Intraspecific competition is a widely regarded principle mechanism in the structuring of communities and has an influence in the spatial dispersion of organisms such as plants. Knowing this, the authors designed an experiment to observe and understand the effect of intraspecific competition using Brassica rapa, operating under the precept that when the plant is grown in an limited space environment, the plants will grow quickly and will be able to produce offspring in a faster more efficient way.
Utilizing a two-treatment group set-up where B. rapa plants were grown in either a low density set-up (2 seeds only) or high density set-up (10 seeds), the researchers found that a low density set-up had several advantages over the high density set up, with plants having higher prop survival and flower production. Thse findings supported the idea that limited space will affect the high density environment, allowing the seeds grown in a low density environment to flourish more effectively. Effect of Intraspecific Competition on Growth and Development of Brassica rapa Plants Introduction
Intraspecific competition is a widely regarded principle mechanism in the structuring of communities (Abramsky and Sellah 1982). In fact, intraspecific competition is known to occur between members of the same species competing for shared, limiting resources such as food and space. Further more, intraspecific competition has an influence in the spatial dispersion of organisms such as plants (Mcginley 2008). Scientist have longed tried to determine whether competition exists between or within species and what effect it has on its survivability and reproduction rate.
It is a known fact that plants that are grown in high density areas only have one choice: allocate the limited resources and grow rapidly (Siemens,et al. 2002) lest the organism fail to thrive and survive. It then becomes apparent that information gained from this area of study will have significant applications outside of the field of botany. In a time where reforestation and rehabilitation is a major issue, knowledge on intraspecific competition can help shape the success of efforts on plant-life conservation.
To further study this mechanism, the researchers developed an experimental set-up that evaluated intraspecific competition among plants. Using space as the experiment’s limiting resource, species of B. rapa were cultivated in two treatment groups and observed for the effects of intraspecific competition. Space is often viewed as a major limiting resource for sessile organisms since taking away another’s space eliminates its ability to acquire food (Vance, 1984, p. 1354).
The plant specie B. rapa was selected as the treatment model of choice since the specie is known for being an ideal experimental subject due to their small size, ease of cultivation and short life cycle. The main objective of the experiment was to observe and understand the effect of intraspecific competition on B. rapa due to limited space. The experiment operated under the main hypothesis that when the Brassica rappa plant is grown in an environment with limited space, the plants grow quickly and is able to produce offspring in a faster more efficient way.
On the other hand, the null hypothesis for this experiment was that the limited space will not play a role in the growth and reproduction of B. rappa. Lastly, the alternative hypothesis for the experiment was that limited space will affect the high density environment, allowing the seeds grown in a low density environment to flourish. Materials and Methods For the experimental set-up, two treatment groups were created. One group was classified as Low density and was comprised of two Brassica rappa seeds while the second group was classified as High density and consisted of 10 Brassica rappa seeds.
Controls determined for the experiment included light source, temperature and water while the considered variables included the biomass of the seeds, the mean biomass of the seeds, the number of pods and the number of flowers each plant produced. The experiment was conducted over a six-week period where data collection recorded the number of survivors per treatment group. The number of pods, flowers and pollinated flowers were also recorded. In the last two weeks of the experiment, treatment groups were harvested and mean height was recorded.
The plants were then dried and the roots and forage material weighed to determine biomass. Seeds were then separated. Data gathered from the experiment were treated using t-tests and Oneway Analysis utilizing treatment means and standard deviations. Results After cultivation of B. rapa in the two treatment groups, the researchers determined the following data using Oneway analysis and t-tests.
Results showed that the mean probability or survival per treatment were 0. 839683 [SD 0. 267817] in the low density set-up and 0. 732283 [SD 0. 262515] in the high density set-up (Appendix A) revealing a slight survival advantage in favor of the low density set-up. On the other hand, the mean height per treatment were 13. 5956 [SD 5. 33474] and 13. 1550 [SD 6. 63392] for the low density and high density set-up respectively (Appendix B) indicating that plants in both set-up flourished equally in terms of height most likely due to non-competition for light source which was a controlled variable.
The mean number of flowers per treatment group was 2. 61684 [SD3. 55681] for the low density set-up and 1. 56520 [SD 1. 72971] for the high density set-up (Appendix C) indicating that the low density treatment group achieved higher performance indicated by being able to reach the reproductive stage more effectively. These values are closely mirrored by the mean number of pods per treatment group which showed that the low density set-up had a mean of 2. 04356 [SD 2. 55931] while the high density set-up had a mean of 1. 68122 [SD 2. 14201] (Appendix D) again reflecting a more successful reproductive course (successful pollination).
Additionally, the mean values obtained for the number of seeds per plant were 5. 18258 [SD 8. 53005] for the low density set-up and 3. 65687 [SD 4. 70787] for the high density set-up (Appendix E) further solidifying the idea that plants in the low density group were able to flourish much better compared to the high density group. In terms of mean seed biomass, the low density set-up had an average mean of 0. 005624 [SD 0. 011844] which was lower in comparison to the high-density setup which had a value of 0. 006139 [SD 0. 014367] (Appendix F).
The mean root biomass obtained were 0. 028744 [SD 0. 099737] for the low density set-up while the high density set-up had an obtained mean value of 0. 021542 [SD 0. 037141] (Appendix G). Lastly, the mean biomass per treatment group values obtained for the experiment were 0. 063467 [SD 0. 097980] for the low density set-up and 0. 069773 [SD 0. 110127] for the high density set-up (Appendix H). Biomass is supposedly a good measure of fitness or how well the plant flourished since the amount of living tissue is said to be regulated by resource availability, i. e. space (Franco & Kelly, 1998, p. 7830). Discussion Data gathered from the two treatment groups indicated that the low density group demonstrated certain advantages over the high density group. In both the areas of surviving prop [t=4. 555, DF=503. 608, p=. 0001] and mean plant height [t=0. 814, DF=471. 852, p=0. 416], the low density group scored higher on average compared to the high density treatment group.
The same can be said in the measures for mean number of flowers, pod and seeds where the low density treatment group also had higher average means in comparison to the high density group. These findings supported the idea that plants in the low density group flourished more effectively in comparison to plants in the high density group.
Additionally, a significant difference in the number of flowers produced [t=4. 168, DF= 352. 016, p= <. 0001] and seeds per plant [t=2. 41465, DF=369. 4544, p=<0. 0162] in each treatment group was identified in favor of the low density treatment group, supporting the alternative hypothesis that that limited space will affect the high density environment, allowing the seeds grown in a low density environment to flourish. These findings mirrored the results in a study conducted by Miller and Schemske (1990) in which they sought to measure the competitive performance of B. rapa. In the said study, three set-ups were created: non-competition, competition – intraspecific and competition – interspecific.
The researchers in the said study found that plants grown in the no-competition setup were larger and had more flower yields in comparison to the two competitive set-ups (p. 995). However, it cannot be ignored that despite the fact that the seeds grown in the high density environment were five times more crowded than the seeds grown in a low density environment, the seeds planted in the high density environment managed to stay competitive as demonstrated by the average number of flowers each plant produced in each treatment. The low density which had two seeds planted produced an average of about 2. 5 flowers while the high density, which had ten seeds planted, produced about 1. 5 flowers.
This is further supported by the results of the t-test which indicated that there was no significant difference in the mean biomass [t= 0. 667, DF= 479. 960, p= 0. 505] seed biomass [t= 0. 426, DF= 455. 694, p= 0. 670] and number of pods produced [t= 1. 684,DF= 462. 848, p= 0. 093] between the two treatment groups. The idea is that with competition, certain measures of fitness would be affected, i. e. in a low competition environment fitness indicators would be higher in comparison to more competitive environments.
However, these results demonstrated the fact that there was no such difference in terms of biomass indicating that plants in the high-density treatment group were able to function at the same levels as the plants in the low-density group at least in terms of biomass achieved. Problems Encountered The experiment was fairly simple and the researchers did not encounter any problems. However, human error could undoubtedly have played a role in the first planting of the seeds. Many seeds could have been placed too close in proximity to one another and this would have caused a greater amount of competition and stress.
Solution Next time it would be advisable to measure the distance between the seeds in both environments to ensure that all seeds have an equal amount of space in which to thrive and thus provide for an equal opportunity and ability to survive. Further Studies To further evaluate the effects of the limiting resource of space and the plants ability to adapt, it would be advisable to observe and calculate the number of viable offspring produced in the next generation. References Abramsky, Z. , Sellah, C. (1982).
Competition and the Role of Habitat Selection in Gerbillus allenbyi and Meriones tristrami: A Removal Experiment. Ecology. 3:1242-1247. Connell, J. H. (1983). Prevelance and Relative Importance of Interspecific Competition. American Natural. 111:119-1144. Franco, M. , Kelly. C. K. (1998). “The inter-specific mass-density relationship and plant geometry” Proceedings of the National Academy of Sciences of the United States of America 95(13): 7830-7835. National Academy of Sciences McGinley, M. (2008). Intraspecific Competition. Encyclopedia of Earth. http://www. eoearth. org/article/Intraspecific_competition
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