Ch.11 Life History-ISCI 3103 – Flashcards
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Life History
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-a record of events relating to its growth, development, reproduction, & survival -It's like a story of a species (life history strategy)
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Characteristics that define the life history of an organism:
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-age & size @ sexual maturity -amount & timing of reproduction -survival & mortality rates
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Individual is to Life History as...
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-weather is to climate -photograph is to video -page is to book *your personal history of survival & reproduction is not a good representation of a species' life history..life history should be the average values for all members of your species
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There will always be variation among individuals within a species in..
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survival, age @ reproduction, mortality rates, etc.
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Life History Strategy
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the life history strategy of a species is the overall pattern in the average timing & nature of life history events. -it is determined by the way the organism divides its time & energy between growth, reproduction, & survival
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Sample Life History Strategies
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-James Bond approach -Ryan Gosling approach -Charlie Sheen approach
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"James Bond" approach
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-r strategist live fast, die young & leave a good looking corpse & a lot of offspring
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"Ryan Gosling" approach
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-k-selected; grow old & gray with that one special someone, raising one perfectly nurtured offspring
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"Charlie Sheen" approach
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-r & k; no kids of your own, but you help a relative raise children while maintaining your freedom; want genes passed along
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How & why have particular life history patterns evolved?
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-the theoretical ideal: life histories are optimal (maximization of fitness) -life history strategies are not necessarily perfectly adapted to maximize fitness @ all times, particularly when environmental conditions change
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Phenotypic plasticity
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-one genotype may produce a continuous range of phenotypes under different environmental conditions (i.e. differences in appearance are NOT due to genetic differences) -environmental conditions is what plasticity is about, not genetic -phenotypic plasticity may produce a continuous range of growth rates; or discrete types---morphs
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Polyphenism
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-a single genotype produces several distinct morphs -winged,non-winged ants -carnivore or omnivore -metamorph (leaves the water) or paedomorph (keeps it gills & stays in water)
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Allometry
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-different body parts grow @ different rates, resulting in differences in shape or proportion
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Life History Strategy Variation
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-reproductive strategy -Gamete size -life cycle complexity -reproductive interval -stress response -dispersal & diapause -changes through Ontogeny
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Reproductive Strategy (life history strategy variation)
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-sexual: fertilization -asexual: simple cell division or simply no fertilization -both
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What are the advantages/disadvantages to sexual &/or asexual reproduction?
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-costs: asexual-no genetic variation; disease; predation: sexual- more time; disease -benefits: asexual-quicker, simple less prone to errors: sexual- population growth; more variation
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Gamete Size (life history strategy variation)
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-isogamy-gametes of relatively equal size -anisogamy- gametes of unequal size
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Gamete Size Hypothesis
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sperm=abundant; cheap to build eggs=limited; expensive to build *Females are the "choosy" sex because they have more invested in reproduction=fewer eggs, greater energy expenditure 1. eggs are expensive, sperm are cheap, females should be picky 2. there is a biological basis for males to be "less discerning" when it come to mating (i.e. sleazy)
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How does the gamete size hypothesis apply to natural selection & evolution?
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-males with the best traits (what constitutes "best" will vary) will reproduce more & pass those traits on
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How has female choice shaped behavior (a.k.a. "what have women done to men?")?
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-larger body size, more aggression, more colorful -sacrifice life to feed pregnant females -steal mating opportunities from friends -establish dominance hierarchies (wolf pack) -act like females just to get close to them -hang around "sexier" males to intercept females -mate guarding -infanticide (lions) -vaginal plugs & scoopers -low threshold for sexual arousal
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In rare cases the female is not "in charge" of reproduction:
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-monogamy- 1 male, 1 female -polygyny (many ginnies)- 1 male, multiple females-most common -polyandry (many andys)- 1 female, multiple males **even after we've mated successfully, females of some species can choose which sperm to fertilize eggs without the many matings they have solicited.
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Choosers often can't ascertain the health of a potential mate's genes by sight, so they often rely on secondary sexual characteristics that indicate health:
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ex: color -calling effort in amphibians -dung beetle, the bigger the dung, the better
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Life Cycle Complexity (Life history strategy variation)
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-complex life cycles involve @ least 2 distinct stages that may have different habitats -transition between stages may be abrupt
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metamorphosis
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-abrupt transition form from the larval to the juvenile stage -about 80% of animal species undergo metamorphosis @ some time in their life cycle *However, some species have lost the complex life cycle & have direct development--the go from fertilized egg to juvenile without passing through a larval stage
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Amphibian metamorphosis represents one of the most dramatic life history transitions of any organism on Earth, which includes:
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1. changes in the digestive system from herbivory to carnivory 2. respiratory system-gills to lungs 3. fish-like locomotion to tetrapod
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Reproductive Interval (Life history strategy variation)
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-semelparous species reproduce only once (ex. salmon, century plant) -iteroparous species can reproduce multiple times **Why would any species reproduce this way? -it works; they cycle still continues -it's a successful strategy
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Stress Response (Life history strategy variation)
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-stress response- more important for plants (immobile) -a classification scheme for plant life histories is based on stress & disturbance (grime)
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stress
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-any factor that reduces vegetative growth
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disturbance
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-any process that destroys plant biomass
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4 habitat types possible:
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-low stress, low disturbance: competitors, rainforests -high stress, low disturbance: dominated by "stress-tolerant" plants; -low stress, high disturbance- ruderal plants -high stress, high disturbance-beach; not suitable for plant growth
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high stress, low disturbance habitats-dominated by "stress-tolerant" plants: how do they tolerate stress?
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-low palatability (taste) to herbivores -slow rates of nutrient + water uptake -phenotypic plasticity *stress tolerators are commonly found in extreme climates: deserts, boreal forest
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low stress, high disturbance areas are dominated by "ruderal" plants:
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-adapted to frequent disturbance typically through short life spans, rapid reproduction, heavy investment in seed production as opposed to vegetative growth -seeds usually adapted to withstand disturbance until conditions are once again suitable -ruderal plants often exploit habitats after a disturbance has remove competitive plants...meaning that, if the disturbance wasn't there the competitive plants would win the war for space
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low stress, low disturbance is the desired situations for plants if they could "choose"..
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-they choose via competition..whoever competes best wins -these habitats are dominated by "competitive plants" **How do they compete? -shading -needles vs. leaves -allelopathy-release toxins through root systems
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Competition for light is one of the primary factors structuring plant communities
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allelopathy
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Allelopathy
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-chemical warfare among plants *What type of distribution among individuals you've learned about should result from allelopathy? Uniform
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The interaction between "competitors", "stress tolerators" & "ruderals" (i.e. disturbance tolerators) is modeled by:
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-Grime's Triangle
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comparing to the r-k continuum:
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-ruderal plants are similar to r-selected species; stress-tolerant plants correspond to k-selected species -competitive plants occupy the middle of the r & k continuum.
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Life History Trade-offs:
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-organisms allocate limited energy or resource to one structure of function at the expense of another
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What kinds of basic tradeoffs can you see that plants & animals (including yourself) might make?
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-roots vs. leaves - reproduction vs. everything else -growth vs. reproduction *Trade-offs shape & constrain life history evolution *Foraging vs. breeding vs. defense vs. habitat choice *most common reproductive tradeoff is between the number of size of offspring
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These tradeoffs between number & size of offspring occur both inter- & intraspecifically:
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-in addition, these tradeoffs may affect characteristics of offspring that influence their survival & fitness
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Lack clutch size:
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-maximum # of offspring a parent can successfully raise to maturity * clutch size is limited by the maximum # of offspring the parents can raise @ one time (how many can you care for before you compromise your fitness? do you have the time, energy, resources to care for more?)
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Trade-offs between current & future reproduction:
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-for an iteroparous organism, the earlier it reproduces, the more times it can reproduce over its lifetime -but not all reproductive events are equally successful. often the # of offspring produced increases with size & age of the organism
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If sexual maturity can be delayed, an organism can invest more energy in growth & survival, & my increase its lifetime reproductive output. Why could this be so?
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-losing #s -storing up energy/resources *under what conditions should an organism allocate energy to growth rather than reproduction? environmental conditions, weather -long life span, high adult survival rates, & increasing fecundity (how many offspring you can have) with body size. -if rates of adult survival are low, future reproduction may never occur, so early reproduction rather than growth would be favored.
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Senescence
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-decline in fitness of an organism with age & physiological deterioration -onset of senescence can set an upper age limit for reproduction -semelparous species undergo very rapid senescence & death following reproduction.
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Dispersal & diapause (Life history strategy variation)
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-some adults &/or their offspring are well-suited for dispersal *benefit of dispersing: variation -dispersal can reduce competition among close relatives & allow colonization of new areas -dispersal can allow escape from areas with diseases or high predation
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Diapause
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-state of suspended animation or dormancy- organisms can survive unfavorable conditions: -many seeds can survive long dormancy periods -many animals can also enter diapause
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Changes through Ontogeny (Life history strategy variation)
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-even in organisms without abrupt shifts between life stages, different sized & aged individuals may have very different ecological roles -a size-or stage-specific ecological role has been called an ontogenetic niche by Werner & Gilliam (Salamander)
