General Ecology: Life Histories

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Fish that spend their life in oceans then reutrn to their natal streams to breed (and die)

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anadromous fish

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Why complex life cycle a common life history?

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Different life stages experience environment very differently, and in ways that may escape some sources of mortality of other stages

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allocation of energy

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Due to limited energy available in environment, allocation of energy to one function or aspect of life history compromises energy available to other functions

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Corollary

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specialization or efficiency in one function necessitates less efficiency in others

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Tradeoff: Adult Survival vs. Reproductive Allocation (age at maturity)

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natural selection appears to favor individuals that breed early when mortality risk is high and delay breeding when mortality risk is low

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Same tradeoff (reproduction vs. survival) seen within spp

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Individual level natural selection adjusts reproductive effort to account for differences in survival

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one reproductive effort, typically after a year of growth (eg: many herbaceous plants, many insects)

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Annual

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grow many years, then reproduce once before dying (eg: salmon, bamboo, a few flowering trees)

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Semelparous

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reproductive effort is spread out over many episodes over a long lifetime (eg: most mammals, birds, herps, and most long-lived plants)

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Iteroparous

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What type of environment may favor iteroparity?

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Uncertain environments favor repeated reproductive efforts

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In what climates do annual plants/insects often prevail?

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Stable. Like dormancy (seeds) in a desert awaiting rain

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bet hedging?

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during unstable environment, living long enough to hit jackpot reproductively during an environmentally favorable period

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Why semelparity?

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-May work as another type of bet hedging strategy in some desert plants
-Plants put their energy into one big bang to make most of rare good conditions
- To saturate predators (eg: 13, 17 year cicada broods) broods on years w prime numbers make it harder for predators to track evolutionarily

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Conditions of semelparity

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seems advantageous with low adult survival probability and long intervals between good years

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Why life history parameter often correlated in distribution across spp, not indep?

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-consideration of disturbed vs stable environments

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r-selected spp terminology?

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from pop models:
-traits increase rmax b/c rapid pop growth and colonization ability are adaptations for disturbed environments

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K-selected species terminology?

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traits increase competitive ability, which are adaptive when pop tends to fill environment (is at carrying capacity=K)

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Periodic life history

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- Large, long-lived, produce many small offspring (sturgeon, salmon, sea turtles)
- combines low juvenile survival, lx, high fecundity, mx, and late maturity, alpha

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Opportunistic life history

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- closest to r-selected, except for low fecundity
- combines low juvenile survival, lx, low fecundity, mx, and early maturity, a.

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Equilibrium life history

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- closest to K-selected, except can be small spp
- combines high juvenile survival, lx, low fecundity, mx, and late maturity, a.

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Polyandry

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- occur when resources are imited or predation rates are high- female must produce many young
- Males mazimize fitness by providing parental care and mating to females that can quickly replace lost clutch
-Females compete for males; females may be brightly colored(reversed sexual dimorphism)

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Resource defense polygyny

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-Males defend breeding territories
- Female may do better on good territory with polygynous male than on poor one w unmated male
- Males gain gain disproportionate mates by defending resources needed by females

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Male dominance polygyny

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- elaborate displays
- no male investment raising young
- May vary with male quality

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Lekking

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Communal courtship and mating behavior

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Scramble polygyny

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- No territory or dominance hierarchy- mad dash for females
- Explosive breeding assemblages. short breeding season

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Facultative polygyny

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-Mating system varies depending upon how resources are distributed through environment
- Monogamy in poor habitats, polygyny is better habitats
- Monogamy is ancestral, polygyny arose when spp inhabiting better-quality habitats could invest more time providing food to young