Affects of Density on Intraspecific Competition in Marigolds Eric Flatt Undergraduate Student (Marine Biology Concentration) Department of Biology Tennessee Tech University Cookeville, TN 38505

Introduction  Plant competition has been the object of ecologists’ studies for several years.  Most experimental studies in plant competition over the past several years have involved manipulating the densities of one or more plant species and quantifying the response of other plants (Miller 1990).  A great deal of research has been devoted to understanding how plant species affect and respond to each other and how the interactions affect the dynamics, structure, and evolution of the plants in the vicinity (Connolly 2001).

Introduction continued…  During intraspecific competition, plants tend to respond with resource allocation. For many species, a density increase results in total weight, height, reproduction and/or survival decrease (Lentz 1999).  The ability of a plant to endure the suppression of its neighbors often varies among species (Peltzer and Wilson 2001).

Objective and Hypothesis  Objective: My objective for this experiment was to find out whether or not density affects intraspecific competition in marigolds.  Hypothesis: Density would have an affect on intraspecific competition in marigolds.  Null Hypothesis: Density would not have any affect on intraspecific competition in marigolds.

Methods and Materials  I accomplished this by planting marigolds in different densities of 2, 4, 8, 16, 32, and 64 in six different flower pots.  Over the next five weeks after they were originally planted the plants were watered once a week and checked to make sure that none had died.  After five weeks I measured the plant density, survivorship, total weight, mean weight, mean stem weight, mean leaf weight, mean stem length, and mean growth rate for the plants of each pot.  This data was then recorded and entered into the following data form.  Data Form Data Form

Results  The data gathered was then organized into the following scatter plots comparing each of the recorded variables vs. plant density. Fig. 1: The mean marigold weight for each density treatment after five weeks. Fig. 2: The total weight of all the marigolds in each density treatment.

Results continued… Fig. 3: The average marigold height in each density treatment after five weeks. Fig. 4: The average stem weight of each marigold in each density treatment after five weeks.

Results continued… Fig. 5: The average leaf weight of the marigolds in each density treatment after five weeks. Fig. 6: The average growth of the marigolds in each density treatment after five weeks.

Results continued… Fig. 7: The survival percentage for the marigolds in each density treatment after five weeks.

Discussion  My results showed a slight decrease in survivorship as the density of marigolds in each pot increased. My results also showed that as the density of marigolds in each pot increased the average weight of the marigolds decreased, but the average height of the marigolds increased as the density increased.  The marigolds did have a decrease in mean leaf and stem weight as density increased which was also shown by Lentz However, there did not seem to be any definite size hierarchy among the marigolds as found by Lentz 1999.

Discussion continued…  In Peltzer and Wilson 2001, it was stated that the ability of a plant to endure the suppression of its neighbors often varies among species. In the case of the Marigolds in this experiment, which were grown alone, they seemed to be able to avoid suppression from each other pretty well considering the percent survival in all the densities was high.  In the end, I think this experiment like others noted in Connolly 2001 will also help people in understanding how plant species affect and respond to each other and how the interactions affect the dynamics, structure, and evolution of the plants in the vicinity.

Conclusions  Density did have an affect on the intraspecific competition between the marigolds.  The higher the density is the more plants such as marigolds are forced to compete for limited resources in the area.  Low densities are more beneficial to the survival and health of marigolds than higher densities.  Future research will have to be done to see what the long term results are when marigolds are forced to face a higher density as opposed to a lower density in a confined amount of space. Also, more research will be done to see if the results would be the same amongst the marigolds in a field experiment rather in a controlled experiment.