Decomposer Communities
In this exercise you will compare the decomposer communities at three sites. For best results, collect from sites that are sheltered and not subject to periodic flooding or desiccation. Choose two sites you believe to be similar to one another, and a third site you believe to be difference. High population density and high species diversity can usually be found in:
Collect a funnel-full of litter from your site. Set up a Berlese funnel in a location where it will not be bumped or disturbed. Excessive vibration will cause dirt to loosen, fall into the preservative, and cloud the solution. Provide a 15 - 40 Watt incandescent bulb to illuminate the leaf litter. Do not substitute a fluorescent bulb since they don't throw enough heat. Incandescent bulbs above 40 Watts will dry the litter too quickly and kill the bugs in the litter (rather than driving them down). Additional clues and information on choosing a site can be found here.
Construction of a Berlese funnel is simple (Fig 1). Place a wire screen in the funnel and fill the funnel with leaf litter. Pour about an inch of ethyl alcohol (gin or vodka will do in a pinch; do NOT use rubbing alcohol!; you can also use automotive antifreeze). Insert the funnel with litter into the collecting jar. Position a 15 - 40 Watt INCANDESCENT bulb above the funnel. Now you're set!
Figure 1. Construction of a Berlese Funnel.
The heat from the bulb dries out the litter. As the litter dries from the top down, insects and other creepy crawlies move to the bottom of the funnel. Eventually, they move through the screen and fall into the preservative. Figure on running the funnel for at least two days before collecting the insects. Repeat this exercise for each of the three sites you selected. Do NOT collect litter from the sites on the same day! The litter collections MUST be fresh, since movement of the animals into the collecting jar depends on their behavior and if the insects die, they won't move!.
Identify 10 of the more common species for each of the sites using the computer-based identification key (here) or the more extensive key found here.
Run the diversity and similarity programs on your data and interpret the results. Discuss the differences among your sites. What ecological/habitat features might explain these differences. What is the importance of the decomposer food chain in the overall stability of the ecosystem? More information on diversity in soil arthropods can be found here. An interesting consequence of global warming is here.
Perform Diversity
Calculations
Run Similarity Program