Behavioural Ecology

This subdiscipline studies the behaviour of individuals in an ecological context.

In general, the behaviours studies are directed toward food,habitat, and mates.

In all three, genetics and evolution play or have played key roles in determining the behaviours we observe. In all three the observed behaviours frequently result from a mixture of innate and learned components.

What regulates behaviour?

There are both genetic and environmental components (i.e.the old ‘nature versus’ nurture controversy).

Evidence of the importance of both components is wide-spread. One example: The learning of bird song in white-crowned sparrows…

Here’s an experiment demonstrating it:

Sparrow chicks were separated into 3 groups 1. Raised in soundproof chambers unable to hear songs 2. Chicks allowed to hear songs for 5 months (still

immature), then deafened 3. Control group

Males normally begin singing what is termed a ‘subsong’at about 150 days, then the song is refined and practiced,until at about 200 days the ‘full’ song is sung.

Here are sonograms of normal song, the subsong, and fullsong in the control group, then what is seen in experimentalgroups...

Normal adult song The subsong sung at ~ 150 days

w/exposure to adult song

in isolated birds

The full song

There is a genetic program which produces the firstgeneralized song, the subsong.

If raised in isolation, the song never changes from thesubsong, which is viewed as a template.

There is a closer match to normal song, even if the normal song is only heard before maturation.

Behaviours that are genetically programmed, and thereforevirtually uniform across all members of a species, are calledinnate or instinctual.

The behaviour is termed (by Tinbergen initially) aFIXED ACTION PATTERN or FAP

The FAP is elicited by a sign stimulus.

sign stimulus: an insect

FAP: complex movement of the tongue to capture the insect

At the opposite end of the spectrum are behaviours that arelearned. An example: bees able to communicate the location of food sources to their hives or digger wasps locating their nests

Learning

Five basic types of learning:1. Habituation – frequent repetition of a signal leads to a loss of response to it

2. Imprinting – during a short sensitive period learned behaviour becomes irreversible and fixed

3. Association – stimuli linked to reward or punishment become associated by learning

4. Imitation – behaviours learned by mimicking others

5. Problem solving – inventive/innovative behaviours that occur in response to new situations

Habituation –

Do you ‘feel’ the clothes you are wearing?

Are you ‘aware’ of the background noise in your environment?

Do you smell the perfume/cologne the person sitting next to you is wearing?

When a stimulus occurs frequently enough (or continuously) you respond at first, but then habituate to it, and response ceases. When you “stop to think about it” you can feel your clothes, hear the background noise, or smell the scent, but, under usual circumstances, you lose awareness and response.

Imprinting –

Babies recognize their mothers within a few days of birth, and respond to them with smiles. The same sort of thing happens in birds, with the famous picture of Konrad Lorenz as ‘mother’ to geese, since he was the first thing they saw after hatching. Once imprinted, he was their ‘mother’ for life.

Association (or associative learning) –

One form is classical conditioning – put rats in a Skinner box where they can press a bar to get food. Once they associate pressing the bar with getting food, they press it a lot.

Another form is trial-and-error learning – a predator learns what is good to eat, and what is not. The text has a painful, but excellent picture if an ‘error’:

a coyote with a face full of porcupine quills

Imitation –

That’s how the sparrow learns the normal adult song. If it can’t imitate what it hears from adults, it can

produce only the innate component of normal song.

Wolves (and many other mammalian predators) take their young (teenage equivalents) along on hunting trips so that they can learn the ‘proper’ technique to successfully capture prey.

Problem solving –

Developing a new behaviour to meet the needs of a novel situation.

Don’t think problem solving is limited to primates (and dolphins).

You’ve already encountered ‘tool use’ by one of Darwin’s finches, using a cactus needle to gather insects.

The text shows raven learning how to raise food hung on a string.

Once a problem-solving behaviour has been ‘discovered’, it can be passed on through imitative learning.

There are a few important Categories of behaviour

1. Territoriality

Territoriality is most likely to occur:

• When density increases

• When there is increased demand for resources

• When competition increases e.g. for resources or mates)

• When resources are aggressively defended

Of these four reasons, three are related to resources, and one to obtaining/keeping mates.

For any territory based on resources to occur,

ANY RESOURCE THAT IS DEFENDED MUST HAVE AN “ECONOMIC GAIN”

Defending a resource provides a benefit … the value of theresource.

The benefits must exceed the costs of defending theterritory.

Otherwise the resource is not worth defending.

There is plenty of evidence for the economic model.

Territory size should vary with the amount of resourceavailable. Here’s data from one study…

Abundant resources- small territories and a largernumber of birds

Sparse resources-fewer, but larger territories toprotect sufficient resources

What determines the size of an animal’s territory?

Simple models provide a rough answer.

First, as territory size increases, benefits increase, but onlyup to a point. As territory size increases, the cost of defensealso escalates…

• there is a larger area to defend• there is contact (and potentially aggressive encounters) with a larger number of animals• the time spent on defense means other functions may be neglected

This suggests a cost-benefit model...

Neither very small nor very large territories are economically defendable. There is an optimum size…where benefits exceed costs to the greatest extent.

How useful is this model in explaining territory size?

In a general sense, the model is correct.It correctly predicts that very large and very small territories are too costly. For example, in some birds low food abundance (low benefit) causes them to abandon defending territories. But when food abundance again increases, territories are again defended.

However, optimal size is very sensitive to the exact shapes of cost and benefit curves. Therefore, the model is of very limited use in making quantitative predictions.

2. Communication

Communication means: not just the sending of a signal, but its reception by another, and that the signal is acted upon.

Communication has many functions. Here are some…

• Status - identification of rank• Begging - solicitation of parental care by offspring• Alarm - warning of the presence of a predator• Distress - a call for aid• Threat - Show of imminent aggression• Appeasement - attempt to dissuade aggression• Sexual receptivity - identification of readiness to mate

Communication can take a number of forms:

Chemical – pheromones for mating, scent marking to set territories

Visual – posing to attract mates, posing to set dominance hierarchies, as a portion of mating rituals

Accoustic – wolf howls tell members of a pack how to get ‘home’, also tell others the pack is there; cricket chirps (and many other insect sounds) are related to mate attraction

Tactile – many mating rituals involve the correct touching or rubbing of the potential mate (and I’m not referring to the human species)

There are also multiple levels for signals. Consider two signal communications…

1) Photinus (firefly) flashes - each species has a specific stereotyped pattern. Males flash, females signal receptivity by flashing back. This is a yes-no signal.

2) The honey bee waggle dance communicates what is called a graded signal, much more than yes-no.

The honey bee flies in repeated figure-8s inside the hive. Angle to the vertical communicates the angle between a food source and the sun. The length of the straight, middle run indicates distance. The intensity of the waggle indicates quantity of food.

3) Aggression

Aggression has the function of achieving dominance byeither physical violence or the threat of it.

Aggression can be involved in defense of territory, butdominance is most important in mating and reproduction.

Aggression associated with mating has obvious fitnessconsequences…• in wolves, only the male mates. Aggression preventing other males from mating mean only his genes will be found in offspring.• In sea lions, males guard harems of females against both other males & desertion by females

Sometimes, aggression is ritualized rather than injurious.To make evolutionary sense, this must be to the advantageof both animals. The risk of injury to both winner andloser is significant. Thus, rapid recognition of dominanceprotects both. The loser can try again later, having grownlarger and stronger with time.

Behaviour involves interactions between/among individuals.There are four possible outcomes to interactive behaviour…

Effect on donor fitness-- +

Effect on -- spitefulness selfishnessrecipientfitness + altruism cooperation

There are numerous observations of cooperation, bothwithin related groups and among unrelated individuals. That’s logical from an evolutionary (fitness) perspective.There are no observations of spitefulness that I know of.That, too, is logical. So is selfishness.

Altruism is a more difficult question.

There are two kinds of altruism. One, reciprocal altruism, is easy to understand.

• Imagine a flock of birds trying to feed.

• When each individual has to defend itself, it has to look around for predators frequently.

• When the group has rotating sentry duty, group defense occurs, each individual has to spend only its time ‘on duty’ checking for predators frequently.

• Therefore, each can spend more time feeding.

• Each individual expects that others will be as vigilant in defense as it was while on duty. The effort is reciprocal.

To understand altruism that is not reciprocal, you need to understand the idea of inclusive fitness.

Evolutionary fitness is measured by the numbers of copiesof ‘your’ genes in the subsequent generation compared tothose of others.

Note that it doesn’t matter whether you or a relative supplied those genes.

An extreme example: You are one of 4 children in a family in a war zone. You are playing together when someone throws a live hand grenade through your door. Would you achieve higher fitness by jumping through a window or jumping on the hand grenade?

The answer: If you survive, you leave behind onecopy of your genes.

If you act in an altruistic way, each ofyour siblings shares (on average) 1/2of your genes by descent from theparents. Saving 3 of them would leave1½ copies of your genes, and giveyou a higher inclusive fitness.

Thus, some altruism is logical and supported by natural selection. However, truly altruistic acts among unrelated individuals are much harder (and still controversial) to explain.