There are three main categories of abundance information that you can collect about animals:

1. Population
2. Community, and
3. Frequency of Occurrence (of a species across your landscape)

1. Population

Here the objective is to estimate the number of individuals of a species in a defined area so that you can make statements about some or all of the following bits of information:

• Changes in population size
• Rates of reproduction, survival, immigration, and emigration.

Your choice of which parameters to measure for a species will be driven by the types of questions you want to answer, the level of resources at your disposal, the types of techniques available, and the degree of bias and variability of those techniques.

2. Community

Here the objective is not to estimate the number of individuals of a species within a defined area, but to estimate the number of species in that area so that you can estimate some or all of the following bits of information about communities:

• Rates of change in species numbers
• Species turnover
• Probabilities of extinction
• Degrees of immigration and emigration.

3. Frequency of Occurrence

Here the objective is not to estimate the abundance of a species or number of species, but to estimate the number of places where the species occurs (presence/abscence over both space and time) so that you can estimate some or all of the following bits of information about the percentage of places or patches a species might occur:

• Rates of change in the percentage of areas occupied
• Probabilities of extinction and immigration within the measured patches.

On to where to place your samples.