Intraspecific competition

Intraspecific competition is an interaction in population ecology, whereby members of the same species compete for limited resources. This leads to a reduction in fitness for both individuals. By contrast, interspecific competition occurs when members of different species compete for a shared resource. Members of the same species have very similar resources requirements whereas different species have a smaller contested resource overlap, resulting in intraspecific competition generally being a stronger force than interspecific competition.

Individuals can compete for food, water, space, light, mates or any other resource which is required for survival or reproduction. The resource must be limited for competition to occur; if every member of the species can obtain a sufficient amount of every resource then individuals do not compete and the population grows exponentially.Exponential growth is very rare in nature because resources are finite and so not every individual in a population can survive, leading to intraspecific competition for the scarce resources.

When resources are limited, an increase in population size reduces the quantity of resources available for each individual, reducing the per capita fitness in the population. As a result, the growth rate of a population slows as intraspecific competition becomes more intense, making it a negatively density dependent process. The falling population growth rate as population increases can be modeled effectively with the logistic growth model. The rate of change of population density eventually falls to zero, the point ecologists have termed the carrying capacity (K). The carrying capacity of a population is the maximum number of individuals that can live in a population stably; numbers larger than this will suffer a negative population growth until eventually reaching the carrying capacity, whereas populations smaller than the carrying capacity will grow until they reach it.

Intraspecific competition doesn't just involve direct interactions between members of the same species (such as male deer locking horns when competing for mates) but can also include indirect interactions where an individual depletes a shared resource (such as a grizzly bear catching a salmon that can then no longer be eaten by bears at different points along a river).

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