3. Population density/ Natality/ Mortality/ B.Sc. I/Animal ecology

Population  density is the number of individuals per unit area, for example, number per square meter, per hectare, per unit volume or per square kilometer. Thus, Population Density = Number of People/Land Area.

For example, a population of 100 insects that live in an area of 100 square meters has a density of 1 insect per square meter. 

 For example: if there are 10,000 people in the city , and the urban area covers 10 square miles, write 10,000/10 square miles would show that the population density is 1,000 people/square mile.

The units of population density differs in different cases, such as the number of squirrels per square kilometer, The number of trees per acre and the number of diatoms per litre of water.Thus the unit of measurement for population density varies for different types of populations.

Population density is often used as a simple relative measure of how an organism responds to local conditions. 

• If conditions are not good for the species, the density will be low (individuals will have died ( Mortality) or moved out ( Emigration) of the sampled area). 
• Whereas if conditions are good the density will be high (Individuals  will have reproduced to gave birth ( Natality) and/or joined ( immigrated)  into the area).

Types of Population density: 

There are two types of the population density, the crude density and the ecological density.

1. Crude density: The crude density is the total number of individuals or biomass per unit of total area or total volume.

2. Ecological density: Ecological density is the number of individuals or the biomass per unit of that area or volume which is actually inhabited by those individuals.