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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
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Chap. 4 Group selection and Individual selection
鄭先祐生態主張者 Ayo
Japalura@hotmail.com
2003 Chap. 4 Group and Individual生態學 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
2003 Chap. 4 Group and Individual生態學 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 wastefulness1. Development of Group Selection
1. Territoriality ( 領域行為 ) of birds2. Increase in emigration correlated with increase in numbers3. 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
2003 Chap. 4 Group and Individual生態學 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 reso
urces 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生態學 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.
2003 Chap. 4 Group and Individual生態學 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
2003 Chap. 4 Group and Individual生態學 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.
2003 Chap. 4 Group and Individual生態學 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.
2003 Chap. 4 Group and Individual生態學 9
Self-Regulation?
• Come from Intraspecific competition– Individuals strive to command as much resourc
es 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)
2003 Chap. 4 Group and Individual生態學 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)
2003 Chap. 4 Group and Individual生態學 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
2003 Chap. 4 Group and Individual生態學 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
2003 Chap. 4 Group and Individual生態學 13
0.25 0.25
grandparents
father
0.5 0.5
mother
0.250.25
0.25
0.25
0.25
0.25
0.5
0.5
1 0.125
grandparents
mate self
daughteror son
granddaughter or grandson
half sib
aunt/uncle
niece ornephew
cousinbrother/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生態學 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
2003 Chap. 4 Group and Individual生態學 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
2003 Chap. 4 Group and Individual生態學 16
Kin selection• Aposematic – contain colors to warn pred
ators 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.
2003 Chap. 4 Group and Individual生態學 17
Num
ber o
f cat
erpi
llar s
pecie
s
0
10
20
30
40
50
Aposematic Cryptic
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)
2003 Chap. 4 Group and Individual生態學 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
2003 Chap. 4 Group and Individual生態學 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
2003 Chap. 4 Group and Individual生態學 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)
2003 Chap. 4 Group and Individual生態學 21
Fig. 4.7 A soldier Amazonian termite
• Altruism in social insects may arise from the unique genetics of their reproduction.
2003 Chap. 4 Group and Individual生態學 22
2003 Chap. 4 Group and Individual生態學 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.
2003 Chap. 4 Group and Individual生態學 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
2003 Chap. 4 Group and Individual生態學 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
2003 Chap. 4 Group and Individual生態學 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 feetMean number of animals= 60
Fig. 4.8 Cross section of naked mole rat colony
2003 Chap. 4 Group and Individual生態學 27
Lifestyles that promote eusociality in mammals1. 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.
2003 Chap. 4 Group and Individual生態學 28
4.3 Group Living
• Dense living, Promote intense competition
• Significant advantages to compensate – Ex. predators (Figure 4.9)
2003 Chap. 4 Group and Individual生態學 29
Scho
o l c
ohe s
ion
7
6
5
Few 1 2 3 4 5 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)
2003 Chap. 4 Group and Individual生態學 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”.
2003 Chap. 4 Group and Individual生態學 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.
2003 Chap. 4 Group and Individual生態學 32
1 2-10 11-50 50
Number of pigeons in flock
0
20
40
60
80
100
Atta
ck su
cces
s (%
)
Fig. 4.11 The larger the flock of pigeons, decreasing the goshawk’s rate of success in attacking.
2003 Chap. 4 Group and Individual生態學 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
2003 Chap. 4 Group and Individual生態學 34
A model of optimal flock size
• Conflicting variables– Competition for food
– Presence of predator
• Figure 4.12
2003 Chap. 4 Group and Individual生態學 35
Perc
enta
ge o
f tim
e
Perc
enta
ge o
f tim
e
Perc
enta
ge o
f tim
e
Optimal flock size
Extra scanning in presence of hawk
Optimal flock size Optimal flock size
Feeding
Scanning
Fighting
Increase in aggression by Dominants at higher food levels
(c)
(a) (b)
2003 Chap. 4 Group and Individual生態學 36
Perc
ent o
f tim
e sp
ent i
n ea
ch a
ctiv
ity
0
20
40
60
80
1 3-4 6-7Flock 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.
2003 Chap. 4 Group and Individual生態學 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
2003 Chap. 4 Group and Individual生態學 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
2003 Chap. 4 Group and Individual生態學 39
問題與討論!
Japalura@hotmail.com
Ayo 台南站: http://mail.nutn.edu.tw/~hycheng/
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