How is species diversity measured?
Species diversity is measured by determining the number of species present in a given area or community and calculating how evenly distributed each species is.
Species diversity is measured by determining the number of species present in a given area or community and calculating how evenly distributed a species is within that community. Indices of species diversity are used which may give more or less weight species that are dominantly found in the landscape. The Simpson's Index and the Shannon's Index are two examples of diversity indices.
There are multiple ways the number and evens can be measured in the field depending on the ecosystem in question, the resources (money, technology available, time, the amount of people available to collect data, etc) of the scientist, and the context in which species diversity is being measured.
Surveys done by scientists, camera traps, environmental DNA, and light traps are all examples of methods used to measure species diversity.
Biologists can traverse a landscape repeatedly, at different times of the day, at different times of the year, in different weather conditions, and so forth and record species presence over time to assemble a rough idea of species diversity. This is often done when one is interested only in a specific type of organism, such as mammals.
Camera traps may be used to determine the number of carnivores present at a site. Camera are placed throughout the study site and take a photo whenever triggered by movement. These images are then sorted and categorized to determine the number of carnivore species present at a site. Data is typically collected over an extended period of time and the camera traps may be moved to new locations to obtain more data.
Scientists setting up a camera trap:
A newer technique is to use environmental DNA, or DNA that can be collected indirectly from the animal through skin the animal has shed, DNA left in the soil, feces, or the water even. DNA collected is then compared to a database of known species to determine what species is present in the landscape. Environmental DNA can be collected to determine the number of fish species in a river. Read about a recent example here.
Another example of a method that may be appropriate depending on the study question is to use light traps to sample insect diversity. This is done by holding up a light to attract insects and then containing the insects in a net or some other sort of trap. Again, this type of sampling may be done repeatedly at different times of the year to determine an accurate estimate.
Scientist using a light trap: