Transcript Chapter 28
Chapter 28: Animal behaviour Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 28-1 Ethology • Ethology is the study of animal behaviour • Ethology documents behaviour and examines the causes and outcomes of observed behaviour • Studies investigate – – – – causation development adaptive value evolutionary history Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 28-2 Evolution of behaviour Because behaviour is part of an animal’s phenotype, it is subject to natural selection and sexual selection • Selection acts where there is variation in behaviour between individuals in a population • Animal behaviour is often a balance between several alternative behaviours • – hide from predators and starve or forage and run the risk of being eaten? Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 28-3 Genetic markers • Behaviour has a genetic basis – mutations in genes may alter behaviour • Studies of fruit flies (Drosophila melanogaster) have identified some behaviours under genetic control – duration of copulation is affected by mutations in muscles and sensory receptors Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 28-4 Selection • Artificial selection is used to develop preferred traits in domesticated animals and plants – coat pattern in cats, grain yield in wheat • It can also be used to select behaviours in animals – behaviour of courting male Gryllus crickets varies—some sing, others are silent – selective breeding from singing males increases frequency of singing in subsequent generations – singing has a genetic basis Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 28-5 Populations with differences • Populations may exhibit differences in behaviour • Garter snakes (Thamnophis elegans) in southwestern United States live in coastal and inland regions – coastal snakes are terrestrial slug-feeders – inland snakes are aquatic frog-feeders • Feeding experiments demonstrated that food preference is inherited – preference results from selection for local conditions Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 28-6 Learning • • • Learning is a long term or permanent change in behaviour due to experience Maturational effects (change in behaviour during development) are not the result of experience so cannot be classified as learning Imprinting is both a learned behaviour and a maturational effect – goslings and other chicks will follow the first moving object they see – imprinting occurs only within a restricted sensitive period (cont.) Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 28-7 Learning (cont.) • • • Galah (Cacatua roseicapilla) chicks raised by pink cockatoos (C. leadbeateri) show learned behaviour Fostered galah chicks give typical galah alarm and begging calls (inherited behaviour) But they give pink cockatoo contact calls (learned behaviour) Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 28-8 Learning • Learning can be associative or non-associative • Associative – learning in response to a stimulus – trial-and-error • Non-associative – learning without a stimulus Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 28-9 Evolutionary basis of behaviour • • Methods for examining the evolutionary basis of behaviour Intraspecific comparisons – comparing behaviour of individuals within a species • Manipulative experiments – focused experimental studies of selected behaviour • Interspecific comparisons – comparing behaviour of individuals in different species Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 28-10 Obtaining food • Animals exhibit a range of diets – have a wide variety of strategies to obtain food – predators may actively forage for prey or sit and wait (ambush) it • Foraging is not random – individuals make decisions that represent the best balance between cost (energy expended in foraging) and benefit (energy gained from food) Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 28-11 Foraging theory • • Foraging theory evaluates costs and benefits and predicts the decision under different conditions Other factors may influence the calculation of cost and benefit – risk of predation – intraspecific competition – interspecific competition Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 28-12 Escaping predation • Defence mechanisms minimise the risk of predation – fast-moving animals may outrun predators – animals may produce noxious chemicals to deter predators – camouflaged animals may be overlooked by predators – animals may mimic unrelated species Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 28-13 Mimicry • • Animals may mimic other organisms by visual, chemical, behavioural or acoustic resemblance Prey animals use defensive mimicry to decreases the chance of predation – harmless species resemble unpalatable or dangerous species to avoid being eaten by predators • Predators use aggressive mimicry to increase the chance of catching prey – example: bolas spiders (Dichrostichus) produce a substance that resembles the mate-attracting pheromones of moths Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 28-14 Living in groups • Living in groups reduces the chance of predation – probability of any individual being caught decreases as the size of the group increases – probability changes with location within the group as those on the edge have a greater chance of being eaten than those in the centre – flocking behaviour may produce a confusion effect and distract predators from singling out individuals – groups of animals may harass (mob) predators and drive them off – groups can detect predators with greater success than can a single animal Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 28-15 Territorial behaviour • • When resources are limited, individuals may compete for them Establishing a territory excludes competitors from resources in that area – territory-holders benefit by having exclusive access to the resources – but they pay a cost in defending the territory • Individuals, pairs or groups may hold territories Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 28-16 Animal contests • Competition for resources frequently involves contests (direct conflicts) between individuals – as both individuals in a contest may suffer injuries in a physical confrontation, contests are usually settled before injury occurs – winners benefit by gaining access to the resource but pay a cost in energy expended (or injury) • Outcome of contests depends on – ability of contestants – value of resource to each contestant – which contestant owns resource Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 28-17 Finding a mate • • Animals use many methods for locating a mate Chemical signals – female moths release pheromones to attract males, which may detect the signal from a distance of several kilometres • Auditory signals – male frogs call to attract females • Visual signals – male fireflies produce flashes of light to attract females Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 28-18 Courtship • • After locating each other, potential mates display courtship behaviour Courtship behaviour – confirms that the potential mates belong to the same species – confirms that the individuals are ready to mate – may provide some indication of the fitness of the signalling mate Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 28-19 Sexual selection • Elaborate displays and ornaments used in courtship are the product of sexual selection – sexual selection acts on the characteristics that influence a male’s chance of fertilising a female’s eggs • Male-male competition – intrasexual selection in which males compete with each other for females • Female choice – intersexual selection in which females choose their mates Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 28-20 Courtship and mating • Gift-giving occurs among some species – male lygaeid bugs provide the female with a nuptial gift containing nutrients that increase the size or number of her eggs • Courtship behaviour reduces the likelihood of sexual cannibalism – eating the male may provide nutrients for egg-production Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 28-21 Sperm competition • • If a female mates with more than one male, there may be competition between sperm to fertilise her eggs Males reduce the risk of sperm competition by – guarding a female to prevent other males mating with her – producing chemicals in ejaculates that make females unreceptive after mating – sealing the female genitalia after mating – dislodging sperm from previous matings Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 28-22 Parental care • • In those species that provide parental care, one or both parents may be involved in taking care of the offspring As with many behaviours, the amount of care depends on the balance between – benefit of increased survival rate of young – cost of lost opportunities for mating • Difference in behaviour – females commonly invest greater effort in rearing offspring than males – males may spend time seeking extra-pair copulations Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 28-23 Mating systems • • An individual may mate with one or more partners during a mating season Mating systems are divided into four categories – monogamy one male mates with one female – polygyny one male mates with several females – polyandry one female mates with several males – promiscuity males and females mate with several partners Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 28-24 Social behaviour • Permanent groups exhibit social behaviour – individuals in a group cooperate to find food defend the group rear young • • Many groups have complex social structures depending on the interests and needs of the individuals Conflict is avoided in some groups by establishment of dominance hierarchies – pecking orders Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 28-25 Cooperative breeding • • Cooperative breeders share the task of rearing young between members of a group Depending on the species, family members and/or unrelated helpers assist parents raise offspring Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 28-26 Insect societies • • Hymenopteran insects (bees, ants, wasps) and termites form complex eusocial societies Eusocial societies are characterised by – overlapping generations – reproductive division of labour • Colonies are composed of – reproductive queen – sterile female workers in one or more specialised castes – reproductive males (cont.) Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 28-27 Insect societies (cont.) • The queen is the only female that produces offspring – fertilised eggs give rise to workers – unfertilised eggs give rise to males • • When the colony reaches a certain size, the queen produces reproductive females, which leave the nest Castes in eusocial insects are often highly specialised – among honey-pot ants (Camponotus), some individuals act as sedentary food stores for others in the colony Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 28-28 Evolution of cooperation • Altruistic behaviour tends to reduce reproductive success of an individual, so why does it persist in some species? – most ‘altruistic’ behaviour has a hidden benefit • Explanations of cooperation in eusocial behaviour – helping is of mutual benefit to parents and workers – workers are manipulated into helping parents – cooperation between individuals that are closely related evolves because they share a higher proportion of genes, so sisters may share more genes than mother and daughter Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 28-29