Having a large amount of genetic diversity in any population means that if there is an ecological disturbance the population may have a greater survival rate compared to one that had few alleles present. Looking at genetic diversity and the loss of it is an important concept in ecology because it can help ecologists better understand the overall health of an ecosystem based on its genetic diversity, such as number of species present. For example, if there was a fire in a forest and there were 50 species present compared to 5, the one with the greater species richness, which is the number of species present in an environment, would probably have the most survivors. That is because with more species present the chance of more being resistant to fire increases.
Different types of habitats have different averages of species present. A desert will have less species present than a forest, but the same ecological disturbances that occur in a forest may not necessarily occur in a desert. Human disturbance is a large problem in forest habitats. A process where continuous patches of forest habitat is being broken into edges and forest patches is called habitat fragmentation. The edges of forests are getting pushed back because of human activity and large continuous forests are getting smaller. As stated before, species richness can be a large factor of resistance to disturbance in ecosystem.
In today’s lab we are looking at tree diversity using the systematic sampling method of a transect, specifically a line transect. We are measuring samples from the edge of a forest trail and off the trail and into the underbrush to see the differences in number of tree species down the line. The transect line measures 165 feet long, and every 5 feet we are stretching a string along the line and counting the number of species that are touching that line. In order to choose which side of the line we are sampling from we flip a coin: heads for the right side, tails for the left.
We wanted to know if there would be a significant different number in species present from the beginning of the line transect to the end that was deeper into the underbrush. I guessed that the farther away from the path we moved the number of species we found would increase.
Picture from class handout
Our method of using the line transect is quick, but it has its drawbacks. We are limited to just counting the species that touch the line, so when scientists use this method they can often underestimate the number of species that are actually present. Another method that is used in sampling is a belt transect. A line is places similarly, but quadrates are used along the transect intervals instead of a string. This sampling method takes a little longer, but you will have a bit better estimate of number of species present. However, because of our short class time we used a line transect in lab. We walked a few minutes into the forest and laid down our transect line.
1.The area our groups measure was in Chattanooga, Tn at Blue Blazes Trail on Moccasin Bend. The area is a few miles from down town and is in a small peninsula that is surrounded by the Tennessee river. The area is mostly flat and forested, although there are small patches of grassy fields along the 1.5 mile trail. The trail is unpaved. From what I saw there were some evidence of disturbance. People pointed our sections of grass areas along the trail, which could potentially be a result of habitat fragmentation. There were large trees as well as smaller ones and it was very cold, in the 30s when we went. It is in November so it is in the months where less sunlight reaches compared to summer months, and the temperature is very cold. It is winter, and so the density of the underbrush is much less than it is in summertime, which can cause our results of tree diversity to perhaps be lower than it would be if we did the same experiment in the spring.
Graph based on group transect line data
2. Overall, we did not see a large difference in number of tree species deeper into the forest compared to what we counted at the edge of the trail. The pattern that is calculated when graphed on a scatterplot between the x and y axis is weak based on the R^2 value of 0.28473. If that value were close to 1, then we could say that our results showed a strong pattern of having a larger tree diversity farther into the forest. However, this is not the case. Our number of species counted only was between 0 and 4. But, we can see that 4, being our maximum number of species present, was only counted at the farthest edges of our transect line deepest into the forest. The pattern mathematically calculated shows a weak pattern on number of tree species, but we can see that we counted 1 more tree species farther into the woods, it is just not enough of a difference to be important to the data analysis.
Data based off regression analysis
3. We did not just graph the data on a scatterplot, but we also did data analysis on it. We performed a regression analysis using the line transect values for the X input, and then the number of species found as the Y. The p-value is what we were interested in. When I ran the regression analysis the p-value was found to be 0.0045. This value is below 0.05 so we can say that the null hypothesis can be rejected and that there is a correlation between our transect lines and number of species found. The relationship is not due just to chance alone.
4. According to an article titled “Effects of Local Tree Diversity on Herbivore Communities Diminish with Increasing Forest Fragmentation on the Landscape Scale”, habitat fragmentation not only alters tree diversity, but also affects feeding patterns of herbivores in forest communities. Fragmentation is a problem in ecosystems and, according to the paper, “has the potential to jeopardize ecosystem functioning and forest regeneration”. Based on my results, with increasing fragmentation, I would expect tree diversity to lower. With lower diversity forest regeneration would not be as successful and I would expect it to take more time. Follow up questions I would have for future studies would be to ask what kind of tree species are more resilient to environmental disturbance and change. Are there certain kinds of trees that are still prevalent even in fragmented environments?
Answers based on the article “Gene Flow Halted by Fragmented Forests” by Asian Science Newsroom
- The river floodplains in Japan are important because they hold a great amount of resources and are ideal habitats for many organisms. They are also important in keeping water ways clear of toxins as well as erosion prevention. It is important for the conservations of river floodplains and prevention of fragmentation because of the importance they have in the overall health of the environment.
2. Gene flow is important for monitoring endangered species because it can provide insights on how the genetics of a species differs based on older and younger trees, such as Acer miyabei have changed over time. As habitat fragmentation occurs patterns of pollination can occur, which can be studied to understand gene flow patterns. Looking at landscape patterns, such as where the environment is fragmented and comparing genetic variation in those plants between those areas, gene flow patterns can be made.
Photo of Acer miyabei leaves
3. The study found that the smaller trees had less genetic variation because they are more isolated from pollinators because of the fragmentation in their habitats. They show “fewer variant forms of the gene”, which can cause them to be more prone to suffer in environmental stress. The trees genetics are changing because of separation between different populations. This research informs that these older plants are important because of their greater genetic diversity so it is important that they should be protected. The plants grow best in river floodplains, so conservation efforts should be made in forests along rivers and as well as the areas around the water.
References
“Gene Flow Halted By Fragmented Forests.” Asian Scientist Magazine. Science, Technology and Medical News Updates from Asia, 12 Mar. 2018,
Peter, Franziska, Dana G. Berens, and Nina Farwig. “Effects of Local Tree Diversity on Herbivore Communities Diminish with Increasing Forest Fragmentation on the Landscape Scale.” PLoS One, vol. 9, no. 4, 2014.
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