Biotic factors are any living factors that affect another organism or shape its environment. Some examples are:
A high abundance of food means that organisms will have less competition for resources and therefore an increased chance of survival. This means that they can reproduce successfully, which increases the population.
Predators have a large impact on an ecosystem, They keep the number of prey down to a reasonable size. In a balanced ecosystem, predators do not catch too much prey to avoid wiping them out completely.
When an organism enters an ecosystem, they normally introduce new pathogens. The population that lives in the ecosystem is unlikely to have immunity or resistance to the new pathogen. So they are more vulnerable to getting completely wiped out before they can develop immunity.
Different organisms compete for the same resources. In an environment with multiple species, one species is likely to be better adapted to the environment than others. The better-adapted species will outcompete the less-adapted species. This will decrease the numbers of the less adapted species until they have too few members to breed successfully.
One species of giraffe has a shorter neck than another species of giraffe and they both lived in the same habitat. The species of giraffe with a longer neck is more adapted to the environment. This is because they can reach into the tall trees and get leaves to eat more easily.
On the other hand, the species with shorter necks are less likely to get food. Therefore, they will slowly start to die out due to starvation and will not be able to produce offspring. Eventually, shorter-necked giraffes will get completely wiped out, whereas longer-necked giraffes will increase in number.