Population and Sustainability

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Carying capacity:

Size of a population depends on the balance between the death rate (mortality) and the rate of reproduction.

Lag phase - Only a few individuals that are acclimatising to their habitat. Rate of reproduction is low, and the growth in population size is slow.

Log phase - Recourses are pleantiful and conditions are good. Rate or reprodiction exceeds mortality. Population size increases rapidly!

Carrying capacity - Population size levels out. Habitat itself cannot support a larger population. Rate of reproduction and mortality are equal, therefore opulation size remains stable.

Limiting factors:

When habitats cannot support a larger population because of factors that limit growth in population size.

May include availability of recources such as:

  • Food 
  • Water
  • Light
  • Oxygen
  • Nesting sites
  • Shelter

May also include the effects of other species including:

  • Parisites
  • Predators
  • Intesnity of competition for recources (inter and intraspecies)

Predators and prey:

Predator - hunts other animals (prey) for food.

The predator and prey populations can affect one another in turn.

1. Predator population increases and more prey are eaten

2. Prey population gets smaller and this leaves less food for the predators.

3. Less food means fewer predators can survive and so the population decreases.

4. Fewer predators means less prey is eaten and their population increases.

5. More prey allows the predator population to increase - the cycle starts again!



Occurs when recources (like food or water) are not present in adequate amounts to satisfy the needs of all the individuals…


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