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Trophic structure of consumers
Herbivores - consume living plants
Detritivores - consume non-living organic matter
Carnivores - consume living animals
Feeding Functional GroupsScrapers - scrape surfaces of substrates
Shredders - tear large particles apart
Collector-gatherers - collect small particles of organic matter
Predators - engulf other animals
Headwater streams
Dominance of allochthonous inputsCanopy shading reduces primary productionAquatic invertebrates dominated by shredders and collectors
Larger streams
Significant inputs of both allochthonous and autochthonous matterAquatic invertebrates dominated by scrapers and collectors
RiversShift toward planktonic primary productionDominance of fine particulate organic matterAquatic invertebrates dominated by collectorsExtensive floodplain development
Riparian AreasLegal - streamsideLinear - edge perspectivePlanar - surface areaFunctional - three-dimensional zone of influenceStructural - mosaics of geomorphic surfaces that are created and maintained by disturbance. The geomorphic surfaces and terrestrial plant succession create the riparian area.
River Continuum Concept
Streams represent a continuum of physical, chemical, and biological characteristics extending from the headwaters to large rivers
Dynamic equilibrium
Steady state systems rarely exhibit exact equilibria.River and its channel tends toward a mean form, definable only in terms of statistical means and extremes.
River Continuum Concept
Over extended river networks, biological communities should become established which approach equilibrium with the dynamic physical conditions of the channel.
Biodiversity
Biodiversity is greater in mid-order reaches
Multiple organic matter sourcesPhysical heterogeneity
Equilibrium of energy flowIndividuals will tend to exploit their environment as efficiently as possibleBiological systems tend to maximize energy consumptionSystems use resources efficiently through resource partitioningSystems tend to process energy uniformly through time
Ecosystem processingIn each reach, some material is processedIn each reach, some material is storedIn each reach, some material is releasedDownstream communities will be influenced by the materials transported from upstream reaches
Time invariance
Disturbances are more frequent and widely distributed in river ecosystems than in most ecosystemsSuccession (sensu Clements) or seralchanges in communities through time are not observed in stream ecosystems
Qualifications in the RCC
RCC developed for relatively unperturbed streamsMany streams deviate from general patterns of autotrophy/heterotrophyTributaries entering the mainstem have localized effects
Criticisms of the RCCEnergy equilibrium
Systems rarely exhibit uniform geology, topography, climate throughout a basinUniform rates of processing through time are unclear. Are seasonal changes considered?Examples from hydraulics were not presented. Velocity, Fr, Re, τ
Criticisms of the RCCEntropy patterns
RCC suggests that there is a constant gain in entropy from headwaters to large riversClarification is neededBiological systems tend to be “negentropic” over short periods of time
Criticisms of the RCCUtilization of energy
Not all systems exhibit seasonal replacement of species (especially tropical systems)Do biotic communities mazimizeutilization of energy? Experiment in Coweeta observed decreased particulate export when invertebrates were eliminated experimental with insecticide.
Criticisms of the RCCSuccession
Ecologists debate the occurrence of succession in streams.Modern concepts of succession are more complex or robust than simple Clementsian succession.
Criticisms of the RCCPatterns of Biological Diversity
Other patterns of diversity and physical heterogeneity; not always in mid-reachesOther explanations (marine systems, other sources of energy or species)Fish, phytoplanton, and other biota do not show same pattern as invertebrates
Major omission
Role of floodplains in longitudinal profiles and interaction with adjacent ecosystems
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