow <br />but they have compositional unity in that there is a cE:rtain probability <br />that certain species will occur together (Odum 1971). The importance of <br />the community concept relates to the fact that diverse organisms survive <br />together in a physical-chemical setting (1.e., an ordet:ly manner) and not <br />in isolation. <br /> <br />.~ <br />'f <br /> <br />" <br />,~ <br /> <br />~ <br />\ <br /> <br />The significance of the biotic community concept is related to the way <br />in which stream communities have been analy"ed. For e.:ample, stream <br />communities have been analyzed according to two contrasiting .approaches: <br />(l)"the lonal approach whereby all of the organisms in a prescribed stream <br />rea~"<<."ntlii!n..a,~inil"U8ted along with a variety e,f qualitative and <br />qua~dti~Ne~tIIeasurements, and (2) tbegradl';,!!ll analyst:.! approach, which <br />involves- ~e,auangement of populations along a un1-dlDlensional or <br />INlti-dimensional environmental gradient or axis with e:ommunity re':ognition <br />Jlased on' frequency distributions, simllar1tl' coefficients and other <br />parameters (Odum 1971, Braus et al. 1983). <br /> <br />~,...... <br />