STREAM ECOLOGY

Lotic (stream) environment

I. Zones and distributions
    A. Physical factors
        1. Changes in water levels – seasonal; some unpredictable
        2. Changes in temperature – changes oxygen capacity
            a. Small streams; unshaded streams
            b. Stratification rare except in pools.
        3. Oxygen
        4. Chemistry – determined by catchment:
            “In every respect, the valley rules the stream” (Hynes 1975)

        5. Light – if stream has canopy or is turbid, low light may limit primary production in the stream itself
        6. Flow
            a. Advantages
                1. respiration
                2. filter feeding
                3. transportation (if organisms can control it)
                4. chemical communication – water flow increases chemical movements – prey can detect upstream predators

            b. Disadvantages –
                1. can dislodge organisms
                2. shearing action of flowing water transports and deposits material, continually changing the physical environment
    B. Riparian zone – normally above water line; may be inundated during floods
        1. Allochthonous inputs – inputs to the system from outside – DOM, leaves, etc.
        2. Water and nutrient inputs

            Chemical transformation -- e.g.,  NH4+ to NO3-
             adsorption of nutrients

    C. Shore zone – often bare; colonization difficult – water level often fluctuates
    D. Water column
        1. Potamoplankton – river plankton; usually algae
        2. ‘tychoplankton’ – don’t belong there but are washed in
        3. drift – mostly aquatic insects – organisms being carried downstream; may include zooplankton in large rivers
        4. fish
    E. Benthos - – attached or free-living on bottom
        1. Aufwuchs – fungi, algae, bacteria, protozoans and some organisms feeding on them
            a. Epipelic
            b. Epilithic
            c. Epiphytic
        2. rooted plants
        3. animals: aquatic insects, mollusks, fish
    F. Hyporheic – “below current”

II. Adaptations
    A. Algae
        1. firmly attached to hard substrates
        2. motile
        3. body form
            a. flattened – trying to remain in boundary layer where there is little current
            b. trailing filaments – increase exposure to nutrients
    B. Higher plants (angiosperms, liverworts, mosses)
        1. attached to rocks
        2. rooted in substrate – tough yet flexible stems
    C. Potamoplankton
        1. River size – there are more potamoplankton as go downstream, with increased size of stream and often get decreased velocity spots
                (pools)
        2. No special adaptations
        3. Seasonal changes due to export from nearby quieter waters

D. Benthic Invertebrates – most adaptations, wide phylogenetic diversity
    1. Diversity
        a. Mollusca (Gastropoda, Bivalvia);
        b. Turbellaria (flatworms)
        c. Crustacea (crayfish, amphipods, isopods),
        d. Oligochaetes, Hirudinea (leeches)
        e. Acari (water mites), Porifera (sponges)
        f. Cnidaria (hydra)
        g. Nematoda (roundworms)
        h. Major orders of stream insects
            a.  Plecoptera - stone flies; mostly in temperate regions; rare in tropics; cool, clean streams of low orders;
                sensitive to low oxygen; tolerant of low pH; adults are poor fliers
            b. Trichoptera - caddis flies; worldwide distribution; both free-living case-building species
            c. Ephemeroptera – mayflies; world-wide distribution; gills for respiration; sensitive to low pH; adult lifespan short and do not feed 
            as adults.
            d. Odonata - dragonflies and damselflies; occur worldwide predators; stalk their prey; can eat vertebrates as well
            e. Diptera (true flies)- midges(Chironomidae - nonbiting midges); black flies (Simuliidae)
            f. Coleoptera (beetles) aquatic beetles tend to live in water both as larvae and as adults
 

   2. Morphology
            a. Flattened and streamlined - decrease resistance to flow; but is also an adaptation for living under rocks
            b. Suckers and hooks - allows to grasp rocks; hooks (tarsal claws)
            c. Tubes -- Chironomid larvae, sticky silk, attached to rock
            d. Ballast - help them to remain on bottom

    3. Behavioral responses to stream flow
            a. Current avoidance
            b. Drift (both a noun and a verb)
                    mostly at night
            c. There is also some movement upstream, but this is relatively slow
            d. Why drift?
                1) Proximate cause (cues) - light

                2) Ultimate or adaptive cause
                    a) None - Accidental -

                    b) None - Catastrophic drift -- pulsed high density movements resulting from major physical and chemical disturbances
                    c) Dispersal - behavioral drift
                        i. critical density of organisms that is too high
                        ii. lack of food
                        iii. avoid pollutants
                        iv. some individuals are genetically more predisposed to drift than others
                    d) Avoid Risks (greatest when moving in the water column) predation by fish

            e. Compensation for drift -- why aren't all the insects in the ocean?  Why are there any left in the streams?
                (1) Colonization cycle – upstream flight

                            Adults fly upstream; not tested until recently
                             -Arctic stream insects were labeled with 15NH4+ by introducing it into the stream
                             -Collected adults upstream later in season when emerging
                             -Any insects above the 15NH4+ emergence point with 15N had to have come from downstream
                            Average distance of flight upstream ~2 km
                            Average distance of downstream drift ~2 km
                            Therefore upstream flight of adults can compensate for drift

                    (2) Excess production hypothesis

                            Even if many drift, there are still a lot left
                            Better success of eggs deposited upstream – less competition
                            Difficult to assess because it is difficult to measure upstream production and combine these
                                    measurements with downstream movement

III. Stream ecosystem ecology
    A. Feeding – functional group concept – ‘guilds’

        1. shredders - biters and chewers; take large food and produce small foods;
                                herbivorous or detritivorous (leaves and microfauna)
        2. scrapers - feed on aufwuchs (on substrates); specialized mouth parts to scrape material on substrates
        3. collectors - spin nets or use setae to collect organic matter; feed on fine particulate organic matter;
                                filter with nets, hairs; cephalic fans (black flies)
        4. predators - carnivorous; swallow prey whole or bite pieces or suck out contents
 

    B. detrital material - much of the food web in a stream is detrital; this detritus is broken up into categories by size
        1. CPOM - coarse particulate organic matter; >1 mm; leaves, wood, litter
        2. FPOM - fine particulate organic matter; 50 mm-1mm
        3. DOM - <~0.45 mm

    C. How do the guilds fit together?
How the various feeding guilds fit together with each other and with organic material in streams
    D. River continuum concept (Vannote et al. 1980)
        - Streams change as you go from the headwaters to the high order rivers
            1. predictable physical features and gradients

            2. predictable biological features --             3. correlation of 1 and 2

Graphic of the river continuum concept

                -Why P<R at 1st order? --

                -In the middle order                 -Higher order streams


        4. criticisms -
            i. oversimplified;
            ii. mostly holds for pristine rivers
            iii. relates only to macroinvertebrates
            iv. if low order streams are devoid of forest then they aren't shaded and don't have high CPOM loads

    E. Resource spiraling concept (Newbold et al. 1982)
        1. closed system (no inputs or outputs; have rate and pathways)
        2. open system (inputs, outputs; rates, pathways, residence time)
        3. open system with spiraling (downstream transport)
            a. rate
            b. pathway
            c. residence time
            d. downhill transport 'spiral length' :

                Slow water, rapid turnover, short spirals
                Fast water, slow turnover, long spirals
                Often as productivity increases, spiral length decreases

                Important for looking at distubances and the responses to disturbances because they propagate downstream

    F. Controls on lotic community structure -- What controls the biosystem?
        1. density dependent = 'biotic interactions'; function of how many organisms are around
            a. competition - for space
            b. predation
            c. parasitism
        2. density independent = 'abiotic factors'
            a. floods
            b. changes in substrate
            c. changes in temperature (e.g. freezing)
        3. Which mechanism dominates? Evidence for both
            a. Abiotic factors have clear influences
            b. Correlational evidence -- density dependent correlations of 1 species with another.
            c. Experiments
                1)  Have shown clear effects of grazers feeding on periphyton
                2)  Manipulation of insect predators in cages have demonstrated biotic density dependent control
                3)  Manipulations of fish predators in cages -- small biotic effects (when you change fish abundance,
                        the abundance of insects doesn't change much), although big behavioral effects

            d. Conclusions
                1) Evidence favors strong abiotic controls
                2) Importance of time scale, large abiotic factors (flood/freeze) reset the system frequently so that you don't get
                    enough time/high enough densities for important biotic effects in many streams
                3) In more stable conditions you get lots of biotic interactions
                3) Really not settled yet
                    a) continuum of regulation -- Peckarsky
                    b) long-term records -- to see how often resetting occurs
                    c) density dependent effects -- often subtle; behavioral

GOOD GENERAL STREAM ECOLOGY TEXT BOOKS (also see Riparia book reference in last handout)

Allan, J.D. 1995. Stream ecology: structure and function of running waters. Chapman &  Hall.
Cushing, C. and J.D. Allan. 2001. Streams: Their Ecology and Life. Academic Press.
Giller and Malmqvist. 1998. The biology of streams and rivers. Oxford University Press.
 
 

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