written by Jason Karl
Abundance – Qualitative
Estimated population count, population estimate
Description and Uses
This technique involves making rapid assessments of the number of individuals in a population at a site by visual estimate. A quick, gross indicator of the size of a population, this technique can sometimes be used for coarse assessments of population trends over time if the change is large. Often, population size can be estimated while collecting presence/absence data. The establishment of protocols and size classes can help remove some of the subjectivity of this method and increase repeatability. Size and visibility of the plants being counted need to be considered as this method breaks down if many individuals are not detected.
Advantages and Limitations
The main advantage of this method is that it is a quick way to collect information on population abundance. The disadvantages to this method are:
- it is highly subjective and repeatability is low
- there can be a large amount of variation between observers
- cryptic species or those difficult to see due to surrounding vegetation can cause significant underestimation.
Measuring and Monitoring Plant Populations (Elzinga et al. 2001) http://www.blm.gov/nstc/library/pdf/MeasAndMon.pdf.
Technical and Application References
- Muir, P. S. and R. K. Moseley. 1994. Responses of Primula alcalina, a threatened species of alkaline seeps, to site and grazing. Natural Areas Journal 14: 269-279.
Quantitative estimates of population size can be obtained using frequency or density methods like
nested frequency, or