Plant Ecology - Chapter 5

1
Plant Ecology - Chapter 5

• Populations

2
Population Growth

• Births
• Deaths
• Immigration
• Emigration

3
Population Growth

• Genets - genetically distinct individuals
• Ramets - physiologically independent but not
  genetically distinct individuals

4
Population Growth

• Birth - seed production, vegetative clones,
  mature pollen grains (gametophyte)?

5
Population Growth

• Individual - distinctly separate plants
  (unitary) or interconnected, related individuals
  (modular)

6
Population Structure

• Population size important, but so is the
  distribution of individuals among different
  ages/sizes/stages
• Have differing importance to population

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Population Structure

• Animal populations usually age-structured
• Age determines role, importance to population
• Age not as important for plants - size is far
  more important
• Plant populations stage-structured

8
Population Structure

• Plant stages frequently based on size - number of
  leaves, mass, height categories, diameter
  categories
• Frequently impossible to determine plant age

9
Population Structure

• Plants have very flexible growth patterns
• Can lose parts and shrink from year to year, go
  through years of dormancy, or not appear above
  ground in a given year

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Population Structure

• Stage structuring difficult under these
  circumstances
• Plants can advance directly through stages,
  remain at some stage, or undergo reversions

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Population Structure

• Plant ecologists must keep track of multiple
  stages and all possible transitions between them

12
Population Structure

• In structured populations, individuals of
  different stages make different contributions to
  future population growth
• Pre-repro, repro, post-repro

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Life Cycle Graphs
Summaries of transitions between stages
14
Life Tables - Cohort
15
Matrix Models
Combine life cycle graphs with life table data to
understand which stage classes have the strongest
effects on population growth
Which stage needs protection? Which stage class
is most affected by fire? Which stage limits
population growth?
16
Matrix Models
Can be used to predict age-based quantities
from stage-based data
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Long-Lived Plants

• Problems studying long-lived plants
• Longer life span than researchers!
• Year-to-year variation in environmental
  conditions, longer intervals between censuses -
  misses younger plants

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Long-Lived Plants

• Static life tables problematic - assumptions such
  as stable age structure impossible to justify
• Incorporate cyclic variability (e.g., pest
  outbreaks)
• Compare old to new photographs

19
Variable Population Growth

• Matrix modeling generalizations allow for
  estimates not possible two decades ago
• Long-run population growth rates
• Extinction probabilities
• Minimum viable population sizes