POPULATION

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POPULATION BIOLOGY
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4.1 Population Dynamics
Ecology can viewed through several hierarchical
"levels of organization. Ecosystem ? Communities
? Populations ? Organisms
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Populations
Groups of organisms of the same species that live
within a given area Key characteristics Disper
sion patterns Population density Growth
rate
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Limiting factorsbiotic or abiotic factor that
prevents population growth A. Physical
factors -- temperature, water, light, soil
acidity B. Biological interactions
--competition, predation, symbiosis C.
Geographical barriers Mountains, deserts,
oceans (Humans sometimes transport species past
these barriers)
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Population Density

• Population density is total population size per
  unit of area.
• Population densities depend on
• Interactions within the environment
• Quality of habitat
• Density dependent factors
• Density independent factors
• Carrying capacity is the maximum number of
  organisms that can be supported in a given
  habitat.

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Limits on Population Growth

• Density Dependent Limits
• Food
• Water
• Shelter
• Disease
• Density Independent Limits
• Weather
• Climate

Water and shelter are critical limiting factors
in the desert.
Fire is an example of a Density independent
Limiting factor.
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Density dependent factors The effect increases
as the population increases.a. Predationb.
Disease c. Intrinsic influences
Physiological stress from overcrowding
Abnormal behavior (aggressive behavior, kill
young, etc.) Competition for resources
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Density independent factors -- Affect
populations regardless of size. a. Abiotic
Environmental factors that effect population
size. (rainfall, temperature, hurricanes) b.
Biotic Biological factors. An organisms
predator or prey species population changes.
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Growth Rate is the change in population size over
time.

• Birth rate--number of births
• Death rate--number of deaths
• Immigration Emigrationnumbers that leave or
  join the population

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Logistic growth (S-shaped curve)Has a carrying
capacity (K) maximum number of individuals that
can survive due to limited resources (food,
light, space, water). Logistic growth often has
an "overshoot" phase, followed by fluctuations in
population.
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Exponential growth (J-shaped curve)-- Assumes no
limitations on resources. Some species have
brief periods of exponential growth, followed by
population crashes.
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Population Growth
Exponential vs. Logistical Growth