L5- Avoiding Predation

Adaptation→

• a heritable trait that enhances the person’s fitness through current benefits and also past benefits

  → not all behaviours are current adaptations

Why are some behaviours non-adaptive?

1. behaviour evolved to adapt to past conditions that no longer exist, has not been replaced, leaving a non-adaptive trait

   • arctic ground squirrels live where snakes don’t but when experimentally exposed to snakes, they behave like squirrels that like with snakes

   • arctic moth do not fly in bat areas but will stop moving when experimentally exposed to ultrasonic bat stimuli

2. behaviour evolved as a side effect of a good adaptation, is genetically linked to it

   • rodents feeding other offspring as well due to their strong parental drive

   • stepparents abusing their stepchildren

3. behaviour is mal-adaptive now that the environment has recently changed, person has not evolved to it yet

   • sea turtles eating plastic bags that resemble jellyfish

Example of an adaptive behaviour→ Mobbing:

• anti-predator trait, group attacks an intruder to drive them off

• e.g. gulls mob any individual near the nest

  • this causes injuries and deaths but it protects the nests

Q→ is mobbing a behavioural adaptation against predators?

• Predict→ mobbing should reduce egg predation if it is a behaviour adaptation against egg predators

• Method→ placed a hen egg every 10m along a line from the outside of the colony to the middle of the colony, measured the amount of mobbing by crows and amount of egg predation

• Results→

  • mobbing was the highest inside the colony BUT

  • egg predation reduces as you get into the colony→ predation lowers with mobbing and therefore increases reproductive success through egg survival

Comparative Method:

• method to test evolutionary hypotheses if experiments are unavailable

• compares different taxa to see if one factor causes another by determining if two factors are correlated

• e.g. if mobbing is adaptive, it is only expected in species where it reduces predation and would not be needed in non-ground dwellers

  • kittiwakes are cliff-dwelling gulls→ have no ground predators

  • predict→ no mobbing occurs in kittiwakes

  • results→ there is no mobbing in kittiwakes, fits prediction

• method requires an accurate phylogeny:

  • e.g. phylogeny shows gulls lost the risky behaviour of mobbing when the cliff-nesting trait evolved

  • e.g. comparing phylogenies of gulls to swallows

    • are different taxonomic groups→ kittiwakes are cliff-nesting and rough-winged swallows are solitary

    • BUT there was convergent evolution to similar selection pressures that lead to the loss of mobbing

Types of Anti-predator Behaviours:

1. Anti-detection

   • crypsis→ camouflage, transparency, nocturnality, subterranean living (underground)

2. Anti-attack→

   • animal has already been detected

   • stotting (Springbok), selfish herding, mimicry, warning colouration

3. Anti-capture→

   • once the predator is about to catch the prey

   • vigilance, running, swimming, flying, jumping (grasshoppers), losing body parts (tail loss in lizards)

4. Anti-consumption→

   • once animal has been captured

   • fighting back, pretending to be dead, releasing chemicals, being hard to swallow (puffer fish)

Anti-Predation Techniques→

Camouflage:

1. camouflage can be of other senses e.g. squirrels eating rattlesnakes skin to smell like them

2. both the prey and the predator can camouflage

e.g. Peppered Moths-

• carbonaria→ black moths, camouflage on black trees

• typica→ white moths, camoflauge on white trees (lycan)

• larvae→ camouflage by looking like a dead twig

Q→ how effective is camouflage in the face of predation? (Pietrewicz and Kamil)

• Method→ showed blue-jays photos of treebarks with moths on, operant conditioning→ rewarded for correct, did not reward for incorrect

• Results→

  • jays detected fewer white underwing moths on white bark than on black bark

  • jays detected even fewer white head on moths (whose lines are in line with the bark)

  → both where and how the moths settle affected the ability of jays to detect them

e.g. Decorator Crabs:

• pile coral/algae/anemone on their backs and let them grow

• are choosy with they choose to grow→ prefer Dictyota menstrualis

Q→ is the preference of Dictyota adaptive?

• Predict→ crabs with Dictyota are less predated

• Method→ had crabs with Dictyota and crabs without in an area with predatory fish

• Results→ the crabs without Dictyota disappeard 5x faster than crabs with Dictyota

Q→ what is the mechanism of Dictyota?

• Results→ Dictyota contains a chemical that repels omnivorous fish

Stotting:

• Thomson’s Gazelles stot when they spot a predator→ jump and display white rump to predator

Q→ why do Thomson’s Gazelles advertise themselves to a predator?

Hypotheses:

1. anti-ambush:

   • lets gazelles see what is ahead and reduces chance of ambush

     • occurs in all habitats, not just long grass

       → NO

2. alarm signal:

   • warns others that a predator is near

     • even solitary gazelles stot, show rumps to predators

       → NO

3. social cohesion:

   • allows gazelles to form groups and flee together

     • even solitary gazelles stot, show rumps to predators

       → NO

4. confusion effect:

   • confuses and distracts the predator

     • even solitary gazelles stot

       → NO

5. unprofitability:

   • tells the predator that they have seen them and are ready to flee

     • is an honest signal of their health

       → MOST LIKELY

• Method→ compared the results of predation between those that slot and those that don’t

• Results→

  • 30% of those that slot are chased vs 50% of those that don’t slot are chased

  • 0% of stotters were eaten vs 20% of non-stotters were eaten

    → stotting is an honest signal as predator runs out of energy, unprofitablity hypothesis is true

Selfish Herding:

• moving together as a group to avoid predation

• benefits the individual but may increase predation risk of group as they are more conspicous

  • individuals in a group still have a lower mortality than alone

• e.g. Bluegill sunfish

  • build nests on the sea floor

  • those in the center are less likely to be attacked than at the edges→ all fish try to get to the middle

    → where the fish affects fitness, which depends on the predation rate, which depends on the group size

Mechanism of selfish herding→ the Dilution Effect:

• 40 individuals with 5 predators, chances of eaten are 5/40= 0.125

• 400 individuals with 5 predators, chances of eaten are 5/400= 0.0125→ the larger the group, the lower the individual chances of being eaten

• e.g. Whirligig Beetles→

  • are aquatic, live on pond surfaces, are predated by fish below

  • experiment looking at strike rate depending on group size

  • results→

    • larger groups are attacked more BUT

    • the likelihood of one individual being predated is less in larger groups

  • food is more abundant on the edge of a group but so is predation risk

  • experiment deprived beetles of food and looked at where they were

  • results→

    • food-deprived beetles tended to be on the edges more where there is more food

    • well-fed beetles tended to be in the center more where there is a lower predation risk

      → there is a trade off between obtaining food and predation risk

      → the dilution effect affects the spacing of individuals

• e.g. Mayflies→

  • live in freshwater, adults emerge and are predated by fish

  • measured the number of adults emerging that were predated

  • results→

    • the days where more mayflies emerged were when there was less predation risk, as the fish became full faster→ the dilution effect is causing selection for synchronised emergence

    • e.g. seabirds lay eggs at the same time to satiate the gulls preying on the chicks

    • e.g. coral spawn at the same time to satiation the animals preying on the gametes

Group Formation and Vigilance:

• being in a group reduces the chance of one individual being predated

• one can warn the others or can escape and the others will see this

• being in a group increases the level of vigilance

Q→ is group formation better for vigilance and then survival? (Kenward, 1978)

• Predict→ individuals in a group react more quickly to threats than solitary individuals

• Method→ released a hawk on groups of different sizes of woodpigeon flocks

• Results→ as the number of individuals in a flock increases, the reaction to the hawk increases→ detection range increases as flock size increases

• Method→ looked at the percentage of successful attacks in each flock

• Results→ there are less successful attacks in larger flocks→ total attack success declines in larger flocks

  → group living has benefits→ lower predation risks

• Group living is also costly→ increases competition for food

• e.g. Sparrows→

  • feed alone or in groups

  • to form a group, they chirrup to attract the others

Q→ is it better to be in a group or solitary at different predation risks?

• Predict→ solitary when predation risk is low, group when risk is high

• Method→ manipulated the risk of predation:

  • distance from predator→ was 25m or 15m away from bird

  • distance from cover→ near (adjacent) or 2m away from bird

  • recorded the number of chirrups→ indicates if they are trying to attract the group

• Results→

  • fewer chirrups when foraging closer to cover and further from predator→ prefer to forage alone when predation risks are low

    → prefer to forage together when predation risks are high

  → have altered their short-term behaviour to avoid the costs of group foraging