Author Topic: The Effects of Resource Quality on Community Structure  (Read 606 times)

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The Effects of Resource Quality on Community Structure
« on: January 04, 2009, 06:23:39 PM »
The Effects of Resource Quality on Community Structure
Allegheny College Department of Biology

By: Albrando Lucino Jr, B.S, B.A

Introduction:
Biological communities from varying environments all share a similar trait in that predators, prey and detritovore are bound via a feeding relationship. What is meant by this is that an autotroph will produce food via the use of photosynthesis and is preyed upon by consumers, the same way as primary producers such as plants are preyed upon by primary consumers such as herbivores who then are consumed by secondary consumers such as predators. This common theme applies for temperate stream ecosystems, which also has a food relationship in that there are multiple taxa that consume leaf litter that fall into the stream during autumn season. Leaf eating taxa such as the craneflies and other shedders will eat decaying leaves; however leaves that are reduced into small fine particles are food for other taxa such as the Hydropsychid trichopterans.
Hydropsychid trichopterans are otherwise known as caddisflies, and feed by spinning thread which then captures fine leaf particles. Therefore it is assumed that Hydropsychid trichopterans population size is correlated with the quantity and quality of food particles in the stream. Thus the purpose of this experiment is to test out the following three hypotheses; the first hypothesis states that there is quantitatively more fine particulate material in Woodcock Creek upstream of the reservoir. The second hypothesis states that fine particulate matter below Woodcock Creek Reservoir is of higher food quality and the third hypothesis states that there will be higher populations of Hydropsychid trichopterans below the reservoir.



Methods:
   First one needs to take a pre washed, dried, pre weighed glass fiber filter and then take samples in both the upstream as well as downstream of the reservoir. The filter is then redried, and reweighed.  If there is an observable weight gain, then it is attributed to suspended particles.  Results are expressed in mg particles per liter of water filtered. After that, weigh each filter, filter a volume of water, then place the filter in a numbered aluminum drying pan in the oven and reweigh after 24 hours.
   To determine the quality of the filtered particles, one needs to determine the organic content; in this case, we will need to reweigh the filters with particulate matter then place the filter in a numbered aluminum drying pan in a muffle furnace at 550 – 600o C for 1 hour.  After heating at 550-600 o C for an hour, allow to cool and then reweigh. The weight lost is proportional to organic matter.
   The determination of Hydropsychid population downstream, one needs to use Surber Samplers, which is a net with a “foot” that delineates a fixed area of stream bottom.  Place the Surber sampler in the direction of the upstream.  Properly make sure to remove the cobble on the stream bottom one piece at a time and wash by scrubbing with your hands into the net.  When clean, pass each piece of cobble to another who will rewash it into a bucket.  When the entire cobble has been removed and washed, pour the washwater in the bucket back into the net.  Then empty the collected samples in the net in a white pan and properly sort out the hydropsychids in the pan. Properly collect all samples and properly make multiple estimates of particulate matter weight, particulate matter organic content, and Hydropsychid density at locations above and below the reservoir. 

The results indicate that there indeed was a higher presence of Hydropsychids “caddisflies” in the downstream area of the reservoir with a total count of 483 and a density of 60; and a lower presence of Hydropsychid in the upstream of the reservoir with a total count of 6 and a density of less than 2. To correlate with that, there was a greater fine particle mass downstream; the downstream mass of particles in a liter of water was at around 4.25 mg/L. Upstream mass of particles in a liter of water was at around 1.75-1.80 mg/L. The percent of organic content indicated a higher organic content percent upstream than downstream with downstream content having 48% organic content and the downstream having an organic content of 80.333%.

 
Discussion:

From our prior understanding that biological communities are bound by food relationships, this was tested in this experiment. This particular experiment actually focused on temperate stream ecosystems and the importance of leaf litter had on biological taxa presence, particularly Hydropsychid trichopterans. Given that there were two sites being taken into consideration, one being the upstream and the second being the downstream of the reservoir. After analyzing the results data, one can assess the three hypotheses being tested. The first hypothesis that said there is quantitatively more fine particulate material in Woodcock Creek upstream of the reservoir. The second hypothesis stated that the fine particulate matter below Woodcock Creek Reservoir is of higher food quality. The third hypothesis stated that higher populations of Hydropsychid trichopterans will be found below the reservoir.
The first hypothesis that stated that there is quantitatively more fine particulate material in Woodcock Creek upstream of the reservoir was supported; Figure 3 shows that there indeed was higher percentage of organic weight upstream as compared to downstream as Figure 3 indicated an organic presence of 80.333% upstream whereas downstream only had an organic presence of 48%. Additionally, Table 4 provided a p value of .0004 indicating a significant difference in % organic content of the particles between the two sites. The second hypothesis that stated the fine particulate matter below Woodcock Creek Reservoir is of higher food quality was supported in that Figure 2 shows a higher mass of particles in a liter of water in the downstream as compared to the upstream. The downstream mass of particles in a liter of water was at around 4.25 mg/L. Upstream mass of particles in a liter of water was at around 1.75-1.80 mg/L, which was substantially higher. Table 3 also shows that there indeed was significant differences between mass of particulate in both downstream and upstream with a p value of <.0001. What one can correlate with this also is that there are higher counts of caddisflies found in downstream compared to upstream. This is critical because caddisflies eat small particles that are left out by shredders, which eat decaying leaves. The fact that there is a high concentration of downstream particulate mass, and a high number of caddisflies in the downstream as shown in Figure 1, Table 1 and Table 2; while only showing minor of caddisflies in the upstream signifies that a high numerical presence of Hydropsychid trichopterans means that there is a high presence of high food quality particulate mass. The third hypothesis which stated that higher populations of Hydropsychid trichopterans will be found below the reservoir was supported. From our analysis of Figure 1 indicated that there indeed was a higher density of caddisflies downstream compared to upstream. Tables 1 and 2 also supported this hypothesis in that the total counts of caddisflies upstream were only 6, while the total count of caddisflies downstream was about 483. Additionally, Table 1 indicated that there was a p value of .0003 indicating a substantial difference in caddisfly densities in downstream and upstream; with higher density downstream.
The probably cause of high amount of particulate matter percent downstream would have to be that there was indeed a high presence of craneflies and other shredders in the reservoir, which would have been responsible for shredding and dessicating decaying leaves and allowing the smaller dessicated particulate matter to be flushed downstream from the reservoir, thus allowing a high presence of caddisflies, which eat small particulate matter. To supplement this, another experiment that can be carried out would be to analyze the amount of craneflies upstream and relate their population numbers with large organic matter presence.


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