Environmental Variables

BS 105 - Environmental Biology

ENVIRONMENTAL VARIABLES

LAB EXERCISE

During this lab we will manipulate a few environmental variables and monitor their effects on a specific animal, the pill bug (genus Armadillidium). These are terrestrial isopods, members of the Phylum Arthropoda, Class Crustacea, which includes other hard-shelled critters such as lobsters, shrimp, and crabs. In essence we will be examining the behavior of the pill bugs in response to external stimuli. Students in each lab section will be divided into several groups, and each group will monitor the behavior of the pill bugs when exposed to a given environmental variable. These variables will include moisture, light, pH, and food availability.

Procedure:

Obtain one experimental choice chamber and one data sheet per group. Be sure to also pick up a soft brush to gently move the pill bugs when necessary. Clearly label the data sheet regarding your treatment condition and the condition of both sides of the chamber.

Obtain two groups of 5 pill bugs each (available in small culture dishes at the front of the room)

Depending on the environmental variable assigned to your specific group, you may also need to obtain one or more of the following items:

a small quantity of fish food flakes
a bottle of distilled water
absorbent paper
mesh screens
bottle of hydrochloric acid + bottle of potassium hydroxide
plastic transfer pipettes

Follow the appropriate procedure below for your specific environmental variable:

Food:

Place a few fish food flakes on one side of the chamber. Do not place any flakes on the other side.

Place 5 pill bugs in each side of the chamber, cover each side with the lid, and record their numbers every minute for 20 minutes in the data table provided.

Moisture:

Place approximately 20 drops of distilled water on the absorbent paper on one side of the choice chamber until it is evenly moist (NOT soaking wet). Leave the other side of the choice chamber dry.

Place 5 pill bugs in each side of the chamber, cover each side with the lid, and record their numbers every minute for 20 minutes in the data table provided.

Light:

Obtain three mesh screens

Place 5 pill bugs in each side of the chamber and cover each side with the lid.

Cover one side of the choice chamber with the mesh screens to limit the amount of light reaching the pill bugs in that side.

Record the number of pill bugs in each chamber every minute for 20 minutes in the data table provided.

Place 15 drops of hydrochloric acid solution on the absorbent paper on one side of the choice chamber until it is evenly moist (NOT soaking wet).

Place 15 drops of potassium hydroxide solution on absorbent paper on the other side of the choice chamber until evenly moist (again, NOT soaking wet).

Place 5 pill bugs in each side of the chamber, cover each side with the lid, and record their numbers every minute for 20 minutes in the data table provided.

Turn in one data table for your group to the instructor before you leave. Clearly print your section number and the names of the group members on the bottom of that page.