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

#2Chapt. 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 )

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

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

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

#6Chapt. 05 Life history strategies Fundamental 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；

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

#8Chapt. 05 Life history strategies Fundamental 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；

#9Chapt. 05 Life history strategies Fundamental 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；

#10Chapt. 05 Life history strategies Fundamental 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；

#11Chapt. 05 Senescence 衰老

#12Chapt. 05 Life history strategies Fundamental 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).

#13Chapt. 05 Reproductive power is limited by two processes: 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.

#14Chapt. 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)

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

#16Chapt. 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.

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

#18Chapt. 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

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

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

#21Chapt. 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

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

#23Chapt. 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

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

#25Chapt. 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

#26Chapt (a) Age distribution in an undisturbed forest (b) Age distribution skewed toward adults where overgrazing has reduced the abundance of young trees Age (years) Percent of trees

#27Chapt. 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

#28Chapt. 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

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

#30Chapt. 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)

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

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

#33Chapt. 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

#34Chapt. 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

#35Chapt. 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

#36Chapt. 05 Number of females per group Number of yearlings per male ( ) Number of yearlings per female ( )

#37Chapt. 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

#38Chapt. 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)

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

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

#41Chapt. 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

#42Chapt. 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

#43Chapt. 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

#44Chapt. 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)

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

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

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

#48Chapt. 05 G Growth Survival Fecundity Semelparous herbs Iteroparous herbs in open habitats Iteroparous herbs in forests Woody trees SF

#49Chapt. 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

#50Chapt. 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

#51Chapt. 05 Applied Ecology K-selected species (cont.). –Population size is small – high risk of inbreeding – Examples Florida panthers Giant sequoia tree

#52Chapt. 05 Applied Ecology –Examples (cont.). Large terrestrial mammals (elephants, rhinoceros, and grizzlies) Large marine mammals (blue and sperm whales)

#53Chapt. 05 Summary Life history concerns lifetime patterns in reproduction and growth patterns –Semelparous –Iteroparous

#54Chapt. 05 Summary Reproductive strategy strongly affects age structure –Low ratio of young to adults – population in decline –High ratio of young to adults – population growing

#55Chapt. 05 Summary Sex ratio –1:1 ratio expected in most populations –Polygynous Males mate with more than one female

#56Chapt. 05 Summary Sex ratio –Polyandrous Females mate with more than one male Monogamous –Each individual has one mate

#57Chapt. 05 Summary –Polygamy is often based on limited resources Categorizing life history strategies –r-K continuum r-selected –Poor competitors

#58Chapt. 05 Summary r-selected (cont.). –High per capita population growth rate –Disperse well –Colonize new habitats K-Selected –Good competitors –Usually exist in mature habitats, close to the carrying capacity –Alternative life history strategies

#59Chapt. 05 Summary –Alternative life history strategies Ruderals, competitors, and stress tolerators classification Growth-longevity-fecundity triangle

#60Chapt. 05 Discussion Question #1 What particular life history strategies are possessed by successful exotic invaders like kudzu in the southeast or zebra mussels in the Great Lakes? Can knowing their life histories help us in the war against exotics?

#61Chapt. 05 Discussion Question #2 How could you test the idea that there is a trade-off between life history strategies? What would happen if you plant salt marsh plants like Spartina grass or mangroves in a terrestrial habitat vs. a freshwater habitat?

#62Chapt. 05 Discussion Question #3 In some species, males are much bigger than females, a property called sexual dimorphism. Speculate about the types of animals in which sexual dimorphism would and would not occur.