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Population �Ecology

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Ecology: Studies the interaction of organisms with other organisms and their environment

Ecology and Evolution are intertwined, because reproductive success (evolution) depends on ecological interactions and vice versa

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Some general ecology definitions to know...

  • Habitat: Place an organism lives
  • Population: Organisms that are the same kind living in the same area
  • Community: All the living things in the same area
  • Ecosystem: All the living things in an area and how they interact with each other and the outside world

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Population Dynamics

  • Three Key Features of Populations
    • Size
    • Density
    • Dispersion

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Three Key Features of Populations

  • Size: number of individuals in an area

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  • Growth Rate:
    • Birth Rate (natality) - Death Rate (mortality)
    • How many individuals are born vs. how many die
    • Birth rate (b) − death rate (d) = rate of natural increase (r)

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Size of the population

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2. Density: measurement of population per unit area or unit volume

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Pop. Density = # of individuals ÷ unit of space

Three Key Features of Populations

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How Do You Affect Density?

  • Immigration: movement of individuals into a population

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  • Emigration: movement of individuals out of a population

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  • Density-dependent factors: Biotic factors in the environment that have an increasing effect as population size increases (disease, competition, parasites)

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  • Density-independent factors: Abiotic factors in the environment that affect populations regardless of their density (temperature, weather)

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Immigration

Emigration

Birth

Mortality

Population

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Factors That Affect Future Population Growth

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3. Population Dispersion:

    • describes the spacing of organisms relative to each other
      • Clumped
      • Uniform
      • Random

Three Key Features of Populations

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Population Dispersion

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How Are Populations Measured?

  • Population density = number of individuals in a given area or volume
  • Count all the individuals in a population
  • Estimate by sampling
  • Mark-Recapture Method

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How Do Populations Grow?

  • Idealized models describe two kinds of population growth:

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    • Exponential Growth

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2. Logistic Growth

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Carrying Capacity

  • Carrying Capacity (k):
    • The maximum population size that can be supported by the available resources
    • There can only be as many organisms as the environmental resources can support
    • Can be limited by: Limited food, accumulating waste, increasing competition

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Exponential Growth Curve

Figure 35.3A

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Logistic Growth Curve

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Factors Limiting Growth Rate

  • Declining birth rate or increasing death rate are caused by several factors including:
    • Limited food supply
    • The buildup of toxic wastes
    • Increased disease
    • Predation

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Density-Dependent Limiting Factors:

  • Factors that affect a population more if the population is larger.
    • Usually biotic factors
      • Parasitism
      • Competition
      • Predation
      • Food available

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Density-Independent Limiting Factors

  • The factor will affect the organisms equally, regardless of the population size
    • Usually abiotic factors
      • Weather
      • Natural disasters

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“Booms” and “Busts”