Population Description (hypothesizing, collecting data; doing analysis; interpretation)
Question: Do individuals of a population of a single species differ between your two sites? In week 2, you should have selected a species that is found in both sites and that you can capture and handle a large number of, such as a particular plant, invertebrate, or maybe even a fish (if you have the appropriate local fishing license).
This week, your task will be to test your hypothesis about how your variable of interest (the physical factor that is different between your two sites) affects this species in a way that you can actually measure. Consider traits that may influence how well the species functions. Examples might include height, leaf length or number, flower length, fish length, invertebrate weight, etc. – choose a trait that you can measure with the tools available to you.
Step 1: Review the single species you chose to focus on and the method you chose to find, capture, and measure it (e.g., transect sampling, plot sampling).
Step 2: Decide on the measurable aspect you will focus on for this exercise.
Step 3: Review/refine your hypothesis (from week 2) about how your variable of interest (the physical factor that differs between your two sites) might affect this measurable aspect.
Step 4: Make a prediction based on that hypothesis: What difference do you expect to see in your measurements between your two study sites?
Step 5: Design a sampling plan for how to sample individuals and collect your measurement data Refresh your memory about sampling strategies here. Your sampling plan should include:
A sampling method (e.g., direct measurement of individual organisms or parts of organisms, plot survey, line transects, or point-count survey)
A target sample size – you must measure at least 40 individuals of your species at each site. Make sure that you are sampling individuals – for example, if you are collecting data on leaf width, you must measure 40 leaves from 40 different individual trees at each site, NOT 40 leaves from the same individual tree! Taking multiple data points from the same individual is called pseudoreplication and can severely bias your study.
A plan for how to select which individuals to measure – remember that your sample selection should be random. One option might be to flip a coin whenever you encounter a tree along your transect line – heads you measure a leaf from it, tails you don’t. Continue along the transect until you’ve measured 40 individuals.
NOTE: While randomized sampling is the ideal, you may find your options constrained. If your study sites are small and you don’t have more than 40 individuals to randomly select from, you can go ahead and measure them all. Just be prepared to discuss this limitation as a potential source of bias in your interpretation of your results.
A clear plan for what you are measuring and how you will measure it.
Step 6: Once you have designed your sampling plan, travel to your site and collect your measurements. Be sure to bring all the measurement and data recording tools you need, and dress appropriately for conditions. If it is hunting season in your region, be sure to wear blaze orange when you go out.
Step 7: If you choose, you may take a selfie of yourself doing the work. If you choose not to include yourself, you must still include the other photo requirements.
Step 8: Analyze your data. Follow along with this video for guidance: Compute the following for each study plot separately:
Sample size (N)
Sample mean (x̅) – this is a measure of the center of your data values
Sample variance (s2) – this and the rest are measures of the variability of your data values
Standard deviation (s)
Standard error (SE)
95% confidence interval lower (LCI) and upper (UCI) limits
Step 9: Make a column graph comparing the means of the two study sites; include error bars depicting the 95% confidence interval around each mean estimate. Here is a video explaining how to do this.
Step 10: Create a table in Excel displaying your summary statistics for each site. Format your table as shown here.
Step 11: What do we know about how your factor of interest affects your organism? Find and read/view two credible sources relating to this question. NOTE: If you can’t find information on your species, extrapolate based on what is known about a similar species.
Submission – Submit the following in a Word document:
Step 1: The steps of your sampling plan in paragraph form, with the following requirements:
Write in the past tense
Write in enough detail that a future ecology student could replicate your exact project using only this text as a guide
Do not include a list of materials, but DO mention materials in context as you describe the steps of your protocol.
Include a sentence at the end that describes your analysis (e.g., “For each site, I computed …”)
Step 2: If you choose, you may take a selfie of yourself doing the work. If you choose not to include yourself, you must still include the other photo requirements.
Step 3: Your summary stats table from #11 above
Step 4: A paragraph comparing the two sites that addresses the following:
How many individuals did you measure in each site?
A brief description of whether or not the means were significantly different, and if so, which plot had the greater mean.
In order to determine whether your means are statistically different, examine your two confidence intervals. If there is overlap (e.g., the upper limit for one is higher than the lower limit for the other), then the means are not significantly different, at least not within your power to detect given your sample sizes and measurement precision. If there is no overlap, then your means are significantly different. This comparison is what you will draw on determining whether or not your hypothesis was supported.
If your mean measurements were significantly different, which site had the greater mean?
Which site had the greater variability?
How did your results compare to your prediction?
Did your results support or negate your hypothesis? Explain.
What other factors do you think may have influenced your findings?
Step 5: A paragraph discussing the results of your literature search (#8 above). Summarize their key points, then relate them to your work here. Did you find the same pattern in your data, or were your results different from what your sources suggest? Cite your references using APA format; include in-text citations.
Step 6: A graph depicting your mean and confidence interval comparison
Last Completed Projects
| topic title | academic level | Writer | delivered |
|---|