Signals 2 (Predator avoidance) Flashcards
The role of co-evolution in predator avoidance
The evolution of predator technology drives the evolution of anti-predator defences.
There is co-evolution arms race.
These strategies exploit different stages of predator cognition (e.g. detection and recognition with crypsis)
Biases in the way that predators receive warning signals can lead to the selection of conspicouss and aggregate signals so that they are memorable and recognisable.
Overview of the methods of predators avoidance
A key method is getting someone else killed
1) Dilution
2) Escaping
3) Hiding
-> Stealth
-> camouflage (countershading, light production, shape scrambling, disruptive colouration)
4) crypsis
-> Masquarade
-> eucrypsis
5) Warning coloration (mimicry)
Dilution
The more prey that are present, the lower the individual prey’s chance of predation
- This can be 1d (frogs), 2d (zebras), 3d (fish) and 4d (bats)
A key way to avoid being killed is to get someone else killed
Other group behaviours:
Circling
Example: must oxen form circle around young and females
Warning
Example: when alarmed smelt release a pheromone into water to warn others
Escape
Escape involves running away from the predator.
Prey often signal their escape potential to the predator to try and move their efforts onto a more economical prey.
e.g. stotting in springboks
E.g. push-up in a okie lizard
Vigilance is important for escape
- There is a trade-off between vigilance and foraging.
- Study with Ostrich shows that the larger the group, the less time each individual spends looking up.
- can vary vigilance depending on threat (e.g. group size, age, sex, body condition, environment)
- can vary who vigilant toward -> cheetahs observe prey is day and predators against young at night
Prey also signal to the predator once they have spotted the predator to try to move the predation efforts onto a less vigilant prey. -> mind reading that helps both parties
e.g. Gerenuk eye contact
Eucrypsis
This is the form of crypsis where the prey resembles a random sample of their background
They are avoiding detection.
Example: brown spider species
- spin webs and then sit and wait for predators
- resemble thorns or broken twigs
Example: green spiders
- spins webs and chose moth covered twigs to wait.
Hiding
Prey also hide to avoid being noticed by predators.
Stealth
- Moving in a way to avoid detection
- e.g. vine snakes
- predators slaps use stealth (e.g. owls -> special feathers to make them silent)
Camouflage
- Visual illusion to evade detection
-> Counter shading (e.g. tuna, Penguin in the water)
-> Light creation (e.g. Hachit fish)
-> Shape scrambling (e.g. algae on crabs/ Comma butterfly)
-> Disruptive coloration to obscure the outline of the prey (e.g. Pennant coral fish)
Crypsis
- Colour matching the background to avoid detection
-> Eucrypsis (random sample of the background): avoid detection
-> Special resemblance (specific resemblance of worthless objects): avoid recognition
- Crypsis is a form of mimicry
Special resemblance
This is a form of crypsis where the prey want to resemble a worthless object so that the prey does not recognise the object.
This is targeting a different cognitie process to eucrypsis which is avoiding detection.
Example: caterpillar resembles bird dropping (citrus swallow tail)
The importance of rarity and mimicry
Mimicry relies on rarity due to frequency-dependent selection. When a mimic become common they are selected against.
This is apostatic selection.
This leads to polymorphisms.
However, the level of polymorphism depends on the number of possible mimicry options (adaptive peaks). More polymorphism with eucrypsis.
Warning coloration (aposematism)
Prey often have warning coloration which acts as a signal to tell the predator not to attack.
This evolved as the prey had anti-predator mechanisms, and the predators learned to recognise this and avoid the prey (mind reading first). This favours prey that advertise their toxicity. (Manipulation second)
The more conspicuous and aggregate the signal, the more memorable and distinctive it is.
Evidence:
Conspicuous: experiment with coloured crumbs and chicks showed that conspicousness enhances avoidance learning.
Aggregate: Experiment with varying number of coloured crumbs and chicks shows that clustering enhances avoidance number and proved that it was a visual effect not a chemical effect.
conclusion: predator cognition drives the evolution of aposematic strategies by favouring conspicuousness and aggregation.
Warning signals and mimicry
Prey can mimic the warning signals of other prey to deter predators.
Batesian: Non-toxic prey mimic toxic prey to deter predators.
-> negative frequency dependancy
-> example: papilio Dardanus
- males are monomorphic while each female morph mimics different toxic butterfly
Mullein: Toxic prey mimic toxic prey to enhance the avoidance of predators by predator confusion.
-> Example: numata long wing
- 7 morphs that mimic melonaea butterflies
- there is positive frequency dependent selection by natural selection due to accelerated learning by predator if morph is more common
- 7 morphs maintained by dissasortative mate preference - heterogenous at super gene (negative frequency by sexual selection -> too common won’t find a mate)
Overview
Prey has many strategies for avoiding predators, which can involve dilution, escape, hiding (stealth, camouflage and crypsis), warning signals and mimicry.
Evolution:
These strategies have evolved through the co-evolution with predator detection.
These strategies can exploit the different stages and processes that go on in predator perception and predator memory
Strategies exploit different stages of predator cognition (e.g. detection and recognition with crypsis)
Biases in the way that predators receive warning signals can lead to the selection of conspicuous and aggregate signals so that they are memorable and recognisable
LOOK AT BACK OF MIND MAP FOR MIMICRY EXAMPLES -> cheating in plants
