Populations

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Populations
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Population Characteristics

• Three important characteristics of a population
  are its distribution, density, and growth rate

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Population Characteristics

• Population density is simply the number of
  individuals per unit area or volume.
• Distribution of these individuals can be uniform,
  random, or clumped.
• Most members of a population are clumped, as are
  the members of a human population.

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Patterns of distribution within a population
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Population Growth

• Population growth is the change in the size of a
  population with time
• Population growth occurs when birthsimmigration
  is greater than deathsemigration

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Population Growth

• Populations do not grow linearly like income
• Populations have exponential growth

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Population Growth

• Exponential growth occurs when individuals in a
  population reproduce at a constant rate

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Population Growth

• Occurs under ideal conditions with unlimited
  resources

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• Exponential growth results in a J-shaped curve
  because as the population increases in size so
  does the expected increase in new members.

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Exponential growth
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Population Growth

• As resources become less available, the growth of
  a population slows or stops

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Population Growth

• Populations cant grow indefinitely
• The leveling off of population size results in a
  S-shaped curve

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Population Growth

• The number of organisms of a population an
  environment can support is known as its carrying
  capacity

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Logistic growth
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Types of Population Growth

• Two life history patterns exist in populations.
• Opportunistic populations have a short lifespan,
  small stature, and produce many offspring to take
  advantage of new resources.

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Types of Population Growth

• Opportunistic populations are successful in
  unpredictable and rapidly changing environments
• EX mosquitoes

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Types of Population Growth

• Equilibrium species live longer, are larger, and
  produce fewer young but have greater parental
  care they hold population size near carrying
  capacity.

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Types of Population Growth

• Equilibrium species live in more stable
  environmental conditions
• EX elephants, bears, whales, cacti, California
  redwoods

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Life history patterns
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• Population growth is limited by both
  density-independent factors (e.g., weather) and
  density-dependent factors (predation,
  competition, and resource availability).

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Limits to Population Growth

• Density-independent factors operate regardless of
  population density.
• Density-dependent factors increase in intensity
  as population size increases.

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Competition

• Competition occurs when two species try to use a
  resource that is in limited supply.
• Competition is an example of a density-dependent
  factor

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Competition between two populations of Paramecium
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Predation

• Predation occurs when one living organism, the
  predator, feeds on another, the prey.
• Predators include lions, whales that filter feed,
  parasites that draw blood from hosts, and
  herbivores that eat grass, trees, and shrubs.

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Predator-Prey Population Dynamics

• Predator-prey interactions between two species
  are influenced by environmental factors.

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Predator-Prey Population Dynamics

• Cycling of population densities may occur, as in
  the case of the Canadian lynx and hare predators
  kill off prey and then the predator population
  declines when food is in short supply.

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Predator-prey interaction lynx and snowshoe hare