Interspecific Competition Effects on Plants: Growth Rate, Plant Height, Plant Weight, and Plant Densities Amy Salamone Undergraduate Student (Marine Biology Concentration) Department of Biology Tennessee Technological University

Introduction  Interspecific competition can be due to a limited supply of nutrients located in the soil (Day et al., 2003). Day, Hutchings, and John’s work lets us conclude that plants grown under higher nutrient levels have higher yields.  Understanding the means that control plant competition is a vital step in calculating the outcome of interspecific competition (Raynaud and Leadley, 2004).

Introduction Cont’d  Understanding the motivations that cause plants to distribute themselves on local, regional, and global scales is one of the major issues ecologists are faced with (Crain et al., 2004).  Competition affects all organisms that experience it. Competition reduces individual plant growth regardless of whether it is for soil or light (Cahill, 2003).

Objective and Hypothesis  Objective: Find out whether or not interspecific competition has any effect on Alyssum or Marigolds. Find out whether or not interspecific competition has any effect on Alyssum or Marigolds.  Hypothesis: Interspecific competition will have an effect on the growth factors of the Alyssum or the Marigolds. Interspecific competition will have an effect on the growth factors of the Alyssum or the Marigolds. Null Hypothesis: Competition will not have an effect on the growth factors of the plants. Competition will not have an effect on the growth factors of the plants.

Methods and Materials  I had four pots which had the following densities of alyssum and marigolds in each: 4 marigold: 4 alyssum 4 marigold: 24 alyssum 4 marigold: 24 alyssum 24 marigold: 4 alyssum 24 marigold: 4 alyssum 24 marigold: 24 alyssum 24 marigold: 24 alyssum  The plants were watered and measured on a weekly basis.

Methods and Materials Every week I measured the plant height and density of each species. At the end of the 6 th week, when the experiment was over, I removed the plants and weighed them on a covered scale. Alyssum Flowers Marigold Flowers

Data Form Interspecificin milligrams (mg)centimeters (cm)cm per day # SurvTotal WtAvg WtAvg Stem LengthAvg Growth Rate% survival 4M:4AAlly M:4AMari M:24AAlly M:24AMari M:4AAlly M:4AMari M:24AAlly M:24AMari

Results Figure 1: Number of survivors of each species arranged by which density they were planted at. Figure 2: Total weight in milligrams of each species organized by the density they were planted at.

Results Figure 3: Mean growth rate in centimeters per day of each species organized by which density they were planted. Figure 4: Average height in centimeters per species arranged by the density they were planted at.

Results (t-tests) Table 1: t-test showing the variance between the total weights of the marigold and the alyssum. t-Test: Two-Sample Assuming Equal Variances P(T<=t) one-tail t Critical one-tail P(T<=t) two-tail t Critical two-tail Total Weight Table 2: t-test showing the variance between the growth rates of the marigold and the alyssum. t-Test: Two-Sample Assuming Equal Variances P(T<=t) one-tail t Critical one-tail P(T<=t) two-tail t Critical two-tail Growth Rate

Results (t-tests) Table 3: t-test showing the variance between the average heights of the marigold and the alyssum. t-Test: Two-Sample Assuming Equal Variances P(T<=t) one-tail t Critical one-tail P(T<=t) two-tail t Critical two-tail Average Height

Discussion  Figure 1 shows that the number of survivors is directly proportional to the number of seeds planted. When there were a greater number of one species, that species had a higher survival rate.  These results are caused by the fact that when one species has a much higher density than another then the higher one will usually out compete the lower one (Raynaud and Leadley 2004).

Discussion  Figure 2 shows the total weight of Marigolds versus Alyssum. Marigolds always weigh more.  Figure 3 shows that Alyssum have a consistent growth rate while the marigolds seem to have a slightly higher growth rate when they have a higher density.

Discussion  With regard to the t-tests, if P(T<=t) two-tail is greater than 0.05 then there is not enough of a difference between the two variables for them to be significantly different.  As shown in Tables 1-3, the p value was always greater than This means that competition was either not taking place or it was on such a minute level that the plants’ growth did not become affected.

Summary and Conclusions  Competition is always taking place in every environment.  Interspecific competition has an effect, either minute or great, on the growth factors of plants.  Plants may be competing for light, nutrients, or water, depending on where their environment is located.  When density is higher, the plants will have a higher level of competition.

Conclusions  In my particular interspecific competition experiment, the marigold and alyssum were not competing enough for there to be a significant difference in growth factors.