Diversity is a crucial part of the natural world. Primarily, it gives insight into the health of an ecosystem. Healthy ecosystems need high diversity in order to function well and provide its variety of services. Most know that biodiversity is different between different ecosystems; desert life is different from rainforest life. However, diversity can also be different within a single ecosystem. Species richness, for example, may change as one travels from the inside of a forest to the outside. Additionally, ecologists study habitat fragmentation, or the creation of new edges and patches from a continuous habitat. The causes of habitat fragmentation can be anthropogenic, like the creation of roads through a forest, but they can also be natural, like a river running through the center of a habitat. Habitat fragmentation can lead to a change in both the abundance and types of species present in the area.
Scientists often approach changes in diversity from the inside to the edge of a forest with a sampling method called transecting. A transect is a straight line that runs from one point to another. Along this line, sampling can occur in two ways: line transects, where the organisms touching the line are recorded, or belt transects, where quadrats are placed at random spots along the line and organisms within the quadrats are recorded. The line transect method is often faster, but belt transects offer a more complete view of the change in biodiversity.
In this exercise, students study tree diversity by transecting an urban forest from the edge to the interior. If students use a line transect to study the forest from edge to interior, they will find more species richness within the interior of the forest. Species within the interior are less exposed to humans, whose activity can negatively impact the habitat and thus the species.
The fall 2019 ecology lab students were unable to collect samples due to weather, but they used data collected by a previous class with a line transect method. Groups of that class obtained a 1.5-meter (5 foot) string. One student in the group took one end, while another student took the other end of the string. The first student remained at the edge of the forest while the second walked the string into the interior of the forest until the string went taunt. Then, a coin was flipped to determine which side of the line would be sampled. Students tracked the number of different tree species along this side of the line.
Once finished, the second student remained where they were while the first student on the edge of the forest walked to the interior until the string was taunt again. A coin was flipped, and students sampled the tree species along the side of the line. This process was repeated until students had taken samples from a total of 165 ft. Back in lab, students analyzed the data by creating a scatter plot with species richness along the y-axis and distance from the trail edge along the x-axis.
Of the second supplied data set, species richness, or number of tree species, varied from zero to four. Students were unable to determine if any species were overly abundant from the given data due to only having the number of species found at the interval of the line. The regression line had an R2 value of 0.1154. Pictured below is Figure 1, the scatter plot depicting the change in species richness from the forest edge to the forest interior.
Figure 1. Scatterplot of the Difference in Species Richness from Forest Edge to Interior
As seen in Figure 1, the species richness at various points along the line transect do not seem to follow the trendline. The R2 value of the plot is 0.1154. This is much less than one, which solidifies the understanding that the data does not match the trendline. Thus, there is not a clear regression or change in species richness from the edge to the interior of the forest. The proposed hypothesis that species richness could be greater in the interior of the forest is rejected. The very beginning of the line had the same biodiversity as around 65 ft. The majority of the line had only one tree species within it. This pattern seems to be random, and so distance from the edge of the forest has no apparent correlation to species richness.
Moving forward, it is important to consider how habitat fragmentation might affect species richness. For one, habitat fragmentation does not affect only plant species. Animal species likely will feel the effects as well. Take the example of a road built through an animal’s habitat. If the animal burrows on one side of the road, but its biggest food source is on the other side, the animal would have to cross the road to obtain food. If the animal travels, it would likely need to cross the road at one point. So, habitat fragmentation might separate an animal species from its home, its food source, or others in its population. Species richness would probably be greater in a fragmented habitat or larger area. In a smaller area, there would not be as much space for organisms. Less reproduction would occur because the habitat may not be able to support many organisms. In a large area, though, more species may coexist.
Exploring Ecology 