Lecture 5 - avoiding predation Flashcards
definition of an adaptation
a heritable trait that enhances the fitness of its bearers
- current benefits
- past benefits and evolutionary history
what is an important thing to remember about adaptations
not every factor that reduces predation is an adaptation against predation
what is anti-predator behaviour
the focus of intense natural selection
4 examples of an anti predator behaviour
1) being hard to detect (e.g. being cryptic)
2) to attack (e.g. being vigilant)
3) to capture (e..g being fast running)
4) to consume (e.g. the puffer fish swallows water to inflate into a spiny ball)
are anti-predator adaptations behavioural?
some are but some are often not primarily behavioural but may have a behavioural component e.g. animals that having warning colours rarely hide away and animals that are cryptic have to position themselves correctly
3 examples of non-adaptive traits
1) trait used to be adaptive to conditions in the past that no longer exist
2) the trait develops a maladaptive side effect of an otherwise adaptive proximate mechanism e.g. next to it is the the gene sequence
3) the trait is expressed as a maladaptive consequence of a recent environmental change
describe the antipredator adaptation mobbing
- Nesting gulls mob intruders
- Risky behaviour for the gulls
- experiments showed this to be a behavioural adaptation against egg predators that increases reproductive success
what is a comparative method?
- used when you cant carry out a successful experiment
- A method for testing evolutionary hypotheses, by comparing different taxa to see who does what, and correlating the occurrence of traits with the benefit of the trait
give an example of a comparative method
- if ground predator mobbing is not needed or not beneficial it ill not occur - e.g. wouldnt be needed in a cliff dwelling gull - this is proved by cliff neting kittiwakes not mobbing
example of how phylogenies can be used for comparative methods
- when looking at gull phylogenies cliff nesting is derived - mobbing evolved in ground nesting gulls but once cliff nesting evolved mobbing was lost as it no longer carried a benefit so is not worth the risk
- when comparing phylogenies of gulls and swallows the mobbing behaviour is lost in both cliff dwelling species of gulls and swallows - example of convergent evolution due to similar selection pressures
antipredator behaviours are extremely diverse - give 4 examples
1) antidetection -crypsis, e.g. camouflage, transparency, nocturnality, subterranean living
2) Anti-attack: Stotting in Springbok, selfish herding, mimicry and warning colouration
3) Anti-capture: vigilance, run, swim or fly fast, body part autotomy (e.g. tail loss in lizards)
4) Anti-consumption: fighting back, feigning death, releasing noxious chemicals, being hard to swallow (e.g. inflation by puffer fish)
what is important to remember about camouflage?
1) Camouflage may involve any of the senses, not just vision
2) Either (or both) prey and predator may be camouflaged
describe the experiment to test wether camouflage works
operant conditioning with blue jays
- trained captive blue-jays to respond to white underwing moths. Head up moths on pale bark hardest to detect
Conclusions: behaviour of moths (i.e. where they settle) affects ability of birds to detect them
describe an animal which links behaviour and camouflage
decorator crab:
- Juvenile crabs preferentially decorate with Dictyota menstrualis - pile algae/ coral on their backs to hide from detection
- Crabs decorated with Dictyota will be less likely to be killed by predatory fish than crabs unable to use this alga
- The alga also contains a chemical that repels omnivorous fish
describe stotting behaviour in Thomsons gazelles
- When Thomson’s Gazelles spot a predator they may stot
- Stotting may signal to predators that “I’ve seen you” and “I’m very fit and ready to flee” = unprofitability hypothesis
- So predators don’t bother to chase animals that stot. Stotting is an honest signal
what did Caro (1986) experiment reveal about stotting
Stotting is a quality indicator as (a) a smaller proportion of stotters versus non-stotters are chased, and (b) predators failed to kill stotters
give an example of the costs and benefits of a selfish herd
- the safest place for a frog to sit around water with a predator snake in
- Assuming the snake is equally likely to move in any direction, the best place is next to another frog. So our frog isn’t the only target
- This benefits the individual
- But selfish herding may increase the total predation risk by making a more tempting target
- If the bunched prey are a more tempting target it will increase predation overall which will be bad
- But individuals in groups can still have lower mortality if the selfish herd effect outweighs the increase in conspicuousness
how can selfish herding affect positioning behaviour
Bluegill sunfish prefer to nest in the centre of groups where they are safer from egg predators
what is the dilution effect?
the chance of being predated is effected by number of other individuals
In a group of 40, chance of being eaten is 5/40 = 0.125
In a group of 400, chance of being eaten is 5/400 = 0.0125
describe selfish herding in whirligig beetles
- they are predated by fish underneath them in water
- Larger groups are more attractive to predators
- In larger groups the predation rate per individual is lower
- risk of predation is greater when you are at edge of the group but food is more abundant there - trade off in obtaining food versus predation risk
- experiments showed that food-deprived beetle were putting up with risk to get food - this affected the positioning behaviour of the individuals
describe the dilution effect in mayfly emergence
- Mayflies have aquatic nymphs and aerial adults
- Predation risk is lower when many adults emerge as their predators become satiated after eating a lower proportion of mayflies
- individuals emerging early or late will be selected against
- This dilution effect will lead to synchrony of emergence i.e. selfish herding in time
2 other examples of synchrony
- Seabird egg-laying is synchronous. This may satiate gulls preying on fledging chicks
- Coral spawning is synchronous. This may satiate animals preying on the gametes
what is the advantage of group formation
Group formation may reduce predator attack/success via greater vigilance. If one individual in a group sees a predator it can warn the rest, or the others can see its escape behaviour
describe the experiment on group formation in pigeon flocks
Prediction: Individuals in a group will react more quickly to a threat than lone individuals
- results show detection range increases as flock size increases - total attack success declines in larger flocks
grouping can carry costs e.g. increased food competition - describe the experiment on sparrows
- sparrows may feed alone or in groups
- when the predation risk is low they are solitary
- when the predation risk is high they stick in a group
- they chirrup to attract others to them
- experiment showed fewer chirrups made when foraging close to safe cover and far from predator
what did the results from the sparrow experiment show
animals can alter their behaviour on a short term basis to increase benefits and reduce costs
- constant arms race with predator prey relationships
