Biotic factors are the living parts of an ecosystem that affect other organisms. They include:• Competition: organisms compete for resources that are in limited supply, such as food, water, light, space, nesting sites and mates. Intraspecific competition is between members of the same species; interspecific competition is between different species.
• Predation: predators kill and eat prey. Predator and prey populations affect each other and often rise and fall in linked cycles.
• Parasitism and disease: parasites and pathogens harm their hosts and can reduce population size.
• Food availability: the number of plants or prey present limits the number of consumers that can be supported.
• Mutualism: both species benefit, for example nitrogen-fixing bacteria in the root nodules of legumes.
• Grazing and trampling: herbivores can stop some plants establishing while allowing others to grow.Biotic factors often depend on population density. For example, disease spreads more easily and competition is fiercer in a dense population. This helps keep populations close to the carrying capacity of the environment.Example: in a playing field, if a new species of beetle arrives that eats the same grass seeds as an existing beetle, interspecific competition may reduce the numbers of the original species, or even exclude it from the area.Biotic factors act together with abiotic factors (covered next) to decide which species live in an ecosystem and how many of each there are.
• Predation: predators kill and eat prey. Predator and prey populations affect each other and often rise and fall in linked cycles.
• Parasitism and disease: parasites and pathogens harm their hosts and can reduce population size.
• Food availability: the number of plants or prey present limits the number of consumers that can be supported.
• Mutualism: both species benefit, for example nitrogen-fixing bacteria in the root nodules of legumes.
• Grazing and trampling: herbivores can stop some plants establishing while allowing others to grow.Biotic factors often depend on population density. For example, disease spreads more easily and competition is fiercer in a dense population. This helps keep populations close to the carrying capacity of the environment.Example: in a playing field, if a new species of beetle arrives that eats the same grass seeds as an existing beetle, interspecific competition may reduce the numbers of the original species, or even exclude it from the area.Biotic factors act together with abiotic factors (covered next) to decide which species live in an ecosystem and how many of each there are.