Ecology is the scientific study, which focuses on the interactions between organisms and their environments as well as interactions with other organisms. Stream ecology is a subset of ecology that observes the interactions between the organisms found within the stream and their interactions with the stream itself. A contributing factor to stream ecology is leaf degradation. Leaves that fall into a stream create a significant impact on the energy flow and nutrient cycling of the stream’s ecosystem.
Leaves provide an abundant amount of organic material for many of the organisms within the stream. Decomposed leaves are a particularly important carbon source for the microbial organisms found in aquatic ecosystems (Nelson, 2011). Various species of leaves fall into the streams, which begs the question of whether there is a preference between leaves. Despite the fact that they are all comprised of energy-rich material, there is a possibility that certain types of leaves are more commonly favored by the microbial organisms.
In lab, the consumption of leaf species commonly found in streams was examined. In the experiment, amphipods feeding preferences were observed by examining the percent consumption differences between the Norway and Silver leaf species. Amphipods are small invertebrate shredders that feed primarily on the soft tissue of leaves. Through this, amphipods convert the coarse particulate organic material into a fine organic matter particulate. The fine organic particulate can then be used as a nutrient source for the filter feeders that also reside within the stream.
The biological hypothesis used for the experiment stated that shredders held a feeding preference that affects the leaf consumption between leaf species. The amphipods were exposed to two different leaf species in order to determine whether one species was favored over the other. The null hypothesis stated that amphipods did not have a significant preference that would affect the mean consumption of the leaf species. The alternative hypothesis stated that these is a significant difference in the feeding habits of shredders, which affects the mean consumption between the leaf species.
It was predicted that the Norway species would be preferred over the Silver species. This prediction arose because the Silver species seemed to be slightly thicker than the Norway species, thus making it more difficult for the shredders to chew up the Silver leaves. Methods The experiment consisted of two separate parts. In the first part of the experiment, the class was divided into groups in order to try to formulate an experimental design capable of answering the experimental question of their choice. Certain members of each group were assigned specific roles in order to construct the various parts of their experiment.
Once the groups finished their design, each group presented their experiment to the class, the class then voted on the experiment that they considered being the best. The group members whose design was chosen were then tasked with leading through their proposed procedure. The design chosen by the class wished to determine if there was a feeding preference towards leaf species among the amphipods found within a stream. The experiment proposed by the winning group consisted of the class dividing into groups of two or three. Each group then had to fill a labeled cup of water with 100 mL of stream water. Groups then had to cut 1. X 1. 5 cm square samples of each leaf species (Norway and Silver). The leaves being cut for samples were leaves that had been soaking in Chicago River water for two weeks prior to lab. Each specific sample was then labeled with a colored pin in order to distinguish the samples and then both samples were placed into the labeled cup of stream water. Finally, three amphipods were placed into the cup containing the two samples. The amphipods were then left in the cup for one week, after which the leaves were removed and bagged by the instructor. After one week, the second half of the experiment was conducted.
This portion of the experiment consisted of each group examining their leaf samples for any signs of consumption. The groups were then tasked with sketching the remains of each sample in a 1. 5 X 1. 5 cm grid. Using these small sketches students then drew a larger image of their samples on a 9. 0 X 9. 0 cm grid. Each group then used their sketches to calculate the percent of material consumed in each leaf sample. The percent-consumed values were then reported in order to perform a statistical test. Results The results of the experiment are presented through a number of images, a graph, and a table.
Also included are the calculations for the percent consumption values for the Norway and Silver leaf samples. The table listed displays the data collected by the class as well as significant values necessary to perform a paired-sample t-test. Finally, the graph shown is a line graph that depicts the raw data collected. Figure 1. Sketch of Norway Leaf Sample Figure 1 is an illustration of the remains of the Norway leaf sample after being consumed by amphipods for one week roughly translated to a 9 X 9 cm grid. The shaded areas represent the portions of the leaf that were consumed.
The percent consumed value for the Norway leaf was calculated by dividing the number of consumed material (number of shaded squares) by the total number of squares, which was equal to 8100. The quotient of those two values was multiplied by one hundred in order to determine the percentage of material consumed. Percent Consumed (Norway): % consumed=((# of shaded squares)/8100)•100% % consumed=(6450/8100)•100% % consumed=79. 63% Figure 2. Sketch of Silver Leaf Sample Figure 2 is a sketch of the Silver leaf sample after one week of being consumed by amphipods. The areas consumed are represented by the dark shaded areas.
The percent-consumed value for the Silver leaf sample was determined by dividing the number of consumed material (number of shaded squares) by the total number of squares, which was equal to 8100. The quotient was then multiplied by one hundred in order to determine the percentage of material consumed. Percent Consumed (Silver): % consumed=((# of shaded squares)/8100)•100% % consumed=((12. 96)/8100):100% % consumed=0. 16% Table 1. Class Data and Statistical Analysis Group Norway (%) Silver (%) Difference (%) 187. 72 8. 64 79. 08 245. 60 12. 30 33. 30 379. 63 0. 160 79. 47 497. 51 097. 51 561. 3 15. 43 46. 30 637. 04 0. 00 37. 04 720. 40 2. 50 17. 90 814. 80 0. 00 14. 80 979. 00 1. 60 77. 40 10 56. 70 30. 80 25. 90 11 72. 99 072. 99 Average 59. 37 6. 49 52. 88 SD 27. 29 9. 79 29. 10
Table 1 displays the data collected in class for the percent consumption of each group’s leaf samples. Also shown the difference in consumption between each group’s silver and Norway leaves. Using this data, the average percent consumption and the mean difference in consumption were calculated. The mean difference and standard deviation values for this experiment were calculated to be 52. 88 + 0. 29.
The tstatistic value was determined to be 6. 04. Figure 3. Line Graph of Class Data Figure 3 is a line graph that depicts the difference in percent consumption values for each groups Norway and Silver leaf samples. Discussion By observing the data collected, it is clear that the leaf species had a significant effect on the rate of consumption by amphipods. This is not only supported by the drawings of the two leaf samples in Figures 1 and 2 but also by the results of statistical analysis. The paired t-test showed a t-statistic value of 6. 048 this value is greater than the t-critical value, which was 2. 228.
A calculated t-statistic value that is greater than the tcritical value is indicative of a <0. 05 probability that the difference in means was found by chance, meaning that the proposed null hypothesis can be rejected. Rejecting the null hypothesis means that there was an observable preference in the amphipod’s leaf consumption. Figure 3 also illustrates the amphipod’s feeding preference as it clearly shows that the Norway leaf samples were commonly more consumed compared to the Silver leaf samples. Knowing this it would be expected that in a stream environment, amphipods would be much more likely to consume Norway leaves than Silver leaves.
This result corresponded to the prediction made before the experiment was conducted. The amphipod feeding preference is probably due to the Norway leaves’ softer texture. Amphipods are capable of chewing on the soft tissue between leaf veins however, as seen with the data collected amphipods seem to favor softer leaf species because amphipods are able to consume softer with much less effort. By favoring the softer Norway leaves, amphipods are able to convert the coarse particulate organic matter into fine particulate matter much easier than the Silver leaves.
This means that softer leaves would offer much more fine leaf particulate matter, which would in turn provide more nutrients and energy sources to lower level feeders in comparison to tougher leaves. Any errors or deviations found within the data were most likely due to a number of possible human errors. An example of this would be inconsistent measurements of the consumed portion of the leaf samples. Another possible source of error could have been due to the confusion of what was consumed in each sample. If group members were unsure of what to consider as consumed, discrepancies within the data would have arisen.
Similar discrepancies would have resulted if the leaf samples were inconsistently cut. One way in which the experimental design can be improved would be to have all of the leaf samples cut by one person. Making this adjust would ensure that the samples used in the experiment would be measured and cut in a uniform fashion. An improvement that could be made for the stream ecology lab would be to allow the class to propose suggestions to improve the winning experiment design. By doing this, the class would ensure that the experiment being performed would be the best version possible.
