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21 Cards in this Set
- Front
- Back
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Describe movement in rivers
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Movement: immigration and emigration
- Floods and droughts are common - Unpredictable reductions in biotic abundance - Colonization often rapid - Adaptation: good colonizer or dispersers (stay or get out quickly) |
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General Model of Movement
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dN/dt = I - mN
I = immigration N = density m = per capita emigration Solution: Nt = (I/m)(1-e^-mt) e^mt = decay rate 01: as t gets large, e^-mt gets small 02: as Nt approaches i/m (the eq'm density) GRAPH: incr then pleateaus - pleateaus as reaches eq'm (immigration = emigration) ---> can only come in when one goes out; what goes in = what goes out - space fills, less resources, thus pleateaus - carrying capacity is determined my space -- At eq'm: dN/dt = 0, 0 = I -mN, I = mN -- Eq'm value: I - mN |
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Experimental Evidence of General Model of Movement
Cibrowski and Clifford: Stoneflies and Simulum |
01: Stoneflies equilibrate in 1-2 days
02: Simulum reach max density in 1 day and then decline -- Blackfly/simulum reaches carrying capacity quicker then drops off radically --- Stoneflies stay, blackflies leave Reasons: Why is 1 a match to model while the other is not? 01: succession: ex. algae; cant use anchor on algae because too slick --- embedded polysacharride matrix on rocks --- biofilm interference with grasp 02: habitat degradation ---also algae and biofilm, leave to find bare substrates 03: Density Dependence --- predation: might get eaten by stoneflies or avoidance --- competitive exclusion |
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Experimental Evidence of General Model of Movement
Shaw and Minshall |
Results:
01: Baetis (mayfly) reach equilibrium density in 4 days 02: Capnia (stonefly) reach equilibrium density in 4 days 03: Chironomidae (midge) still increasing after 2 months Reasons: Baetis and Capni match model, why not Chironomidae? 01: Mayflies and stoneflies are good swimmers and drifters, they colonize very quickly. --- 1 and 2 have different means of arrival but are both fast at immigration 02: Midges are slow colonizers --- drift in high propensity, but are slow swimmers --- drift in low density, never reach equilibrium --- succession: environment must change before midge finds it suitable --- density dependence: another organism may be responsible for conditioning the environment before them ---- High drift rates tend to match model, depends on organism characteristics |
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Where are the sources of colonists? Where do they come from?
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01: Downstream: crawl upstream
-- Very cost efficient, fight the current -- Stoneflies: get under and crawl 02: Aerial: fly in -- ex. beatles: true bugs (hemiptorins) -- have wings, are both aquatic and terrestrial, rapid colonizer 03: Vertical: organisms in the sediments, migrate toward the top 04: Upstream: drift -- most common -- low E expenditure -- drift down current ---sources change depending on season, species composition and habitat |
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Rank the colonists and provide percentages
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Observed via colonization trays: containers that eliminated aspects of other colonization techniques, but still flawed (ex. found snails in aerial...overest. aerial)
A: from upstream (drift) 40% B: from downstream 18% C: hyporheic (lower bottom sediments) 19% D: Aerial 28 % - hyporheic/aerial and downstream movement vary but DRIFT is #1 typically |
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Who drifts? How can you measure drift?
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Drift is measured by drift nets.
Drift rate: #/time or drift density #/vol of discharge Mayflies, dipterans (midges), some stoneflies, caddisflies (kinds that build nets) |
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Categorizations of drift
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01: Catastrophic (floods)
02: Constant drift (continuous) - backed up stuff in water column --> accidental drift 03: Behavioural (response/ active choice) - diel periodicity: peaks in drift - night drift > day drift - 2 peaks: sunset and sunrise - aperiodic: day = night drift Why big peaks? --> predators: peak because hungry, come out to eat algae on top of rocks ---> sensitivity: sun, etc. ---> peaks due to FEEDING: cycle of full and hungry 01: First peak: hunger, first meal 02: Intermediary: hungry 03: Final peak: last chance to feed or find a new place to hide |
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Why drift?
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01: Colonize: find new habitata
02: New resources: poor resources / depletion 03: Leave unfavourable patches: new loc, new resources, bad food resources 04: Predator/Competition avoidance 05: Low cost dispersal: easy to do |
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Why drift at night?**
Hypothesis #1 |
Hypothesis #1: Accidental Drift:
- animals are more active at night on top of substrate (more likely to dislodge at this time) - entering the drift is accidental - drift is a passive process - veloc at top > low, get knocked off Experimental Evidence: 01: Bailey: Animals more common on tops of stones at night (feeding) - correlation of activity on tops of rocks and drift at night 02: Kohler: manipulated activity levels via STARVATION - starved mayflies as active during day as fed mayflies at night - should see high drift rates during the day (alter behaviour) Results: drift was still nocturnal --> not a passive process, it is a behavioural, active decision |
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Why drift at night?
Hypothesis #2 |
Hypothesis #2: Predator Avoidance
Anecdotal Evidence for: 01: larger animals tend to drift more at night -- big: don't want exposure during day due to predation - Anecdotal Evidence against: 01: meiofauna (small) show nocturnal drift (Why? Nothing is eating them) ---> genetically hardwired: smaller versions of soon to be large bugs Experimental Evidence: If you take insects out of a fish stream and put into a fishless stream (still drift at night) Suggests: - nocturnal drift behaviour is genetically fixed (DNA) - cue is programmed in response to light (programmed cue) -- If behaviour is plastic, drift times should change in presence of predators ---> Can it be shifted? ---> Everything has a genetic component, all that varies is the felxibility ---> Conditioning tests that flexibility |
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Why drift at night
Experiment: Andes mountains (Drift behavior in fish and fishless stream) |
- Compared drift at night / drift at day (N/D)
01: Fish stream - N/D > 1 (nocturnal drift) 02: Fishless stream - N/D =1 aperiodic drift) --> no change in drift, stay the same - Test if the effect is plastic or fixed by adding fish to a fishless stream (see if they will still start to drift). - Cage the fish so no drift mortality (sew, glue mouths, mesh: bugs can see and smell preds; can't be eaten) Results: INCR in preds, DECR in DAY drift, INCR in NIGHT drift ---> Drift is an active process: flexible behaviour response (underlying genetic components) ---> flexibility: aperiodic --> periodic ---> adjusted so quickly that must be hardwired and not learnes |
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Factors affecting propensity to drift: List
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01: Unsuitable physical/chemical/biological conditions
-- poison, toxic, etc. 02: Food availability: DECR algal biomass, INCR grazer drift rate 03: Density of competitors (conspecific) 04: Antagonistic Encounters 05: Predators: (drift feeders vs. benthic feeders) |
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Factors affecting propensity to drift:
Density Independent vs Density Dependent |
If density independent:
- no change in behaviour with density - linear relationship between drift and density If density dependent: - change in behaviour with density - curvilinear relationship between drift and density --- As population size increases, more inverts drift -----> regulates the population, maintains population at equilibrium, stability -----> density dependent |
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Factors affecting propensity to drift:
Antagonistic Encounters |
- Agressive interactions increases drift rates
- Ex. hydropsychid caddisfly aggressions - Increases with density (battle over nets) ---> judge size by signal strength of rubbing body limbs together ---> if caddisfly is smaller, will flee, if bigger, stay, and same size, will fight |
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Factors affecting propensity to drift:
Predation |
- drift feeders vs. benthic feeders
- expt: BENTHIC feeders (Kratz) ---> prey responded to benthic predatos by INCREASING drift rates - Expt: DRIFT feeders (Forester) ---> rainbow trout typically ---> VARIABLE prey response, increase or decrease drift rates WHY? Increase: - may be foraging down at rocks and jump off to avoid predators - weighing risks and rewards Decrease: - hide or freeze (fish are motion detectors) |
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Consequences of Drift: Upstream Depletion
Hypothesis #1 |
Hypothesis #1: Colonization Cycle
- compensatory upstream flight - everything is drifting - expect headwaters to have less and less bugs ---> but no observable differences (seasonal) ---> can see depletions in cycle, but don't last ----> explained by reproduction: drift downstream in larval forms then fly back to reproduce |
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Upstream Depletion:
Expt: Neves and Hershey |
01: Screens with sticky paper to track upstream flight
- Which collects more bugs? (-) Wind can blow bugs into them - However, typically see more bugs coming downstream to upstream 02: Labeled algae with 15N, tracer eaten by mayflies: how far before taken up by biota? - went up trophic levels: incorporated by algae then herbivores - noted downstream depletion - yet equal amounts of upstream and downstream at the start of next year - labeled bugs returned by flight - 2nd gen still had label left in them - Drifts in high concentration - Downstream depletion: hardly any in larval forms anymore, fly back |
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Consequences of Drift: Upstream Depletion
Hypothesis #2 |
Hypothesis #2: Surplus Production
- Drift is surplus production in excess of carrying capacity - Every substrate has a carrying capacity on nutrients - When it is exceeded, more organisms present, have an excess that can't be supported by carrying capacity ----> Surplus - less that 0.1% of bugs are in suspension at any one time (more at bottom) |
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Fish Movements (Migrations): What are the two types?
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01: Anadromous
- Spawn in fresh water and live in salt - ex. salmonids, herrings, lampreys, sturgeon - homing (smell way home) (-) cost efficient and dams, which destroy pops 02: Catadromous - spawn in salt water and live in fresh - ex. American and European eels WHY? -- > no one else is doing it, wide open niche space salt: lots of food, lots of preds fresh: little food, little preds |
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Fish Movements (Migrations):
Flood Plains |
ex. Nile River Valley
Main stem (migration route) - flood plain (production zone) Types of Fish: ex. Africa 01: White fish: migrate onto floodplain - not much in the US: constrained flood plain from reaching levies - levy breaches, lay eggs, feed, leave - ride wave, flow in then out - fusiform fish, made to handle fast speeds and turbulent waters - current fighting - handles cold H2O - high O2 regulation 02: Black fish: remain on floodplain all year - adaptations to high temperature (warm H2O) and low O2 - darker, laterally compressed - macophyte - agile movability |
