Lecture 17 - Competition - Observations

Density dependence slows the growth rate and limits the population size as N approaches K. This process can also be called competition.

Competition - use or defense of a resource by one individual that reduces resource availability for other individuals.

Competition may be:

  • Intraspecific - among individuals of the same species

    or

  • Interspecific - among individuals of at least two species

Intraspecific competition is built into logistic growth - As resources are used they become unavailable to other individuals in the population, and population growth slows.

Examples of competition:

  • male elk fighting for access to females is an example of interference competition.

  • the first barnacles to arrive deplete a resource (space), making it unavailable for later individuals is an example of resource competition.

Interference competition - a form of competition involving direct antagonistic interactions between individuals, including territoriality, chemical poisoning, and overgrowing, which result in direct harm or reducing the competitor’s access to resources, such as food or light.

Resource competition - intraspecific or interspecific competition for limited resources, generally not involving direct antagonistic interactions between individuals.

Intraspecific competition in plants- in theory, only a small number of large individuals can be supported, regardless of the initial number or biomass

Niche - the environmental factors that influence the growth, survival, and reproduction of a species.

May be abiotic:

  • temperature

  • rainfall

  • dissolved oxygen

  • magnesium

  • etc

Or biotic

  • prey

  • predators

  • parasites

  • etc…

There are multidimensional descriptions of the species’ niche, which is just adding more axes/variables to explain

Fundamental niche - the physical conditions under which a species can live in the absence of interactions with other species

Realized niche- the actual conditions under which a species lives. The realized niche is always reduced from the fundamental niche due to interactions with other species.

The dominant competitor should gain resources to the exclusion of the weaker competitor.

Competitive exclusion principle - Two species cannot coexist indefinitely if they require the same limiting resource