2) Angus McIntosh

Question 1

Predation definitions

• true predators
• grazers
• parasitism
• parasitoids

Answer 1

• true predators: kill prey straight after attacking it
• grazers: effects is rarely lethal, remove only part of an individual. Attack large no.s of individuals in a lifetime.
• parasitism: effect is rarely lethal, or takes a long time to kill an individual. Removes only part but usually only attack on individual
• parasitoids - intimately associated withe one host. does not cause immediate death, bu eventually death is inevitable

Question 2

Predator strategies

Answer 2

• sit and wait predators: select profitable locations. location determines encounter rate.
• active predators - search, encounter determined by predator movement/behaviour.

Question 3

Mayfly and Stonefly example: aggregations of predators and prey

Answer 3

• context - little insects that sit and wait - build webs in streams.
• Study looks at the proportion of larva doing wide-spread movement or net building - they feed some and didn’t feed others.
• Well fed larva did little widespread movement and built nets first.
• The not fed larva did more widespread movement - net building is expensice.
• Positive correlation between the biomass of prey per sample and mean number of predators per sample.

Question 4

Mayfly and stonefly - why is there no correlation between prey desnity and predator density?

Answer 4

• there is no correlation between prey density and predator density
• because the mayfly are running away because they dont want to be eaten
• more oppurtunity to detect predators because they are more obvious.

Question 5

Optimal Foraging

Answer 5

• Assumption: predators seek to maximise their net energy intake and therefore maximise evolutionary fitness.
• Predators have to make decisions whether the prey is worth getting, energy available from the prey, prey abundance, competition, predation risk, knowledge of the landscape (distribution of resources, limiting nutrients - is it healthy?).

Question 6

Optimal foraging model for diet width

• draw and label

Answer 6

• handling time - time spent processing and eating it.
• If this model then predators shoulf always eat prey one becasue it is the most profitable prey.
• If it finds prey 2 it should eat it if the gain exceeds the gain of rejecting it and finding prey 1.
• You should always go for prey one when search time is low.

Question 7

Predictions from the optimal foraging model

Answer 7

• A predator will specialize on one prey only if: The average search time for that prey is relatively low
• An optimally foraging predator will switch from being a specialist to being a generalist: As search time for prey 1 increases
• Predators with short handling times: Should be generalists
• Predators should have broader diets in: Unproductive habitats Equation does not depend on: Search time (& therefore abundance) of prey 2
• The equation is not dependant on search time and abundance of prey 2, it is dependant on prey 1.

Question 8

Simple optimal foraging model where S1 is the search time for prey 1

Answer 8

Question 9

Issues with optimal foraging

Answer 9

• Gathering of energy may be less critical than some other dietary constituent. Predators may be foraging for some particular nutrients in their diet.
• Animals are not “all‐knowing” - they don’t know the knowledge of the landscape, don’t know the input of resources in one place from another.
• Model does not predict a perfect correspondence between observation and expectation. Model is useful for making predictions.

Question 10

Size-selective predation and the importance of body size

Answer 10

• most things eat things smaller than themselves
• predation is influenced by how big their mouth is
• individuals at a higher trophic level woulf be expected to be larger
• you’d expect lots of small things

Question 11

Relationship betweem body size and prey body size

The relationship has a good spread across the chart - positive correlation.

why does this happen?

Answer 11

• when the consumer is small relative to the resource, the attack rate becomes difficult
• its hard to find something if the prey is particularly small compared to you
• you’re unlikely to eat something a lot smaller because you don’t get that much energy
• decrease in capture succes when things get quite big - handling time is difficult i.e. lions eat baby gazelle.

Question 12

Trying to understand how big something is may be able to tell you….

Answer 12

where it fits in the food web, what it eats, who eats it etc.

Question 13

Prey Defences

Answer 13

• Pre‐contact defences
  
  • Camouflage
  • Habitat selection
  • life history - pattern of growth and development - when things do things i.e. producing few big offspring that outgrow the size of predators, or not to be born when predators are aorund.
• Post‐contact defences
  
  • Aposematic colouration - warning colouration
  • Mimicry
  • Masting/aggregation
  • Morphology - structures for harnessing prey

Question 14

Trade offs and non-lethal costs: mayfly case study

Answer 14

• mayflies in drift streams
• experiment - cattle tanks turned into false streams with jets. looked at the behaviour of mayflys. what do they do in response to dealing with lots of predators?
• glues the stoneflys mouths shut - so continued to forage but couldnt open their mouths
• to prodcue non-lethal effects of fish they harnessed the essence of trout eating mayflies - chemicals in the water that mayflies could detect.
• mayflies changed their behavioru to become nocturnal when the trout weren’t around.
• effects of predator on behaviour
  
  • trout restrict mayfly foraging - daytiem feeder
  • trout restrict stonefly movemenet - don’t forage during the day
  • stoneflies disrupt mayfly foraging
  • mostly night time feeder
• with fish odour presetn the head width of male and female mayflies are reduced in size.
• mayflies also become smaller and reduce the amount of eggs laid.
• they aren’t being eaten but they are being scared by the presence of the predators which changed their behaviour
• cant forage when you are avoiding predators - trade off.

Question 15

How do mayflies avoid being eaten while also capturing resources?

Answer 15

Mayfly species solve this trade‐off involving varying:

• morphology
• behaviours
• and subsequent foraging opportunities

some swim, some crawl and some do a scorpion posture and point their tales at the stonefly detering them away - also grow lots of spines

but there are COSTS: if you dont swim and dont move you are forced to live on the bottom and eat detritus - bad food. cant be good at swimming and have defences because you wont be aerodynamic.

Question 16

defences of mayflies reflects coevolutionary constraints

Answer 16

• swimming mayflys - solve it by being mobile - better resource aquisition but mortality rate increases when they’re mobile.
• crawling mayflies - maximise net energy intake by crawling but mortality rate inreases when they swim
• freeze posture mayflies - mortality rate increases when they swim but freeze posturing doesn’t waste energy - not avoiding anything but they have to eat bad food.

Question 17

Ecology of fear in elks and wolves

Answer 17

• apaprent in interactions between elks and wolves
• predator repression - wolves killed because they were eating farm animals
• trophic cascade where the wolves were scaring elk and eating them so less herbivory on riparian areas.
• more trees so less erosion occuring

Question 18

An evolutionary arms race?

Answer 18

• co-evolution - evolutinary change in two or more species underpins teh arms race
• arms race between –> predators always catching prey, prey cant always get away.
• selection for predators to be efficient at catbcing prey and prey selected ot be good at avoiding predation.
• consequences for failing i.e. predators - dont find food so they get skinny might not find mates and eventually die and prey - if they don’t escape they die - doesn’t seem very symmetrical.
• depends whether they are a specialist or a generalist - if a specialist there may be lot sof co-evolution occuring. if a generalist - they can afforsd to switch to another prey if one is difficult to catch.

Question 19

Parasite influences on hosts - Hairworms as parasites on orthoptera i.e. weta and grasshoppers

Question 20

• life cycle of hairworm
• adult produces offspring in a stream
• the larvae emerge - cycts are the stream insect host
• insect host flys across the stream from the aquatic to terrestrial system
• emerges out and the hariworms infect from the host into the weta/grasshopper - the parasites manipulate the behaviour of the host. they force the host out of the water and then it emerges out the adomen and the host dies
• another dimension - the parasites manipulating the host provides 60% of annual energy of japanese trout. fish benefit from alteration of the behaviour.

Question 21

Effects of parasites on morphology

Answer 21

• nematodes can change teh sex of the parasitesed insect
• if anematode infects a male, because the feamle lays eggs in a stream -male wont go back to the stream which is not what eh nematode wants.
• so the nematode changes the sex of the mayfly in order to return to the water.

Question 22

Parasites and the “red queen” hypothesis

Answer 22

• sexzual reproduction costs are high compared to asexual reproduction
• benefit of sex may be to overcome parasite attack. constant attack by aprasites without change in host phenotype = reduction in host fitness.
• sexual reproduction = new pheonotypes may pose new problems for few parasites
• another example of continuous co-evolutionary change.

Question 23

Stephen island wren and tibbles the cat

Answer 23

• the cat decimated the population of wrens
• the cat was so influential because the wren was flightless and not used to mammilian predation - lack of co-evolution
• In NZ lots of birds eat on the ground on islands - some have been able to alter their behaviour to stay alive with mammilian predators. lack of co-evolutionary history - no capacity to respond to predators.

Question 24

Variation in predator influence:

why do only 60% of the time predation shows a significant effect on community structure? why are predators having effects on some communities and not others?

Answer 24

a) underlying dynamics - some predator prey systems tend to cycle. popultions increase - more food, predator populations increase because they kncok down prey numbers, because prey decrease so do predators - cyclic.

Question 25

The lotka-Volterra model

Answer 25

• in the absence of predators, prey grow exponentially
• predators remove prey - driven by search and attack rate
• if search and attack rate is high then cycles will have high amplitude but if predators cant find prey then it will go slowly.
• prey are controlled by food avalibility - with no food they die at a certian mortality rate which counteracted by predators birth.
• overall effect is that there is a tendancy to cycle.

Question 26

Real predator prey cycles

snowshoe hare and lynx

and NZ example of cats, mustelids and rabbits

Answer 26

• lagged predator prey cycle of snowshoe hare and lynx.
• snowshoe hare peak and then lynx peak.
• predators suppress prey and then the prey increases
• why? the only thing around in winter are hares and lynx. the lag because lynx live longer and take longer to produce babies. hares produce offpsring quickly
• specialist predator prey relationship - lynx only feed on the hare, if the hare decline there is nothing else to eat.

NZ example:

• wanted to see if introducing a predator woudl kill rabbits - cats and mustelids adn rabbits in an enclosed area.
• cycle of few rabbits and then lots
• in the wild cats and mustelids dont control rabbit popualtions - resources and refugia do.
• why does this happen? forced the cats and mustelids to eat rabbits becasie there is nothing else to eat.

Question 27

What underlies varibale predator prey population dynamics?

Answer 27

1. Tendency to cycle involving regulation by both predator & prey pops combined with time lags, whether the population is open or closed, and number of predator & prey spp
2. Different functional responses
3. Dispersal & spatial subdivision leading to metapopulations
4. Predators may consume demographically unimportant individuals
5. Extent of predator-prey co-evolution

Question 28

2. Different functional responses

Answer 28

• functional response is the relation between predators consumption rate and local prey density
• sometimes you dont get functional responses where the predators dont control the prey popualtion size at certain points in their density
  
  • proportion of prey being killed decreases - only so mcuh predators can eat.
  • at low population densitys predators consume less than expected - low because search rate is low, handling time is low, encounter rate is low
  • both destabilising
• example: wolf functional response
  
  • island with moose and wolves
  • killing rate of moose levels off by the time you have density of 1.5sq km
  • graph levels off because the wolves stop killing moose - takes a lot fo energy and theres only so much a wolf can eat.

Question 29

Predator and prey as metapopualtions: two mite species.

Answer 29

Two mites and oragnes experiment - created a metapopualtion where each sub population was an orange. the mites had to swing from orange to orange. Made it more difficult for predators to catch up with the prey.

• got more random fluctuations in the popualtions, got co-exisistence of two tupes of mites
• in an arena with no patches/sub popualtions the predator and prey mites increased dramatically with a lag cycle and then the predator mites drove the prey extinct - predators eventually went extinct becasue they have no prey.

3) dipersal and spatial subdivision leading to metapopulations

another reason that may rpevent dramatic cyles in predators and predators driving prey extinct is because they exist in metapopualtions.

Question 30

4. predators may consume demographically unimportant inviduals

Answer 30

• cheetahs and wild dogs eat fawns and adolescents but not adults because they are too hard to catch
• easiest prey to catch so eating prey that may have died anyway
• there are only a certian amount of resources to available to support life so 60-80% of the population may have died anyway.
• no predator control on population size. abundance of resources controls the population size.

Question 31

Top down and bottom up influences on snowshoe hare and lynx cycle

Answer 31

• field experiment summary
  
  • naturally ahres cycle - with both predator and food effets present.
  • with predator and food effects absent the hare numbers increase 10 fold and stay high.
  • either food effect or predator effect present and hares double, then drop, cycle is retained.
• both drivign the system in the same direction, when there is peak hare abundance food is short and theres lots of predators- both drivign hare populations down.
• when hare popualtions are low there is lots of food and low predator numbers driving numbers up
• therefore top down bottom up factors are driving the population in the same direction.

Question 32

HSS theory

Answer 32

• HSS theory - “The world is green because of predators suppressing herbivores)
• Has the top down view theory - predators suppress herbivores which allows primary producers to escape predation.
• control flows from top to bottom

opposite is the bottom up view - bottom up resources important. the abundance of energy at the troophic level deteermines what can live above it. many prey can feed on many predators.

Question 33

Trophic cascades

salt lakes example: top down interaction

Answer 33

salt lakes example - algae making the lake pink, do well in salty conditions.

algae are grazed by brin shrimp. waterboatman are predators of brin shrimp

• when salinity drops below 90 grams the waterboatman can colonise - can’t handle salinty
• when it rains the water dilutesa and the brine shrimp graze lots. little chlorophyll A and clearwater
• when salinity drops the waterboatman come in and the food web changes from two trophic levels to three trophic level food web. they graze the brine shrimp so water transparency decreases and theres more chlorophyll A.
• Top down interaction and trophic cascade wehre the waterboatman influnce the algae by the brine shrimp.

Question 34

Bottom up example - Lake Washington

Answer 34

• sewage and treated sweage into the lake - high organic matter and lots of phosphorus from dishwashing liquid
• also had diatoms - organism made of silica - type of algae - increased after treated sewage
• siphoned the aflfuence and managed to dcrease the P - limiting nutrient. the amount of algae increased and chlorophyll A decreased. water transparency increased.
• driven by reduction of bottom up factor - reducing amount og nutrients for algae to grow on the bottom
• but a top down infleunce occurs now bcause clear water means zooplankton back so more daphnia - enhanced reduction of grazing by algae.
• with climate warming - mismatches between when the algal blooms occur and when grazers are present. lake organisms are specific to particular temps at particular times of the year.

Question 35

Top down control - elk and wolves - yellowstone

Answer 35

• wolves scaring the elk abundance allowing plants to grow, stabilising banks - less erosion

Question 36

Interaction of top down and bottom up forces in the forests

Answer 36

• piper plant lives in a mutalistic association with ants.
• plants provide little fatty bodies of food in the petioles and the ant give protection to the plants by chasing away the herbivores.
  
  • cascade:
  • ants eat the herbivores which eat the piper plants
  • herbivores suppress the plants, ants suppress herbivores, beetles predatory on the ants
  • four level trophic cascade
  • beetles suppress ants so herbivores are high - looks barren
• HSS theory says that if there is an odd number of trophic levels the plant looks green and with an even number it looks barren.
• if you remove beetles you get more ants, reduced number of herbivores and more leaf area.

Question 37

Experiment on rich and poor soils - piper plants and ants mutalism

Answer 37

• manipulated top down bottom up effects by changing species richness
• in rich soils with a predator suppressing the ants, this releases herbivores, reducing numbers of plants species. if you just have ants suppressing herbivores you get more plants on rich soils.
• on poor soils there is no significatn difference. doesnt work because no nutrients go to the plants - not enough ants because plants can’t produce fatty bodies to support lots of ants. in low nutrient soils you dont get much species anyway
• only top down effects in rich soils

Question 38

Lady bug, grass aphids and nettle aphids - interacting top down bottom up interactions.

Answer 38

• fertilised feild has few nettle aphids (specialist) and lots of gras aphids and lots of predators - lady bugs
• unfertilised lots of nettle aphids, few predators and grass aphids/

why more predators in the fertilised plot - mroe prey because ore grass, more grass becasue more fertile - bottom up processes. more predators because more productive

fewer predators in unfertilised plot because tehre are fewer aphids so less prodcutive. grass aphids drive predator numbers - less predation on nettle aphids. bottom up influence affecting a herbivore through a top down process.