Citizen science and global biodiversity
Citizen science and global biodiversity

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Citizen science and global biodiversity

4 Types of biological key

Given that there is a very large number of species to choose from, how is it possible, when identifying an organism, to narrow down the choices and arrive at a correct identification? The traditional approach is to use a biological key, which uses a series of attributes – usually morphological characters – to separate one species from all the rest.

There are three main types of biological key.

Dichotomous keys consist of a series of questions, each of which has only two mutually exclusive alternative answers, for example (a) twig hairy or (b) twig not hairy. Answers to these questions then lead on to further questions until a definite identification is made. However,with just one mistake it’s possible to take a completely wrong path and arrive at an inaccurate identification.

Multi-access keys consist of characters with their individual states that can be chosen in any order. For example, the character ‘flower colour’ may have states ‘yellow’, ‘red’, ‘blue’ and ‘orange’. Multi-access keys are normally computer-based and give the species that matches all of the character states chosen. Species are dropped from consideration if their characters don’t match. A definite identification is reached when only a single species remains. Multi-access keys allow the user to input only the data that they can observe on the organism at the time. For example, if the plant isn’t in flower then the flower’s characteristics do not have to be entered. Whereas with a dichotomous key it may not be possible to achieve any identification at all without inputting the flower’s characters.

Bayesian multi-access keys (shortened to Bayesian keys) are similar to multi-access keys, but the identification is based on how many characters match. The more characters that match, the more likely the specimen is to be a particular species. This method is based on Bayesian statistics, a branch of statistics that specialises in predictions from limited prior knowledge. One advantage is that, if there are a few species of similar probability being considered, they can all be shown and easily compared.

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