Plant Competition Paper Rough Draft PDF

Preview

Summary

Scientific paper over plant competiton ...

Description

Tara Velasquez Sect. 252

Velasquez 1 Investigating the Effect of Intraspecific Competition in Brassica rapa on Flower Count and Survivorship

Abstract The effect of intraspecific competition in Brassica rapa on flower growth and survivorship were studied under minimal density, medium density, and high density. We predicted that as the density of the environment in which plants were grown increased, flower count and survivorship would decrease due to increased intraspecific competition. Mean flower count was the highest for plants at low density and the lowest at high density. Survivorship among low, medium, and high density conditions was found to not be statistically significant, as number of survivors at each density was similar. Our results suggest that as the density of the environment that Brassica rapa are grown in is increased, intraspecific competition among the plants is also increased, therefore causing their performance to decline as they compete for resources. Introduction Intraspecific competition in plants refers to the interaction between two plants of the same species where they compete for limited resources (Miller, 1995). Many studies have shown that plant competition could be a major driving factor for evolution of different species of plants (Miller, 1995). Plants compete in environments where there are limited resources such as sunlight, water, and space for roots to spread (Gurevitch et al., 1996). In competitive environments, it is known that there is a higher level of genetic variation than in non-competitive agricultural systems (Miller & Schemske 1990).

Velasquez 2

Tara Velasquez Sect. 252

For this experiment, intraspecific competition among Brassica rapa, or field mustard, will be studied for the duration of its lifespan. Brassica rapa is known to have a rapid life cycle while also being easy to breed, small in stature, and genetically varied, making it suitable for this experiment (Miller, 1995). When grown in an environment with high levels of competition, Brassica rapa are known to show a significant reduction in flower count and biomass (Miller & Schemske, 1990). In order to test the hypothesis that intraspecific competition exists among Brassica rapa, we compared survivorship and flower count of plants grown in low, medium, and high densities. It was predicted that plants grown in a high density environment would show lower survivorship and flower count than those grown in medium and low density environments. The plants grown at high density should have the lowest rate of survival and flower count while plants grown at low density should have the highest rate of survival and flower count.

Methods In order to test for intraspecific competition in Brassica rapa, seeds were planted at three treatments: low, medium, and high density. Each pot was filled halfway with soil and six fertilizer balls were placed evenly spaced in each pot. The soil was then watered lightly and the pot was filled the rest of the way with soil and watered lightly once more. Then, small holes were made for seed placement, all evenly spaced. Two seeds were planted for low density, five seeds for medium density, and ten seeds for high density. A thin layer of soil was then placed carefully over the seeds and were very lightly watered. The pots were then labeled and placed under a lamp, no closer than 6-8 cm from the light. We kept the number of fertilizer balls, amount of water, amount of soil, air temperature, and

Tara Velasquez Sect. 252

Velasquez 3

distance from the lamps constant for the duration of the experiment. Each week, flower number per plant and survivorship was measured and recorded. After 6 weeks, we harvested the plants with the roots intact and measured other variables such as biomass and length of each plant.

Results The results of this experiment show that the plants grown at low density (2 seeds per pot) had a greater mean number of flowers per plant than did plants grown at medium (5 seeds per pot) and high (10 seeds per pot) density. This data is statistically significant with a p value of .0075., which is less than p=.05. (x ± SE density: low density: 2.33 ± .213; medium density: 1.69 ± .213; high density: 1.41 ± .213; ANOVA = F2,239=4.99,; p = 0.0075; Figure 1). The data for survivorship by density had a p value of p=.360 which is greater than .05; therefore, the data is not statistically significant. (ANOVA = F2,275=1.03,; p = 0.360; Figure 2).

Figure 1. Mean number of flowers present per plant at low (2), medium (5), and high (10) density.

Tara Velasquez Sect. 252

Velasquez 4

Figure 2. Mean survivorship for plants grown in low (2), medium (5), and high (10) density. Mean(Mean Flowers) vs. Density Mean 2.5

Mean Flowers

2.0

1.5

1.0

0.5

0.0

10

2 Density

5

Discussion

From this experiment, we expected to find that with increasing the amount of plants per pot would lead to an increase in intraspecific competition. This prediction was based on the idea that at higher densities rather than low density, plants would be competing for resources such as water, nutrients, light, space for their roots, and light. Our results that plants grown at low density had a higher mean number of flowers per plants indicates that intraspecific competition among Brassica rapa does exist. Since the p value was less than .05, the data for mean flowers vs. density is considered statistically significant and the null hypothesis, intraspecific competition in Brassica rapa does not occur, is not accepted and the results agree with our prediction. The implications of the outcome of this experiment could lead to new ways to conserve different plant species. If a species is in need of conservation, decreasing intraspecific competition could lead to higher success for that particular species. Our results are similar to the results of an experiment done by the Department of Ecology and Evolution at State University of New York in Stony Brook, NY. They concluded that increasing the densities of the environments where

Tara Velasquez Sect. 252

Velasquez 5

Brassica rapa were grown led to increased completion, shown by the decreasing number of flowers per plant as density was increased (Gurevitch et al., 1996). A study done by the Department of Ecology and Evolution at the University of Chicago also found that flower count decreased as intraspecific competition was increased (Miller & Schemske,1990). The data for survivorship vs. density was found not be statistically different due to its p value being greater than .05, therefore the null hypothesis is accepted. We predicted that plants at lower density would have a higher survivorship than plants at medium and high density, however the data does not support this prediction. The reason that survivorship for low, medium, and high densities was statistically insignificant could be because most of the plants received a sufficient amount of nutrients allowing them to grow initially. All seeds at each density were planted with the same amount of water, soil, and fertilizer balls, giving the seeds the resources they needed to germinate. The plants were then in a competitive environment after germination occurred and were forced to compete for resources that would have a greater effect on other variables, such as flower growth. This explains why the plants at all densities had statistically similar survivorship and decreasing flower growth with increasing competition. To improve this experiment for future investigations, we could measure a larger range of densities which would allow us to see greater effects of intraspecific competition.

Velasquez 6

Tara Velasquez Sect. 252

References Gurevitch, J., Taub, D.R., Morton, T.C., Gomez, P.L., & Wang, I. (1996). Competition and genetic background in a rapid cycling cultivar of Brassica Rapa (Brassicaceae). American Journal of Botany, (7), 932-938. Miller, T.E. (1995). Evolution of Brassica rapa L. (Cruciferae) populations in intra- and interspecific competition. Evolution, (49), 1125-1133. Miller, T.E. and Schemske, D.W. (1990). An experimental study of competitive performance in Brassica rapa (Cruciferae). American Journal of Botany, (77), 993-998. Seimens, D., Garner, S., Mitchell-Olds, T., and Callaway, R. (2002). Cost of Defense in the context of plant competition: Brassica rapa may grow and defend. Ecology, (2), 505-517....