Summary: Ecology

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  • Ecology

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  • Four Aspects of a Species' Life History

    1. Metamorphosis
    • Organisms undergo radical changes in morphology, physiology, and ecology over the course of their life cycle.

    2. Diapause
    • Presence of a resting stage somewhere in life cycle

    3. Senescence 
    • Process and timing of aging and death of an organism and why

    4. Reproductive Patterns
    • Magnitude and time of reproductive events
  • Metamorphosis Ecological Advantages

    1. Reduces Competition (w/n species)
    • Different niches
    • Higher # in given habitat

    2. Easy to exploit predictably variable habitats (predictable transient life cycle)
    • Compartmentalize Life Stages (can predict when habitat/resources w/n the habitat will disappear)
    • Young: feeding & growth
    • Adult: dispersal & repro.


    • Use transient resources
    • Body plan changes to match other needs in the life cycle
  • Strategies in harsh Unpredictable environments

    1. Resistant stages at set time intervals (doesn't really take environmental cues but time intervals "like ticking of a clock")
    • Ex. Freshwater sponges

    2. Multiple young in different developmental stage simultaneously
    • Ex. Kangaroos having multiple babies a different developing stages


    3. Accelerated Development + Diapuse
    • Conditions harsh for long periods --> organism in diapause
    • Favorable conditions occur infrequently & last a short time
    •     Compressed lifecycle
    •     Harsh conditions --> diapause  (Spadefoot Toad)
  • Evolutionary Senescence Model

    • "bad" mutations affecting young: strongly selected against
    • Bad mutation affecting old: persists (don't impinge on the fitness of the organism; doesn't affect the next generation)
    • Antagonistic Pleiotropy: Genes, which benefit early reproduction, have deleterious effects later in the lifespan. (Deterimental to older individuals but good for younger individuals)
  • Mortality and Reproductive pattern

    Increase survivorship or decrease reproduction

    Decrease survivorship or increase production
  • 2. Present vs. Future Reproduction

    Reproductive value: Vx = (mx) (lx)
    • decrease reprod (mx) >> increase Vx (& vice versa); if fairly low, then each individual is important
    • increase Survival (lx) >>  decrease Vx (& vice versa); each individual isn't as valuable, b/c they don't have to replace and individual as soon.

    Increase Reproduction --> Decrease Survival

    • Optimal strategy balances: Benefit of reproduction now vs cost of future reproduction.
  • 3. Age at Sexual Maturity

    Natural Selection favors maturity at Early Age
    • More you can have over life
    • Low adult survival
    • ++ if semelparity species (But most species do not have offspring at a young age)


    When delayed reproduction is favored
    • High adult survival (invest yourself)
    • Reproductive success dependent on age, size, experience, etc. (male elk defending his harem)
  • Theory of r and K (selection) species

    1. Classification
    2. For Each, distinct strategies evolve
    3. Bet-Hedging strategy
  • For r & K, distinct strategies evolve

    r species
    • Natural selection favors E energy invested in reproduction over competitive ability (quick turnover rate)


    K species
    • Natural selection favors E energy invested in competitive ability over reproduction (can compete better; Maintenance over reproduction)
  • Grimes' Plant Life History Strategy

    1. Environment variations ---> variable strategies

    2. Matched plant strategy with environment
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