John Johnson
Abstract:
Competition between various species can differ on the amount of abundant or limited resource availability and the rate at which resources can be consumed. The competitive exclusion principle is that two organisms cannot occupy the same niche. However if two species do not completely overlap, then we see instances of coexistence between each species. However, competition variability is seen between same specie organisms and among differing species. Competition between two of the same species is known as intraspecific competition while competition seen between different species is referred to as interspecific competition. Our competitive study models the two types of competition previously stated while measuring the results to show the effects of each. Our study hoped to show that if there were no intraspecific interaction between species A then there would be no difference in the amount of survivors nor a difference in the average mass of survivors. We show how intraspecific competition is more important than interspecific competition based on the fact that each individual in a population of the same species has a higher need for limited resource availability.
Introduction:
The purpose of our experiment was to compare competition interactions between (interspecific) and among (intraspecific) species at various density levels. Competition can be defined as any impact of one species over another that results in an adverse reaction or impact of that species (Mangla et al. 2010). Interspecific competition occurs between two differing species for certain resources while intraspecific competition occurs between the same species in a population. These competing factors can cause the differing niche overlap dependent on resources (Bolnick et al 2010). In addition, these interactions can drive resource acquisition to increase survivability (Mangla et al. 2010). Individual must tolerate each kind of competition if they are going to survive in their habitat. Interspecific and intraspecific interactions must maintain some sort of equilibrium for the species to continue to survive (Bolnick et al. 2010). These interactions can drive species to have different niche similarities or niche expansion (Violle et al.2011). Species compete for resources in various niches in the area they live. Species have both fundamental and realized niches. A fundamental niche is any area that a species has the potential to exist whereas the realized niche is a certain area inside of a fundamental niche where a species exist due to limiting factors on their habitat. Competition exclusion principle states that two organisms cannot occupy the same niche. However if two species do not completely overlap, then we see instances of coexistence between each species. (Violle et al. 2011). Competing factors within or between species are strongly correlated with the abundance of available resources or lack thereof (Mangla et al.2010). In addition, biotic factors such as weather can change available resources and increase or limit certain resources (Bocedi et al. 2013). When this occurs, fitness levels of species can change while interspecific competition drives the species to change in response to those biotic factors (Bocedi et al. 2013). In our study, we compared the different types of competition and the effect it had on the number of survivors. We looked at number of surviving individuals per available resources in direct competition. We hypothesize (Ho) that if there is no intraspecific interaction between species A then there will be no difference in the amount of survivors nor a difference in the average mass of survivors. We also hypothesize (Ha) that if there is intraspecific interaction between species A then there will be a difference in the amount of survivors or a difference in the average mass of survivors.
Methods:
For this experiment we needed 16 participants, a set of poker chips, 16 dixie cups, a group leader, a data recorder, and a timer. Our experiment took place inside of our classroom due to deteriorated weather conditions. We used the open carpet area at the front of our classroom as the “playing field” for this environment. Each participating individual represented a plant species. The poker chips were given designations as follows: Red = nutrients, Green = mass (1 gram each), Blue = water, and White = sunlight. We began our experiment with four individuals designated as species A. The rules of the game stated that each individual must remain in the same spot with there feet planted in that location without moving them. Also, only one chip could be collected at a time and once a chip was touched it was deemed to be that individuals chip as long as they did not drop it. Each trial was run for a total of thirty seconds. A predetermined number of chips were scattered by the group leader (20 red, 40 green, 40 blue, and 30 white). Our first experiment dealt with only species A and modeled intraspecific competition. Survivability was governed by the ability to be able to collect the proper resources (3 red, 3 blue, 2 white, and any number of green). Two trials of this experiment were repeated, and then the number of individual species A was increased to six, eight, and ten respectively and ran twice each as well. We then added individual species B participants. Four A and four B species started the experiment and modeled interspecific competition. The same resources were required for the survivability of species A while species B resources were noted as (1 red, 3 white, 3 blue, and any number of green). We ran each of these trials twice with the same time limits and then changed the amount of individual species. Two trials were ran following the same guidelines with 4 A species and 8 B species and then switched to 8 A species and 4 B species. We then used 8 A and 8 B species and repeated for four trials. Data was compiled for each ecology lab as a whole and used for this experiment to analyze our results. By watching Kevin’s videos we learned to calculate the percentage of survivors (number of survivors divided by number of players and multiplying times 100). We also learned to calculate the amount of mass per survivor (amount of mass per that survivor divided number of survivors). Intraspecific competition t-test was utilized by the t-test excel function comparing the mass of the individual at the highest and lowest levels.

Results:

Figure 1: There is a decreasing trend for intraspecific interactions. The average weight per survivor has an overall decrease with an increase in plant density.

Figure 2: There is a decreasing trend for intraspecific interactions. This decreasing trend shows that as plant density increases, there is a decrease in average percent survived.

Figure 3: Interspecific competition shows a higher average weight of survived species B in each case.

Figure 4: Intraspecific competition is shown in solid lines while interspecific competition is shown in dashed lines. In species A, average weight decreases as number of plants increase in both instances.

Figure 5: Intraspecific competition is shown in solid lines while interspecific competition is shown in dashed lines. In species B average weight decreases per individual between species B and A as a result of intraspecific competition between 4B and 4A and interspecific competition between 4B and 4B. Average weight increases as individual density increases in intraspecific competition between 4B and 8B as well as interspecific increase occurs between 8B and 8B.

Intraspecific (Species A ONLY) | | Density | Mean plant Wt per survivor (g) | Mean % Survived | | | 4 | 3.266666667 | 57.5 | | | 6 | 3.691666667 | 48.33333333 | | | 8 | 3.427083333 | 29.6875 | | | 10 | 2.212962963 | 24.44444444 | | | | | | | | | | | | | T-TESTS: Assuming Equal Variances | | Trial | Plant wt (g) when density = 4 | Plant wt (g) when density = 10 | | 1 | 0 | 5 | | | 2 | 3 | 5 | | | 3 | 1 | 0 | | | 4 | 8 | 1 | | | 5 | 0 | 7 | | | 6 | 2 | 11 | | | 7 | 16 | 5 | | | 8 | 25 | 15 | | | 9 | 28 | 10 | | | 10 | 31 | | | | 11 | | | | | 12 | | | | | | | | | | T-test results: | 0.145313244 | Reject null if p < .05 | | | | | | | | Interspecific (BOTH Species) | | Density ratio | Avg # survivors from both species (total survivors) | Mean wt of surviving Species A(g) | Mean wt of surviving Species B (g) | Total density within pot | 4A:4B | 4.6 | 2.875 | 3.75 | 8 | 4A:8B | 3.666666667 | 2.166666667 | 2.75 | 12 | 8A:4B | 3 | 1.75 | 2.138888889 | 12 | 8A:8B | 3.6 | 1.6 | 2.926666667 | 16 |

Discussion: Intraspecific competition: Figures 1 and 2 both show a decreasing trend in intraspecific competition. While figure 1 shows a decrease in average weight per survivor as plant density increases, figure 2 shows a decrease in average percent of survivors as plant density increases. Figure 1shows that as plant density increases, thinning or plant mass decreases. This relationship was weighed and R squared value of 0.46 shows this. However in figure 2, as density increased the average percentage of survivors decreased. This relationship was calculated as well with a much higher r squared value of 0.96. When comparing the R squared values, we see that much more importance is put on the effects of density per average number of survivors than there is on the effects of density per average weight (it is more important to live than it is to decrease mass). A t-test was ran assuming equal variance for the intraspecific competition of species A. This test resulted in a p value of 0.15; when p value < 0.05 we reject our previously stated Ho. Due to our p value, we accept our Ho showing there is no intraspecific interaction between species A in the in the amount of survivors nor a difference in the average mass of survivors when comparing density levels of 4 and 10 respectively. Interspecific competition: Figure 3 shows the interspecific density ratios of each scenario we tested when compared to the average weight of that particular surviving species. In every trial we ran, we see species B outcompeting species A in the average mass of survived species. Due to decreased amount of resources required for species B, this species is able to outcompete species A in the amount of mass acquired. Due to the increased mass of species B and a larger number of resources driving species A to pay more attention to resources and put less energy into acquisition of mass, species B will likely thrive while species A will be driven to possible extinction. De Wit plots: De Wit plots show the relationship of each trial as well as the correlation between inter and intraspecific competition. Each solid line represents the intraspecific relationships while the dashed lines show interspecific relationship. Figures 4 (species A) and 5 (species B) show the importance of each type of competition per species. In figure 4 we see intraspecific competition shown in solid lines while interspecific competition is shown in dashed lines. In species A, average weight decreases as number of plants increase more in intraspecific competition likely due to increase resource requirements of species A. However in figure 5 we see intraspecific competition shown in solid lines while interspecific competition is shown in dashed lines. In species B average weight decreases per individual between species B and A as a result of intraspecific competition between 4B and 4A and interspecific competition between 4B and 4B. Average weight increases as individual density increases in intraspecific competition between 4B and 8B as well as interspecific increase occurs between 8B and 8B. These results are indicative of interspecific competition showing the importance thereof due to a slightly steeper trend line in those instances. Possible errors in our experiment were individuals grabbing more resources than allowed per turn. As well as we saw that the resource containers were previously mislabeled by other students leading us to believe there was sampling error of other groups. If this experiment were repeated, we could enforce more stringent rules or use the effects of predation including other organisms.

Appendix: Intraspecific | | | | | # of players | # of survivors | # of mass chips | %Survival | Mass per survived plant (g) | 4 | 0 | 0 | 0 | 0 | 4 | 1 | 3 | 25 | 3 | 4 | 1 | 1 | 25 | 1 | 4 | 3 | 8 | 75 | 2.666666667 | 4 | 0 | 0 | 0 | 0 | 4 | 2 | 2 | 50 | 1 | 4 | 4 | 16 | 100 | 4 | 4 | 4 | 25 | 100 | 6.25 | 4 | 4 | 28 | 100 | 7 | 4 | 4 | 31 | 100 | 7.75 | 6 | 3 | 8 | 50 | 2.666666667 | 6 | 2 | 6 | 33.33333333 | 3 | 6 | 1 | 1 | 16.66666667 | 1 | 6 | 2 | 1 | 33.33333333 | 0.5 | 6 | 1 | 3 | 16.66666667 | 3 | 6 | 1 | 1 | 16.66666667 | 1 | 6 | 5 | 30 | 83.33333333 | 6 | 6 | 4 | 28 | 66.66666667 | 7 | 6 | 6 | 36 | 100 | 6 | 6 | 4 | 27 | 66.66666667 | 6.75 | 8 | 4 | 6 | 50 | 1.5 | 8 | 2 | 9 | 25 | 4.5 | 8 | 0 | 0 | 0 | 0 | 8 | 0 | 0 | 0 | 0 | 8 | 3 | 15 | 37.5 | 5 | 8 | 3 | 17 | 37.5 | 5.666666667 | 8 | 3 | 18 | 37.5 | 6 | 8 | 4 | 19 | 50 | 4.75 | 10 | 3 | 5 | 30 | 1.666666667 | 10 | 3 | 5 | 30 | 1.666666667 | 10 | 0 | 0 | 0 | 0 | 10 | 1 | 1 | 10 | 1 | 10 | 3 | 7 | 30 | 2.333333333 | 10 | 3 | 11 | 30 | 3.666666667 | 10 | 2 | 5 | 20 | 2.5 | 10 | 4 | 15 | 40 | 3.75 | 10 | 3 | 10 | 30 | 3.333333333 |

Works Cited
Bocedi, G, Atkins, K, Liao, J, Henry, R, Travis, J, & Hellmann, J 2013, 'Effects of local adaptation and interspecific competition on species' responses to climate change', Annals Of The New York Academy Of Sciences, 1297, 1, pp. 83-97.
Bolnick D.I., T. Ingram, W.E. Stutz, L.K. Snowberg, O.L. Lau, and J.S. Paull. 2010. Ecological release from interspecific competition leads to decoupled changes in population and individual niche width. Proceedings of the Royal Society B.
Mangla S., R.L. Sheley, J.L. James, and S.R. Radosevich. 2011. Intra and interspecific competition among invasive and native species during early stages of plant growth. Plant Ecology 212: 531-542.
Violle, C, Nemergut, D, Pu, Z, & Jiang, L 2011, 'Phylogenetic limiting similarity and competitive exclusion', Ecology Letters, 14, 8, pp. 782-787.