Effects of Intraspecific and Interspecific Competition in Plants.

Michael Graf

Undergraduate in Fisheries Science

Biology Dept., Tennessee Technological University

Cookeville, Tennessee

February 20, 2006

TABLE OF CONTENTS:

PROJECT SUMMARY:

KEY WORDS:

Intraspecific

Interspecific

Competition

Marigolds

Tagetes Sp.

Alyssum

Lobulari maritima

Plant

Densities

Growth rate

INTRODUCTION:

Competition in the natural world is a very common form of interaction. As with most living organisms, plants must be able exhibit a competitive behavior in order to survive. Plants react differently under certain conditions, which could be positive of stressful. It is to the plants benefit to be able to compensate or take advantage of these conditions. This competitive behavior can have a number of different forms and characteristics. One specific type of competition is Intraspecific, which is how members of the same species compete with one another. When dealing with plants, this may include competition for factors such as sunlight, water, nutrients, waste disposal, or rooting. The overall growth of the plant depends on how well they adapt to their surrounding conditions. The biomass of populations may evolve locally in response to plant density or other population characteristics (Agele 1999). By conducting studies on six populations of Impatiens textor, Agele showed that both plant size and the other population-level factors affected biomass variation. Another study on intraspecific competition resulted in mass flowering of Polymnia canadensis (Bender 2002). Bender concluded that the mass flowering of the older, more dominant plants played a role in population cycling. There are many ways in which intraspecific competition can alter plant behavior.

Another way plant behavior can be altered is by interspecific competition. Interspecific competition is how two of more different species react with one another. There are even more factors involved than intraspecific. Interspecific competition in natural plant communities is highly dependent on nutrient availability (Aerts 1999).

In our experiments, we will test for both intraspecific and interspecific competition. To test for intraspecific, we will grow separate densities of the same plant, to see whether or not the density effects the growth. The plants that are chosen for this are Marigolds (Tagetes sp). The neighborhood effect (density) on the growth of individual plants is apparent in some species through some measure of size (plant height of plant weight) and also in some models, but negligible in others (Hara 1994). The null hypothesis for this experiment is that the growth and weight of the plants will not be affected by density.

We will use Marigolds and Alyssum to study the effects of interspecific competition. We will use several different combinations of densities, which will be discussed in the methods. Our null hypothesis for this experiment is that the growth and weight of the plants will not be affected by density

METHODS AND MATERIALS

Experiment 1: Intraspecific competition

To prepare for the intraspecific competition experiment, we obtained six flower pots, potting soil, and a bag of Marigold seeds. We planted six different densities in each of the pots. The densities planted were 3, 5, 10, 18, 34, and 68 seeds per pot. Each seed was planted roughly ½ inch below the surface and they were evenly spaced throughout the pot. We then watered the seeds evenly and placed then onto a flat. The flat was taken by the lab instructor to the TTU greenhouse until the following weeks lab. The next week, after we received our flat, we randomly thinned our original densities down to 2, 4, 8, 16, 32, and 64 seedlings per pot. We intentionally over planted the week before just incase some of the seeds would not germinate. Of the remaining plants, we then took measurements of the stem lengths. After recording the date, we watered the plants and placed them back on the flats. This process of data collection was continued for the remainder of the six week period. For the final collection, there were several additional steps involved. After our usual data collection, we then pulled the plants and cut their roots off. We then weighed the total weight of all the plants for each density. Next, we separated the stems from the leaves and weighed just the leaves by themselves. By subtracting the leaves weight from the total, we are able to compare the mass of the leaves vs. the mass of the stems. In order to get the average plant weight for each density, we simply divided the total weight by the number of plants that survived. We also calculated the averages for the stems and leaves in the same way. We then gave a copy of our results for the instructor, who then calculated the averages for the entire class and posted the results. This allows us to compare our results to the entire class. The results will be concerned with are:

1)growth rate

2)survivorship

3)average plant weight

4)total plant weight

5)stem length

6)average stem weight

7)average leaf weight.

We made scatter plots of plant density vs. each of these variables. T-tests were also conducted to compare: (1) 4 plants to 32, (2) 4 plants to 64, and (3) 32 plants to 64. We did this for both mean plant weight and mean growth rate.

Experiment 2: Interspecific competition

For the interspecific competition experiment, we obtained 4 flower pots, potting soil, and a bag of Marigold seeds and a bag of Alyssum seeds. We planted 4 different combinations of seeds: (1) 4 Marigold and 4 Alyssum, (2) 4 Marigold and 24 Alyssum, (3) 24 Marigold and 4 Alyssum, (4) 24 Marigold and 24 Alyssum. The same procedures for planting, watering, measuring, data collection and time apply to this experiment the same as in the first. In order to analyze the data, bar graphs were drawn to compare the average plant weight, total plant weight, average plant height, and survivorship for both species. We also made a De Witt replacement plot for both species. T-tests were used to compare (1) mean plant weights and (2) mean growth rates. For marigolds, we did this for groups (A) 4M:4A to 4M:24A, and (B) 24M:4A to 24M:24A. For Alyssum, we did this for groups (C) 4M:4A to 24M:4A, and (D) 4M:24A to 24M:24A.

EXPECTED RESULTS AND BENEFITS

PERSONELL

ETHICS

PROJECT TIMELINE

LITERATURE CITED

BUDGET