Sonoran Desert Knowledge Exchange (SDKE)

Learning About Sonoran Desert Biodiversity

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Designing a study

Before we start sampling the arthropods in our schoolyards, we need to think carefully about the purpose of our study. Using the data we collect we would like to be able to compare:

1. the diversity of the different schoolyards across Tucson
2. the diversity of the different microhabitats within individual schoolyards

We will use pitfall traps, which are are simply open containers set into the ground in such a way that unsuspecting arthropods walking along the soil surface fall into the container. These traps are widely used by scientists to monitor insect diversity and to investigate effects of different land uses. Refer back to your field notebooks to make a list of the different microhabitats you encountered in your schoolyard. If we want to capture the total diversity of ground dwelling arthropod in the schoolyard we need to sample from each microhabitat. Although you might have recorded many microhabitats, you might only be able to sample some of them. After you have selected the microhabitats you will sample, it’s time to set your traps. The first decisions you have to make are how many traps and how to arrange the traps. Since we are hoping that you will compare your data to data from other schools, it will be important that we all follow a similar protocol. We suggest that you use five pitfall traps in each microhabitat and that you space your traps five meters apart along a line that runs through the center of the microhabitat. This would result in a line 20 meters long.

Although this seems like a reasonable distance you might have smaller microhabitats in which a 20 meter long line will not fit. For example, suppose you only have one tree in your schoolyard, and the rest of the area is open and sunny. You’ve decided that the tree constitutes one microhabitat and the rest of the schoolyard another microhabitat, but there isn’t enough room under the tree canopy to set a 20 meter long line of pitfall traps. In this case you will have to decide on your own protocol. It is extremely important that you record your protocol in your field notebook because if we don’t know how the data were collected, the data become rather useless.

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