Name ______________________
Intraspecific and Interspecific Competition
Objectives
1.To assess the effect of competition among plants at different population densities on the
growth of plants
2.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, grass seeds, 9 cups per group, perlite, water)
Pre-lab Questions:
1.Define competition
2.Define biomass
3.Define interspecific and intraspecific
4.Define density (in terms of plant population)
5.Make a hypothesis to describe your prediction for the resulting biomass of:
a.the intraspecific radish and grass pots
b.the interspecific radish and grass pot.
Procedure:
Intraspecific competition–
Radish
1. Obtain 3 8 cm (3-inch) pots and fill to within 2 cm of the top with perlite. Press down gently.
2. Carefully place radish seeds on the perlite and cover with about 1 cm of additional perlite as
follows:
In pot 1, plant one seed.
In pot 2, plant ten seeds.
In pot 3, plant twenty seeds.
3. Pour water into the pot until it begins to run out the bottom.
4. Place in a warm, well-lit place.
5. Examine daily and water the plants when the surface becomes dry.
Intraspecific competition–
Grass
1. Obtain 3 8 cm (3-inch) pots and fill to within 2 cm of the top with perlite. Press down gently.
2. Carefully place grass seeds on the perlite and cover with about 1 cm of additional perlite as
follows:
In pot 1, plant one seed.
In pot 2, plant ten seeds.
In pot 3, plant twenty seeds.
3. Pour water into the pot until it begins to run out the bottom.
4. Place in a warm, well-lit place.
5. Examine daily and water the plants when the surface becomes dry.
Interspecific Competition:
Radish and Grass
1.Obtain 3 8 cm (3-inch) pots and fill to within 2 cm of the top with perlite. Press down gently.
2. Carefully place radish and grass seeds on the perlite and cover with about 1 cm of additional
perlite as follows: In pot 1, plant one seed of each.
In pot 2, plant ten seeds of each.
In pot 3, plant twenty seeds of each.
3. Pour water into the pot until it begins to run out the bottom.
4. Place in a warm, well-lit place.
5. Examine daily and water the plants when the surface becomes dry.
Intraspecific Competition Radish
Seeds per pot
Total Biomass per pot
Avg Biomass= total
biomass/# of seeds
Intraspecific Competition Grass
Seeds per pot
Total Biomass per pot
Avg Biomass= total
biomass/# of seeds
Interspecific Competition Radish and Grass
Seeds per pot
Total Biomass per pot
Avg Biomass= total
biomass/# of seeds per pot
Post-lab Questions:
***you should use your graphs and data tables to complete these questions***
1.Describe the relationship between biomass and density of radish seeds.
2.Describe the relationship between biomass and density of grass seeds.
3.Describe the relationship between biomass and density of radish and grass together.
4.If you placed 15 radish seeds in a pot, what biomass would you predict?
5.If you placed 5 grass seeds in a pot, what biomass would you predict?
6.If you placed 25 grass and 25 radish seeds in a pot, what biomass would you predict?
7.What are some limiting factors that impact the amount of biomass?
8.Propose a reason why one of the seeds grew better than the other.
9.What abiotic factors may have impacted your results?
10.Write a final conclusion about the lab. Explain whether your hypothesis was correct or not,
and include data to support your conclusion.