Animal Behaviour Flashcards
It can be said that the study of animal behaviour has fallen into 3 broad categories.
- Learning theory
- Animal cognition
- Ethological/behavioural ecology
Information on Learning theory, animal cognition and ethologic perspective viewpoint
Learning Theory: Examined ‘proximate’ causes of behaviour.
Each aimed to understand the elementary units of behaviour.
These were psychologists.
Typically employed lab animals as models for human behaviour
Animal cognition: Tends to examine what animals can do cognitively and how clever they are…
Ethological perspective: This began in Germany in the 1930s. Interested in distal (‘ultimate’) or evolutionary causes of behaviour.
Stressed the importance of natural settings when examining animal behaviour.
Not psychologists (associated more with biology).
Lamarck’s theory of evolution.
He argued that species develop via two interacting processes…..
- Use and disuse
Those organs of the body that are used often develop in some way during the organism’s lifetime. e.g., muscles grow, soles of feet get harder.
2) Inheritance of acquired characteristics
Those traits learned/acquired by an animal are passed on to its offspring.
-Animals strive - uses appropriate organs – organs develop – this is inherited by offspring - thus evolution of a trait occurs
The Darwin-Wallace theory of evolution by Natural Selection.
Interaction of 4 principles:
1.Variation within species
2.Hereditability of characteristics
3.Competition for limited resources
- Nature selects favourable variations
The 4 principles of the Darwin-Wallace Theory explained.
- Variation within species
All traits within species vary. Some animals have faster legs than others, some have better camouflage, some are better at digesting proteins in food etc etc….
2) Hereditability of characteristics
Some traits animals possess are inherited by their offspring via genes. Darwin and Wallace did not know about the mechanisms of inheritance (i.e., genes). They wrote of the ‘blending’ of characteristics.
3) Competition for limited resources
The environment is not infinite. There is simply not enough food or room for all the possible number of animals that could exist. Some must die without reproducing.
4) Nature selects favourable variations
If an organism possesses a favourable trait it has a higher probability of reproducing and hence passing that trait on. Thus favourable variations are selected naturally.
Consequently, the population will be dominated by the favourable variations with the unfavourable variations dying away.
A basic model based on the speed that Gazelles in a population can run…
Note that speed, as with all traits, is actually determined both by genetic inheritance and environmental influences.
What happens when all the variation runs out?
Natural selection requires variation (within a species). But this can soon run out.
Variation provides “the materials for selection to work on”, “otherwise natural selection can do nothing”
What decides which traits should evolve?
A selection pressure is a pressure from the local ecology (i.e., environment) to drive an evolutionary trait.
e.g., there is a strong selection pressure for a fish to swim. Any individual who is not particularly good at swimming is less likely to reproduce and that trait (for poor swimming ability) will not be passed on.
Selection pressures can change (i.e., local ecological conditions change).
Classic example: Peppered moth colour change during the industrial revolution.
Lack of a selection pressure can abolish traits
This principle can act to abolish a trait when a selection pressure disappears.
e.g., the flightless cormorant lost its wings due to the disappearance of its ground predators.
natural selection acts mainly by culling traits that differ from the optimum.
In the words of George C. Williams (one of the great figures of evolutionary biology)…
So the process proposed by Darwin as the major cause of evolution is now thought to operate mainly to prevent evolution” (Williams, 1996).
e.g., a mutant mole that possessed colour vision would have no advantage; the trait would not evolve in the mole population.
Ethology
Began as a movement in the 1930s.
Tinbergen defined ethology as the ‘biological basis of behaviour’.
Aimed to determine which behaviours have evolved as a result of evolution by natural selection. That is, they were interested in phylogeny and especially function.
The two leading figures were Konrad Lorenz and Niko Tinbergen.
“You cannot understand any form of life, any structure, without understanding its use and its interaction with the environment.”
Tinbergen’s ‘four questions’
- Ontogeny
How does a behavioural trait develop within the lifetime of an animal?
2) Causation
What are the proximate causes of a behaviour?
3) Phylogeny
What is the evolutionary history of a trait? Is it unique to a species or shared with others?
4) Function
What has a trait been selected to do?
Phylogeny
Phylogeny is concerned with the connections between all groups of organisms as understood by ancestor/descendant relationships. Is one part of the larger field of ‘systematics’, which includes ‘taxonomy’ - the science of naming and classifying organisms.
Homology and Analogy
Richard Owen (1804-1892) made the important distinction between Homology and Analogy.
The same trait is often seen in two different species.
If that trait has a common evolutionary origin, it is said to be homologous – the descent implies a direct genetic relationship.
If that trait does not have a common evolutionary origin, it is said to be analogous – there is no direct genetic relationship.
Darwin and behaviour
Darwin did make the fundamental point that natural selection will not only act upon form but also behaviour; “Habits”.
In the words of Tinbergen (1969): “With remarkable foresight he realised that if his theory were to explain evolution of animal species by means of natural selection he had to apply it to all properties of animals, whether ‘structural’ or ‘functional’, and therefore could not ignore behaviour”. Tinbergen goes on to say, “Darwin’s procedure could be characterised by saying that he treated behaviour patterns as organs – as components of an animals equipment for survival”.
Harre (1981): Darwin “…had seen the central idea of ethology, that animal behavioural routines should be regarded as aspects of the animal’s adaptation to its environment as its anatomical structure or its physiological processes. And he had drawn the conclusion that routines must be inherited and naturally selected”.
Some pre-ethological work: Instinct (1/2)
William James (1890) ‘Principles of Psychology’
“instinct is usually defined as the faculty of acting in such a way as to produce certain ends, without foresight of the ends, and without previous education in the performance”.
Imprinting
Is usually attributed to Lorenz but it was reported by Douglas Spalding then Heinroth.
Spalding (1873): “Instinct, with Original Observations on Young Animals.” in Macmillan’s Magazine. Stated that newly hatched chicks will follow almost any moving figure. Regarded such behaviour as ‘un-acquired’ rather than learned.
He suggested that these animals’ ability to
recognize parents, as distinct from their
approach and following behaviour, is not
instinctive, but is, in fact, learned
When does imprinting occur?
Lorenz found that a bird can be imprinted on an object only during a specific time period and that this varied between species.
Kept a group of duckings together in isolation; saw no other stimuli. When isolated for more than 25 hours they did not have the ability to imprint. Concluded that their must be a critical period for attachment to occur.
Sluckin (1961) however suggested that imprinting had already occurred during the ‘isolation’ period; the ducklings had imprinted on each other.
Imprinting seems to be based on effort exerted rather than time.
Greater imprinting occurred when the ducks were required to climb over obstacles.
Fixed action patterns
Lorenz noticed that many animals exhibited behaviour routines that are repetitive and fixed.
Like the structure or form of an animal, these behaviours can be a distinguishing characteristic of a particular animal species.
Lorenz asked questions such as: Are these behaviours innate? How rigid are they? What are their parameters? Which stimuli in the environment ‘trigger’ them?
Lorenz suggested that fixed action patterns once started become independent of the external stimulus.
Lorenz and Tinbergen removed eggs when geese were in the middle of rolling them back. Rather than stopping the action, the geese continued the (fixed) movement until its beak returned to the nest.
Lorenz argued that FAPs were invariant. That is, an individual would perform the routine in the same way every time and this would not differ from other members of the species.
Sign Stimuli
(or Innate Releasing Mechanism; ‘Releasers’)
Tinbergen suggested that FAPs were linked to stimuli that induce them – sign stimuli.
These were thought to be specific stimuli in the environment that ‘trigger’ the FAP.
An early major aspect of Tinbergen’s research was to identify releasers…
Such as the red belly of a stickleback or the red dot on a gulls beak causing newly hatched gulls to bed for food.
Tinbergen’s Hawk-swan
Tinbergen (1948) showed that a stimulus could act as a releaser if it moved in one direction and have no releasing effect if it moved in the other direction.
Supernormal stimuli
Various animals respond to exaggerated versions of a sign stimulus, sometimes known as ‘supernormal’ stimuli.
Exploiting sign stimuli
Various organisms use sign stimuli to manipulate the behaviour of other organisms.
e.g., The fly orchid mimics a fly, presumably in order to attract wasps and bees for pollination.
Lorenz’s animal motivation model
In the model motivation increases with the passage of time between certain actions. This motivation (‘action specific energy’ is specific for one type of behaviour (e.g. either feeding, or fighting or sexual behaviour).
The Innate Releasing Mechanism describes a neural mechanism that handles the link between external stimulus, internal motivation and behavioural output.
One feature of the model is that after the animal has engaged in a particular behaviour (FAP) there is a period of time when they less likely to respond even if the same stimulus is presented again - behavioural quiescence.
‘Vacuum activity’ in non-human animals
Many tame animals exhibit instinctual ‘vacuum activity’ behaviours in the absence of external inducing stimuli.
e.g., the sudden sprint that many cats engage in with no apparent provocation.
Animals that instinctually bury objects attempt to do so when caged.
The bees waggle dance
Several aspects of the waggle dance contain information about distance.
e.g. Von Frisch (1967) found that speed (tempo) of circuits (circuits per 15 seconds) coded for distance.
Tempo increases as flight/food distance decreases.
Von Frisch suggested the energy consumption hypothesis: forager bees determine their flight distance by estimating the amount of energy used in the flight.
Supported by several observations:
- Bees loaded with lead weights overestimate the nest-food distance.
2.Bees flying in a head wind overestimate the nest-food distance compared with a tail wind.
3.Bees flying uphill overestimate the nest-food distance compared to when returning downhill.
Darwin’s Problem with Altruism?
The problem revolved around 2 related questions:
1) How can altruism evolve?
2) What is the ‘unit’ of selection?
Our own observations of the natural world tells us that animals are primarily concerned and motivated by a few goals. All ultimately concerned with reproduction.
Given that ‘nature is red in tooth and claw’ why are there so many examples of altruistic acts?
Some examples of Altruism
Florida scrub jay. The basic social unit is a monogamous breeding pair together with offspring from the past 2-3 years. The mature offspring assist younger siblings (e.g., guarding the nest, providing food).
Moehlman (1986) reported that one third of the young remain with their parents throughout the following breeding season and assist in rearing.
Alarm calls in birds.
Do ‘helpers’ really help?
Is an important question given that animal behaviour scientists (from an ethological tradition) are primarily concerned with function. i.e., why has helping behaviour been selected?
If it doesn’t help then that behaviour can’t have been selected (essentially that behaviour doesn’t exist).
One way to find out whether bird helpers really do help is to experimentally remove them from the nest.
Emlen (in 1991) reported results from 3 such
studies assessing reproductive success.
The table clearly shows that helpers do indeed help.
“For the good of the species”
The common explanation was that animals act for the ‘good of the species’ or ‘for the good of the group’.
Believed by many senior scientists, e.g., Lorenz.
Even Darwin; “There can be no doubt that a tribe including many members who, from possessing in a high degree the spirit of patriotism, fidelity, obedience, courage, and sympathy, were always ready to give aid to each other and to sacrifice themselves for the common good, would be victorious over most other tribes; and this would be natural selection”.
The idea existed, almost implicitly, for decades but was formalised by V. C. Wynne-Edwards in 1962 (“Animal dispersion in relation to social behaviour”).
Suggested that birds assess their population and if food is short they (self) restrict the number of offspring each will produce.
What is the ‘unit’ of selection?
Natural selection means that, by definition, nature is selecting something. What exactly is it selecting?
What is in competition with each other?
Individuals -> Kin -> Groups -> Species (Genus, Family, Order).
The common answer was the species; species were said to be in competition with each other.
The notion that the species is the unit of selection and hence that animals therefore act for the good of the species (e.g., altruism) was/is known as ‘group selectionism’.
Problems with group selectionism
1) Species don’t exist, they are constructed. (Many phenomena are constructed: weeds, terrorism. This is itself examined by psychologists, ‘social constructionism’). Ability to mate is not a good definition of species, e.g., sheep and goats.
2) Those individuals who act selfishly (‘defect’) will
always have an advantage.
E.g. A murmuration of Starlings.
An individual will not look around for any predators. Allowing it to eat more and to then have more time to reproduce. That is why selfish gene individuals always have an advantage. They they reproduce and make more selfish animals. Meaning overtime all individuals of that population of species will become “selfish”.
Applies even when everyone is acting for the good of the group. A defector mutation will always gain an advantage.
How A ‘defector’ will always gain an advantage.
What if a defector occurs who doesn’t bother doing any looking, just gets on with feeding. That starling will have quite a large advantage over its colleagues.
Why? For instance, because it doesn’t spend anytime looking, just eating, it is satiated quicker. It can then spend more time on other things.
It is therefore more likely to have offspring, and if that trait for not looking up is inherited its offspring will also not look for predators when feeding.
Soon the whole population will comprise individuals who do not bother to look for predators when feeding.
However, this clearly does not happen – the starlings act altruistically.
This defector-advantage principle can be seen in Wynne-Edwards theory of population regulation.
A mutation may arise in the population that predisposes a bird to lay six eggs for instance instead of two. If there are enough resources for these six individuals to survive then the genetic tendency to lay six eggs will be passed on.
It would not take many generations of six egg-laying individuals to over exploit the resources.
What then is the unit of selection?
The ‘answer’ is that the unit of selection is the gene.
This was proposed by Bill Hamilton in a legendary paper published in 1963 in The American Naturalist and then in a longer paper published the following year in The Journal of Theoretical Biology.
Ignored at first, then the idea took off in the 1970s.
Now it’s the most famous and significant paper/idea in evolutionary biology and its this that started the revolution (in evolutionary biology).
The critical idea of Hamilton’s with Altruism
A gene will influence the body it sits in to behave altruistically towards other animals that share that gene.
If a gene could talk it would say: “To propagate myself as much as possible, I need to help other individuals who are closely related because a copy of myself resides inside those individuals”.
This is known as ‘kin-selection’ or ‘inclusive fitness’.
In other words, if an animal has a gene which leads the animal to behave in an altruistic way to a relative (who is likely to also have that gene), the gene will spread through the population.
Genetically speaking, one individual is equivalent to two siblings, or four cousins etc.
Each is worth as much. That is, one individual has 1 gene (of course) for a certain trait; two siblings have the equivalent of 1 gene because there is a 50% chance of that one individual’s gene being in one of the siblings.
Another example – one individual has 1 gene for a certain trait; 4 niece/nephews have the equivalent of 1 gene because there is a 25% chance of that one individual’s gene being in one of the 4.
The mathematics of Hamilton’s idea
A gene coding for an altruistic act will be selected if the cost to the individual is less than the benefit gained by the recipients of the altruistic act. That is, if the benefits of the altruistic act outweigh the costs, then selection will favour the behaviour.
‘Benefits’ and ‘costs’ are measured in terms of ‘fitness’, i.e. reproductive success.
The fitness of a behaviour therefore is determined by the direct effect of the behaviour on the fitness of the individual, as well as the summation of indirect fitness effects across all kin that are affected, and, importantly, adjusting for the degree of relationship of the kin.
Hamilton expressed his idea in a simple mathematical formula that describes the concept of ‘inclusive fitness’ (i.e., ‘kin selection‘): The gene for acting altruistically will be selected if: -
C < B X R
Where C is the cost to the altruist,
B is the benefit to the recipient/s
R is the degree of relatedness between the altruist and recipient/s.
Can explain altruism in starlings
“For the good of the group” – No. A defector will always do better.
For the good of the individual – No. Altruism exists.
For the good of the gene – Yes. A gene that predisposes an individual to act altruistically (i.e., scan for predators) will spread. It will be selected. It is a ‘selfish gene’.
Its selfishness has generated altruistic behaviour.
Selection at the level of the gene
Altruism is only one aspect of a gene’s ‘goal’: to replicate itself as much as possible; to dominate the gene pool; to be ‘selfish’.
Altruism is an addition to the most obvious way a gene can replicate itself: Influence the body it sits in to act in a way that ensures the body survives to pass on copies of the gene. Thus, make it good at avoiding predators; good at finding food; finding a mate (doesn’t find a mate, it will not be replicated), finding shelter, making good webs if it’s a spider, good vision if its an eagle. etc etc…
How can a single gene exert its effect when it is one of many thousands of genes?
i.e., there are many genes influencing behaviour.
Dawkins (Chapter 3) gives the example of an oarsman who realises that a particular crew member tends to be in the boat when fast times are recorded. (The same principle as isolating one factor amongst many in a standard psychology experiment).
What is the evidence for Hamilton’s rule?
Hymenoptera sex ratios:
Hamilton said that it is no coincidence that the extreme example of altruism is seen in the Hymenoptera (e.g., wasps, bees, ants).
In these species, most famously in the bees, ‘workers’ don’t reproduce they cooperate with fellow workers. Its no coincidence because females share a greater proportion of their genes with their sisters (75%) than their own daughters (50%).
Haldane even got close to the mathematics of the inclusive fitness idea with this famous quip with Altruism:
“If one or two of my brothers were drowning in this river, I might perhaps not risk my life to save them but if more than two of my brothers were drowning, I might attempt to save them at a risk to my life”.
Essential behaviour ecologists and optimality
Essentially, behavioural ecologists work out what the most efficient behaviour is in a certain situation and then examine whether animals perform this ‘optimal’ behaviour.
Or, similarly, they observe what animals actually do and work out whether this is the most efficient way of performing that goal.
As humans we are quite often conscious about acting optimally
Which line should I queue in? The line with three half baskets or one full trolley?
We essentially perform a cost/benefit analysis.
The cost = larger queue. The benefit = less items to check-out. The net result is the time it takes us to pass through.
In this situation, we tend to apply something akin to Hamilton’s formula…
Remember that ‘Hamilton’s rule’ is mathematical
(We could empirically assess whether humans act optimally in this situation. i.e., find out what the best strategy is and see if humans do it. But remember, humans are likely to be thinking consciously, animals are not).
Costs and benefits weighted against each other are central to the Selfish Gene theory and thus the notion of optimality.
Hunting in a group of 4 is the most efficient system and should therefore be selected.
Each individual animal can expect to hunt for 40 minutes in order to eat a complete prey item.
We could go into the field and test this. i.e., Find out what the most efficient strategy actually is, by observing the different strategies (if there are different ones), and see if lions adopt it.
What is the Optimal number of offspring?
Doesn’t the Selfish Gene predict that offspring number will keep on increasing? No.
“All models of the evolution of family size assume that there is a trade-off between the number of progeny produced and the fitness of each of them” (Krebs & Davies, 1978). This is empirically true….
Similarly, number of offspring relates to survival rate.
Clearly a negative relationship, and the principle of dividing one’s resources too thinly.
Do birds lay an optimal number of eggs?
The great ornithologist of the 1950s and 60s David Lack first argued that birds do. Suggested that those who laid the optimal number of eggs would leave the most offspring.
He undertook a long term study of the great tit in Wytham woods, near Oxford (the work was followed- up by Perrins).
This population lay a single clutch of 8-9 eggs
Following Lack, researchers have employed a basic paradigm for assessing whether birds lay optimally.
Add (or take away) eggs from a nest and see whether this manipulation increases offspring success.
If birds are acting optimally, such manipulation should not increase success.
Put another way; determine which is the most efficient clutch size number through experimental manipulation and see whether this number is what a bird actually lays.
This figure shows the optimum brood size based on survival from egg number manipulation experiments.
The optimum of 8-11 is close to the real figure of 8-9 but is a bit more, i.e., the birds appear to be laying below optimum.
Although, these data suggest that about 8 is optimal in the great tit.
It supports the actual number they lay.
(The ‘recaptures per brood’ measurement may not be the most appropriate. It may not take into account more long-term success. Remember a basic principle of behavioural science; the dependent measure is important).
Why are clutch sizes below minimum?
Charnov and Krebs (1974) suggest a reason why birds underestimate their brood breeding ability.
The probability that a parent will survive to breed the following year is also dependent on brood size, the larger the brood size the smaller the chance of survival (extra work, etc)………
So the parent should not just consider its optimum output for one brood for a single year but for all its broods over its entire lifetime.
The dilution effect.
An anti-predation effect without increased vigilance.
Water skaters sit on the surface of ponds and are predated by small fish.
Attack rates do not differ with size of group.
But, predation is still lower per individual as group size increases.
There is just less chance of being one of the unlucky few (Foster & Treherne, 1981).
A dilution effect was empirically supported by Duncan and Vigne (1979) in the semi-wild horses that live in the marshy delta of Carmargue in southern France.
In the summer the horses are plagued by biting tabanid flies. The horses form groups.
Measurements of tabanid numbers showed that there were less per horse for larger groups compared with smaller groups.
This was confirmed by an experiment in which horses were transferred between smaller and larger groups and vice versa.
Costs and benefits of different group sizes.
As well as benefits to groups there are clearly costs of larger groups.
Increased competition for food. Increased incidence of disease as a result of close proximity with others, (Hoogland, 1979).
Brown and Brown (1986) showed that larger colonies of cliff swallows have more blood sucking swallow bugs per nest than smaller colonies.
Optimal foraging theory
Has been the main concern of optimality theory.
The rationale is very simple:
Economically define an optimal strategy for finding and eating food then observe animals to see whether they do indeed act optimally.
Again, the assumption is that natural selection chooses the best strategy for eating food.
“Let us assume that natural selection will favor the development…. of feeding preferences that will…..maximize the net caloric intake per individual of that species per unit time”.
Zach, (1979) optimal foraging in Northwestern crows on the coast of Canada.
Feed on whelks.
Drop them on rocks in an attempt to smash them open.
A basic trade off exists between height and success.
Is there an optimum for breaking open shells?
Yes.
An animal cannot always eat the most profitable items. Often other factors have to be taken into account.
e.g., shore crabs
The larger the muscle the more calories it contains. It would therefore seem to make sense to eat the largest muscles.
However, the relationship between size of muscle and effort required to open it is not likely to be linear.
However, whilst they avoid the very large and very small muscles, they don’t just eat muscles between 2-3 cms, they eat many smaller and many larger. Why?
What does the crab have to take into account?
It has to consider search time.
Little point in wasting energy by searching for the most profitable muscles if you don’t come across them that often.
You might as well take the one which are not quite optimal as well.
Charnov’s Prey Model.
Decisions such as these (i.e., when to reject a prey item) is inherent in Charnov’s Prey Model.
Charnov proposed that foraging involves a continuous cycle.
- The search. This includes any activity that involves looking for food.
- Occurs once a prey item has been found. Should this prey item be perused?
Thus the cycle is one of search, encounter, and decide.
The critical information that the animal needs to ‘know’ is:
- The energy gained from eating a particular prey.
- The energy cost in searching for a particular type of prey and catching it, called the handling time.
- How often is particular prey item likely to be encountered. The third one is important because this will affect 2.
It’s essentially a cost-benefit analysis for each prey type.
The ‘ideal free distribution’
A simple model of competition:
Two habitats, one is rich in resources the other poorer.
An animal will chose the former, later arrivals will do the same.
However, as more animals use the habitat the resources will be depleted making it less profitable to latecomers.
Eventually a point will be reached where late arrivals will do better occupying the ‘poorer’ location, where although poorer in resources, there is less competition.
Thus an equilibrium will be reached where the two habitats will become equally profitable per individual (containing more individuals in the rich habitat).
Criticisms of optimality models
1.A behaviour may not be adaptive, (i.e., is not ‘functional’; not due to evolution; More on this in Lecture 9).
2) If a behaviour is found not to be optimal other explanations are easily at hand: The wrong units of
optimising were used; the experiments were not done well enough; the model is wrong.
- One of the issues is what units of fitness success are appropriate.
- The general problem of adding factors in modelling. Take optimal group size. Optimal behaviour is going to depend on many interacting factors….
What is the optimal group size?
Will clearly depends on many factors.
Pulliman (1976) and Caraco et al. (1980) attempted to model the main factors (feeding, fighting, scanning).
Other factors include the behaviour of other animals, as this shows. Also, the changing ecology (i.e., environment) will be another factor in any optimality model.
Optimal copulation in Dungflies.
This will also depend on many factors.
Recall that the data suggested that he should stop when the line starts becoming more horizontal than vertical (i.e., at about 45 minutes).
However, it may be more optimal to carry on mating if the chances of finding another female are low.
The additional factor here is the search time to find another willing female.
Or, consider our first example where humans act consciously
Which line should I queue in? The line with four half baskets or one full trolley?
We essentially perform a cost/benefit analysis:
We often take into account many other factors.
e.g., Speed of the check-out assistant. ‘He/she seems to be talking a lot’. ‘What kind of items are actually in the baskets and trolley’?
(to be fair, this last issue occurs with all theory generation, i.e., adding factors).
What is game theory in animals?
A game theoretic approach should be used to understand the behavior of animals whenever there are reasons to believe that the strategy or the behavior of one organism is affected by the behavior of the other and vice versa.
