Lecture 5: Avoiding Predation Flashcards
what is an adaptation?
a heritable trait that enhances the fitness of it bearers
-through current benefits, or past benefits & evolutionary history
is every factor that reduces predation an adaption against predation?
NO
current benefits of Mobbing: Kruuk 1964
- nesting gulls mob intruders
- risky behaviour for gulls
- prediction: if mobbing is behavioural adaption against egg predators, then mobbing should reduce egg predation
- experiment: hens egg every 10m, outside gull colony & into gull colony
- results: inside colony more likely crows will attack predation, predation reduces as you enter colony
when would you use the comparative method?
when an experiment can’t be used
-way of comparing evolutionary hypothesis by comparing different taxa
e,g, of using a comparitive method: Mobbing
- two taxa (kittiwake - cliff gull, black headed gull - ground nesting gull)
- first gull = ground nesting
- kittiwake shouldn’t use mobbing as not necessary
- to use comparative method you need good phylogeny
- if some cliff did mob and some ground didn’t then prediction would be wrong
to use comparative method you need a strong
phylogeny method
antipredator adaptations 4 groups:
- Anti-detection
- Anti-attack
- Anti-capture
- Anti-consumption
anti detection example
Crypsis, e.g. camouflage, transparency, nocturnally, subterranean living
anti Attack examples
-stotting in Springbok, selfish herding, mimicry and warning colouration
anti capture examples:
Vigilance, run, swim or fly fast, body part autotomy (tail loss in lizards)
anti-consumption adaptations
fighting back, feigning death, releasing noxious chemicals, being hard to swallow (e.g. inflation by puffer fish)
camouflage: Peppered moth
- makes peppered moth less detectable to predators
- 2 subspecies; light form and melanic form
- larvae also camouflaged = dead twig
camouflage points to remember:
1) camouflage may involve any of the sense, not just vision
2) either (or both) prey / predator may be camouflaged
Testing whether camouflage words: Pietrewicz and Kamil
-trained captive blue-jays to respond to white underwing moths
-head up moths on pale bark hardest to detect!
Conclusions: behaviour of moths (where they settle) affects ability to detect them
–> so yea, it works
Behaviour & camouflage: Decorator crab
the crabs pile algae, sea anemones, coral on back to hide
- choosey about what species to decorate with, Dictyota menstrualis
- crabs without this species were 5 times more likely to be predated
- the alga contains a chemical that repels omnivorous fish
Stotting by Thomson’s Gazelles
- stot when see predator
- jump up in air with legs down, signal to predators ‘Ive seen you and I’m v fit and ready to flee’
Stotting by Thomson’s Gazelles: “Ive seen you and am ready to flee” is known as the what hypothesis
Unprofitability hypothesis == the likely hypothesis
Stotting by Thomson’s Gazelles: Anti ambush hypothesis
stating lets gazelles see what is ahead and reduces the chances they will be ambushed
–> but stotting occurs in all habitats including short grass
Stotting by Thomson’s Gazelles: Alarm signal hypothesis
sotting warns conspecifics, especially offspring that predator is near
–> but even solitary animals Stot
Stotting by Thomson’s Gazelles: Social cohesion hypothesis
stotting enables gazelles to form groups & flee in a coordinated manner
-but solitary animals stot
Stotting by Thomson’s Gazelles: confusion effect hypothesis
- stotting confuses and distracts a predator preventing it focusing on one animal
- but solitary animals stot
Stotting by Thomson’s Gazelles: is it an indicator of quality?
YES, lower proportion of stotters, than non stotters chased & predators fail to kill stotters
-honest signal of animals health
The selfish herd: Snake in pond where safest place for frog to sit
- frogs best close to other frog
- snake attacks then no individual target, selfish strategy
- benefits individual, but not group (if all sat together may make a bigger target bad for group)
selfish herd is an example of
Game theory
selfish herding affects ___ behaviour
positioning
-Bluegill sunfish prefer to nest in the centre of groups where they are safer from egg predators
selfish herding works through mechanisms known as
dilution effect
–larger the group, lower individuals chances of being eaten
selfish herding in Whirligig Beetles
- sits on surface on pond, eats small insects
- predated by fish that come up from below
- larger groups more attractive to predators
- BUT larger groups the predation rate for each individual is less
Whirligig beetles trade off :
- Food & predation risk
- -food more abundant on outside of group but predation risk greater
Mayfly Emergence: Dilution effect (in time)
-nymphs = aquatic
-adults = aerial
predation risk is lower when many adults emerge as predators become satiated –> dilution effect, leading to synchrony of emergence
Similarity between: Gamete release in coral & Sea-bird egg laying
SYNCHRONY to benefit from dilution effect –> satiate predators preying on gametes/chicks
Group formation / vigilance
-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.
Can grouping be costly?
--increased food competition Sparrows; may feed alone/group -"chirrup" calls signal to form a group -predation risk = low = solitary -predation risk = high = group
