Plant Ecology - Chapter 8

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Plant Ecology - Chapter 8

• Plant Life Histories

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Life History Strategies
r strategist Unstable environment, density independent K strategist Stable environment, density dependent
Small size of organism Large size of organism
Much energy for reproduction Little energy for reproduction
Many offspring produced Few offspring produced
Early maturity Late maturity (often after parental care)
Short life expectancy Long life expectancy
Semelparous Iteroparous
Type III survivorship curve Type I or II survivorship curve
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Grimes Triangular Model
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Grimes Triangular Model
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Grimes Triangular Model
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Dealing with Variation

• Hedging their bets to maximize fitness in a
  varying environment
• Spread reproduction more evenly among years
• Increase seed dispersal area
• Increase dispersal time via seed banks

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Dealing with Variation

• When should seeds germinate?
• Controlled by temperature, light, moisture,
  others
• Can plants evolve predictable germination? -
  depends on predictability of environment
• Fire?

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Dealing with Variation

• Masting - large and erratic variation among years
  in the size of the seed crop produced
• Synchronized among plants within the population

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Dealing with Variation

• Often explained as a response to avoid seed
  predators
• Overwhelm abilities of predators to eat all the
  seed - some survive to germinate

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Dealing with Variation

• May actually be adaptation in wind-pollinated
  plants to reduce pollen limitations
• Many plants are pollen-limited, and increasing
  pollen densities increases pollination efficiency

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Dealing with Variation

• Synchrony achieved by low reproduction one year
  (bad weather, low pollen), low resource
  expenditures, greater likelihood of more
  reproduction next year

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Plant Phenology

• Timing of growth and reproduction within a year
• Much variation among species, populations,
  individuals
• Constrained mostly by temperature, moisture

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Vegetative Phenology

• Forest floor plants in temperate regions grow,
  flower before tree leaf expansion
• Get sunlight before canopy closes, but much
  colder than trees experience for their growth,
  flowering

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Vegetative Phenology

• Plants use temperature (degree-days) and
  photoperiod to determine phenologies
• Photoperiod prevents growth during mid-winter
  warm periods

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Vegetative Phenology

• In warmer climates, moisture is major controller
  of vegetative phenology
• Grow leaves, lose leaves in response to changes
  in moisture

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Reproductive Phenology

• Flowering regulated by many abiotic factors
  temperature, light availability, moisture
• Belief that moisture limitation and related
  stressors induce flowering not fully supported
  not in annuals, weak in perennials

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Reproductive Phenology biotic factors

• Biotic factors can influence reproductive
  phenology, especially pollinators
• Pollen-limited, animal-pollinated plants may be
  strongly controlled

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Reproductive Phenology biotic factors

• Two structuring forces possible
• Competition for pollinators may lead to temporal
  separation of flowering, or
• Similar phenologies may attract more pollinators
  than separate flowering
• Little evidence for either

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Reproductive Phenology biotic factors

• Fruit or seed eaters more likely to be affected
  by plant phenology than to affect it
• Crowding by neighbors delays flowering, may
  select for faster growth or earlier flowering

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Reproductive Vegetative Phenologies linked?

• Link generally weak, especially for longer-lived
  plants like forest trees
• Plants can store products of photosynthesis at
  one time and use them at another
• Temperate trees flower when leafless