Populations and Cycles

HideShow resource information


- Birth Rate: the reproductive capacity of the population

 - Emigration: The movement of individuals out of a population

- Immigration: the movement of individuals into a population

- Population: a group of organisms of a single species interbreeding and occupying a particular area


Sigmoid Curve 


1. Lag Phase: Little multiplication or growth. Only few individuals therefore slow growth/breeding rate. Period of adaptation or preparation for growth. Lots of metabolic activity, ie, enzyme synthesis.

2. Exponential phase: Increasing numbers = increasing repro.

3. Stationary phase. Birth rate = Death rate. Population reaches carrying capacity (or maximum size able to be supported by habitat or area)

4. Death phase: Death rate higher than birth rate. For example in terms of microbiology, maybe all the food in a solution has been used up.


  • Environmental resistance. Population growth slows down due to the followung
    • available food
    • predatioon
    • parasitism
    • disease
    • overcrowding
    • competition
    • accumulation of toxic waste
    • weather

DENSITY DEPENDENT FACTORS (effect of factor increases depending on how dense a population is/the proximity)

  • Accumlation of toxic waste
  • Disease
  • Parasitism
  • Depeletion of food supply

DENSITY INDEPENDENT FACTORS (all plants/animals affected no matter size of pop)

  • Freezing
  • Flood
  • Fire
  • Other natural disasters

Populations fluctuate in numbers. This may be the consequence of weather patterns or temperature. Population oscillations are regulated by negative feedback.

Negative feedback: when there is a change in a monitored variable, a response is trigged to counteract the initial fluctuation/change

For example: occassional the greenfly population will explode in numbers. This could be a reduction in the numbers of their predators. However this will self regulate due to competition for resources between the greenflies.


  • light
  • water
  • nutrients
  • mates
  • space

There are two types of competition

Intraspecific Competition is competition between one species.

Interspecific Competition is competition between other species.


  • Pests directly cause disease in crop organisms
  • make infection by pathogens more likely
  • Can spoil food during transport or storage


No comments have yet been made

Similar Biology resources:

See all Biology resources »See all Ecology, ecosystems and environmental biology resources »