Populations and Sustainability

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A habitat cannot support a population larger than its carrying capacity because of limiting factors which place a limit on population size. The limiting factors may include:

  • Resources
  • Food
  • Water
  • Light
  • Oxygen
  • Nesting sites
  • Shelter
  • Effects of other species
  • Predators
  • Parasites
  • Intensity of competition for resources

Extinction is more likely if a sepcies is rare intitially and is has a slow reproductive rate and its prey numbers have reduced.

Carrying capacity: The maximum population that can be maintained over a period of time in a particular habitat. A population does not increase in size indefinately due to limiting factors determining a carrying capacity. There will be intraspecific competition for food and nesting sites and interspecific competition with other species. Larger populations attract more predators as well as parasites and diseases spreading more easily.

When the predator population gets bigger, more prey are eaten. The prey population then gets smaller, leaving less food for the predators. With less food, fewer predators can survive, and their population size decreases. With fewer predators, fewer prey are eaten, and their population size increases. With more prey, the predatory population gets bigger, and the cycle continues. 

Interspecific competition: Competition between individuals of different species can affect both the population size and the distribution of a species in an ecosystem as no two species can occupy the same niche.
Red vs Grey squirrels compete for the same food. The Red squirrel outcompetes the Grey in conifer forests, but the Grey squirrel outcompetes the red in forests with less than 75% conifers. 

Intraspecific competition: Competition between individuals of the same species. If food supply becomes a limiting factor, the individuals best adapted to obtaining food will survive and reproduce, whereas those less well adapted will die out and fail to pass on their genes.

Conservation is the maintenance of biodiversity, but the area can still be sustainably exploited. Preservation protects species by leaving their habitat untouched.

Selective felling: Some mature trees, diseased trees and unwanted species are harvested, leaving other trees to develop and distribute seeds to fill the gaps. This leads to a variety of heights, branch lengths etc and therefore increases biodiversity.
***** felling: Small patches, or strips, of forest are cleared completely, leaving other patches untouched. Large areas are not felled at the same time, so loss of species and soil erosion are avoided and shade is maintained. It also


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