Population Ecology

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Population Ecology

• Population
• Density
• Crude
• Ecological

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Distributions and scale
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Colorado distribution of a triploid
parthenogenetic species of recent origin genus
Aspidoscelis
3n
2n
2n
A. neotesselata
A. tesselata
A. sexlineata
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Aspidoscelis tesselata (2n) maternal progenitor
of neotesselata
Aspidoscelis sexlineata paternal progenitor of
neotesselata
Maps from Hammerson (1999)
Aspidoscelis neotesselata (3n) hybrid,
parthenogenetic derivative of the two
parental species above
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• Small scale distributions of individuals
• Dispersion (vs. dispersal)
• Three patterns

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Small scale distributions of individuals
dispersion patterns random, regular, and clumped
Large scale distributions are always clumped.
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Some distributions shift with maturity of stand
e.g. , creosote bush
   
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Estimating population density mobile animals

• Mark-recapture technique (Lincoln-Peterson
  Index)
• N M n m
• N/M n/m
• N population estimate
• M number captured time 1 and released back into
  population
• n total number captured at time 2
• m number marked individuals captured at time 2
• N Mn/m (overestimates population size)
• Bailey correction N M(n 1)/m 1)

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100 m2 sampled to determine the density of animal
species X N ? M 140 n 130 m 50 Density
estimate is 364 individuals of X/100 m2 With
Yates correction 360 individuals of X/100 m2
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Field research on effects of patch size on
movements among three rodent species
Sigmodon Microtus Peromyscus
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Scale
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Significance of patch size depends on organism
Fractal geometry developed in 1982 (Benoit
Mandelbrot) Now used to quantify dimensions of
complex shapes Size of patch depends on scale
used
1. Bald eagle nest spacing (0.782 km) perimeter
of island c. 760 km 2. Barnacle spacing (each
requires c. 2 cm of coastline perimeter of
island c. 11,000 km
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• Metapopulations disjunct conspecific populations
  linked by the movement of individuals

Snail kite
Disjunct habitat patches
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• Metapopulation patterns
• Best case scenario
• Dispersal among patches sufficiently high that
  populations are rescued from local extinctions.

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• Core-satellite pattern
• Persistence depends on one or more
  extinction-resistant (source) populations.
• Surplus individuals produced
• Maintain peripheral (sink) populations
• a pop. unable to produce
• sufficient individuals
• to maintain itself

Low quality habitat
High quality habitat
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• Example of a metapopulation study
• Bay checkerspot butterfly
• 1987 population of 106 adult butterflies on a
  2,000 hectare habitat (Jasper Ridge, Stanford
  University).
• ha 2.471 acres or 10,000 m2
• Source population (Morgan Hill) for nine other
  populations of 10 to 350 adult butterflies on
  patches of 1 to 250 ha.

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Extinct in 1976, recolonized in1986
27 patches of suitable habitat No difference in
quality Serpentine soils
Colonized in 1986
Morgan Hill
Distance factor Poor dispersal ability
10 km
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• Glass half empty (rare species)
• Local extinctions occur during an overall
  regional decline.
• Ineffective population dispersal failure to
  rescue populations from extermination.