Abstract
McPherson preserve is a very important botanical preserve located in north-central Oklahoma. It is used in various research experiments and holds a plethora of species for students to study closely. We conducted this study to gain information on the effect that disturbances have on species diversity. We found that various metrics such as species richness, dominance, diversity, and evenness, are not significantly altered by high disturbance. Diversity however, was most notably influenced by disturbance, or lack thereof depending on region of quadrat along the marked trail.
KEY TERMS
ANOVA (test), Intermediate Disturbance Hypothesis, Shannon-Weiner Diversity Index (H’), Species Evenness (J’), Species Richness, Simpson’s Index (D; aka: Species Dominance), Fisher’s Least Significant Difference (LSD).
Introduction
Disturbances can have various influences on environments. These disturbances can range from human to natural and it is important to consider both when looking at the relationships of different metrics such as: diversity, evenness, richness, and dominance between species. Joseph Connell (1978) initially proposed the “intermediate disturbance hypothesis,” which in an attempt to explain how species diversity within a community can be influenced, and to what extent. This hypothesis brought forth this question, asked by David Cole (1995): how can we preserve our national parks and wilderness areas while still leaving them open to educational recreation? Cole was later joined by Christopher Monz (2002) to conduct a study to question the intermediate disturbance hypothesis, finding that disturbances, in this case human, can have a huge impact on the damage and recovery of certain plant communities; in their case, the high elevation of the Wind River Mountains in Wyoming. In order to combat this, they drew the conclusion that the concentration of trampling and disturbance needed to dispersed to other available regions in order for highly damaged trail flora to recover. Catherine Pickering, and Andrew Growcock (2009) conducted an experiment within similar conditions (similar in that the flora was already more disturbance-tolerant due to exposure to harsher elements). Dissimilarly, we conducted our study in a more mild-temperature region of the united states, Oklahoma. For our study, we hypothesized that diversity would be much lower towards the center of the trail, due to some plant’s low tolerance to disturbance. In order to test this hypothesis, we collected data on types of flora, their frequency, and their location along the trail.
METHODS
Study Site: McPherson Preserve, Stillwater, Oklahoma. A 180-acre botanical preserve including riparian, prairie, and old-field habitats for studies and experiments. The data was collected during mid morning, late September.
Field Procedures: Two different belt transects were set up along a 100m tape running along a trail within the McPherson Preserve location. Both belt transects consisted of 10 adjoining 10cm x 50cm quadrats; each quadrat was parallel to the center of the trail, which was marked by the meter tape. Transects were placed through random selection on either the left or right side of the tape. We were provided a data packet containing photos and names of frequently occurring species of flora native to that area. Working one quadrat at a time, we recorded the quantity of identifiable plant species with green material less than 1m from the ground (this allowed inclusion of seedlings of tree and shrub species, but excluded trees and tall shrubs as well as bryophytes and algae). Some quadrats were devoid of any active flora. Any plants that could not be identified were labeled as numbered unknowns and counted. Data was collected by 7 groups at different points along the meter tape.
Lab Procedures and Data Analysis: Data from all participating groups was summarized, allowing us to form accurate graphs and to perform the appropriate statistical tests; in this case, the ANOVA test (aka: F-test). For the data analysis, 4 metrics were considered to calculate overall species diversity: species richness, Shannon-Weiner diversity index (H’), species evenness (J’), and Simpson’s Index (D’). For the ANOVA of Shannon-Weiner Diversity index, our null hypothesis stated that there would be no difference between data collected in intermediate and in highly disturbed regions of the quadrats along the trail. Alternatively, we hypothesized that there would be a significant difference in the aforementioned factors. For the ANOVA of species richness, our statistical null hypothesis stated that there would be no data to show variance in species richness in different regions of the quadrats. We alternatively hypothesized that there would be significant variance in species richness. For the ANOVA of species evenness, our null hypothesis stated that there would be no variance in species evenness along the trail. We alternatively hypothesized that there would be measurable variance in species evenness at different regions of the trail. For the ANOVA of species dominance, our null hypothesis stated that there would be no notable variance in species dominance along the trail. Alternatively, we hypothesized that there would be significant variance in species richness along the trail. Our biological hypotheses stated that there would be significant variance in H’ (diversity), species richness, and species evenness; all occurring within the intermediate region of the quadrats. Relatively, the intermediate region would have lower dominance than the center and edge regions. We used used SPSS (computer program) to generate charts based on data collected.
RESULTS
According to the SPSS charts for each metric, we found that there was variance in diversity and species richness, and more evenness, but not dominance in the intermediate region of the trail. Table 1 shows a sig. figure of .022, meaning, as the sig. closest to 0, species richness exhibited the greatest affect from disturbance. The post-hoc tests reveal the statistical conclusion that for species richness (Figure 1), there is a significant difference in species between the edge and center of the trail (the intermediate region). Figures 2, 3, and 4 show that although the significance was not as great as richness, the other metrics were still affected.
DISCUSSION
The differences in results seen among the 4 metrics of species could be attributed to the fact that the center of the trail is a highly disturbed area, so species diversity is low. Likewise, species diversity is low in the edge region of the trail, because more resistant species may dominate. Due to the balance of not being completely disturbed nor completely untouched, higher species diversity is the result of being able to thrive in the intermediate region of the trail. From the results of this study, we can biologically conclude that the center and edge of the trail had lower species richness than the intermediate region of the trail, thus supporting our initial hypotheses stating the affect of disturbance on the flora along a trail (Table 1).
An implication to this study that we encountered was that the trail was experiencing even more disturbance during the time of our data collection, as all groups were randomly assigned points on the meter tape. Because of this, many people were walking back and forth along the tape, adding disturbance that otherwise would not have been as much of an immediately altering factor. In order to avoid this, we may need to set up more than one tape, and have each group more spread out along the tape, as well as be more aware of where feet are placed.
Hiroki Ikeda (2003) conducted an experiment measuring the same metrics as we did, however the data collection for this particular study was spread over a 4-year time frame, whereas our data collection was completed within 2 hours. Despite these time-frame differences, results similar to ours were found. Additionally, Ikeda (2003) suggested that variance in diversity might also be affected by competitive fauna interactions, but this wasn’t noted until further into the data collection. If we were to expand on this study, I think it would behoove us to consider competitive interactions between species of flora.