LIFE HISTORIES: multiple solutions to multiple challenges Flashcards
1
Q
Life History:
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- those traits that help individuals achieve fitness (genetic contribution by an individual’s descendants to future generations).
- Ultimately an organism’s life history patterns are geared towards increasing survival and reproduction to maximize fitness.
2
Q
The adaptation – driven by natural selection
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that is manifested by this genetic potential for survival and reproduction includes a wide variety of attributes pertaining to:
- Morphology
- Physiology
- Behavior
3
Q
Life Histories pt 2
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- description of typical patterns of development, reproduction, survival
4
Q
Life-history Traits
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- Characteristics that directly affect development, reproduction, lifespan
5
Q
Life history strategies
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suites of life history traits common to groups of species
6
Q
Life- History Traits pt 2
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- Developmental rate
- Body size
- Age at maturity
- Mode of reproduction (asexual vs. sexual)
- N offspring per litter
- N reproductive episodes
- – Semelparous – one reproductive episode, then die
- – Iteroparous – multiple reproductive episodes
- Degree of parental care
- Lifespan
*
7
Q
Life history traits pt 3
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- When trying to understand variation in life-history traits, it helps to consider two things:
- Allocation trade-offs
- Mortality schedules
8
Q
Allocation Trade-offs
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- Allocation = distribution of a limited quantity of resources across multiple operations
- Energy and nutrients are limiting
- With those resources, organisms must grow, maintain themselves, and reproduce
- Trade-offs are ubiquitous; the phenotype represents a compromise to meet multiple requirements for the individual to live.
9
Q
How many times to reproduce? 2 basic strategies- Semelparity
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- Semelparity (semelparous): one major reproductive effort in a lifetime
semel: “once”
Concept applies to both animals and plants
10
Q
Reasons to be semelparous
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- Adults are more likely to be healthy at time of reproduction because they have invested more energy into growth, development, and energy storage
- Adults (plants as well) can time reproduction to favorable year. “Carpe diem”
- Long intervals between good years
- For animals rearing of young can be exhausting
- Examples: most insects and many plants (annuals and short-lived perennials)
11
Q
How many times to reproduce? 2 basic strategies - Iteroparity
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- repeat reproduction (and production of fewer young per event) in a lifetime
- itero: “to repeat”
12
Q
Reasons to be iteroparous
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- Increases chances of offspring success at least once because conditions should be favorable in at least one year.
- A good strategy if the chances of adult survival are high → adults will live long enough to have reproductive events over several years. (If adults have very low survival chances, it doesn’t make sense for them to be iteroparous).
- Examples of iteroparous organisms: most vertebrates, many invertebrates, most perennial plants, including trees
13
Q
Allocation Trade- Offs graph
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14
Q
Allocation Trade-offs and litter size example
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15
Q
Mortality and Age of Female Deer
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16
Q
Mortality schedules affect patterns of natural selection
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- After thousands of generations with these patterns of mortality, what sorts of life history traits would selection favor?
17
Q
Mortality schedules affect patterns of natural selection pt 2
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- Early reproduction
- Fast development
- Small body size
- Many offspring per reproductive episode
- Extended reproduction
- Slower development
- Larger body size
- Fewer offspring per reproductive episode
18
Q
Age at Senescence
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- Evidence - Higher extrinsic mortality rates correlate with faster senescence and shorter potential life spans
19
Q
Classification of Life History
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- Life history traits tend to cluster
- “Life history strategies”
- Several classifications exist
- r and K selection
- Grime’s triangular model of plant life history
20
Q
Life History - r and K-selection
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- r-selection and K-selection describe two ends of a reproductive strategy continuum.
- r is the intrinsic rate of increase of a population.
- r-selection: Selection for high population growth rates; an advantage in newly disturbed habitats and uncrowded condition.
21
Q
Life History - K
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- K is the carrying capacity for a population.
- K-selection: Selection for lower growth rates in populations that are at or near K; an advantage in crowded conditions; efficient reproduction is favored.
22
Q
Life History - r
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- r-selected (“live fast, die young”):
- Short life spans, rapid development, early maturation, low parental investment, high reproduction rates
- Most insects, small vertebrates such as mice, weedy plant species
23
Q
Life History - K pt 2
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- K-selected (“slow and steady”):
- Long-lived, develop slowly, late maturation, invest heavily in each offspring, low reproduction rates
- Large mammals, reptiles such as tortoises and crocodiles, and long-lived plants such as oak and maple trees
24
Q
K - Selected Species
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- Evolution in populations close to K
- Around K, expect intraspecific competition
- Organisms selected to compete well in stable environments
- Large body size
- Slow development
- Long lifespan
- Late maturity
- Few offspring per reproductive episode
- High parental investment
25
Q
K - Selected Species pt 2
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- Examples of K-selected species
- Elephant
- Albatross
- Chestnut, mangosteen
26
Q
r - Selected Species
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- Evolution in populations that can rarely reach K
- Unstable environments, high probability of early death
- Selection for weedy, short-lived species with high reproductive output
- Small body size
- Fast development
- Short lifespan
- Early maturity
- Many offspring per reproductive episode
- Little parental investment
27
Q
r vs K Selection
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- Examples of “r-selected” species:
- Dandelions, many annual grasses
- Many insects & spiders
- Mice & rabbits
- Heuristic tool
- r and K classification identifies extremes of a continuum
- More useful in relative (e.g. within genera or families) than absolute terms
28
Q
Grime’s triangular model of plant life histories
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- Reasoned two factors limit success of plant
- Stress – external abiotic factors that affect reduce performance (temperature, water, nutrients, shading)
- Disturbance – any process that destroys plant biomass (herbivory, fire, mowing, construction)
29
Q
Grime’s triangular model of plant life histories pt 2
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Three habitat types characterized:
- Low stress, low disturbance = Competitive plants
- High stress, low disturbance = Stress tolerant plants
- Low stress, high disturbance = Ruderals (weedy)
- (High stress, high disturbance deemed unsuitable for any species)
- BOLD = life history type
30
Q
Life History Triangle
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31
Q
Life Equation ( a concept )
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- (The conundrum of wrapping up genetic material in a package that can survive and reproduce)
- S = f (G x (a + b + c + ………i))
- S = Species of a certain fitness
- G = genetic makeup of species S
- a, b, c, …i = environmental challenges
32
Q
Many Solutions to Life Equation
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- The “life equation” has many solutions (S).
- Each species (or ecotype), by virtue of their unique life history, represents a solution to the “life equation”:
- white-crowned sparrows, blue whales, >400,000 species of beetles (!)
- Each solution (S) represents an aggregate of the interaction of genetics and environment in an attempt to compromise amongst the multiple challenges of in the environment –
- To live long enough to pass on your genetic material to the next generation
