Includes how to prove the competitive exclusion principle, the flour beetles experiment as a case study, colonisation and competition, keystone species, interference competition, and apparent competition.
Proving the competitive exclusion principle
- Example: British tits.
- All have short beaks and hunt for food on twigs, leaves and occasionally on the ground. All
nest in holes.
- However, a closer inspection may reveal subtle differences in where they look for food and
the type of insect prey they consume.
- Thus, one may suggest that they coexist by resource partitioning. However, this would
require evidence.
- This would be done by proving they compete (done via removal experiments), or that they
have competed in the past, and now exploit slightly different niches (difficult to prove). Thus,
to demonstrate resource partitioning is a consequence of interspecific competition is
difficult.
- Interspecific competition is often associated with niche differentiation, but cause and effect
are rarely established.
Park’s flour beetles
- Trilobium castaneum and T. confusum live in flour, so there should be competitive exclusion.
- Indeed, when grown together, the former species won 12/18 replicates.
- However, when the sporozoan parasite Adelina was added to the culture, T. confusum won
66/74 (89%) of replicates because it was more resistant to the parasite, even when a higher
number of T. castaneum were added.
- In effect, the presence of the parasite altered the outcome of interspecific competition.
- Also, when the parasite was absent, the outcome was quite mixed. Sometimes T. castaneum
won (67%), sometimes T. confusum won (33%).
- Random events (i.e., the quality or age of beetles used to start off the culture) appeared to
play a role in determining the outcome.
Altering the outcome of interspecific competition
- The result of interspecific competition could vary as a function of temperature, moisture,
parasitism, and genetic strain.
- Plus, an element of stochasticity.
- Thus, the outcome of interspecific competition in the wild is likely to be quite unpredictable
due to environmental heterogeneity.
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