Population

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Population
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How do populations grow?
Population
Deaths
Births
Immigration
Emigration
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Population Growth Models

• Linearprobably not realistic
• Exponential (geometric) dN/dt rN
• rintrinsic rate of increase(b-d)
• Npopulation size
• Logistic dN/dt rN (K-N/K)
• Includes carrying capacity term (K-N/K) or
  (1-(N/K))
• More realistic due to environmental factors
• Others with competition, stage-based (age or size
  specific), etc.

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Geometric or Exponential Growth
Phlox drummondii
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Anatomy of the Exponential Growth Model
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Another example of exponential growth whooping
cranes
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Logistic Growth (includes carrying capacity term)
Yeast
African Buffalo
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What determines limits to Population Growth?

• Density-dependentbiotic factors like disease,
  competition, or predation
• Density-independentabiotic factors like climate,
  fire, nutrients, sunlight, etc.

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Adaptive Radiation Galapagos Finches
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Galapagos Islands

• Darwin studied in 1830s Vecchi later re-studied
  them in 2007
• Found some birds he thought were unrelated
• In fact, they were closely related finches in
  different species

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To quote Darwin

• "It is very remarkable that a nearly perfect
  gradation of structure in this one group can be
  traced in the form of the beak, from one
  exceeding in dimensions that of the largest
  gros-beak, to another differing but little from
  that of a warbler."

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Environment Varies Leading to Density independent
regulation of population
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Medium Ground Finch benefits from increased
rainfall
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Cactus Finches

• Eat flower pollen from buds
• Eat seeds
• Drink nectar
• Eat insects
• Some seed dispersal
• Some pollination

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Opuntia helleri prickly pear cactus

• El Nino damaged them by water-logging and salt
  spray (density independent factors)
• Damage is also by competition from other plants
  and cactus finches (density dependent factors)

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Cactus flower abundance and damage by cactus
finches
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Human Population Growth
LOOK!! Humans are subject to carrying capacity,
too!!

• Expected to reach 9.5 billion or so by 2050
• Most of this in developing countries

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Trends in human population growth

• 1800 1 billion
• 1930 2 billion
• 1960 3 billion
• 1975 4 billion
• 1987 5 billion
• 1999 6 billion
• Current 6.5 billion

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Human Population Growth

• 3 Revolutions
• Agricultural 10,000 ybp
• Industrial 225 ybp
• Medical/technological 50 ybp

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Age-Sex Pyramids developed vs. developing
nations
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The Impact of Epidemics
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With and without AIDS
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