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Implicit in the concept of carrying capacity is competition among individuals for essential resources. Competition occurs when individuals use a common resource that is in short supply relative to the number seeking it. [...] When resources are limited, a population may exhibit one of two responses: scramble competition or contest competition.

Scramble competition occurs when growth and reproduction are depressed equally across individuals in a population as the intensity of competition increases.

Contest competition takes place when some individuals claim enough resources while denying others a share.

In many cases, competing individuals do not directly interact with one another.

Sviluppo

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As population density increases toward a point at which resources are insufficient to provide for all individuals in the population, some (contest competition) or all individuals (scramble competition) reduce their intake of resources. That reduction slows the rate of growth and development. The result is an inverse relationship between population density and individual growth, referred to as density-dependent growth.

Mortalità

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In addition to suppressing the growth of individuals, competition for resources at high population densities can function to reduce survival (Figure 11.8). In turn, mortality functions to increase per capita resource availability, allowing for increased growth of the surviving individuals. This link between densitydependent mortality, resource availability, and growth rate is particularly apparent in organisms that exhibit indeterminate growth rates that respond strongly to resource availability,

Fecondità

Besides directly influencing the survival and growth of individuals, competition within a population can reduce fecundity. The timing of the response depends on the nature of the population, and the mechanisms by which competition influences reproductive rate can vary with species.
For animal species that exhibit indeterminate rates of growth and development, density-dependent growth is a potentially powerful mechanism of population regulation because fecundity is typically related to body size

Stress

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As a population reaches a high density, individual living space can become restricted. Often, aggressive contacts among individuals increase. One hypothesis of population regulation in animals is that increased crowding and social contact cause stress. Such stress triggers hormonal changes that can suppress growth, curtail reproductive functions, and delay sexual activity. They may also suppress the immune system and break down white blood cells, increasing vulnerability to disease