Ecology: Lecture 6 Flashcards
What might behavioural ecology observe?
Why particular behaviours persist in animal populations even if they seem counterintuitive, even if it seems like they should be eliminated by natural selection and evolution.
Looks at COSTS and BENEFITS
Through what lens do we look at behavioural ecology?
Through an evolutionary lens.
Who will pass on their genes?
Those with more appropriate behaviour will pass on more genes:
- More likely to survive
- More likely to produce offspring
- Those passing on genes might end up making the behaviour fixed in future populations.
What are behaviours composed of?
Innate behaviour and learned behaviour. If they are unfavourable, they will likely die and these behaviours will disappear.
How do we explain behaviour?
We explain behaviour in terms of effect on individual fitness.
What is “appropriate behaviour”
Appropriate in the context of the environment.
- Abiotic: climate
- Biotic: interactions within species and individuals.
High fitness vs. low fitness?
High = pass on genes
Low = poorly adapted environment and they are more likely to due before they’re able to pass on genes
What are benefits and costs in terms of fitness?
Benefit (high fitness) if fitness increases
Cost (low fitness) if fitness decreases
What is fitness (evolutionary)?
High fitness = more likely to survive
Low fitness = less likely to survive
Evolutionary fitness?
How likely an individual is to pass on its genes.
Actor?
The animal performing the behaviour
Recipient?
The other animals involved.
Altruism is ___?
Counterintuitive. It incurs a cost, and should be eliminated…?
Cooperative?
Actor = +
Recipient = +
Examples: defence and hunting
Selfish?
Actor = +
Recipient = -
Example: Territoriality
Spiteful?
Actor = -
Recipient = -
Example: surplus killing
Altruistic?
Actor = -
Recipient = +
Example: involves risk and harm, fitness would be lowered. eliminated?
Pika?
Related to rabbits
- live in rocky mountainous environments
- social groups with alarm calls made for predators.
Alarm calls do what?
Warns others - entire group of the predators
Increases risk to self - bringing attention to itself
Behaviour cost-benefit analysis?
Is benefit > cost?
Cooperative ( + + )
Selfish ( + - )
Altruistic ( - + ) NO!!
Inclusive fitness?
The total effect on number of genes passed on:
1. producing offspring
2. aid relatives to produce more offspring
What is inclusive fitness composed of?
there is more going on in passing genes than 1 individual and their offspring.
- Individual fitness + other evolutionary benefit of relatives passing on genetic material. Also passes on own behaviour.
Kin selection?
Selection for an act that enhances a relative’s reproductive success.
- Some genetic material is shared with relatives
- Genes are passed on not just through offspring but also through relative’s offspring.
Hamilton’s Rule?
Natural selection (evolution) favours an act if:
C < r x B
C = cost to altruist (lost reproduction)
r = relatedness (fraction of shared genes)
B = benefit to recipient (increased reproduction)
Relatedness?
Parent and child share half their alleles, therefore their relatedness is 0.5.
r = 0.5
Grandmother and granddaughter?
0.5 times 0.5 = 0.25, or 25% relatedness
Relatedness of siblings?
Trace links to both parents.
r = 0.25 for each parent,
0.25 + 0.25 = 0.5
r = 0.5 for full siblings
Successive generations - relatedness?
r = 0.5^n
n = # of links
parent and grandchild
n = 2
r = (0.5)^2
r = 0.25
Certain death to save a full sibling?
C = 2 lost
r = 0.5
B = 2 gained
2 < 0.5 * 2
UNTRUE, therefore dying to save a sibling does not increase inclusive fitness
Chance (0.2) of death to save a full sibling?
C = 0.2 * 2 = 0.4
r = 0.5
B = 2
0.4 < 0.5 * 2
TRUE, therefore risking death to save a full sibling will increase inclusive fitness.
Answer of the fitness scenarios?
Answer depends on the cost, as other factors must be looked at
Pikas analysis?
Must look at following variables:
- Cost of alarm (small, not certain death)
- Relation to neighbours (very high for pikas - small neighbourhoods)
Therefore, for pikas, Hamilton’s law is true. The behaviour (alarms) will persist.
Reciprocal altruism between non-relatives?
Idea that favours will and must be returned.
- Tit for tat
- Makes social groups stable.
CANNOT AND SHOULD NOT ACCOUNT FOR HUMAN BEHAVIOUR
Social organization is what?
Being social - when and why is it worth it to live in a group?
Benefits of being social?
- Cooperative feeding (easier to get more good)
- Defence of group (not picked off as easily)
Costs of being social?
- Disease/parasites (rate increases)
- Restricted reproduction (unable to pass on genes - typically leave and find an area where they can reproduce)
When does group living evolve?
when benefits outweigh the costs
Examples of cooperative breeding?
Wolves and Scrub Jays
What is cooperative breeding?
Individuals may delay their own reproduction to stick around and help raise other offspring in the group.
Examples of Eusocial societies?
Army wants and naked mole rats
What are eusocial societies?
A division of animals into different castes.
Features of wolf societies?
Dominance heirarchies
- Some animals live in packs/groups
Restricted reproductions
- social hierarchy: only some breed
- Dominant individuals
Why do helpers stay?
- Inclusive fitness
Benefits of staying to help for wolves?
- Kin selection
- Individual fitness
THIS IS A WIN-WIN
Kin selection?
Sibling survival - offspring survive better in packs with helpers
- Raising siblings (even when sexually mature) increases chance of survival for siblings
Individual fitness benefits?
- Get stronger and gain experience
- More likely to survive when they leave
- Higher lifetime reproduction when they do eventually leave.
Florida Scrub Jay?
- Live on territories in family groups
- Live in patchy habitat (scrub oak)
Florida Scrub Jay benefits of staying?
Breeding pair
* Build nest
* Incubate eggs
Mature young stay on territory
* Feed younger siblings
* Defend territory
* Warn of predators
Juvenile males help more than juvenile females
Why do juvenile males stay?
-Scrub oak habitat is very limited
- Few chances of finding an open territory
- Oldest juvenile male gets family territory if
* Father dies
* Territory partitioned
Meanwhile, Juvenile females never inherit family territory
Overall benefit of staying to help?
Kin selection
* Sibling survival
Individual reproductive fitness
* Inherit territory in the future – juvenile males only
Eusocial societies?
Eusocial insects (division of labour and behaviour into reproductive and
non-reproductive groups called castes)
Ex. Ants, Wasps, Termites, Bees
Army ants?
Reproduction
* One queen
* Several males
Workers (all sterile females)
* Defense
* Foraging
* Care of young
Unusually high relatedness for army ants?
Their genetics are different, therefore there is an unusually high benefit for helping.
r = 0.5 normally
r = 0.75 for ants
Benefits of staying for army ants?
- Kin selection
* Sibling survival - Individual reproductive fitness
* None
Naked Mole Rat society?
- Arid habitats, Horn of Africa
- Colonies live in underground burrows
How do their societies function?
Male & Female workers
* Dig tunnels
* Gather food & nest material for
young
Soldiers
* Defend burrow
Reproduction?
Reproduction:
* 1 female
* 1-3 males
Coercion
Queen suppresses reproduction in the colony
- Rewards non-reproductive behaviour and punishes reproductive behaviour.
- Behaviour (aggression/killing those trying to reproduce)
- Chemicals (hormonal cues or chemical signalling)
Why don’t naked mole rats leave?
- Harsh environment
- Food is very scarce
- Can’t survive in small groups
- If they leave, fitness = 0
- If they stay, inclusive fitness > 0
- Cost is high for leaving, doesn’t make sense to leave. therefore, they stay
Naked mole rat benefits of staying?
- Kin selection
* Sibling survival - Individual reproductive fitness
* None
Environmental influence?
Environment influences costs and benefits of group living.
Where does group living evolve?
When:
total fitness for staying in the group
>
independent reproduction
What do we see in different groups or societies?
We can see it in different groups and societies that there may be different pressures to rationales or behaviours that lead to individuals staying in the group
When does it pay to give up or delay reproduction?
If:
- Chance of independent reproduction is low
- Survival is difficult (harsh environment – mole rat)
- Opportunities for reproduction are few (limited habitat – scrub jay)
- A delay increases future reproduction potential (pack animals)
Types of mating systems?
- Monogamous
- Polygamous
- Promiscuous
Monogamous?
Single pair bond
- heavy parental investments, both parents are needed to raise offspring and give best chance of survival
Polygamous?
Two types: Polygynous and Polyandrous
- One individual mates with several of the other sex
Polygynous?
1 male and many females
Polyandrous?
1 female and many males
Promiscuous?
No strong mating bonds
Polyandry in spotted sandpipers?
Females first to arrive at breeding grounds
* Compete for males as they arrive (females larger)
* Females desert nest after eggs are laid
* Produce eggs with another male
Environmental conditions
* Enough food for one parent to rear chicks
* Females produce few eggs at a time (high investment)
* Season long enough for more than one clutch of eggs (maximize potential)
* not harsh enough environment to be harmful to children.
So, Why do animals behave the way that they do?
Behaviour shaped by selection
* Benefits > costs (explains behaviours)
* Inclusive fitness & kin selection
* Vary with environment
