Additional Laboratory Notes for BIO 2020

© 20 April 2004, Mary Jean Holland

Intraspecific Competition I

Each group: Obtain 12 pots. Using tape and wax pencils label the pots 1A, 1B, 2A, 2B, 4A, 4B, 8A, 8B, 16A, 16B, 32A, 32B. Fill each pot with vermiculite provided. Plant bean seeds in the each pot as indicated by the numbers on the pot. For example, pot marked 2B gets 2 seeds; pot marked 32A gets 32 seeds. Place pots in a tray and water them until thoroughly moistened. We will examine these pots in about two weeks.

Intraspecific Competition II

Today you will be examining plants produced from bean seeds you sowed about two or three weeks ago. You will be investigating the effect of competition for limited resources among organisms of the same species, specifically the effects of intraspecific competition on bean seed germination rates, shoot growth and leaf formation and biomass per plant.

Record Data and Make Calculations: Spread some paper on the bench top. Examine the plants in each pot, one pot at a time. Count the number of plants. For each plant, measure the height (shoot length) and count the number of leaves. Calculate the median height for the plants in the pot and median number of leaves per plant. Carefully shake the contents of the pot onto the paper. Examine the germinated seeds. If any seeds fail to germinate, calculate the percent of germination for that pot. (If all sown seeds germinate, the percent of germination is 100.) For each pot, weigh all of the plants (together as a group). This weight is the total biomass per pot. Also calculate the mean biomass per plant. Record your data in the table provided. Average the duplicates to obtain values for graphing.

Graph the Results: Make a bar graph sowing the effect of seed density (# of seeds per pot) on four of the variables observed (percent germination, median shoot length, median leaf number per plant, mean biomass).


1. You did this experiment in duplicate. Do the two data sets basically agree?

2. What are the sources of variation that might make the data in the two sets different?

3. Look at the graphs. At what seed density does the intraspecific competition begin having an adverse impact on growth?

4. Do you think population densities that are too low might also have an adverse effect on growth? Why or why not?

Pot # Number Seeds Sown Number Germ. Seeds Percent Germ. Seeds Median Shoot Height Median Number Leaves Total Biomass in Pot Mean Biomass per Plant
Mean 1A-B              
Mean 2A-B              
Mean 4A-B              
Mean 8A-B              
Mean 16A-B              
Mean 32A-B              

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Last updated 20 April 2004 (MJCH/JHW)