Chapter 51 Behavioural Ecology

Recall... Behavioural ecologists distinguish between proximate and ultimate causes of behaviour What are the questions that must be answered to understand any behaviour? 1.What is the mechanistic basis of the behaviour, including chemical, anatomical, physiological mechanisms? 2.How does development of an animal influence behaviour (sign stimuli)? 3.What is the evolutionary history of the behaviour? 4.How does behaviour contribute to survival & reproduction (fitness)?

Behaviours typically studied by ethologists Fixed Action Patterns Fixed action pattern (FAP) Imprinting

Many behaviours have a strong genetic component –innate behaviours Directed movements – kinesis – taxis – migration

Animal Signals and Communication Genetic Influences on Mating and Parental behaviour

Environment influences the development of behaviours Dietary Influence on Mate Choice behaviour Social Environment and Aggressive behaviour Learned behaviours – Habituation – Spatial learning – Cognitive maps – Associative learning – Cognition

Concept 51.4: Behavioural traits can evolve by natural selection Because of the influence of genes on behaviour – natural selection can result in the evolution of behavioural traits in populations

Behavioural Variation in Natural Populations When behavioural variation within a species – corresponds to variation in the environment, it may be evidence of past evolution

Variation in Prey Selection Differences in prey selection in populations of garter snakes – are due to prey availability and are evidence of behavioural evolution Figure 51.18a, b (a) A garter snake (Thamnophis elegans) (b) A banana slug (Ariolimus californicus); not to scale

Variation in Aggressive behaviour Funnel spiders living in different habitats – exhibit differing degrees of aggressiveness in defense and foraging behaviour Figure Time to attack (seconds) Field Lab-raised generation 1 Lab-raised generation 2 Desert grassland population Riparian population 60 Population

Experimental Evidence for behavioural Evolution Laboratory and field experiments – can demonstrate the evolution of behaviour

Laboratory Studies of Drosophila Foraging behaviour Studies of Drosophila populations raised in high- and low-density conditions – show a clear divergence in behaviour linked to specific genes Figure Average path length (cm) 4 L1L2L3H1H2H3H4 H5 D. Melanogaster lineages Low population density High population density

Migratory Patterns in Blackcaps Field and laboratory studies of Blackcap birds – have documented a change in their migratory behaviour

Birds placed in funnel cages – left marks indicating the direction they were trying to migrate Figure 51.21a (a) Blackcaps placed in a funnel cage left marks indicating the direction in which they were trying to migrate.

Migratory orientation of wintering adult birds captured in Britain – was very similar to that of laboratory-raised birds Figure 51.21b (b) Wintering blackcaps captured in Britain and their laboratory-raised offspring had a migratory orientation toward the west, while young birds from Germany were oriented toward the southwest. N E S W Adults from Britain and F 1 offspring of British adults N E S W Young from SW Germany Mediterranean Sea BRITAIN GERMANY

Concept 51.5: Natural selection favours behaviours that increase survival and reproductive success The genetic components of behaviour – evolve through natural selection Behaviour can affect fitness – through its influence on foraging and mate choice

Foraging behaviour Optimal foraging theory – views foraging behaviour as a compromise between the benefits of nutrition and the costs of obtaining food

Energy Costs and Benefits Reto Zach – conducted a cost-benefit analysis of feeding behaviour in crows The crows eat molluscs called whelks – but must drop them from the air to crack the shells

Zach determined that the optimal flight height in foraging behaviour – correlated with a fewer number of drops, indicating a trade-off between energy gained (food) and energy expended Figure Average number of drops Average number of drops Drop height preferred by crows Total flight height Total flight height (number of drops  drop height) Height of drop (m)

In bluegill sunfish – prey selection behaviour is related to prey density Figure Low prey densityHigh prey density 33% 32.5% 35% 2% 40% 57% 100% 50% 35% 14% 33% Small prey Medium prey Large prey Small prey Medium prey Large prey Small prey Medium prey Large prey Percentage available Predicted percentage in diet Observed percentage in diet Large prey at far distance Small prey at middle distance Small prey at close distance

Risk of Predation Research on mule deer populations – has shown that predation risk affects where the deer choose to feed Figure Predation occurrence (%) 50 Relative deer use Predation risk Open Forest edge Habitat Forest interior

Mating behaviour and Mate Choice Mating behaviour – is the product of a form of natural selection called sexual selection

Mating Systems and Mate Choice The mating relationship between males and females – varies a great deal from species to species In many species, mating is promiscuous – with no strong pair-bonds or lasting relationships

In monogamous relationships – one male mates with one female Figure 51.25a (a) Since monogamous species, such as these trumpeter swans, are often monomorphic, males and females are difficult to distinguish using external characteristics only.

In a system called polygyny – one male mates with many females – the males are often more showy and larger than the females Figure 51.25b Among polygynous species, such as elk, the male (left) is often highly ornamented. (b)

In polyandrous systems – one female mates with many males – the females are often more showy than the males Figure 51.25c (c) In polyandrous species, such as these Wilson’s phalaropes, females (top) are generally more ornamented than males.

The needs of the young – are an important factor constraining the evolution of mating systems The certainty of paternity – influences parental care and mating behaviour

In species that produce large numbers of offspring – parental care is at least as likely to be carried out by males as females Figure Eggs

Sexual Selection and Mate Choice In intersexual selection – members of one sex choose mates on the basis of particular characteristics Intrasexual selection – involves competition among members of one sex for mates

Mate Choice by Females Male zebra finches – are more ornate than females, a trait that may affect mate choice by the females Figure 51.27

Imprinting of female chicks on males with more ornamentation – affects mate selection as adults Figure Experimental Groups Control Group Parents not ornamented Both parents ornamented Males ornamented Females ornamented Results Females reared by ornamented parents or ornamented fathers preferred ornamented males as mates. Females reared by ornamented mothers or nonornamented parents showed no preference for either ornamented or nonornamented males. Males reared by all experimental groups showed no preference for either ornamented or nonornamented female mates.

The size of eyestalks in stalk-eyed flies – affects which males the females choose to mate with Figure 51.29

Male Competition for Mates Male competition for mates – is a source of intrasexual selection that can reduce variation among males

Such competition may involve agonistic behaviour – an often ritualized contest that determines which competitor gains access to a resource Figure 51.30

Morphology affects the mating behaviour – in isopods of the same species that are genetically distinct Figure Large Paracerceis  males defend harems of females within intertidal sponges.      Tiny  males are able to invade and live within large harems.  males mimic female morphology and behaviour and do not elicit a defensive reponse in  males and so are able to gain access to guarded harems.

Applying Game Theory Game theory evaluates alternative behavioural strategies in situations – where the outcome depends on each individual’s strategy and the strategy of other individuals

Mating success of male side-blotched lizards – was found to be influenced by male polymorphism and the abundance of different males in a given area Figure 51.32

Concept 51.6: The concept of inclusive fitness can account for most altruistic social behaviour Many social behaviours are selfish Natural selection favours behaviour – that maximizes an individual’s survival and reproduction

Altruism On occasion, some animals – behave in ways that reduce their individual fitness but increase the fitness of others This kind of behaviour – is called altruism, or selflessness

In naked mole rat populations – nonreproductive individuals may sacrifice their lives protecting the reproductive individuals from predators Figure 51.33

Inclusive Fitness Altruistic behaviour can be explained by inclusive fitness – the total effect an individual has on proliferating its genes by producing its own offspring and by providing aid that enables close relatives to produce offspring

Hamilton’s Rule and Kin Selection Hamilton proposed a quantitative measure – for predicting when natural selection would favour altruistic acts among related individuals

The three key variables in an altruistic act are – the benefit to the recipient = B – the cost to the altruist = C – the coefficient of relatedness = r

The coefficient of relatedness – is the probability that two relatives may share the same genes Figure Parent AParent B  OR Sibling 1 Sibling 2 1 / 2 (0.5) probability

Natural selection favours altruism when the benefit to the recipient – multiplied by the coefficient of relatedness exceeds the cost to the altruist This inequality – is called Hamilton’s rule Hamilton’s rule = rB > C – more closely related two individuals are, greater value of altruism

Kin selection is the natural selection – that favours this kind of altruistic behaviour by enhancing reproductive success of relatives

An example of kin selection and altruism – is the warning behaviour observed in Belding’s ground squirrels Male Female Age (months) Mean distance moved from natal burrow (m) Figure 51.35

Reciprocal Altruism Altruistic behaviour toward unrelated individuals – can be adaptive if the aided individual returns the favour in the future This type of altruism – is called reciprocal altruism

Social Learning Social learning – forms the roots of culture Culture can be defined as a system of information transfer through observation or teaching – that influences the behaviour of individuals in a population

Mate Choice Copying Mate choice copying – is a behaviour in which individuals in a population copy the mate choice of others

This type of behaviour – has been extensively studied in the guppy Poecilia reticulata Figure Male guppies with varying degrees of coloration Control Sample Female guppies prefer males with more orange coloration. Experimental Sample Female model engaged in courtship with less orange male Female guppies prefer less orange males that are associated with another female.

Social Learning of Alarm Calls Vervet monkeys – produce a complex set of alarm calls

Infant monkeys give undiscriminating alarm calls at first – but learn to fine-tune them by the time they are adults Figure 51.37

No other species – comes close to matching the social learning and cultural transmission that occurs among humans Figure 51.38

Evolution and Human Culture Human culture – is related to evolutionary theory in the distinct discipline of sociobiology

Human behaviour, like that of other species – is the result of interactions between genes and environment However, our social and cultural institutions – may provide the only feature in which there is no continuum between humans and other animals