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Ecology Index

Ecology : Introduction
The Competitive Exclusion Principle
Ecological Succession: Lake - Woodland Transition
Modelling Population Growth
Biodiversity and conservation
What can be done to stop the loss of biodiversity?
Conservation Alternatives
The Carbon Cycle
The Nitrogen Cycle Flow Chart
The Nitrogen Cycle
Eutrophication
Methanogens and Biogas

Topic Chapters Index

 

Measuring populations

  • Total count (census)

  • Sampling

  • Random sampling

  • Systematic sampling (grid, transect)

  • Sample size, quadrats

  • Numbers of samples

Estimating population density
Measuring a population's area
Calculating population size (density x area)

 

Influences on a population

  • Abiotic factors (e.g. climate, nesting sites) often independent of density.

  • Biotic factors (e.g. disease, food supply, predation) often density dependent.

 

ECOLOGY

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Populations and Sampling

What is a population?

Definition: A group of organism of the same species which live in the same habitat at the same time where they can freely interbreed.

 

Describing a population

  • Size: Numbers

  • Density: Numbers per unit area (or volume in aquatic ecosystems)

  • Distribution: Random, clumped, uniform

     

    distribution

     

  • Growth: Changes with time: (immigration - emigration) + (natality - mortality)

 

The sigmoid or S-shaped population growth curve

 

sigmoid curve

Phase 1: Log or exponential phase. Unlimited population growth. Abundant food, no disease, no predators etc.

Phase 2: Decline or transitional phase. Limiting factors slowing population growth.

Phase 3: Plateau or stationary phase. No growth. The limiting factors balance the population's capacity to increase. The population reaches the Carrying Capacity (K) of the environment. Added limiting factors will lower K. Removing a limiting factor will raise K.

 

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