Biotic factors are the effects of living organisms on other organisms in an ecosystem. The main ones are:
• Food availability: the amount of food produced by other organisms.
• Competition: organisms competing for limited resources such as food, light, water, space or mates. Intraspecific competition is between members of the same species; interspecific competition is between different species.
• Predation: one animal killing and eating another.
• Parasitism and disease: organisms living on or in a host and harming it.
• Finding a mate and holding a territory.
• Mutualism: close relationships that benefit both species.
Most of these have their own lessons later in the topic.Many biotic factors are density dependent: their effect is greater when the population is larger, because food runs short and disease spreads more easily.Interspecific competition can affect distribution. If two species need the same resource, the better competitor increases and the other declines in that area. For example, the red squirrel has disappeared from much of Britain since the introduction of the grey squirrel, partly because the grey squirrel competes more effectively for food.Organisms can also change abiotic factors. Trees shade the ground and add humus to the soil, and earthworms improve soil aeration. This is important in succession, where each community alters the conditions for the next.
• Food availability: the amount of food produced by other organisms.
• Competition: organisms competing for limited resources such as food, light, water, space or mates. Intraspecific competition is between members of the same species; interspecific competition is between different species.
• Predation: one animal killing and eating another.
• Parasitism and disease: organisms living on or in a host and harming it.
• Finding a mate and holding a territory.
• Mutualism: close relationships that benefit both species.
Most of these have their own lessons later in the topic.Many biotic factors are density dependent: their effect is greater when the population is larger, because food runs short and disease spreads more easily.Interspecific competition can affect distribution. If two species need the same resource, the better competitor increases and the other declines in that area. For example, the red squirrel has disappeared from much of Britain since the introduction of the grey squirrel, partly because the grey squirrel competes more effectively for food.Organisms can also change abiotic factors. Trees shade the ground and add humus to the soil, and earthworms improve soil aeration. This is important in succession, where each community alters the conditions for the next.