Oct 05 2010
Davidson Ecological Preserve
On Friday October 1st, the Environmental Science classes took the day off from school and traveled down to Davidson College for a hands on experience in creating controlled experiments and data gathering in the field. We started off with a presentation on Bernese pythons and how they are ravaging the southern parts of Florida. Although we do not know the source of the problem, we do know that these foreign species of giant snakes (adults can get more than 9 feet long) are procreating very readily and consuming native wildlife with seemingly no natural predators in the area, possibly toppling over an otherwise delicately balanced ecosystem. Although the topic of the presentation was interesting, the main points that we left with (or should have left with) were, field research makes a huge difference in understanding the ecological systems around us, and designing controlled experiments, regardless of the seemingly uncontrollable nature of nature, is completely possible.
From there, we went into the ecological preserve to look into methods for sampling nature. The first that we looked at was a technique called drift fencing. This approach primarily targets small creatures, but has been adapted for slightly larger animals with varying degrees of success. The underlying idea behind this approach is as follows: An animal encounters a large fence, large enough such that it cannot burrow under nor fly over it. In order to get past the obstacle, it must traverse the perimeter of the fence, which while doing so, may fall into a 5 gallon bucket ‘trap’ or larger animals might get stuck in boxes with one way doors. Using this method, we can get an idea of what creatures inhabit the immediate surroundings.
Another method was much simpler: Coverboards were placed in open areas, providing shade to cold blooded animals to help regulate their metabolism. By lifting these coverboards during sunny times, we might be able to observe and document critters who might be taking refuge underneath and, again, get an idea of what animals are around us.
Finally, we tried our hands at acquiring a representative sample of an ecosystem for controlled experiments. Our lab required samples from both pine and oak forests, but acquiring these samples raises two questions: where do we get our samples from, and how much do we get? The inherent laziness of people might cause us to only sample the outer edge of the forest; what lives there might not be the same as what lives slightly deeper. also, we had no method of regulating the sizes of each sample collected. To solve this, we have a device called a quadrat, and transect. A quadrat is merely a rigid square that is placed on the floor of the area in study such that we can analyze what is inside it. It sets boundaries and keeps our sample size constant. A transect is a method to randomly sample parts of the area in question such that we get a representative sample. there are two measuring tapes; one going down the middle of the area, and another placed perpendicular to the first, essentially creating a coordinate-grid system. using a random two digit number generator, or a phone book, we can randomly pick ‘coordinates’ and sample them. the first digit tells us how far down the first tape measure to go, and the second digit indicates how far left or right we move from the first tape measure. We alternate sides (left/right) each sample. For example, if the number was 45, we would travel out 4 meteres and then to the right 5 meteres, place our quadrat at that location and sample whatever was contained within.
The small white frame is a quadrat. We sample only what is contained within its boundaries and take it back to the lab
Drift Fencing is merely a fence that critters must travel around the perimeter to get across, hopefully falling in a trap such that we can count them
Finally, we also looked into how to sample rapidly moving insects that might be on long stemmed plants. Using a large net called a sweep net, we can ‘sweep’ the tops of the stems and catch whatever might be living on them at the moment. By controlling the number of ‘sweeps’ done by the net and sweep area, we can keep the sample size constant and acquire a representative sample size.
