Ecological Niches (SL IB Biology)

• 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
  • Exactly where in a habitat a species feeds
• 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

Adaptation to ecological niche

• Species can only survive in habitats in which they are well adapted to their niche; they must be adapted to a habitat's:
  • Abiotic factors, e.g.
    • Plants must have enough light for photosynthesis in order to produce carbohydrates
    • Aquatic organisms must be able to absorb enough oxygen from the surrounding water for respiration
  • Biotic factors, e.g.
    • A prey organism being camouflaged to avoid predation
    • A plant growing fast enough to outcompete nearby plants for sunlight

• 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