EEMB 148: Midterm 3

what are the two components of movement in a river?

immigration and emigration

what are five reasons rivers are considered disturbed habitats?

1. floods and droughts are common

2. unpredictable reductions in biotic abundance

3. colonization is often rapid

4. habitat heterogeneity is high

5. resources are patchy in space and time

what is the general model equation for movement and colonization? what do each of the terms mean?

dN/dt = I - mN

• I = immigration

• N = density

• m = per capita emigration

change in density is a factor of the change in time

how does the general model change at equilibrium (where immigration equals emigration)?

I = mN

organisms come into the space fast and stay

what are the results of the Cibrowski and Clifford experiment testing the general model on stoneflies?

stoneflies equilibriate in 1-2 days

MODEL MATCH

what are the results of the Cibrowski and Clifford experiment testing the general model on Simulium?

Simulium reach max density in 1 day and then decline

Simulium do NOT stay

NOT A MODEL MATCH

why were Simulium not a model match in the Cibrowski and Clifford experiment? (three possibilities)

predation: Simulium are eaten by stoneflies

succession/habitat degradation: rocks become smoother → biofilm forms → leads to filamentous algae → Simulium can no longer attach to rocks

density dependence: filter feeding organisms compete with each other for resources

what are the results of the Shaw and Minshall experiment testing the general model on Baetis (mayfly)?

Baetis reach equilibrium density in 4 days

MODEL MATCH

what are the results of the Shaw and Minshall experiment testing the general model on Capnia (stonefly)?

Capnia reach equilibrium density in 4 days

MODEL MATCH

what are the results of the Shaw and Minshall experiment testing the general model on Chironomidae (midge)?

Chironomidae still increasing after 2 months

Chironomidae do NOT get there fast

NOT A MODEL MATCH

why were Chironomidae not a model match in the Cibrowski and Clifford experiment? (three possibilities)

Chironomidae have low drift rates

succession: habitat gets better over time → more resources for them to settle

inverse density dependence: need more competition in order to settle

what are the four sources of colonists?

1. downstream (down to up)

2. upstream (up to down) (drift)

3. aerial (top to bottom) (flight)

4. hyporheic (bottom to top)

what was the experiment that Williams and Hynes did on the source of colonists? what were the results?

used colonization trays to measure drift rate/density

results: majority of movement is upstream to downstream

what were the two issues with the Williams and Hynes experiment?

• underestimates downstream to upstream

  • trout uses the nets to feed 

    • combination of slow water current and lots of bugs creates a good place for trout to stay

• overestimate aerial

  • snails climb the tethered net and eats the algae

what are the three types of drift?

1. catastrophic (floods): organism is forced to move

2. constant drift (continuous): organism moves by accident by slipping

3. behavioral: organism moves by choice

what is the difference between diel periodicity and aperiodic?

diel periodicity: night drift > day drift

aperiodic: night drift = day drift

what are the five reasons why organisms drift?

1. colonize

2. new resources

3. leave unfavorable patches

4. predator/competition avoidance

5. low cost dispersal

what is hypothesis #1 for why organisms drift at night?

accidental drift:

• animals are move active at night (top of substrate)

• entering the drift is accidental

• drift is a passive process

what is the experimental evidence from Bailey?

• animals more common on tops of stones at night (feeding)

  • correlation of activity on tops of rocks and drift at night

what is the experimental evidence from Kohler?

manipulated activity levels via starvation

• starved mayflies during the night → should be hungry during the day

• observed NO change in drift

results: drift was still nocturnal and not a passive process

what is hypothesis #2 for why organisms drift at night? what is the evidence for and against this hypothesis?

predator avoidance:

• evidence for: larger animals tend to drift more at night

• evidence against: meiofauna (small) show nocturnal drift

what is the experimental evidence for hypothesis #2?

if you put insects from a fish stream into a fish-less stream, the insects still drift at night

suggests that nocturnal drift behavior is genetically fixed (cue is a programmed response to light)

what were the results of Flecker’s comparison in fish and fish-less streams in the Andes mountains that helped to show if drift behavior was plastic or not?

• drift behavior in fish and fishless streams in the Andes mountains

  • compared drift at night / day (N/D)

  • results:

    • fish streams: N/D > 1 (nocturnal drift)

    • fishless streams: N/D = 1 (aperiodic drift)

what were the results when Flecker added fish into a fish-less stream? is drift behavior plastic?

• cage with fine mesh to prevent fish from feeding on the drifters

• results: 

  • increased predator → decreased day density → increased night density

drift is an active process — flexible behavioral response

what is the first factor affecting propensity to drift?

unsuitable physical/chemical/biological conditions

what is the second factor affecting propensity to drift?

food availability: ⬇ algal biomass ⬆ grazer drift rate

what is the third factor affecting propensity to drift?

density of competitors

• more competitors = harder to make a living

  • density dependence: lots of competitors = greater proportion will enter the drift

  • density independence: lots of competitors = no change in proportion drifting

what is the forth factor affecting propensity to drift?

antagonistic encounters: aggressive interactions increase drift rates

what is the fifth factor affecting propensity to drift? what did the Kratz/Even and Forester experiments show?

predator: drift feeders vs. benthic feeders

• Kratz and Even: benthic predators lead to increased drift

• Forester: drift predators lead to variable results (either drift at night or hide)

what is the first hypothesis used to explain why upstream depletion is not a seen consequence of drift?

Muller’s Colonization Cycle – compensatory upstream flight

what was the results of the Neves experiment that tested the colonization cycle hypothesis? Were there any problems with the design?

Neves: screens with sticky paper to measure upstream flight

• error: weak fliers – heavily influenced by wind

what was the results of the Hershey experiment that tested the colonization cycle hypothesis?

Hershey et al.: labeled algae with radioactive nitrogen, measured downstream depletion

• found that there were equal amounts upstream and downstream at the start of the next year

  • offspring of the original mayflies 

  • parents flew upstream to lay eggs

what is the second hypothesis used to explain why upstream depletion is not a seen consequence of drift?

Water’s surplus production — drift is surplus production in excess of carrying capacity

what is anadromous fish movements?

spawn in fresh water and live in salt water

• less predation in fresh water

• more resources in salt water

what is catadromous fish movements?

spawn in salt water and live in fresh water

• no competition

• open niche in fresh water

what are the movements of white fish? what adaptations do they have?

migrate onto floodplain 

• eat quick and lays eggs

• water starts to retreat → adults and juveniles leave

adaptations to low water temperatures and high oxygen

what are the movements of black fish? what adaptations do they have?

remain on floodplains all year

• moves from deep to shallow areas

adaptations to high temperatures, low oxygen, and camouflage

are stream communities structured by abiotic or biotic factors?

it depends

flashy streams: changes in discharge = controlling factor

stable streams: biological interactions = controlling factors

what is competition?

negative interaction where organisms are harmed by the association (-, -)

occurs over resources (food, space, light, nutrients, etc.)

what are the three conditions for competition to occur?

1. resources must be limiting

2. densities of organisms are high

3. environment is stable

what is intraspecific competition?

within one species

what is interspecific competition?

between two species

what is interference competition?

direct, physical interaction

what is exploitative competition?

indirect, typically mediated via a resource

what is the first idea within resource partitioning?

competitive exclusion principle → complete competitors can not coexist in the same niche

what is the second idea within resource partitioning?

ghost of competition past → past competition has led to niche diversification

what is niche overlap? how can you test for niche overlap?

• niche overlap: experiences both intra- and interspecific competition

  • species will diversify and separate decreasing the amount of niche overlap

• test: remove one species and observe the other species 

  • experience competitive release and undergo a niche shift

  • could not shift over → may be genetically or physiologically fixed

what is the first way to measure resource partitioning? what did the Winemiller experiment show?

large scale habitat use, temporal (seasonality), microhabitat, food resources

• ex. Winemiller – lack of diet overlap in tropical fishes

  • wet season – when food is abundant: ⬆ C ⬇ diet overlap

  • dry season – when food is scarce: ⬇ C ⬆ diet overlap

suggests competition is currently operating

what is the second way to measure resource partitioning? what did the Hynes experiment show?

distributional comparison (allopatry vs. sympatry)

• Is the niche breadth wider where competitors are absent?

  •  ex. Hynes – Great Britain vs. Isle of Mann

    • Great Britain: strong competition keeping these species apart

    • Isle of Mann: species A occupies the entire stream

suggests competitive release = niche shift

what is the third way to measure resource partitioning? what did the Hydropsychid caddisfly and black flies experiment show?

density relationships (negative correlation suggests competition)

• problem with spatial scale (from the perspective of the organism)

• ex. hydropsychid caddisfly and blackflies

  • species interact on a spatial scale of centimeters, not meters

  • compete for space in the best filtering locations

experimental test #1: intraspecific interference competition between riffle bugs

size of bugs determines preferred feeding size 

• directly fight over a resource

experimental test #2: interspecific interference competition between brown trout and brook trout interaction

• brown trout utilize the best locations

• removed brown trout → brook trout changed resting sites into vacated areas

  • demonstrates competitive release

• brown trout bite the brook trout to maintain the best spaces

experimental test #3: intraspecific exploitative competition between Helicopsyche

• observations: ⬆Helicopsyche ⬇ algae ⬇ Helicopsyche growth

  • no aggression noted

• increased food → increase Helicopsyche → increase Helicopsyche growth 

experimental test #4: interspecific exploitative competition between Glossoma and other grazers

• observations: ⬆ Glossoma ⬇ algae ⬇ grazers 

• experiment:

  • no Glossoma = high algae = ⬆ grazers

  • no Glossoma = low algae = ⬇ grazers

    • resource dependent

  • Glossoma present = low algae = ⬇ grazer

    • G depletes resources which decreases grazers

why are there so many species and how is diversity maintained? what predictions does that lead to?

• ghost of competition past: evolutionary time scale

  • diversity maintained by speciation 

  • environmental stability = higher diversity

what are the diversity trends for fish and insects in tropical vs. temperate streams?

• fish density tends to increase towards the equator

• no trend for insects

  • insects are able to fly and share their genes

what is the theory of ongoing competition? how does that effect diversity?

competitive exclusion → diversity reduced by strong competition

what maintains diversity with ongoing competition?

disturbance

• remove organisms and free spaces for inferior competitors

• tradeoff between competitive ability and colonization ability

example of ongoing competition in sedentary invertebrates: Hydropsyche and Simulium observations

successional replacement over the summer

is the replacement driven by abiotic (season) or biotic (competition) factors?

what happened in the treatment where you removed Hydropsyche?

⬇ Hydropsyche ⬆ Simulium

Simulium is able to survive through summer → not abiotic factors

what happened in the treatment where you removed Simulium?

no change Hydropsyche ⬇ Simulium

Simulium has no impact on Hydropsyche → asymmetrical competition

what happened in the treatment where you removed both Hydropsyche and Simulium?

⬇ Hydropsyche ⬆ Simulium

Simulium is the better colonizer/reproducer

what kind of competition occurs between Hydropsyche and Simulium?

Hydropsyche outcompetes Simulium for space by cutting Simulium in half

interspecific interference competition

how do the results of the Hydropsyche and Simulium experiment change with intermediate levels of disturbance?

Hydropsyche and Simulium are able to co-exist through summer

what are the effects of predation?

• reduce prey

• effects on habitat use and foraging

• cascading interactions

what are the two types of predators?

1. invertebrate

2. vertebrate

how do predators respond to an increase in prey density?

predator functional response: the consumption rate of prey by predator changes with prey density

what is a type 1 predator functional response?

• # of prey killed increases with density

  • ⬆ predator ⬆ feeding rates

• proportion killed is a flat line

• predators CANNOT regulate the population

• unrealistic in nature

  • issues with satiation and handling

what is a type 2 predator functional response?

• # of prey killed increases then flatlines

• proportion killed decreases

  • predators become full and cannot eat any faster

• predators CANNOT regulate the population

• rare in nauture

  • sand/bedrock rivers

  • artificial channels

what is a type 3 predator functional response?

• # of prey killed is a logistic curve showing a lag for search time, predator eats a whole bunch, and reaches equilibrium

• proportion killed is a u-shaped curve

  • low to intermediate densities are regulated by predators

  • at high densities → predator swamping

what does the size selectivity curve expected to look like for predators that don’t have size selection vs. those that do?

no size selection = flat line

size selection = u-shaped curve where at some point prey is too big to be eaten or fights back

what does the size selectivity curve actually look like for invertebrates?

invertebrates demonstrate size selectivity

MODEL MATCH

what does the size selectivity curve actually look like for fish?

fish do not demonstrate size selectivity as there is almost no prey that is too big for fish to consume

NOT A MODEL MATCH

what does predator size influence?

determines diet breadth

what determines the minimize prey size consumed?

gill raker → acts as a cage within fish

what determines the maximum prey size consumed?

gape (how wide the mouth opens)

what is the first adaptation that prey use to avoid being eaten?

reduce activity ⬇ encounter rates ⬇ resource acquisition

what is the second adaptation that prey use to avoid being eaten?

avoid top of substrate ⬇ encounter rates ⬇ resource acquisition

what is the third adaptation that prey use to avoid being eaten?

nocturnal activity ⬇ encounter rates ⬇ resource acquisition 

• effective against visual predators like fish

• not effective against tactile predators like invertebrates (use sense of smell)

what is the forth adaptation that prey use to avoid being eaten?

morphological defense (armor)

• energetically costly 

what is the fifth adaptation that prey use to avoid being eaten?

escape responses

• drift 

  • effective against invertebrate 

  • fish would immediately consume

• posturing (looking bigger)

  • effective against invertebrates because of poor eye sight and prey size limits

  • fish would want to eat the prey even more

what are the two mechanisms of predator effects?

1. consumption (global effect)

2. behavioral modification (local effect)

what is interaction modifications?

the interaction between two species is modified by the presence of a third species

what are the two types of interaction modifications?

1. facilitation (+)

2. inhibition (-)

what did Soluk and Richardson observe in channels with and without trout? what did their observation lack?

trout grow faster in the presence of stoneflies

• lacked a mechanism for this effect

what were the two predictions of Even’s experiment in Southern California streams to uncover the mechanism for the previous observation?

1. predators will decrease prey

2. multiple predators will significantly decrease prey

what were the results in the treatment measuring density / consumption?

odonate: ⬇ prey

trout: ⬇ prey

odonate and trout: ⬇ prey

impact is no larger with both species

what were the results in the treatment measuring emigration / escape?

odonate: ⬆ prey

trout: ⬆ prey

odonate and trout: ⬆⬆ prey

what were the results in the treatment measuring exposure / hiding?

odonate: ⬇ prey

trout: ⬇ prey

odonate and trout: ⬇ prey

what were the overall results from Even’s initial experiment?

no significant different in number of prey consumed by multiple predators and predators in isolation

what did Even do to determine the why there was no significant different in prey consumed?

examined the stomach contents of trout and odonates

what were the results when Even examined the stomach contents?

trout decreased foraging rates of odonates

• trout harass odonates causing them to hide → inhibition

odonates increase foraging rate of trout

• when odonates hide, prey chose to escape and drift

• when prey drift, they are consumed by the trout

no net effect = compensatory mechanism

what is the equation for predator impact? what do each of the terms mean?

PI = - ln(Np/No)

• Np = prey density in cages with predators

• No = prey density in cages without predators

what is the general model equation for predator exchange rates?

dN/dt = c(Ne-Ni) - aNiP

• c = exchange rate  = the rate at which an organism moves across a boundary

• Ne = prey population density exterior of cage

• Ni = prey population density interior of cage

• aNiP = number of prey consumed

  • a = attack rate 

  • P = number of predators

what are the three predictions of the predator exchange rate model?

1. as a increases, PI increases

2. as P increases, PI increases

3. as c increases, PI decreases

predator effects on prey density are greater in habitats with reduced prey exchange

what were the two predictions for the Even and Cooper experiment in Sierra Nevada streams?

1. predators will decrease prey

2. increase in exchange rates = decrease predator impact (PI)

what were the two treatments for the Even and Cooper experiment in Sierra Nevada streams?

1. added trout and stoneflies

2. across a gradient of prey (baetid mayfly) exchange rates in channels

explain this results graph from the Even and Cooper experiment in Sierra Nevada streams.

NOT A MODEL MATCH

• low exchange rates, prey are in refuge

  • type 3 → cannot find prey → search and attack is low

  • PI is low

• at intermediate exchange rates, prey are exposed

  • too high of prey density → cannot all hide

  • replacement is low

  • PI is high

• at high exchange rates, predator impact is swamped

  • PI is low

why was the Even and Cooper experiment in Sierra Nevada streams not a model match?

model was too simple → immigration and emigration are not equal

bugs: I < E

fish: I > E

what is a trophic cascade?

the effects of upper trophic levels cascade via direct and indirect effects through lower trophic levels