Intro To Behavioural Ecology:

Question 1

What is Behavioural Ecology?

Answer 1

Animal Behaviour covers questions regarding the mechanism, development, function and evolution of behaviour (Tinbergen’s ‘Four Questions’)

focuses on the function of behaviour - its adaptive nature; and its evolution under ecological constraints

Question 2

Genetic basis of behaviour:

Answer 2

variation and selection

‣ ‘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’

Question 3

Ecology -

Answer 3

Behaviour impacts ecosystems, food chains, habitats

E.g. grazing patterns affect what plants grow in a particular area

Question 4

Ethology:

Answer 4

Behaviour is shaped by ecological context

E.g. behavioural mechanisms

Question 5

Evolution:

Answer 5

Behaviour is both a product and driver of evolution

Question 6

J Crook: the birth of behavioural ecology

Answer 6

Pioneered the Comparative approach - by linking social organisation in birds and primates to ecological factors

Comparative approach: relate observed species variation in behaviour patterns to ecology, and then map this to phylogeny.

Question 7

J Crook’s Weaver birds:

Answer 7

species of sparrow-like passerines found in Africa and Asia

Different species inhabit very different habitats (cover, food type, predation)

Parallel variation in species-specific patterns of social behaviour - e.g. nesting dispersion (solitary vs. ‘cities’ and mating systems (pairs vs. polygamy)

Question 8

MacArthur/ Orians / Brown -

Answer 8

Established that hypotheses about behaviour could be couched in mathematical terms.

There are costs and benefits to any behaviour:

e.g. watching out / running from a predator…
‣ 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’.

Question 9

Predictive optimality models consist of 3 components:

Answer 9

• Assumptions about what choices are available
• Assumptions about what is being maximised
• Assumptions about constraints.

Question 10

Hamilton / Maynard-smith:

Answer 10

showed the importance of ideas of kin selection, inclusive fitness and evolutionary stable strategies (game theory).

E.g. altruism

Question 11

Altruism:

Answer 11

behaviour that benefits the survival/fitness of others at the expense of the survival/fitness of that individual

Observed in animals populations; co-operative breeding (scrub jays), collective offspring care (lions).

Question 12

Kin selection:

Answer 12

Evolutionary stratagem that favours reproductive success of an animals relatives at the cost of its own reproduction

Hamilton realised that relatedness is important:

‣ Parents-offspring share 50% of their genes

‣ Brothers/sisters share 50% of genes

‣ Grandchildren / parents share 25%, cousins 12.5%

Question 13

Inclusive fitness:

Answer 13

success of genes you share with others being transmitted to future generations

• The number of offspring equivalents an individual rears, rescues or other-wise supports through its behaviour (regardless of not birthing them).

Question 14

Tinbergen / Lorenz / von Frisch

Answer 14

Pioneered the testing of hypotheses about survival value of behaviour, using field and laboratory experiments

◦ Eggshell removal in black-headed gulls - gills remove shells from nest (disadvantage to itself - leaving chicks)

‣ Why do gulls remove shells from nests after chicks hatch?

‣ Tinbergen painted hens’ eggs to resemble gulls eggs and placed them in the gull colony, some next to broken shells; recorded egg losses

‣ 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 - gull egg is well camouflage but inside of egg = white - attracts predators (benefit = reduce egg predation)

Question 15

Tinbergen’s Four Questions:

Answer 15

• Causation – What proximate factors cause the behaviour (hormones etc.)?
• Development – What are the roles of genetic and ontogenetic factors in the development of a behaviour?
• Evolution – How did the behaviour evolve from that of its ancestors, e.g., in the face of competition from other species?
• Function – How does the behaviour contribute to the survival of the individual and / or enhance its genetic contribution to the next generation?

Question 16

Example of Tinbergen’s four questions:

Answer 16

Serengeti lions - live in prides

• fewer adult males than females
• females adults are all related
• females born in pride remain there and reproduce
• males born in pride leave and become nomadic before attempting to take over another pride - have a short reproductive life as are driven out by other males

Question 17

Lion example:

All females in pride enter oestrus at the same time…

Answer 17

Causal explanation = chemical/pheromone cues synchronise oestrus cycles

Functional explanation =
‣ Cubs born synchronously survive better.
‣ Synchronous and communal suckling.
‣ Greater chance of male cubs having a related, same age companion male to leave pride with.

Question 18

Lion example:

Despite high rate of copulation, birth rate is low…

Answer 18

• Causal explanations - Female infertility?Concealed time of ovulation?
• Functional explanations -

‣ Advantageous for female to be receptive at times when conception is unlikely: male encouraged to stay with group.

‣ Increases paternity uncertainty amongst males = males don’t know which cubs are there’s = reduces risk of males killing cubs

‣ Reduces competition between males

‣ Incites sperm competition, possibly increasing the chance of a high-quality male being the father

Question 19

Lion example:

All young die when new male takes over…

Answer 19

• Causal explanations:
‣ Aggressive male kill cubs
‣ Hormonal changes in females resulting from the (stressful) takeover causes abortion of unborn young

• Functional explanations:

‣ females come into oestrus quicker when not nursing cubs, allowing new males to produce own cubs sooner

‣ male removes non-related offspring, which would compete with its own offspring (not interested in raising non-related cubs).

Question 20

Natural selection acts at the level of

Answer 20

of the individual.

group selection - “for the good of the species” explanations - are not true?
◦ e.g. Male lion killing cubs is not good for the species…

• Individuals therefore typically act selfishly - to maximise their lifetime reproductive fitness (pass on genes)

= therefore actually acts at the level of the genes

Question 21

There is a…

Answer 21

Genetic component to behaviour - individuals act selfishly to pass on genes

Unit of selection acts at the level of genes
‣ 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.

Question 22

evidence of selfishness: Great tits example

Answer 22

Lay 8-9 eggs - egg addition experiments show that more can successfully be hatched - But meant chicks weight decreased as parents cannot support due to food availability

Found that 8-12 eggs maximised the success of offspring - but this experiment ignored lifetime reproductive success (female less likely to survive) - by adding eggs female got them for ‘free’ = ignores cost of production

Restriction of clutch size is therefore optimal and selfish