Why estimate density?

Density is a “state variable”

Density = Number of individuals per unit area

Density is calculated as the population size in a given region, divided by the area of that region. For example, 90 individuals in 20km² gives a density of 4.5 per km²

Density is a state variable

State variable = A numerical value that indicates the status of a wildlife population, which we can use to evaluate how well it’s doing

Other state variables include:

• Proportion of area occupied (occupancy)
• Rate of population increase/decline
• Proportion of breeding individuals in a population

Density in conservation

We can use population density or size to determine how ‘at risk’ a population is

Monitoring density helps us know whether human activities are having a deleterious effect on a species, and whether our conservation efforts are effective in helping the population to recover

Understanding the density of a species is useful for many conservation questions:

• Where is a species common or rare?
• Is population size is increasing or declining?
• Does a species prefer a particular land-use/land-cover type?
• Does a species exist at higher densities in the presence or absence of other species?
• What ecological or human factors influence density? Climate change, predation, disease etc
• The influence of conservation management decisions on all these

Distance sampling in conservation

Distance sampling is a method to:

1. Determine the density of a species at a particular point in time
2. Assess the rate of change in density
3. Investigate what influences density

Distance sampling can help us answer conservation questions related to density and population size