Competition

competition

results when resources are limited

important in natural settings.

Some species are more likely to be strongly affected by competition than others

strength and outcomes between species can vary among environments

fundamental niche

complete set of conditions under which an organism could potentially survive and reproduce.

realized niche

describing the conditions, under which an organism actually lives, given limitations created by interactions with other species.

competitive exclusion principle

states that no two species can coexist in exactly the same niche.

indirect competition

resource competition

occurs when individuals compete by consuming a shared resource.

direct competition

interference competition

includes allelopathy, territoriality, preemption

allelopathy

occurs when plants release chemicals that inhibit the growth of their competitors.

Territoriality

describes the establishment by an organism or group of a defended area, from which others are excluded.

Preemption

occurs when individuals prevent others from using a location by occupying it first.

intraspecific competition

competition for resources among individuals of the same species.

increases as population density increases & reduces health (e.g., size, survival rate, birth rate) of individuals in the population.

unlimited resources

individuals in a population will not compete

population will be able to grow exponentially at its intrinsic rate of growth, r.

resource limitation

population's birth rate and death rate are equal (and greater than zero)

population is said to be at its carrying capacity (symbolized by K).

logistic growth equation

simple model of population growth in the presence of a limiting resource. The equation is:

dN/dt = r⁢N⁢(1−N/K)

interspecific competition

competition for resources among individuals of different species.

Lotka-Volterra competition equations

used to model competition between populations of two species.

predict that species can only coexist if intraspecific competition is stronger than interspecific competition.

assumptions frequently violated in the real world, leading to more complex outcomes.

• dN1/dt = r1N1(1 − N1+α12⁢N2/K1)

• dN2/dt = r2N2(1 − N2+α21⁢N1/K2)

dN₁/dt and dN₂/dt

instantaneous population growth rates

Subscripts 1 and 2 refer to species 1 and 2, respectively.

r₁ and r₂

per capita intrinsic growth rates.

N₁ and N₂

population sizes.

K₁ and K₂

carrying capacities.

α₁₂ and α₂₁

competition coefficients, describing the per capita effect of one species on population growth of the other.

isoclines of zero population growth for the Lotka-Volterra competition equations

viewed in a phase plane

provide a graphical way of determining the possible outcomes of competition between two species

strength and outcome of competition

can vary among environments.

ex. species A might outcompete species B in a wet environment, while B outcompetes A in a dry environment.

trade-offs in adapting

interspecific competition can lead to character displacement, reducing the strength of competition between species.

other interaction types (predation, mutualism, etc)

can reduce the degree of competition within or between species.