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

3. 生態學 2003 Chap. 4 Group and Individual 2 Chap. 4 Group selection and Individual selection 1. Group selection vs. individual selfishness 2.Altruism ( 利他主義 ) 3.Benefits and trade-offs of group living Road Map

4. 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 1.Development of Group Selection 1.Territoriality ( 領域行為 ) of birds 2.Increase in emigration correlated with increase in numbers 3.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

5. 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.

6. 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.

7. 生態學 2003 Chap. 4 Group and Individual 6 Individual selection Williams (1966), Adaptation and Natural selection, argued against group selection 1.Mutation –Cheater scenario –Clutch size based on maximizing the number of surviving chicks (Figure 4.1) 2.Immigration –Selfish individuals can migrate to new areas 3.Individual selection 4.Resource prediction

8. 生態學 2003 Chap. 4 Group and Individual 7 Individual selection 3.Individual selection –Individuals die out more quickly than groups –Individual selection a more powerful evolutionary force 4.Resource prediction –Group selection needs a reliable and predictable source of food –No evidence that they can.

9. 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.

10. 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)

11. 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)

12. 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

13. 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

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

15. 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

16. 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

17. 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.

18. 生態學 2003 Chap. 4 Group and Individual 17 Number of caterpillar species 0 10 20 30 40 50 AposematicCryptic Large family groups Solitary Fig. 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)

19. 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

20. 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

21. 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)

22. 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.

23. 生態學 2003 Chap. 4 Group and Individual 22

24. 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.

25. 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

26. 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

27. 生態學 2003 Chap. 4 Group and Individual 26 Snake predators may venture into surface burrows 5 cm Blocked off burrow 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

28. 生態學 2003 Chap. 4 Group and Individual 27 Lifestyles that promote eusociality in mammals 1.Individuals are confined to burrows or nests 2.Food is abundant enough to support high concentrations of individuals 3.Adults exhibit parental care 4.Mothers can manipulate other individuals 5.When “ heroism ” is possible, whereby individuals give up their lives and, by so doing, can save the queen.

29. 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)

30. 生態學 2003 Chap. 4 Group and Individual 29 School cohesion 7 6 5 Few 1 2 345 6 Many Predator abundance (streams in rank order) Fig. 4.9 variation in group size may be related to defense against predators. Guppies (Poecilia reticulata)

31. 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 ”.

32. 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.

33. 生態學 2003 Chap. 4 Group and Individual 32 1 2-1011-50 50 Number of pigeons in flock 0 20 40 60 80 100 Attack success (%) Fig. 4.11 The larger the flock of pigeons, decreasing the goshawk’s rate of success in attacking.

34. 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

35. 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

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

37. 生態學 2003 Chap. 4 Group and Individual 36 Percent of time spent in each activity 0 20 40 60 80 1 3-46-7 Flock size Scanning Fighting Feeding 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.

38. 生態學 2003 Chap. 4 Group and Individual 37 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. Applied Ecology

39. 生態學 2003 Chap. 4 Group and Individual 38 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. Applied Ecology

40. 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/http://mail.nutn.edu.tw/~hycheng/