Populations and Cycles

KEY WORDS

- 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.

FACTORS CONTROLLING GROWTH

• 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.

COMPETITION

• 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.

PEST CONTROL

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

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