Lotic Ecosystems - RCCs

Lotic Ecosystems

Allochthonous inputsLeaves and needles

HerbaceousShrubsTrees

WoodFine particulate matter

FrassSoil

Autochthonous inputsAlgaeMossesVascular macrophytes

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.

Riparian AreasEcotones

Interfaces between adjacent ecosystems

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

Forested riparian systems

Non-forested riparian systems

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

Floodplain systems