Measuring Biomass and Diversity in Ecosystems

Even the snakes at my house are curious! (Image credit: Brad Kremer)

Even the snakes at my house are curious! (Image credit: Brad Kremer)

Environmental scientists, national park wardens, reserve managers, and conservation officers are the people making the decisions about Tanzania’s abundant wildlife resources. Many of the choices they make about the areas and organisms they protect are based on political and/or economic considerations, but most of those decisions will have at least some foundation in scientific knowledge.

How do we know which living resources are present in a national park or reserve? How do we know the number of elephants or eland or egrets in a wildlife management area? These are some essential questions for anyone charged with sustainably managing a country’s natural resources. Luckily for all of us, science has some answers!

The Lincoln Index is a tool used to estimate populations of mobile organisms in an ecosystem. The Lincoln index answers the question, “How many?” There are 4 key steps to properly conducting a Lincoln Index survey:

  1. Capture: systematically catch organisms without harming them

    Lincoln Index formula. See the syllabus for a further explanation on its use.

    Lincoln Index formula. See the syllabus for a further explanation on its use.

  2. Mark: mark the organisms in a way that does not harm them
  3. Release: let them return to their natural habitat
  4. Recapture: catch another

These 4 steps will provide some key data points, which can be plugged into a mathematical formula, shown at right, which estimates the total size of the population in the area sampled.

Another highly useful tool for measuring biotic components of ecosystems is the Simpson Index, or the Simpson Reciprocal Index. The Simpson Index measures the diversity of an ecosystem. Simpson accounts for both aspects of diversity, as defined in our ESS syllabus: species richness (the total number of species present) and species evenness (the number of individuals of each species present). The process for calculating Simpson’s D-value is a little more complicated than that for calculating Lincoln, but not much. Please check the ESS syllabus for details.

Simpson's Diversity Index. See the syllabus for further details on its use.

Simpson’s Diversity Index. See the syllabus for further details on its use.

We’ll be simulating 3 different ecosystems in class over the next couple of days, so you should have plenty of opportunity to test out these formulae and manipulate some of the variables within them. Both of these procedures will help you tremendously on the ESP week of field work in Zanzibar. (Hint, Hint)

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