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25 Cards in this Set
- Front
- Back
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Sockeye Salmon→
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- lives to be 4 – 6 yrs old
- Feeding to spawning→ spends several years in sea growing rapidly and then migrates 6,000 km upriver to reach spawning ground - Thousands of eggs - Dies after single reproductive event |
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Life History
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1. The timing of key events
- birth - growth - death 2. Allocation of resources to activities at different times of life - reproduction - growth - survival |
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Life History Traits
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1. age at first reproduction
2. reproductive rate - parity - fecundity 3. life span - traits vary consistently with respect to habitat or conditions in the environment - variation in one trait is often correlated with variation in other traits |
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Influences on Life History
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- body plan and life style
- evolutionary responses to: - physical conditions - food supple - predators - other biotic factors, such as competition |
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Lack's Classic Study
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- Tropical songbirds lay fewer eggs per clutch than their
temperate counterparts - Clutch size is food limited - Food amount is limited by foraging time - Temperate/Arctic zones have longer days during summer (breeding season) →Clutch size has evolved as adaptation to different environments |
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European Magpie
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- Manipulated clutch sizes by moving eggs between nests, enlarging some clutches and reducing others
- Optimal number of chicks fledged in experimentally manipulated magpie nests was 7 - The natural nest size was 7 eggs |
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Ideal Life History
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- live forever, reproduce immediately, and reproduce continuously
- however, time is limited, energy is limited, nutrients are limited, and other resources may be limited - organisms have adaptive modifications of form and function that either increase the resources available to individuals or allow them to use those resources to their best advantage |
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Trade-Off
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- resources used for one function cannot be used for another function
- must allocate scarce resources: - time, energy, and materials - obey the law of diminishing returns: benefits decrease while cost increases with each additional increment of effort - altering resource allocation affects fitness - must find balance between fecundity and adult growth and survival→ between present and future reproduction - different environmental pressures result in different optimal solutions |
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Continuum of Life Histories
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- different paradigms represent different solutions to the problem of allocating resources among activities
- generally, larger organisms have longer life spans and lower reproductive rates |
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Paradigms
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- long life, delayed reproduction, few offspring per reproductive bout (low reproduction rates), slow development, delayed maturity, high parental investment
- elephants, giant tortoises, and oak trees - short life, early reproduction, many offspring per reproductive bout, rapid development, low parental investment - mice, fruit flies, weedy plants |
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Plant Life History Paradigm
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- Life history traits lay between three extreme apexes:
1. Competitors- grow large, mature at large sizes, and exhibit long life spans - requires more constant and predictable environment 2. Ruderals/weeds- colonize disturbed patches of habitat, exhibit rapid growth, early maturation, high reproductive rates, and easily dispersed seeds - traits enable them to reproduce quickly and disperse progeny to other disturbed sites before being overgrown by superior competitors |
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Plant Life History Paradigm Continued
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3. Stress tolerators- live under extreme conditions; grow slowly, conserve resources, and rely heavily on vegetative spread
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Annual Life History
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- completion of life cycle within a single year
- can undertake more than one episode of reproduction or even prolonged continuous reproduction within a season Occurs when: - when survival between breeding seasons is low - when survival requires large sacrifices in fecundity |
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Charnov and Schaffer’s Model
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- Currency is the discrete time per capita population growth→ how many get into the future for each one counted now?
- ANNUALS: The proportion of new babies that survive to be 1 year olds - λa= SoBa - PERENNIALS: We must add the proportion of adults that survive another year - λp= SoBp + S |
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Perennials are better when:
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S/ S0> Ba - Bp
- the fecundity advantage of the annuals is less than the ratio of adult survival to juvenile survival - when adult survival is high and juvenile survival low, then the ratio is a big number and it would be easy for perennials to win - annuals win in any environment where it is difficult to survive the whole year |
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Predation and Life History
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Guppies:
- in lower streams, live with a number of predatory fish - Smaller size (and earlier age) at first reproduction - Higher reproductive effort from females - Smaller size offspring - at higher elevations, have been able to ascend small waterfalls to areas blocked from predators - within a few generations of bringing predators to these areas, life histories came to resemble those of the populations below |
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- organisms store up energy when there is
- a nonlinear increase in success per amount of growth - costly reproduction OR - rare opportunities for recruitment OR - predator satiation Semelparity: BIG BANG |
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Semelparity
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- organisms that experience a single reproductive episode before death (usually large and fatal)
- individuals must survive at least one non-breeding season before maturing, reproducing, and they dying - opposite of iteroparity - arises when preparation for production is extremely costly (migration to breeding grounds) or when payoff for reproduction is highly variable but favorable conditions are predictable from environmental clues |
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Semelparity Continued
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- favored by variable environments if reproduction can be planned to occur during a good year, if interval between good years is long, and by massive floral displays to attract pollinators
- rare among long-lived animals and plants - bamboos and agaves |
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Bamboos
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- Woody tropical to warm-temperate grasses
- reproduction does not have substantial costs, but few opportunities for successful seed germination 1. grow vegetatively (asexually) for many years until the habitat is saturated (vegetative growth severely limited) 2. exhibit synchronous seed production followed by death of adults - may facilitate fertilization or overwhelm seed predators |
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Agaves
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- The century plants of deserts
1. grow vegetatively for several years as rosette of leaves produced from single meristem 2. produce a gigantic flowering stalk, draining plant’s stored reserves - growth is too rapid to be fully supported by photosynthesis or water uptake by roots so necessary nutrients and water are drawn from leaves which die soon after |
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Why Not Live Forever
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- Senescence
- Selection on traits expressed in old age is diminished - Few individuals make it to old age - Their reproductive value is low |
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Senescence
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- biological aging→ decline in physiological function with increasing age; gradual increase in mortality and decrease in fecundity
- may be inevitable but rates are influenced by natural selection - may be due to accumulation of molecular defects - ionizing radiation and reactive forms of oxygen break chemical bonds - macromolecules become cross-linked - DNA accumulates mutations |
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Senescence Continued
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- Lack of selection for repair in post reproductive individuals
- mechanisms might require allocations of resources and might be costly→ reduced reproduction at younger ages - allocation depends on expected life span - should appear earlier and progress faster in populations with high rates of mortality due to extrinsic causes (accidents, predators, weather) |
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Life History Definitions
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- maturity- first reproduction
- parity- number of episodes of reproduction - fecundity- number of offspring produced per reproductive episode - longevity- life span of an individual |
