Discuss the factors which influence the size of populations in an ecosystem.

• Natality or birth rate; this is the rate at which new members are added to a population by reproduction. In any community, the birth of a young one increases the population size.
• Mortality or death rate; the rate are which individuals die out. It reduces population size.
• Immigration rate; the rate at which individuals move into a population from outside increase population size.
• Emigration rate; the rate at which individuals move out of a population reduces population size.
• Environmental factors changes in environmental factors affect population size. These can be biotic or abiotic.

Abiotic factors that affect population size include;

• Weather; this includes daily duration of sun light and its intensity, rainfall, humidity and temperature. Most organisms adapt to live in specific weather conditions. Their population increases when conditions are favorable and reduces when conditions become unfavorable.
• Natural calamities such as drought, famine, flood, fire or earthquakes cause large scale deaths or emigrations of population leading to massive population reduction.
• Food and space are the major limiting factors for animal populations. When food, water and space are in plenty, a population increases in size, otherwise it will reduce biotic factors control population size through producer-consumer relationships and pathogens.
• Availability of shelter

Biotic factors

• Psychological factors: these take the form of overcrowding and stress which lead to abnormal behaviours such as cannibalism
• Desease
• Intraspecific competition
• Accumulation of metabolic wastes
• Parasitism
• Commensalism
• mutualism
• Predator-prey relationships. Availability of predator reduces the population of prey while reduction of prey reduces predator population and vice versa.
• Interspecific versus intraspecific competition. Increase in population in a given area increases competition for resources among organisms in that area. The more similar the organisms are species, the fiercer is the competition. This reduces the population of the out competed organism.