The effects of Intraspecific The effects of Intraspecific competition in competition in Trifolium repens Trifolium repens

L.L.

Brian RobertsBrian RobertsStudentStudent

Education DepartmentEducation DepartmentTennessee Tech UniversityTennessee Tech University

Cookeville, Tennessee 38505Cookeville, Tennessee 38505

Introduction Introduction

Do plants compete for resources? Do plants compete for resources?

Does this competition affect growth or survival?Does this competition affect growth or survival?

It is important to understand how organisms interact with each It is important to understand how organisms interact with each other. other.

Organisms interact in a variety of ways, some of which may be Organisms interact in a variety of ways, some of which may be harmful. One of these interactions is called competition, in which harmful. One of these interactions is called competition, in which individuals compete for resources such as food, nutrients, water, individuals compete for resources such as food, nutrients, water, light, and so on. light, and so on.

Intraspecific competition is when individuals compete only with Intraspecific competition is when individuals compete only with members of the same species. Intraspecific competition is defined members of the same species. Intraspecific competition is defined as the relative reduction of germling growth and survival in high-as the relative reduction of germling growth and survival in high-density cultures compared with low-density cultures (Steen 2003). density cultures compared with low-density cultures (Steen 2003).

IntroductionIntroduction

Because plants are sessile after they germinate, local Because plants are sessile after they germinate, local conditions around individual plants, including the conditions around individual plants, including the densities and sizes of neighboring plants, have a crucial densities and sizes of neighboring plants, have a crucial influence on growth and survival (Suzuki et al. 2003). influence on growth and survival (Suzuki et al. 2003).

Three general effects of intraspecific competition have Three general effects of intraspecific competition have been identified for plants growing in dense stands (Yoda been identified for plants growing in dense stands (Yoda et al. 1963). Stands with higher densities generally have et al. 1963). Stands with higher densities generally have reduced sizes, reduced survival probabilities, and reduced sizes, reduced survival probabilities, and changes in size-distribution. changes in size-distribution.

The experiment was done to determine the effects of The experiment was done to determine the effects of intraspecific competition in intraspecific competition in Trifolium repens L.Trifolium repens L. (white (white clover) on survival and growth. clover) on survival and growth.

Introduction Introduction

Intraspecific competition was tested by planting clover in Intraspecific competition was tested by planting clover in different densities and then measuring variables (growth different densities and then measuring variables (growth rate, survival, average plant mass, ect...) over a five rate, survival, average plant mass, ect...) over a five week span. week span.

I expected that the plants grown in larger densities would I expected that the plants grown in larger densities would display a lower survival rate and would exhibit growth display a lower survival rate and would exhibit growth differences. differences.

The experiment was expected to disprove the null The experiment was expected to disprove the null hypothesis, which states the clovers’ growth and survival hypothesis, which states the clovers’ growth and survival will not be affected by intraspecific competition. will not be affected by intraspecific competition.

Objective/HypothesisObjective/Hypothesis StatementStatement

Objective StatementObjective Statement To determine the effects of intraspecific To determine the effects of intraspecific

competition in competition in Trifolium repens L.Trifolium repens L. on on survival and growth.survival and growth.

Null HypothesisNull Hypothesis Intraspecific competition will not have an Intraspecific competition will not have an

effect on the survival or growth of effect on the survival or growth of Trifolium Trifolium repens L.repens L.

Methods and MaterialsMethods and Materials

The methods and statistical approach used in this The methods and statistical approach used in this experiment were taken from a lab manual (Brown 2004). experiment were taken from a lab manual (Brown 2004). The only variation to the original experiment is the The only variation to the original experiment is the deletion of some of the variables measured.deletion of some of the variables measured.

We took pots and filled each with soil up to within 1 cm We took pots and filled each with soil up to within 1 cm of the top of the pot. of the top of the pot.

Then, we planted different density sets of clover in each Then, we planted different density sets of clover in each of the pots. The densities were: 3, 5, 10, 18, 34, and 68 of the pots. The densities were: 3, 5, 10, 18, 34, and 68 seeds in their respective pots. seeds in their respective pots.

We thinned the pots to 2, 4, 8, 16, 32, or 64 plants after We thinned the pots to 2, 4, 8, 16, 32, or 64 plants after

germination.germination.

Methods and MaterialsMethods and Materials

Over a 5 week period, we provided water and sunlight Over a 5 week period, we provided water and sunlight for the plants and made the following measurements: for the plants and made the following measurements: growth rates, survivorship, average plant mass, and growth rates, survivorship, average plant mass, and stem mass per plant.stem mass per plant.

Data Analysis:Data Analysis:

We used We used tt-tests to compare mean plant weight, mean -tests to compare mean plant weight, mean stem weight, and mean growth rate for the different stem weight, and mean growth rate for the different densities. densities.

ResultsResults

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DiscussionDiscussion

In chart 2 the mean plant weight shows a slight In chart 2 the mean plant weight shows a slight decrease as density increases. decrease as density increases.

This may be an effect of intraspecific competition This may be an effect of intraspecific competition although the t-test results show there is not although the t-test results show there is not enough significant evidence to reject the null enough significant evidence to reject the null hypothesis involving mean plant weight for any hypothesis involving mean plant weight for any of the densities. of the densities.

ResultsResults

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Chart 3 illustrates the result of intraspecific Chart 3 illustrates the result of intraspecific competition on mean stem weight is a competition on mean stem weight is a decrease in mean stem weight as density decrease in mean stem weight as density increases. increases.

Again, the t-tests show there is not enough Again, the t-tests show there is not enough evidence to reject the null hypothesis in all evidence to reject the null hypothesis in all of the densities of the densities

ResultsResults

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DiscussionDiscussion

Chart 6 compares mean growth rate with Chart 6 compares mean growth rate with density. density.

Again, we see a slight decrease in the variable Again, we see a slight decrease in the variable (mean growth rate) as density increases. (mean growth rate) as density increases.

But again, the t-test results are nonsignificant But again, the t-test results are nonsignificant and fail to reject the null hypothesis in all of the and fail to reject the null hypothesis in all of the densities. densities.

Therefore, intraspecific competition does not Therefore, intraspecific competition does not affect the mean growth rate of our clover plants.affect the mean growth rate of our clover plants.

ResultsResults

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DiscussionDiscussion In chart 7, the number of plants originally planted is compared to the In chart 7, the number of plants originally planted is compared to the

number of plants surviving. number of plants surviving.

The chart illustrates an increase in the number of plants surviving as The chart illustrates an increase in the number of plants surviving as the density of original plants planted increases. the density of original plants planted increases.

However, the percentage of plants surviving reduces by almost half However, the percentage of plants surviving reduces by almost half

from the lowest density (100%) to the highest density (53%). from the lowest density (100%) to the highest density (53%).

The densities and the percentage of plants surviving are as follows; The densities and the percentage of plants surviving are as follows; 2:100%, 4:91%, 8:81%, 16:80%, 32:79%, and 64:53%. 2:100%, 4:91%, 8:81%, 16:80%, 32:79%, and 64:53%.

So, the percentage of plants surviving decreases as the density So, the percentage of plants surviving decreases as the density increases, which could be due to intraspecific competition. increases, which could be due to intraspecific competition.

ConclusionConclusion Overall, the results fail to reject the null hypothesis in the Overall, the results fail to reject the null hypothesis in the

interspecific experiment, which states intraspecific interspecific experiment, which states intraspecific competition will not effect the survival and growth of the competition will not effect the survival and growth of the clover plants.clover plants.

Although the effects differ for different variables, none Although the effects differ for different variables, none

were strong enough to be significant according to the t-were strong enough to be significant according to the t-tests.tests.

The results disagree with the research done in support of The results disagree with the research done in support of the effects of intraspecific competition by Yoda, Steen, the effects of intraspecific competition by Yoda, Steen, and others mentioned previously. and others mentioned previously.