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What is relative abundance?

Relative abundance basically describes how common or rare a species is relative to another species to other species in an area. Relative abundance is usually estimated within the level of a biodiversity taxon/group or trophic level because such species usually compete for resources and the abundance of one will thus directly or indirectly influence the abundance of another in an ecosystem.


What is it’s purpose?


Relative abundance data can be used for monitoring changes in a species community over time due to disturbances (such as anthropogenic influence). It is also a key component required for most  biodiversity measurement indices.


How is this data collected?

Relative abundance data is collected by noting the number of individuals observed of each species (or any category of which you want to calculate relative abundance) during a study.  


How does relative abundance data collection differ from the data collection used for simple inventories (species lists)?

When collecting data for a simple species list it just noting the species observed that are new to the study in the area the study is being carried out is enough to produce a simple inventory of a particular biodiversity group/taxon for that area. Relative abundance involves the counting and noting each individual of each species sighted during a study. Thus more effort is required but the data can be used for producing results that are much more useful for conservation.


Absolute abundance -


There are many methods (such as  distance sampling(coming soon) or plot/quadrat based samplingthat allow you to estimate densities of individuals. When the density of a species (which is the number of individuals per unit area of a species) estimated for a part of the study area is extrapolated to the entire study area it can give you an estimate for the absolute abundance of the individuals of a species in that area. Thus absolute abundance is literal abundance and is more useful to conservation than relative abundance estimates. Also absolute abundance can also be used to quantitatively compare different areas unlike relative abundance estimates which can only be used to measure minor differences or changes in the same area.



About the Author of this Article


Magurran A. Measuring Biodiversity.