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lecture note 19 for BGYB50


Biological Sciences
Course Code
Herbert Kronzucker

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- Competition between cells, organisms, populations, and species can either be:
(a) direct (also known as contest or interference competition) or
(b) indirect (also known as resource or scramble competition)
- When individuals of the same species compete, we speak of intraspecific competition; if
individuals of different species compete, we call it interspecific
- Biological competition is defined by:
(a) the direct or indirectstruggle” for a limiting resource (e.g. space, food, sexual
(b) reduction of resource availability due to the activity of the competing organisms,
(c) mutual (!) impact upon growth, survival or fecundity (genetic fitness!), i.e. both
partners in a competition scenario are affected (a -/- interaction)
- Plants can engage in direct competition as well, e.g. through allelopathy, the production
of chemicals that inhibit the germination or growth of neighbouring plants (it is a form of
“chemical warfare; many allelopathically active chemicals are also of medicinal value)
- Competition also plays itself out at the cellular level
- For competition to become manifest, resources (most often space, food, or mating
partners) must be limiting
- Central to the understanding of competition, as to so many other things, is the concept
of ecological optima and tolerance limits of biological organisms: Because the majority
of organisms in a population in principlelike similar things (e.g. one type of food,
spaces with a certain temperature), organisms are forced to compete for the latter when
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