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Interspecific Competition Part 1
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Covers competitive exclusion, different types of ecological niche, competitive release, resource partitioning, character displacement and a couple of examples.
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EcologyLecture 3 Interspecific Competition 1 22/02/21
Competitive Exclusion Principle
- “Complete competitors cannot co-exist” – Gause, 1934.
- Essentially, two species cannot co-exist on the same limiting resource.
- He experimented with two species of Paramecium (P. aurelia and P. caudatum), which were
grown both together and separately. When grown separately, both species survived.
However, when they were grown together, P. aurelia outcompeted P. caudatum.
- This is also seen in the wild; one example of this is two species of barnacle living in the
intertidal zone (Chthamalus stellatus and Balanus balanoides).
- - Survival of Chthamalus is reduced where
Balanus growth is higher, thus showing that
Balanus does exclude Chthamalus.
Ecological niches
- A multidimensional space representing all the conditions in which a species can survive.
- For example, temperature. Species can survive within certain limits. These limits represent
the species niche in one dimension.
- A second condition could be humidity. If we add this to temperature, it becomes a two-
dimensional niche.
- A third condition added, such as salinity, creates a three-dimensional niche.
- There are many other biotic and abiotic factors, so each species exists in an n-dimensional
niche.
Fundamental ecological niche
- An organism free of interference from other species (competitors, predators, parasites etc.)
could use the full range of conditions and resources to survive and reproduce. This would be
its fundamental niche.
- Another way to think of it is the niche it could potentially occupy.
Realised ecological niche
- In the presence of competitors (and/or predators) the species is restricted to it’s realised
niche.
- E.g., C. stellatus – fundamental niche exists down to the shore. B. balanoides restricts it to its
realised niche, high on the upper shore.
Competitive release
- Expansion of niche due to reduction in intensity of interspecific competition.
- E.g., ground doves on the New Guinea archipelago.
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