Chap. 4 Group selection and Individual selection

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Chap. 4 Group selection and Individual selection. 鄭先祐 生態主張者 Ayo Japalura@hotmail.com. Road Map. Chap. 4 Group selection and Individual selection. Group selection vs. individual selfishness Altruism ( 利他主義 ) Benefits and trade-offs of group living. 4.1 Group and Individual Selection. - PowerPoint PPT Presentation

Text of Chap. 4 Group selection and Individual selection

  • Chap. 4 Group selection and Individual selection AyoJapalura@hotmail.com

    2003 Chap. 4 Group and Individual

  • Chap. 4 Group selection and Individual selection Group selection vs. individual selfishnessAltruism ()Benefits and trade-offs of group livingRoad Map

    2003 Chap. 4 Group and Individual

  • 4.1 Group and Individual SelectionRegulation of populations early thoughtsLevels below which competition becomes importantNature is neat, tidy and harmonious, avoid wastefulnessDevelopment of Group SelectionTerritoriality () of birdsIncrease in emigration correlated with increase in numbersHigh variation in reproductive ratesExamples of self-regulation () or external regulationTropics vs. temperate (Self-regulation of song birds)1940s, David Lack vs. Alexander Skutch

    2003 Chap. 4 Group and Individual

  • High variation in reproductive ratesSongbirds typically lay a clutch of four to six eggs in temperate regions of North America and EuropeOnly two or three in the tropics.Lack, birds in the tropics couldnt gather enough resources to fledge more than two to three young, so the availability ot resources provided a limitation on reproduction.Skutch, tropical populations were self-regulated to ensure that no resources were wasted.

    2003 Chap. 4 Group and Individual

  • Self-regulation viewpointIn 1962, the self-regulation viewpoint was championed by Wynne-Edwards, who articulated the full concept of self-regulation in a book called Animal dispersion in relation to social behavior.Groups of individuals control their numbers to avoid extinctionTheory known as Group SelectionIn the late1960s, the idea came under severe attack.

    2003 Chap. 4 Group and Individual

  • Individual selectionWilliams (1966), Adaptation and Natural selection , argued against group selectionMutationCheater scenarioClutch size based on maximizing the number of surviving chicks (Figure 4.1)ImmigrationSelfish individuals can migrate to new areasIndividual selectionResource prediction

    2003 Chap. 4 Group and Individual

  • Individual selection

    Individual selectionIndividuals die out more quickly than groupsIndividual selection a more powerful evolutionary forceResource predictionGroup selection needs a reliable and predictable source of foodNo evidence that they can.

    2003 Chap. 4 Group and Individual

  • Fig. 4.1 Great tits, parus major. There are four surviving nestlings.Group selection implies that individuals should not over utilize their resources for the good of the group.Individual selection entails anevery one for themselves more likely than group selection in nature.

    2003 Chap. 4 Group and Individual

  • Self-Regulation?Come from Intraspecific competitionIndividuals strive to command as much resources as they can.Ex. Male lions that that kill existing cubs when they take over pride. Increase their own offspringEx. Male langur monkeys kill infants (Figure 4.2)

    2003 Chap. 4 Group and Individual

  • Self-Regulation?Come from Intraspecific competitionEx. Female giant water bugs kill eggs in masses being taken care of by males (Figure 4.3)

    2003 Chap. 4 Group and Individual

  • 4.2 AltruismApparent cooperationGroomingHuntingWarning signalsCaring for copies of ones genesGenes in offspringCoefficient of relatedness = rProbability of sharing a copy of a particular gene

    2003 Chap. 4 Group and Individual

  • Caring for copies of ones genes

    Probability of sharing a copy of a particular geneParents to its offspring; r = 0.5Brothers and sisters; r = 0.5Grandparents to grandchildren; r = 0.25Cousins to each other; r = 0.125Figure 4.4

    2003 Chap. 4 Group and Individual

  • 0.250.25grandparentsfather0.50.5mother0.250.250.250.250.250.250.50.510.125grandparentsmateselfdaughteror songranddaughter or grandsonhalf sibaunt/uncleniece ornephewcousinbrother/sister(full sib) Fig. 4.4 Degree of genetic relatedness to oneself in a diploid organism. Open circles represent completely unrelated individuals.

    2003 Chap. 4 Group and Individual

  • Implications of relatedness to altruism1964, W.D. HamiltonImportance of passing on ones genes through offspring as well as related individuals.Inclusive fitnessTotal copies of genes passed on to all relativesKin selection Lowers individual chance of reproductionRaises chances of relatives reproduction

    2003 Chap. 4 Group and Individual

  • Quantifying kin selectionrB C > 0 r = coefficient of relatedness C = number of offspring sacrificed by donor B = number of offspring gained by recipient

    2003 Chap. 4 Group and Individual

  • Kin selectionAposematic contain colors to warn predators of bad taste or poisonDatana caterpillars (Figure 4.5)Predator must kill one to learnAll the larvae in the group are likely to be the progeny of one egg mass from one adult female moth.

    2003 Chap. 4 Group and Individual

  • Number of caterpillar species01020304050AposematicCrypticLarge family groupsSolitaryFig. 4.6 Brightly colored species of caterpillars of British butterflies are more likely to be aggregated than are cryptic species. Advantage of animals to congregate in groups (Figure 4.6)

    2003 Chap. 4 Group and Individual

  • Alarms from sentries () Increased risk of being attacked Animals living nearsentrymost likely relatives Favors kin selection Alternative to kin selectionSentries that are forced to live at the fringeAlert for their own safetyIf sentry is successful, predator may seek new areaSentry increases chances of own survival

    2003 Chap. 4 Group and Individual

  • Unrelated individualsAltruism between unrelated individualsYou scratch my back, Ill scratch yoursReciprocal altruismEvidenceBrooding success correlated to availability of helpers ()Social huntingBenefit: Bigger preyCost: Sharing meat

    2003 Chap. 4 Group and Individual

  • Altruism in social insectsExtreme example of altruism sterile castes in social insectsFemale workersRarely reproduceAssist queen with her offspring (eusociality)Soldier castes () (Figure 4.7)Social insect reproduction (Table 4.1)

    2003 Chap. 4 Group and Individual

  • Fig. 4.7 A soldier Amazonian termiteAltruism in social insects may arise from the unique genetics of their reproduction.

    2003 Chap. 4 Group and Individual

  • 2003 Chap. 4 Group and Individual

  • Relatedness (haplo-diploid organisms)Females are diploidMales are haploidFormed without meiosisEach sperm is identicalSister relatednessEach daughter receives an identical set of genes from her fatherHalf of a females genes come from her diploid motherTotal relatedness of sisters: 0.5 from father + 0.25 from mother = 0.75.

    2003 Chap. 4 Group and Individual

  • Relatedness (haplo-diploid organisms)Sister relatednessSons and daughters; r = 0.5Average relatedness for sterile workers would be 0.5Queen, Maximize reproductive potential = 50:50 sex ratioHowever from the workers; viewpoint, it is far better to have more sisters.Colonies usually have more females than males

    2003 Chap. 4 Group and Individual

  • Non-haplodiploid coloniesTermitesMole rat from South Africa (Figure 4.8)There is only one breeding female, the queen.The other castes perform different types of work.Frequent workers, infrequent workers, nonworkers

    2003 Chap. 4 Group and Individual

  • Snake predators may venture into surface burrows5 cmBlocked off burrowLarger non-workersact in defense20cm40-50 cm Mean burrow length= 545 feetMean number of animals= 60Fig. 4.8 Cross section of naked mole rat colony

    2003 Chap. 4 Group and Individual

  • Lifestyles that promote eusociality in mammalsIndividuals are confined to burrows or nestsFood is abundant enough to support high concentrations of individualsAdults exhibit parental careMothers can manipulate other individualsWhen heroism is possible, whereby individuals give up their lives and, by so doing, can save the queen.

    2003 Chap. 4 Group and Individual

  • 4.3 Group LivingDense living, Promote intense competitionSignificant advantages to compensate Ex. predators (Figure 4.9)

    2003 Chap. 4 Group and Individual

  • School cohesion765Few123456ManyPredator abundance (streams in rank order)Fig. 4.9 variation in group size may be related to defense against predators.Guppies (Poecilia reticulata)

    2003 Chap. 4 Group and Individual

  • Group livingMany-eyes hypothesisSuccess of predator attacksPrey alerted to attack (Figure 4.10)Ex. Goshawks less successful attacking large flocks of pigeons (Columba palumbus)The bigger the flock (more eyes) the more likely the prey will be alerted to the presence of a predator (Figure 4.11)Cheating vs. the advantages of not cheating discourage cheating.

    2003 Chap. 4 Group and Individual

  • Fig. 4.10 For these snow geese large flocks may be better able to detect predators, such as the bald eagle shown here just skyward of the flock.

    2003 Chap. 4 Group and Individual

  • 12-1011-5050Number of pigeons in flock020406080100Attack success (%)Fig. 4.11 The larger the flock of pigeons, decreasing the goshawks rate of success in attacking.

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  • Group livingSelfish-herd theoryThe bigger the herd, the lower the probability of an individual prey being takenLarger herds are attacked more, but probability of being taken would still favor individualGeometry of the selfish herd1971, W.D. HamiltonPrey prefer middle of herd to avoid predatorPredator difficulty in tracking large numbers of preyPeripheral prey easier to visually isolateMore difficult for predator to reach the center of herdLarge herds are better able to defend t