PDS APES 8th Period 2009-10

This is for those that missed our most excellent field trip Monday and for those that want a good review.  I made this 6.5 minute video podcast a few years ago, but it still hits all the highlights:

On Friday, September 25, we set off to Davidson to learn about Experimental Design outside of the lab.

First, Dr. Stanback, an Avian Behavior Scientist explained several of his experiments. In particular, he studies the survival and preferences of different species of birds. This type of experiment is directly applicable to real world populations. For example, he wondered who is dominant between birds and wasps. So, he set up an experiment outside and concluded that birds are dominant over wasps, so there is no need to worry extra about one’s birds when wasps are present. “Wonder is the key” to experimental design.

Next, we heard from Evan A. Eskew, a biology major who is passionate about the effects of Urbanization/ Habitat Fragmentation on turtles. To track turtles, he set up traps in five different ponds and marked the turtles he caught. Eskew replaced the turtles in the pond and observed them again later. Then he could compare survivorship using a computer program which accounts for different variables. While has not reached any conclusive evidence that habitat effects survivorship, the experiment is continuing; it’s a long process.

Then, with Mr. Willard, we gathered leaf litter samples for our lab. In order to gain random samples from each of the two forests, we used a transect and a random number table. This means that we extended a measuring tape 100 meters into the pine forest–the transect–and using the random number table, we picked the distance out from the measuring tape we would go. At this random location, we would place the square quadrat on the ground. From within the bounds of the quadrat, we  gathered the O layer of soil–the leaf litter–into separate plastic bags. The quadrat is an effective means to gather a controlled quantity of material outside of the lab. We continued to use the random number table to find several more locations and gather a random sample of each forest’s leaf litter; we repeated the process starting with the trisect in the oak forest.

Gathering Leaf Litter by Quadrat

Dr. Grant, a spider expert and retired Biology professor at Davidson, took us into an open field with tall grasses. He used a sweep net to sweep around the grasses and collect spiders and other organisms. He dumped the contents of the net onto a sheet where we could observe the critters. Sweepnets are a fairly random way to collect data, but they do not allow for controlled measurement.

Sweep Net Sampling in a Field

Later, we went with Peggy, a herpetology major into the woods. She showed us coverboards that collect smaller critters underneath them. Essentially, a coverboard is a piece of plywood that acts like a doormat and collects insects underneath it. Note: coverboards do not provide a sample of everything present in an ecosystem, only what will fit under the coverboard and what chooses to go under it.

Checking a Coverboard

Also, we observed drift fences which are plastic fences with a shoebox size trap–a box trap–in the middle.  Animals crawl around and eventually get stuck in a funnel leading to the box. Note: the box traps must be checked everyday, and they tend to attract reptiles and amphibians. It does not fairly represent the diversity of the entire community.

A summary of our discussion of lab experiments vs. field experiments:

This 18-minute video was made by me a few years ago. While it is a bit grainy, it covers the major field research techniques I try to show students at Davidson each year. It’s mandatory viewing if you did not go, and a good review if you did:

*Note: The Internet filter at school will not let you view YouTube videos, so you have to watch it at home.