Ecology Lesson 6 Flashcards
Behavioural ecology
Why particular kinds of behaviours persist in animal populations even if they seem counterintuitive/ will eliminate others.
Behaviour and natural selection
Those with more appropriate behavior pass on more genes (in context of the environment):
* More likely to survive
* More likely to produce offspring
Passing on genes makes it become fixed.
How can genes disappear?
If an individual dies before it gets the chance to reproduce.
Individual fitness with benefit and costs
- Benefit: if fitness increases
- Cost: if fitness decreases
Fitness
Refers to evolutionary fitness. How likely an individual is to pass on its genes.
Actor
the animal performing the behaviour
Recipient
is or are the other animals involved
Cooperative
+ for both actor and recipient.
ie. defense and hunting for living in a pack.
Selfish
Actor is + and recipient is -.
ie. territoriality, as the actor gets the resources but the recipient gets none of the resources.
Spiteful
- for both actor and recipient.
ie. killing more food than you can eat.
Altruism
- for actor and + for recipient.
ie. alarm calls in pikas
Pika
Live in the rocky areas in North America. They live in groups. One will have do an alarm call to warn others of predators (like weasels) to tell others to go and hide, but this increases risk to self. There relatedness is high, so it’s worth it to do it.
Inclusive fitness
There is more going on in terms of passing in genetic material.
Total effect on number of genes passed on:
1. Producing offspring
2. Aid relatives to produce more offspring (as you share some genetics with your relatives) so it increases the number of copies of some of your genes in the gene pool.
Kin selection
Selection for an act that enhances a relative’s reproductive success. Some genetic material is shared with relatives (i.e. have some of the same genes).
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*B
* C: Cost to altruist (lost reproduction)
* r: Relatedness (fraction of genes shared)
* B: Benefit to recipient (increased reproduction)
Relatedness (r)
The child gets one set of alleles form each parent. Parent and child share half their alleles. Therefore, their relatedness is ½ (0.5).
Relatedness equation for successive generations?
r=(1/2)^n
n= number of links
Relatedness between grandmother and granddaughter?
It’s 0.25
Relatedness of siblings?
r=0.5
Does it increase (evolutionary) fitness to save
a sibling if you die in process?
c=2 r=0.5 b=2
2 is not less than 1
Answer: No
Does it increase (evolutionary) fitness to save
a sibling if you may die in process?
C = Risk of dying x lost reproduction. Assume a risk of dying of 20% (0.2). C = 0.2 x 2 children (average)
C = 0.4, r=0.5, b=2
0.4<1
Answer: Yes
What does C depend on?
The risk of dying and the risk that you don’t succeed in saving the other people.
Reciprocal altruism between non-relatives
- Tit for tat. Chimps may groom another chimp hoping it will do the same for the them in the future.
- Stable social groups for it to work.
A part of social cohesion that keeps animals living together in groups.
Social Organization (benefits and costs)
Being social – when is it worth it to live in a group?
Benefits
* Cooperative feeding
* Defense of group (safer)
Costs
* Disease/parasites (higher chance of getting one)
* Restricted reproduction (can’t pass on genes)
Group living evolves when benefits > costs
Cooperative breeding
Delay own reproduction to stick around and help others raise their offspring. Dominance hierarchies and the higher level ones may limit reproductive.
* Some animals live in packs/groups
Restricted reproduction
* Social hierarchy – only some breed
* Dominant individual(s)
ie. Wolves and florida scrub jay
Benefits of staying to help in cooperative breeding
Kin selection (inclusive fitness)
* Sibling survival – offspring survive better in
packs with helpers
Individual fitness in raising young
* Get stronger and gain experience
* More likely to survive when they leave
* Higher lifetime reproduction
Helping behaviour: win-win
(in wolves)
Florida Scrub Jay
- Live on territories in family groups
- Live in patchy habitat (scrub Oak) and surrounded by other habitat unsuited for it.
Benefits of staying to help for the Florida Scrub Jay
Breeding pair
* Build nest
* Incubate eggs
Mature young stay on territory but can’t reproduce
* Feed younger siblings
* Defend territory
* Warn of predators
Juvenile males help more than juvenile females
Kin selection
* Sibling survival
Individual reproductive fitness
* Inherit territory in the future – juvenile males only
Why do juvenile males stay?
Scrub oak habitat is very limited and Few chances of finding an open territory.
Oldest juvenile male gets family territory if
* Father dies
* Territory partitioned
Juvenile females never inherit family territory. They stick around to gain experience.
Eusocial societies
Division of animals into castes. Eusocial insects (division of labour and behaviour into reproductive and non-reproductive groups called castes). Ie. army ants live in groups to hunt cooperatively.
Army Ants
Reproduction
* One queen
* Several males to reproduce with.
Workers (all sterile females so can’t reproduce)
* Defense
* Foraging
* Care of young
The relativness is quit high in sisters at 0.72.
Benefits of staying to help with army ants
- Kin selection
* Sibling survival - Individual reproductive fitness
* None
Naked mole rat
- Arid habitats, Horn of Africa
- Colonies live in underground burrows
They are blind.
Male & Female workers
* Dig tunnels
* Gather food & nest material for young
Soldiers
* Defend burrow, can die doing this.
Reproduction:
* 1 female (queen)
* 1-3 males to reproduce with
Coercion with naked mole rats
Queen suppresses reproduction in the colony
* Behaviour (attacking and killing others)
* Chemicals (hormonal cues that repress others reproductive hormones).
Rewarding non-reproductive behaviour and penalizing reproductive behaviours.
Why don’t naked mole rats leave the colony
and reproduce on their own?
- Harsh environment, so goo chance they will die on their own.
- Food is very scarce
Can’t survive in small groups
* If they leave, fitness = 0
* If they stay, inclusive fitness > 0
- Kin selection
* Sibling survival - Individual reproductive fitness
* None but cost too high for leaving.
Group living evolves where what?
Total fitness for staying in the group
>
independent reproduction
When does it pays to give up or delay independent reproduction?
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. Two parents very involved and both needed to raise offspring and for it to survive. ie. prairie vole.
Polygamous
One individual mates with several of the other sex.
Polygynous: one man (ie. elk)
Polyandrous: one female (ie. spotted sandpiper)
Promiscuous
No strong mating bonds. Parents don’t stick around after reproduction.
Polyandry in spotted sandpipers
Females first to arrive at breeding grounds. After migrating from North America.
* Compete for males as they arrive (females larger).
* Females desert nest after eggs are laid and males takes care of it.
* Produce eggs with another male
Environmental conditions (why one parent)
* Enough food for one parent to rear chicks
* Females produce few eggs at a time
* Season long enough for more than one clutch of eggs
Behaviour shaped by selection
- Benefits > costs
- Inclusive fitness & kin selection
- Vary with environment
