Evolution and Ecology Lab (BIOL 3113)

Spring 2003

Intraspecific competition

Click here to access the pre-lab questions for this lab.


Anyone who has grown plants in a garden or raised fish in an aquarium knows that there is a limit to the number of individuals that can survive in an area. For example, you cannot raise 4,582 tomato plants in a 1-gallon flower pot. Nor can 712 guppies survive happily in a small fishbowl. The reason for this is that resources such as space, nutrients, and water are limited and this will automatically result in the process called competition. Competition occurs when organisms have an adverse effect on each other as a result of requiring the same resource.

Competition occurs between two or more organisms. When these organisms belong to the same species it is referred to as intraspecific competition. When it occurs between individuals of different species it is interspecific competition. The goal of this lab is to measure the intensity of intraspecific competition in FastPlants (Brassica rapa).


Each lab bench will be responsible for planting a group of seeds that will experience competition and another group of seeds that will serve as a control (i.e.,they will not experience competition). Each group will get 20 plastic film canisters, 10 of which will be your controls and 10 of which will be your experimentals.

As before, insert a wick into the hole in the bottom of each canister, and fill it loosely with potting soil level with the top of the canister. Before planting, soak the canister from the bottom in water until thoroughly moist.

For the controls, one seed will be planted in each well. For the competition treatment, four seeds will be planted in each well; one of these will be the target plant and the other three will be the competitors. For the control and the target seed in competition, plant the seed in the middle of the well. Mark each canister with a label. Put your group name, class time, and whether it is a control or experimental unit on the label.

It is important that you plant the seed just below the surface of the soil. Do not stick it deep into the soil otherwise the seed will not germinate.

Like those from the first lab, your plants will go into a self-watering system. During the next two labs you will observe your plants and take measurements on growth. Plants will be measured for 2 weeks. The first week you will record data on the following traits:

Maximum plant height
Number of leaves
Number of flowers

During the second week you will again collect data on the above three parameters. In addition you will measure the above-ground biomass by clipping the target plant at its base and weighing it on an analytical balance.

Once you have accumulated all your data, enter it into the web-based form on the lab computer. This data will allow you to address the question of how, exactly, intraspecific competition affects growth and development in B. rapa.

Return to the Evolution and Ecology Lab home page