Competition Lab
Intraspecific and Interspecific Competition
Objectives:
- To assess the effect of competition among plants at different population densities on the growth of plants
- To assess the relative competitiveness of two species of plants when they are planted together
Background:
Competition is an interaction between organisms in which both are harmed by the interaction. Competition can occur among members of the same species and is called intraspecific competition or it can occur between members of different species, in which case is called interspecific competition. Competition of animals can involve: fights over food, water, nesting sites or mates; or may involve less overt forms of conflict such as greater height allowing some animals access to food that others cannot reach. Competition is usually difficult to visualize among plants. However, certain resources, such as water, soil nutrients, and sunlight are in limited supply. Plants that have special abilities to capture these resources should be more successful in competition.
In this exercise, we will examine the impact of seed growth at different densities and in competition with another type of plant.
Materials (radish seeds, wheat seeds, 3 cups per group, sand, water)
Pre-lab Questions:
- Define competition
- Define biomass
- Define interspecific and intraspecific
- Define density (in terms of plant population)
- Make a hypothesis to describe your prediction for the resulting biomass of:
- the intraspecific radish and wheat pots
- the interspecific radish and wheat pot.
Post-lab Questions: ***you should use your graphs and data tables to complete these questions***
- Describe the relationship between biomass and density of radish seeds.
- Describe the relationship between biomass and density of wheat seeds.
- Describe the relationship between biomass and density of radish and wheat together.
- If you placed 15 radish seeds in a pot, what biomass would you predict?
- If you placed 5 wheat seeds in a pot, what biomass would you predict?
- If you placed 25 wheat and 25 radish seats in a pot, what biomass would you predict?
- What are some limiting factors that impact the amount of biomass?
- Propose a reason why one of the seeds grew better than the other.
- What abiotic factors may have impacted your results?
- Write a final conclusion about the lab. Explain whether your hypothesis was correct or not, and include data to support your conclusion.
Procedure
There will be a total of 6 groups: 2 groups will study intraspecific competition among radish seeds, 2 groups will study intraspecific competition among wheat seeds, and 2 groups will study interspecific competition among both radish and wheat seeds. The teacher will assign your group to one of the 3 areas.
***Use the procedure below that correlates with the area of study that your group is conducting.***
11.1 Intraspecific competition – Radish
1. Obtain radish seeds that have been soaked so that they are beginning to sprout.
2. Obtain three 8 cm (3-inch) pots and fill to within 2 cm of the top with sand. Press down gently.
3. Carefully place sprouting radish seeds on the sand and cover with about 1 cm of additional sand as follows:
In pot 1, plant one seed.
In pot 2, plant ten seeds.
In pot 3, plant twenty seeds.
4. Pour water into the pot until it begins to run out the bottom.
5. Place in a warm, well-lit place.
6. Examine daily and water the plants when the surface becomes dry.
7. After three weeks, remove the plants from each pot, including roots.
8. Weigh the total biomass produced from each pot, determine the average biomass per plant, and record on the data sheet.
11.2 Intraspecific Competition – Wheat
1. Obtain wheat seeds that have been soaked so that they are beginning to sprout.
2. Obtain three 8 cm (3-inch) pots and fill to within 2 cm of the top with sand. Press down gently.
3. Carefully place sprouting wheat seeds on the sand and cover with about 1 cm of additional sand as follows:
In pot 1, plant one seed.
In pot 2, plant ten seeds.
In pot 3, plant twenty seeds.
4. Pour water into the pot until it begins to run out the bottom.
5. Place in a warm, well-lit place.
6. Examine daily and water the plants when the surface becomes dry.
7. After three weeks, remove the plants from each pot, including roots.
8. Weigh the total biomass produced from each pot, determine the average biomass per plant, and record on the data sheet.
11.3 Interspecific Competition – Radish and Wheat
1. Obtain radish and wheat seeds that have been soaked so that they are beginning to sprout.
2. Obtain three 8 cm (3-inch) pots and fill to within 2 cm of the top with sand. Press down gently.
3. Carefully place sprouting seeds on the sand and cover with about 1 cm of additional sand as follows:
In pot 1, plant one radish seed and one wheat seed.
In pot 2, plant ten radish seeds and ten wheat seeds.
In pot 3, plant twenty radish seeds and twenty wheat seeds.
4. Pour water into the pot until it begins to run out the bottom.
5. Place in a warm, well-lit place.
6. Examine daily and water the plants when the surface becomes dry.
7. After three weeks, remove the plants from each pot, including roots.
8. Separately weigh the total biomass of radish and wheat plants produced from each pot, determine the average biomass per plant for both the radish and wheat plants, and record on the data sheet.
Exercise 11.1 Radish: Intraspecific Competition
Seeds per pot / Total biomass per pot (grams) / Average biomass = Total biomass .Number of seeds per pot
1
10
20
**Graph your results below.
Exercise 11.2 Wheat: Intraspecific Competition
Seeds per pot / Total biomass per pot (grams) / Average biomass = Total biomass .Number of seeds per pot
1
10
20
**Graph your results below.
Exercise 11.3 Interspecific Competition (Radish and Wheat)
Seeds per pot / Total biomass per pot (grams) / Average biomass = Total biomass .Number of seeds per pot
1 radish
1 wheat
10 radish
10 wheat
20 radish
20 wheat