8.4 Effect of Density in Populations

• Population density

  How close individuals within a population live near one another
• Abundance of food available

  Population can become dense, higher reproductive rate, space is limited
• Food is limited

  Density of population may decrease, lower reproductive rate, individuals can spread out in limited space
• Limits to population growth

  • Density dependent factors
  • Density independent factors
• Density dependent factors

  Abiotic or biotic factors whose effect on population size relies on population densities (e.g. competition for resources, territoriality, disease, predation)
• Density independent factors

  Abiotic or biotic factors that affect population size regardless of population density (e.g. natural disasters, pollution)
• A population can produce a density of organisms that exceeds the system's resource availability
• Logistic growth model

  Population growth that initially starts slowly, immediately followed by exponential and ends with a relatively stable maximum growth, illustrated as an S-shaped curve
• Carrying capacity

  Maximum number of individuals the environment can sustain
• Density dependent and density independent limiting factors can cause a population to reach carrying capacity
• Under certain conditions, a population can temporarily exceed the carrying capacity
• Fluctuations in population size can naturally occur at or near carrying capacity
• When density dependent and density independent factors are imposed, a logistic growth model generally ensues
• Density Independent Factors


  Natural Disasters

  Pollution
• Density Dependent Factors


  Competition for resources

  Territoriality

  Disease

  Predation