Chapter 5 Life History Strategies

1. Chapter 5Life History Strategies 生活史策略 © 2002 by Prentice Hall, Inc. Upper Saddle River, NJ 07458

2. Chapt. 05 Outline • Reproductive strategies • Species that reproduce throughout their lifetimes (iteroparous反覆生殖) • Species that reproduce just once (semelparous單次生殖)

3. Chapt. 05 Outline • Age structure • Growing populations • Declining populations • Classification of mating systems

4. Chapt. 05 Outline • Continuum of life history strategies • r-selected • K-selected • Carrying capacity承載量

5. Chapt. 05 Life history strategiesFundamental aspects: 1.   Size體型： 2.   Metamorphosis變態； 3.   Diapause滯育； 4.   Senescence衰老；5.   Reproductive patterns繁殖模式；

6. Chapt. 05 Life history strategiesFundamental aspects: 1.   Size體型：The mass and dimensions typical of adult individuals of a species. 2.   Metamorphosis變態； 3.   Diapause滯育； 4.   Senescence衰老；5.   Reproductive patterns繁殖模式；

7. The effects of body size. Chapt. 05 體型 體表面積 附肢 比例 食物、代謝、 運動能力

8. Chapt. 05 Life history strategiesFundamental aspects: 1.   Size體型： 2.   Metamorphosis變態；The presence of a major developmental change in shape of form from the juvenile to the adult. 3.   Diapause滯育； 4.   Senescence衰老；5.   Reproductive patterns繁殖模式；

9. Chapt. 05 Life history strategiesFundamental aspects: 1.   Size體型： 2.   Metamorphosis變態； 3.   Diapause滯育；The present of a resting stage in the life history. 4.   Senescence衰老；5.   Reproductive patterns繁殖模式；

10. Chapt. 05 Life history strategiesFundamental aspects: 1.   Size體型： 2.   Metamorphosis變態； 3.   Diapause滯育； 4.   Senescence衰老；The process and timing of aging, degeneration, and death.5.   Reproductive patterns繁殖模式；

11. Senescence衰老 Chapt. 05

12. Chapt. 05 Life history strategiesFundamental aspects: 1.   Size體型： 2.   Metamorphosis變態； 3.   Diapause滯育； 4.   Senescence衰老；5.   Reproductive patterns繁殖模式；The magnitude and timing of reproductive events (clutch size, age at reproductive maturity, size of young, number of reproductive events in a life time, amount of parental investment and care, and the like).

13. Reproductive power is limited by two processes: Chapt. 05 1. The acquisition of energy, which increases with mass raised to the 0.75power. 2. The rate of conversion of energy to offspring, which changes as a function of mass to the –0.25 power.

14. Chapt. 05 Reproductive Strategies • Semelparity • Organisms that produce all of their offspring in a single reproductive event. • May live several years before reproducing or lifespan is one year (ex. Annual plants)

15. Chapt. 05 Reproductive Strategies • Semelparity (cont.). • Ex. Figure 5.1.

16. Chapt. 05 Reproductive Strategies • Iteroparity • Organisms that reproduce in successive years or breeding seasons • Variation in the number of clutches and number of offspring per clutch.

17. Chapt. 05 Reproductive Strategies • Iteroparity (cont.). • Some species have distinct breeding seasons • Ex. Temperate birds and temperate forest trees • Lead to distinct generations

18. Chapt. 05 Reproductive Strategies • Iteroparity (cont.). • Some species reproduce repeatedly and at any time during the year (continuous iteroparity) • Ex. Some tropical species, many parasites, and humans

19. Chapt. 05 Reproductive Strategies • Environmental Uncertainty • Favors iteroparity • Survival of juveniles is poor and unpredictable • Selection favors • Repeated reproduction • Long reproductive life

20. Chapt. 05 Reproductive Strategies • Environmental Uncertainty • Spread the risk over a longer period (“bet hedging”) • Environmental Stable • Favors semelparity

21. Chapt. 05 Reproductive Strategies • Environmental Stable (cont). • More energy can be devoted to seed production rather than maintenance • Annuals rely on seed storage during environmentally unstable years

22. 洄游性鮭魚的產卵策略 Chapt. 05 陸封型鮭魚的產卵策略又如何？

23. Chapt. 05 Age Structure • Semelparous organisms • Often produce groups of same-aged young – cohorts • Cohorts grow at similar rates • Iteroparous organisms • Many young at different ages

24. Chapt. 05 Age Structure • Increasing populations – large number of young • Decreasing populations – few young • Loss of age classes • Influence on population

25. Chapt. 05 Age Structure • Loss of age classes (cont.). • Ex. Overexploited fish populations – older age classes • Reproductive age classes removed • Reproductive failure • Results in population collapse • Ex. Younger age classes, deer removing young trees • Figure 5.2

26. Chapt. 05 60 (a) Age distribution in an undisturbed forest 40 20 Percent of trees (b) Age distribution skewed toward adults where overgrazing has reduced the abundance of young trees 60 40 20 10 20 30 40 50 60 70 Age (years)

27. Chapt. 05 Mating Systems • Sex ratio • Applied ecology • Hunters prefer deer populations dominated by males • Effects of too many males on population growth • Analysis of the ratio

28. Chapt. 05 Mating Systems • Why is the sex ratio usually 1:1? • Aren’t males superfluous? • Answer: Selfish genes! • Populations – predominately female • Populations – predominately male • Over time, sex ratio would be kept at 1:1 • Selection would favor sons • Selection would favor daughters

29. Chapt. 05 Mating Systems • Exception to 1:1 • One male dominates in breeding • Occurs in species with • Low powers of dispersal • Inbreeding is frequent

30. Chapt. 05 Mating Systems • Ex. The parasitic Hymenoptera • Females mate once and store sperm • Females control sex ratio • Use sperm to create females • Without sperm to create males • Process termed haplodiploid • Ex. The mite Acarophenox (Figure 5.3)

31. Chapt. 05 Mating Systems • Mating systems in animals • Monogamy • Exclusive mating • Common among birds (~90%) of species

32. Chapt. 05 Mating Systems • Polygamy • Individuals mate with multiple partners • Polygyny • One male mates with multiple females • Females mate with one male

33. Chapt. 05 Mating Systems • Polyandry • One female mates with multiple males • Males mate with one female • Polygyny • Females must care for the young • Mammals tend to be polygynous • Ex. Figure 5.4

34. Chapt. 05 Mating Systems • Polygyny (cont.). • Influenced by spatial and temporal distribution of females • Monogamous relationships result from all females becoming sexually receptive at the same time • Female receptiveness spread over weeks or months – polygyny can result

35. Chapt. 05 Mating Systems • Resource-based polygyny • Critical resource is patchily distributed or in short supply • Male can dominate resource and breed with more than one visiting female • Disadvantages for the female • Must share resources • More females means less success • Figure 5.5

36. Chapt. 05 5 1.25 4 1.0 3 Number of yearlings per male ( ) Number of yearlings per female ( ) 0.75 2 0.5 1 1 2 3 4 5 6 Number of females per group

37. Chapt. 05 Mating Systems • Non-resource based polygyny • Harem-based • Common in groups or herds • Protection from predators • Harem master does not remain for long • Communal courting areas – leks • Figure 5.6

38. Chapt. 05 Mating Systems • Polyandry • Practiced by a few species of birds • Ex. Spotted sandpiper in the Arctic tundra • Reproductive success not limited by food • Limited by the number of males needed to incubate eggs. • Ex. American jacana (Figure 5.7)

39. Chapt. 05 Life History Strategies • Success of populations • Reproductive strategies • Survival strategies • Habitat usage • Competition with other organisms

40. Chapt. 05 Life History Strategies • K-Selected • Populations increase slowly toward the carrying capacity • (K) of the environment • Low reproductive allocations • Iteroparous • High competitive abilities

41. Chapt. 05 Life History Strategies • Ex. Mature forest • Non-disturbed habitat • Grow slowly • Reach reproductive age late • Devote large amounts of energy to growth and maintenance

42. Chapt. 05 Life History Strategies • Ex. Mature forest (cont.). • Grow to large sizes and shade-out r-selected species • Long-lived and produce seeds repeatedly every year while mature • Seeds are bigger than r-selected species – provide food reserves to help them get started

43. Chapt. 05 Life History Strategies • Alternatives to the r and K continuum • Ruderals, competitors, and stress tolerators (Grime 1977 and 1979) • Ruderals (botanical term for weed) • Adapted to cope with habitat disturbances

44. Chapt. 05 Life History Strategies • Competitors • Adapted to live in highly competitive but benign environments (e.g., tropics) • Stress tolerators • Adapted to cope with severe environmental conditions (e.g., salt marsh plants)

45. Chapt. 05 Life History Strategies • Stress, disturbance and competition triangle • Figure 5.9

46. Chapt. 05 STRESS TOLERATORS COMPETITORS RUDERALS CHARACTERISTIC Life form Large herbs, shrubs or trees Lichens, herbs,shrubs Small herbs Leaf size • Large • Small • Large • Short • Long Life span • Long • Large Seed production • Small • Small Growth rate • Rapid • Rapid • Slow • Various • High • Low Palatability Vegetative spread • Yes • Yes • No High Low Competitors Leaf litter production • High • Low • Low Disturbance Competition Intermediate Life histories Trees Perennial herbs Annual plants Low Lichens High Stress tolerators Ruderals Bryophytes High Low Stress

47. Chapt. 05 Life History Strategies • Demographic interpretation (Silverton et al. 1992, 1993) • Growth-survival and fecundity triangle • Figure 5.10

48. Chapt. 05 G 0.0 1.0 0.8 0.2 0.6 0.4 Survival Growth 0.4 0.6 0.2 0.8 0.0 1.0 0.4 F S 1.0 0.8 0.6 0.2 0.0 Fecundity Semelparous herbs Iteroparous herbs in open habitats Iteroparous herbs in forests Woody trees

49. Chapt. 05 Applied Ecology • Life history and the risk of extinction • K-selected species • All attributes set them at risk to extinction • Tend to be bigger – need bigger habitat

50. Chapt. 05 Applied Ecology • K-selected species (cont.). • Fewer offspring – populations can not recover as fast from disturbance • Breed later in life – generation time is long