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What does behavioural ecology focus on

Behavioural Ecology focuses on the function of behaviour, its adaptive nature, and its evolution under ecological constraints:
- ‘The study of the survival value of behaviour’
- ‘How behaviour contributes to reproductive success’
- ‘The study of how an organism’s behaviour affects its chances of passing on genes to the next generation’


Describe Crook's weaver birds

- Ploceidae
- Speciose group of sparrow-like passerines; Africa & Asia
- Different species inhabit very diverse habitats (cover, food type, predation threat)
- Parallel variation in species-specific patterns of behaviour (inc. nesting dispersion, feeding behaviour, mating systems)


Describe Crook's comparative approach

- Attempt to relate observed species variation in behaviour patterns to ecology, and then map this to phylogeny


Describes MacArthur's costs and benefits model

- Costs may be energetic or ‘lost opportunity’
- Benefits may be direct or indirect
- Trade-offs needed to balance costs and benefits
- Natural selection favours animals that make economically-valid ‘decisions’
- ‘Optimality models’ of behaviour can be generated


Describe the three components of MacArthur's models

- Assumptions about what choices are available
- Assumptions about what is being maximised
- Assumptions about constraints


Basically describe altruism and eg.

- Behaviour that increases the survival of others whilst decreasing the survival of the altruist
- Observed in natural animals populations; co-operative breeding (scrub jays), collective offspring care (lions)


Hamilton's altruism and relatedness

- Parents-offspring share 50% of their genes
- Brothers/sisters share 50% of genes
- Grandchildren / grandparents share 25% of genes
- Cousins share 12% of genes
- Inclusive fitness is the success of all genes you share with others being transmitted to future generations


Describe Tinbergen's gulls

- Eggshell removal - black-headed gulls
- Tinbergen painted hens’eggs to resemble gulls eggs
- Placed them in the gull colony, some next to broken shells
- Eggs next to broken shells were more likely to be discovered and eaten
- Removal of empty shells therefore appears to be an adaptive response to the presence of predators


Describe serengeti lions

- Panthera leo
- Live in prides
3-12 adult females (related)
1-6 adult males
Several cubs

- Females born in pride remain there and reproduce from age 4-18

- Male offspring leave pride when 3 years old and become nomadic before attempting to over a pride

- Males only remain in a pride for 2-3 years until driven out by others


Observation 1: All females in a pride enter oestrus at the same time – WHY?

Causal explanations:
- Chemical / pheromone cues synchronise oestrus cycles

Functional explanations:
- Cubs born synchronously survive better
- Synchronous and communal suckling
- Greater chance of male cubs having a related, same age companion to leave pride with


Observation 2: Despite phenomenal rate of copulation, birth rate is low – WHY?

Causal explanations
- Female infertility?
- Concealed time of ovulation

Functional explanations
- Advantageous to females to be receptive at times when conception is unlikely
- 1:3000 chance that a copulation will result in a birth
- Increases paternity uncertainty amongst males
- Reduces competition between males
- Incites sperm competition, possibly increasing the chance of a high quality male being the father


Observation 3: All young die when new males take over – WHY?

Causal explanations
- Aggressive males kill cubs
- Hormonal changes in females resulting from the takeover causes abortion of unborn young

Functional explanations
- Females come into oestrus quicker when not nursing cubs
- Males remove non-related offspring, which would compete with their offspring


Describe the way genes attribute to behaviour

- Natural selection acts at the level of the individual
(Beware ‘group selectionist’ ideas and arguments!)
- But individuals only act as temporary vehicles for genes…
- Individuals therefore typically act selfishly
~ To maximise their lifetime reproductive fitness
- There is a genetic component to behaviour


Give an overview of an example of empirical evidence of selfishness

- Great tits (Parus major) Wytham Woods, Oxford
- Long-term (40-year+) study
- Most pairs lay 8-9 eggs
- Egg addition experiments show that more can be successfully incubated and hatched


Why do great tits not lay more eggs

- Mean fledgling weight decreases with increasing clutch size
- So parents cannot support larger clutches in most years
- Food availability and parental effort is limited
- Heavier fledglings have a greater chance of survival
40% of fledglings >20g are recovered after 3 months cf only 5% of


Why was the optimal clutch size larger than thought

- Experimental manipulation of clutch sizes performed
- Clutch sizes that maximised the success of offspring peaked at 8-12
- Expected optimal clutch size was larger than observed
- Visser & Lessels (2001) experimentally manipulated clutch size in different ways
- ‘Free eggs’ and ‘free chicks’ increased female fitness
- But when they had to pay ‘full costs’ of incubation, then fitness was reduced for ‘enhanced clutch’ females
- Restriction of clutch size is therefore optimal and selfish


What are the three types of evidence for genes

- Genetic mutants
- Artificial selection experiments
- Population level genetic differences


Describe the genetic mutant experiements

Benzer (1973) used radiation and chemicals to produce reproductive mutations in Drosophila fruit flies:
- normal copulation takes 20min
- ♂ ‘stuck’ mutant phenotype failed to disengage after copulating with females
- ♂ ‘coitus interruptus’ mutants disengaged after only 10mins

Learning mutants have also been isolated:
- ‘Dunce’ mutants do not learn to avoid odours associated with a subsequent electric shock
- ‘Dunce’ phenotyope caused by abnormality in the gene for cyclic AMP phosphodiesterase, which breaks down the intracellular messenger cyclic AMP
- ‘Rutabaga’ mutants also do not learn
- ‘Rutabaga’ phenotype caused by abnormality in the gene for adenyl cyclase, which converts ATP to cyclic AMP
- All learning mutants have perturbed secondary cellular messaging systems (also called ‘learning pathways’)


Describe artificial selection experiments

Manning (1961) artificially selected for two different mating speeds in fruit flies by performing controlled crosses:
- ‘Slow’ and ‘fast’ males identified in one generation and bred with females in separate colonies
- Slowest and fastest males then selected from each new generation
- Mating speed diverged even further over generation time
Likely additive genetic effects


Describe studies of populations with genetic differences

Geographically distinct populations of a single species often differ in morphology and behaviour
- These differences often reflect differing ecological conditions
- Prey preferences of garter snakes (Arnold, 1981) slugs

(Sylvia atricapilla)
- Populations vary in their degree of migration
- All German birds migrate
- British blackcaps are partial migrants; some migrate, others over-winter
- All Cape Verde Islands birds are non-migratory


Describe evidence for the genetic basis of behaviour

- Berthold (1990) crossed migratory (German) x Non-migratory (Cape Verde) birds
- Crosses gave 40/60 migratory/non-migratory offspring
- Direction of migration of F1s was like German parents
- Suggests >1 gene is involved
- Selective breeding from one partial migrant population also allowed migratory and non-migratory strains to be recovered


Describe genetic determinism

Not necessarily one gene per behaviour
- Behaviours are complex, multigenic traits
- But differences in behaviour may be due to differences in one gene, since genes code for enzymes which affect development

Genes do not determine behaviour alone
- Nature vs. nurture debate!
- Environmental effects are important
- The development of behaviour is a result of complex interactions between genes and environment


Describe genes as units of selection

- Richard Dawkins, Oxford University.
- Genes create phenotypes, which are then selected on by natural selection
- The most successful genes will be those that maximise survival and reproductive success
- Therefore we expect individuals to behave so as to promote gene survival
- ‘Because of the way natural selection works, it is reasonable for us to picture an animal as a machine designed to preserve and propagate the genes which ride inside it…’ (Dawkins and Krebs, 1978)


Modern explanation of Darwin's theory (7)

1) Organisms have genes which code for protein synthesis

2) These proteins regulate the development of the nervous system, muscles and structure of an organism and therefore influence behaviour

3) Many genes exist in two or more forms (alleles) which code for slightly different forms of the same protein

4) Different alleles confer slight differences in development and behaviour, generating variation in a population

5) There is competition on the chromosome between alleles of a gene for space (at a locus)

6) Any allele making more surviving copies of itself will eventually replace the alternative form in the population

7) Natural selection is the differential survival of alternative alleles



Behavioural Ecology is the study of the function of behaviour

BE can be defined as ‘The study of how an organism’s behaviour affects its chances of passing on genes to the next generation’

BE was formed as a result of the convergence of ideas from field ecology, ethology, mathematical ecology, theoretical biology and evolutionary biology

Aspects of the behaviour of Lions in the Serengeti can be explained in both causal and functional terms

BE has an extensive, readily-accessible literature

Studies on the clutch size of great tits identified that individuals appear to act selfishly to maximise their own chances of producing ‘fit’ offspring

We examined the evidence for a genetic basis of behaviour, and the problems of ‘genetic determinism’

We then considered whether individuals or genes are the units of selection

We examined the Dawkins view of selfish genes

We examined how Darwin's theory of Evolution by Natural Selection can be ‘modernised’ and made relevant to behaviour


Briefly describe optimality modelling in BE

- Natural selection is iterative and competitive, producing behavioural phenotypes that represent the best achievable balance of costs and benefits
- Individuals exhibiting sub-optimal cost-benefit balances (trade-offs) will leave fewer offspring
- Hence, individuals are expected to evolve to behave optimally (within the bounds of ontogenetic constraints)
- Based on cost:benefit analysis
- Makes quantitative predictions about behaviour
- Seeks to identify what trade-off between costs and benefits of a behaviour will maximise net fitness
- Use models to generate testable hypotheses


Optimality modelling key concepts

- All behaviour takes time
which cannot then be allocated to other activities
- All behaviour costs energy
which cannot then be allocated to other activities
- If animals do try to carry out two types of behaviour at once, efficiency in both is typically lost
foraging / keeping watch for predators
multitasking in humans
- The benefits of any behaviour are context dependent
- Temporal variation (daily, tidal, oestral, seasonal or developmental)


Describe welk-dropping by corvids

- Crows in coastal areas feed on shellfish
- Whelks (Nucella) dropped onto rocks from height
- Take-off and vertical flight is very costly for birds
- Observed dropping height supports the hypothesis that crows open whelks using the minimum energy possible


What are the two approaches to modelling?

Verbal models
- Advantages: easily understood
- Disadvantages: ‘woolly’,

Formal mathematical models
- Advantages: explicit; clarify exactly what is assumed and what is predicted
- Disadvantages: requires some effort!


Describe the optimal foraging methods

- The functional approach:
Comparing actions in terms of their contribution to future reproductive success (FRS, the ‘ultimate currency’)
- But difficult to assess FRS
Instead focus on simpler ‘currencies’
- Net rate of energetic gain (, gamma)
- Foraging efficiency (E/h, energy/handling time)
-Others (starvation / predation avoidance, nutrient limitation)