Plant Ecology Chapter 16

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Plant Ecology - Chapter 16

• Landscape Ecology

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Landscape Ecology

• Study of the spatial distributions of
  individuals, populations, and communities, and
  the causes and consequences of those spatial
  patterns

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Island Biogeography

• Equilibrium theory of island biogeography by
  MacArthur Wilson (1967)
• Island size and isolation both play important
  roles in determining number of species present on
  islands
• Number of species is a balance between
  immigration and extinction, which vary with
  island size and isolation

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Island Biogeography Predictions

• Number of species should eventually become
  constant through time
• Continual turnover of species, extinction vs.
  immigration
• Large islands should support more species than
  small islands
• Species number should decline with remoteness
  (isolation) of an island

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Island Biogeography
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Island Biogeography

• Remoteness a strong influence (bird species more
  impoverished on far rather than near islands)

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Island Biogeography

• But it takes time to establish the species
  equilibrium (new island being slowly colonized by
  new species)
• Local evolution, speciation processes also must
  be considered (fruit flies on Hawaiian islands -
  more important than immigration, extinction)

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Metapopulation Theory

• The population size of a species on any island
  is a result of local population dynamics, plus
  immigration minus emigration
• The population on an island may go extinct, but
  new immigrants may repopulate

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Metapopulation Theory

• The equilibrium between immigration and
  extinction determines the number of surviving
  populations on different islands, their average
  size, and the total size of the metapopulation

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Metapopulation Theory
Source and sink populations - some populations
may not be self-sustaining
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Metapopulation Theory
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Metapopulation Theory

• Do plant populations have high enough rates of
  migration, extinction to have an impact on
  distributions and population sizes?

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Metapopulation Theory

• Prediction 1 If extinction rates are dependent
  on the frequency of occupied patches, those
  species occurring in many patches will have large
  populations when present
• For most plant species, studies show that
  occupancy and abundance are positively correlated

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Metapopulation Theory

• Prediction 2 If immigration, extinction depend
  on frequency of occupied patches, patch occupancy
  by a species should have a bimodal distribution
• Core species - common satellite species - rare

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Metapopulation Theory

• Prediction supported at small scales (lt 1 km2),
  but not at larger scales
• Spatial structure and dispersal OK at small
  scale, but not at larger scale - immigration and
  extinction rates of plants too low for model

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Metapopulation Theory
Konza Prairie

• Species-time-area relationships
• Number of species observed in plot each year
  wont change, but extinction/immigration will
  result in new species being observed in plots
  over the years
• Larger plots have more species
• Larger plots contain metapopulations of all
  species in landscape, small plots do not

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Conservation Reserves

• Forest fragmentation and species richness?
• SLOSS - single large or several small reserves
• Which gives the most protection per area?

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Conservation Reserves

• Island biogeography
• Metapopulation theory

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Conservation Reserves

• Testing concepts in Brazil

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Conservation Reserves

• Corridors can also be important - connectivity -
  seeds for dispersal into sink regions

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Conservation Reserves

• Bigger should be better
• More species, larger populations, less chance of
  extinction
• Reality take whatever size you can get

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Conservation Reserves

• Edge effects
• Higher mortality near edges - wind, pathogens
• More prone to invasive species - unprotected
  edges - fewer barriers to seed dispersal