Ecological Niches (DP IB Biology): Revision Note

Ecological Niches

• The place where a species lives is known as its habitat

• Species will occupy a specific niche within a habitat

• The term niche can be defined as

The role of a species within its habitat

• The role of a species includes

  • What it eats

  • Which other species depend on it for food

  • What time of day a species is active

  • Exactly where in a habitat a species lives and feeds

  • The abiotic factors acting on a species

  • The biotic factors acting on a species

• No two species can fill the same niche within a habitat; if this ever happens the two species will be in direct competition with each other for resources, and one of the two species will out-compete the other, causing it to die out in that particular habitat

  • It can sometimes seem as though species are occupying the same niche, but there will still be subtle differences in their role; e.g. they might feed at different times of day, or have different food sources

Feeding niches diagram

Feeding location is an example of a feature that may differ between niches

Anaerobes & Aerobes

• All living organisms carry out some form of respiration

  • Aerobic respiration requires oxygen:

• Anaerobic respiration does not require oxygen:

• Some organisms can survive using either aerobic or anaerobic respiration, while some can only survive using one type or the other; organisms are said to be either

  • Obligate anaerobes

  • Facultative anaerobes

  • Obligate aerobes

Obligate anaerobes

• These are single-celled organisms that can only carry out anaerobic respiration

  • They cannot tolerate oxygen

• Early bacteria were obligate anaerobes; they were able to survive in the atmosphere of early Earth due to its lack of oxygen

• Photosynthesis has since introduced oxygen to the earth's atmosphere, meaning that obligate anaerobes can now only be found in oxygen-free environments, e.g. lower layers of soil, deep water, and inside the bodies of other groups of organisms

Facultative anaerobes

• These organisms mainly respire aerobically, but have the ability to switch fully to anaerobic respiration in the absence of oxygen

  • The switch to anaerobic respiration has no negative effects for facultative anaerobes

• Examples of facultative anaerobes include

  • Brewers yeast, Saccharomyces cerevisiae

  • Escherichia coli, a species of bacteria

Obligate aerobes

• These organisms cannot survive in the absence of oxygen; they rely on aerobic respiration to release energy from food
  

  • They may be able to carry out anaerobic respiration in some cells for short periods, but the damaging effects are too great to do this for longer than a few seconds

• Examples of obligate aerobes include

  • Most animals

  • Most fungi (not yeast)

  • Some bacteria, e.g. Mycobacterium tuberculosis