Population sizes are limited by factors that have a greater effect as the population increases in size. These density-dependent limiting factors are usually biotic and include

The density-dependent limiting factors that are usually biotic and include

--> migration of organisms to other habitats

--> invasion and colonization by new species and

--> increase or decrease in birth rates and death rates.

Explanation:

Population density in an ecosystem is defined as the average number of individuals of a species per unit area of the habitat. It can be used to estimate the total number of individuals of a population, that is population size, in a habitat in the following way:

Density × Area of habitat = Population size

For any population, there is an optimum density that can be reached in a given habitat under the operating environmental conditions. Population in a habitat often show changes especially in SIZE and distribution. These are due to biotic limiting factor such as:

--> migration of organisms to other habitats

--> invasion and colonization by new species and

--> increase or decrease in birth rates and death rates.

These factors are known to operate during:

--> seasonal climatic changes

--> changes in food availablity

--> breeding periods and

--> unfavourable natural events such as fires and droughts.