This week, in Dr. Beasley’s Ecology lab, we focused our studies on dispersion patterns of organisms, with a specific focus on Paspalum distichum, or dallisgrass. Paspalum distichum is a monocot, and a perennial grass that can be found all across North America. It is most commonly found in wet areas, or along the shores of streams and ponds, but it can also be found in dry, or well-drained areas.
In order to understand dispersion patterns, we must first understand that population distribution is defined as the spatial arrangement, or geographic range, of individuals in a local population. Population distribution also includes shape, size, and location of that area. Dispersion patterns can be classified as clumped, regular, or random. Clumped dispersion patterns are the most common type of dispersion, and are typical when patchy resources are available or among social organisms. Regular, or uniform dispersion patterns occur when there is uniform distribution of scarce resources, or where there is intraspecific competition for resources. Random distribution is a rare type of distribution, and occurs when the environment is relatively uniform and resources are equally available.
For this week’s lab, we practiced the quadrant plant sampling method in order to collect data on dispersion patterns of Paspalum distichum. We collected our data in a nearby Confederate Cemetery that is adjacent to the UTC campus. The quadrant plant sampling method is a sampling procedure in which randomly selected plots, or quads, of an ecosystem are examined and species within these quads are then quantified. Each quad was measured by a 1 meter squared quadrant made out of PVC pipe. Using a random number generator, our group randomly selected each quadrant by selecting a random number, walking that amount of paces, placing the PVC quadrant on the ground, and counting the number of Paspalum distichum individuals found within the quadrant. If 50% or more of the plant was present in the PVC quadrat, we counted that plant in our data. We repeated this method until we had sampled 15 quadrants and recorded the numbers of individuals in each quadrant.
After collecting our data, I calculated the density of our samples by dividing the total number of all individuals of Paspalum distichum in all quadrants by fifteen meters squared. My result was 11.06 per square meter.
Paspalum distichum is known to grow in moist or wet areas, along the shores of streams and ponds, and in wet prairie areas. When we collected our data, it was a dry and warm sunny day. We noted that Paspalum distichum was less abundant in the shadier quadrants we sampled, and appeared to be more abundant in sunnier areas. We also noted that Paspalum distichum was not found in close proximity to any of the large trees with vast root systems in the area. This could be due to reduced water availability resulting from the tree roots.
Based on our data collection and observations, I predict that the overall distribution of the Paspalum distichum in the Confederate Cemetery is clumped. We observed these individuals in patches of high abundance that was clearly separated by areas of low abundance. There were some quadrants for which we recorded a zero count for individuals present, and there were other quadrants in which up to 52 individuals were observed and counted. This clumped distribution is due to the attraction between these individuals to a common resource, in this case, most likely sunlight and available water.
References
Paspalum distichum (Knotgrass), www.cabi.org/isc/datasheet/38952.
HUANG, W. Z., et al. “Effects of temperature, light and certain growth regulating substances on sprouting, rooting and growth of single‐node rhizome and shoot segments of Paspalum distichum L.” Weed Research, Blackwell Publishing Ltd, 28 July 2006, onlinelibrary.wiley.com/doi/10.1111/j.1365-3180.1987.tb00737.x/full.
“Center for Aquatic and Invasive Plants.” UFIFAS Center for Aquatic and Invasive Plants, plants.ifas.ufl.edu/plant-directory/paspalum-distichum/.
Harry, Rose. Paspalum distichum flowerhead3. South West Rocks, 13 Jan. 2009.
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