Chap. 4 Group selection and Individual selection

1. Chap. 4 Group selection and Individual selection 鄭先祐 生態主張者 Ayo Japalura@hotmail.com

2. 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 生態學 2003 Chap. 4 Group and Individual

3. 4.1 Group and Individual Selection • Regulation of populations – early thoughts • Levels below which competition becomes important • Nature is neat, tidy and harmonious, avoid wastefulness • Development of Group Selection • Territoriality (領域行為) of birds • Increase in emigration correlated with increase in numbers • High variation in reproductive rates • Examples of self-regulation (自我調控) or external regulation • Tropics vs. temperate (Self-regulation of song birds) • 1940s, David Lack vs. Alexander Skutch 生態學 2003 Chap. 4 Group and Individual

4. High variation in reproductive rates • 現象： • Songbirds typically lay a clutch of four to six eggs in temperate regions of North America and Europe • Only two or three in the tropics. • 解釋 • Lack, birds in the tropics couldn’t 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. 生態學 2003 Chap. 4 Group and Individual

5. Self-regulation viewpoint • In 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 extinction • Theory known as Group Selection • In the late1960s, the idea came under severe attack. 生態學 2003 Chap. 4 Group and Individual

6. Individual selection • Williams (1966), Adaptation and Natural selection , argued against group selection • Mutation • Cheater scenario • Clutch size based on maximizing the number of surviving chicks (Figure 4.1) • Immigration • Selfish individuals can migrate to new areas • Individual selection • Resource prediction 生態學 2003 Chap. 4 Group and Individual

7. Individual selection • Individual selection • Individuals die out more quickly than groups • Individual selection a more powerful evolutionary force • Resource prediction • Group selection needs a reliable and predictable source of food • No evidence that they can. 生態學 2003 Chap. 4 Group and Individual

8. 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 an”every one for themselves more likely than group selection in nature. 生態學 2003 Chap. 4 Group and Individual

9. Self-Regulation? • Come from Intraspecific competition • Individuals 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 offspring • Ex. Male langur monkeys kill infants (Figure 4.2) 生態學 2003 Chap. 4 Group and Individual

10. Self-Regulation? • Come from Intraspecific competition • Ex. Female giant water bugs kill eggs in masses being taken care of by males (Figure 4.3) 生態學 2003 Chap. 4 Group and Individual

11. 4.2 Altruism • Apparent cooperation • Grooming • Hunting • Warning signals • Caring for copies of one’s genes • Genes in offspring • Coefficient of relatedness = r • Probability of sharing a copy of a particular gene 生態學 2003 Chap. 4 Group and Individual

12. Caring for copies of one’s genes • Probability of sharing a copy of a particular gene • Parents to its offspring; r = 0.5 • Brothers and sisters; r = 0.5 • Grandparents to grandchildren; r = 0.25 • Cousins to each other; r = 0.125 • Figure 4.4 生態學 2003 Chap. 4 Group and Individual

13. grandparents grandparents 0.25 0.25 0.25 0.25 0.25 0.5 0.5 aunt/ uncle father mother 0.125 1 0.5 0.25 self cousin mate brother/ sister (full sib) half sib 0.5 0.25 niece or nephew daughter or son Fig. 4.4 Degree of genetic relatedness to oneself in a diploid organism. Open circles represent completely unrelated individuals. 0.25 granddaughter or grandson 生態學 2003 Chap. 4 Group and Individual

14. Implications of relatedness to altruism • 1964, W.D. Hamilton • Importance of passing on one’s genes through offspring as well as related individuals. • Inclusive fitness • Total copies of genes passed on to all relatives • Kin selection • Lowers individual chance of reproduction • Raises chances of relatives’ reproduction 生態學 2003 Chap. 4 Group and Individual

15. Quantifying kin selection • rB – C > 0 • r = coefficient of relatedness • C = number of offspring sacrificed by donor • B = number of offspring gained by recipient 生態學 2003 Chap. 4 Group and Individual

16. Kin selection • Aposematic – contain colors to warn predators of bad taste or poison • Datana caterpillars (Figure 4.5) • Predator must kill one to learn All the larvae in the group are likely to be the progeny of one egg mass from one adult female moth. 生態學 2003 Chap. 4 Group and Individual

17. Advantage of animals to congregate in groups (Figure 4.6) 50 Fig. 4.6 Brightly colored species of caterpillars of British butterflies are more likely to be aggregated than are cryptic species. 40 30 Number of caterpillar species Large family groups Solitary 20 10 0 Aposematic Cryptic 生態學 2003 Chap. 4 Group and Individual

18. Alarms from ‘sentries’(哨兵) • Increased risk of being attacked • Animals living near‘sentry’most likely relatives • Favors kin selection • Alternative to kin selection • ‘Sentries’ that are forced to live at the fringe • Alert for their own safety • If ‘sentry’ is successful, predator may seek new area • Sentry’ increases chances of own survival 生態學 2003 Chap. 4 Group and Individual

19. Unrelated individuals • Altruism between unrelated individuals • “You scratch my back, I’ll scratch yours” • Reciprocal altruism • Evidence • Brooding success correlated to availability of helpers (台灣藍鵲) • Social hunting • Benefit: Bigger prey • Cost: Sharing meat 生態學 2003 Chap. 4 Group and Individual

20. Altruism in social insects • Extreme example of altruism – sterile castes in social insects • Female workers • Rarely reproduce • Assist queen with her offspring (eusociality) • Soldier castes (士兵身份) (Figure 4.7) • Social insect reproduction (Table 4.1) 生態學 2003 Chap. 4 Group and Individual

21. Fig. 4.7 A soldier Amazonian termite • Altruism in social insects may arise from the unique genetics of their reproduction. 生態學 2003 Chap. 4 Group and Individual

22. 生態學 2003 Chap. 4 Group and Individual

23. Relatedness (haplo-diploid organisms) • Females are diploid • Males are haploid • Formed without meiosis • Each sperm is identical • Sister relatedness • Each daughter receives an identical set of genes from her father • Half of a female’s genes come from her diploid mother • Total relatedness of sisters: 0.5 from father + 0.25 from mother = 0.75. 生態學 2003 Chap. 4 Group and Individual

24. Relatedness (haplo-diploid organisms) • Sister relatedness • Sons and daughters; r = 0.5 • Average relatedness for sterile workers would be 0.5 • Queen, Maximize reproductive potential = 50:50 sex ratio • However from the workers; viewpoint, it is far better to have more sisters. • Colonies usually have more females than males 生態學 2003 Chap. 4 Group and Individual

25. Non-haplodiploid colonies • Termites • Mole 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 生態學 2003 Chap. 4 Group and Individual

26. Snake predators may venture into surface burrows Blocked off burrow 5 cm Larger “non-workers” act in defense 20cm 40-50 cm Mean burrow length= 545 feet Mean number of animals= 60 Fig. 4.8 Cross section of naked mole rat colony 生態學 2003 Chap. 4 Group and Individual

27. Lifestyles that promote eusociality in mammals • Individuals are confined to burrows or nests • Food is abundant enough to support high concentrations of individuals • Adults exhibit parental care • Mothers can manipulate other individuals • When “heroism” is possible, whereby individuals give up their lives and, by so doing, can save the queen. 生態學 2003 Chap. 4 Group and Individual

28. 4.3 Group Living • Dense living, Promote intense competition • Significant advantages to compensate • Ex. predators (Figure 4.9) 生態學 2003 Chap. 4 Group and Individual

29. Fig. 4.9 variation in group size may be related to defense against predators. 7 6 School cohesion 5 Guppies (Poecilia reticulata) Many Few 1 2 3 4 5 6 Predator abundance (streams in rank order) 生態學 2003 Chap. 4 Group and Individual

30. Group living • “Many-eyes hypothesis” • Success of predator attacks • Prey 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 • 值班觀察到掠食者，本身逃走的機會較大，這可以 discourage “cheating”. 生態學 2003 Chap. 4 Group and Individual

31. 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. 生態學 2003 Chap. 4 Group and Individual

32. Fig. 4.11 The larger the flock of pigeons, decreasing the goshawk’s rate of success in attacking. 100 80 60 Attack success (%) 40 20 0 1 2-10 11-50 50 Number of pigeons in flock 生態學 2003 Chap. 4 Group and Individual

33. Group living • Selfish-herd theory • The bigger the herd, the lower the probability of an individual prey being taken • Larger herds are attacked more, but probability of being taken would still favor individual • Geometry of the selfish herd • 1971, W.D. Hamilton • Prey prefer middle of herd to avoid predator • Predator difficulty in tracking large numbers of prey • Peripheral prey easier to visually isolate • More difficult for predator to reach the center of herd • Large herds are better able to defend themselves 生態學 2003 Chap. 4 Group and Individual

34. A model of optimal flock size • Conflicting variables • Competition for food • Presence of predator • Figure 4.12 生態學 2003 Chap. 4 Group and Individual

35. (c) Percentage of time Extra scanning in presence of hawk Optimal flock size Increase in aggression by Dominants at higher food levels (a) (b) Feeding Fighting Percentage of time Percentage of time Scanning Optimal flock size Optimal flock size 生態學 2003 Chap. 4 Group and Individual

36. 80 Fig. 4.13 The increase in fighting and decrease in scanning of yellow-eyed juncos with increasing flock size yields the highest rate of feeding at intermediate flock size. Scanning 60 Fighting Feeding Percent of time spent in each activity 40 20 0 3-4 6-7 1 Flock size 生態學 2003 Chap. 4 Group and Individual

37. Applied Ecology The tragedy of the commons • Garrett Hardin (1968) “Tragedy of the Commons” (公共財的悲劇) • Ex. Carrying capacity on a piece of land - 1000 cattle • 10 ranchers share land, each with a 100 cattle • One individual wants to add one cattle more than his/her share • Maximizes his/her profits at expense of others • All of the cattle suffer very little. 生態學 2003 Chap. 4 Group and Individual

38. Applied Ecology The tragedy of the commons • What would happen if all ranchers did this? • Overgrazing • Not sustainable • Benefits of the environment often accrue to single individuals, but the Cost of using the environment is usually borne by the entire population. 生態學 2003 Chap. 4 Group and Individual

39. 問題與討論！ Japalura@hotmail.com Ayo 台南站： http://mail.nutn.edu.tw/~hycheng/ 生態學 2003 Chap. 4 Group and Individual