Effects of Intraspecific Competition on Varying Groups of Marigolds Tiffany Landis Microbiology Major Tennessee Technological University Cookeville, TN 38505

Introduction  “The purpose of making plant competition studies is ultimately to be able to predict the dynamics of natural plant communities.” (Damgaard, 1998 )  “For many plants, an increase in density results in a decrease in reproduction, total biomass, height and/or survival.” (Antonovics and Levin, 1980)  The more crowded a population the more competition there is for resources.” (Tansley, 1917)  “Spatial arrangement of plants in a community can be an important determinant of species coexistence and biodiversity” (Stoll et al, 2001).

Introduction Continued…..  “Plants biomass and seed production were always higher in plants growing with reduced competition” (Aquiar et al., 2001).  In my experiment with marigolds I looked to Intraspecific competition to determine if plants with more competitors will end up smaller than plants grown with fewer competitors.  The idea being that competitors will take up light and nutrients and leave a lot less of those nutrients for the other plants.

Methods and Materials  I obtained six pots and labeled them according to the number of seeds in each pot.  The plants were kept in a sunroom and watered regularly. Each of the six pots was filled with soil until it came to about one centimeter from the top of the pot.  I obtained marigold seeds and planted the following densities of seeds in each pot: 3, 5, 10, 18, 34, or 68 seeds. After germination, the plant populations were thinned to 2, 4, 8, 16, 32, or 64 plants per pot. I then placed more soil on top of the seeds and watered them. Starting with higher initial densities will increase the likely hood of getting more germinated seedlings. (Damgaard, 1998 )  Each week I measured the number of leaves on each plant in each pot, heights of the plant stems, and number of flowers on each plant.  I then gathered detailed information from each pot number of plants, weights of plant stems, number of leaves and length of stems.  I obtained stem weights of the plants by clipping out the plants at soil level, clipping off the leaves and placing them on a scale.

Results As density goes up plant weight goes up, which would not be expected if nutrients were being depleted due to competition. Despite density survival rates for the pots with 16 and 64 marigolds was the same. The survival rate was higher in the pot with 32 marigolds. Fig. 1 Fig. 2

Results Leaf weight began accurate to plant competition standards, but then the pot with 64 marigolds was weighed the average leaf weight increased instead of decreased. Fig. 3 Fig. 4 Stem length began accurate to plant competition standards but as seen with the leaf weight the pot with 64 marigolds increased instead of decreased.

Results Explained  As can be seen by the various graphs density had little or no effect on the growth of the marigolds.  My results proved my null hypothesis.  My results went against the norms of many other experiments done in this field.

Discussion  My null hypotheses was found to be correct. According to the graphs the density had, no effect on the growth of the plants. Thus, concluding that there is no significant difference in all aspects of growth of the plants. The results were not conclusive enough to say that competition affected their growth. Studies done by scientists as mentioned in the introduction were conducted over a longer period and proved that competition intra- had an effect on plant growth. The experiments that I conducted was over a shorter period and thus we could not prove that competition intra- had a significant effect on plant growth. However, through my various researches on this topic I found that competition can be avoided and that the plants through natural selection would be allowed to converge. Avoidance of competition may imply that the species have gotten used to each other’s presence.

Conclusion  Density did not affect the amount of intraspecific competition among the marigolds.  My results showed that there was little plant competition among the marigolds. This could be because the plants grew for a short amount of time and never reached full maturity.