Interpreting your results for a species diversity study

Vocabulary:

Morphospecies: Individuals grouped together as a result of having common features.  Grouping individuals by morphospecies can prove very useful when one lacks advanced taxonomic knowledge (i.e., all ants with a yellow spot on the back of their thorax are grouped together, all springtails that appear identical to each other and have three tails are grouped together, etc.).

Frequency: Number of times an event occurs.

Sorenson Index: Measures the "overlap" between communities; "How many species do they have in common?"

t-Test: A tool to test whether or not the means of two groups are different.  The null hypothesis, or the starting assumption, is that the means of the two groups are the same.  If the p-value is greater than 0.05, we can not reject the null hypothesis (that is to say, there is no statistically significant difference between the means of the two groups).  If the p-value is less than 0.05, we reject the null hypothesis (meaning the means are significantly different).

 

Below is a chart intended to help students keep a record of their findings and interpret their results.

Species composition

1- List species from most abundant to the least abundant for Site 1 (native). Match each morphospecies also found in Site 2 (disturbed) by filling in its ranking in the appropriate space along with its frequency in the third column on the table below. Also add in the name of additional morphospecies found only at site 2 along with the appropriate ranking.

Name of morphospecies

Frequency at Site 1 (Native)

Frequency at Site 2 (Disturbed)

 

 

 

 

 

 

2- How many morphospecies collected at each of the two sites were found exclusively in one of the two sites?
Site 1 number of unique morphospecies:
Site 2 number of unique morphospecies:

3- For each site, calculate the percentage of the total number of morphospecies collected that these represent. (number of unique morphospecies divided by total number collected)
Site 1 percentage:         Site 2 percentage:

4- Did one site have substantially more unique species than the other?

5- If so, what possible environmental explanations can you find that could explain why you got those results?
If there was no substantial difference, why do you think you got those results?

6- Remember that a reading of 1 represents total similarity, whereas a reading close to 0 represents dissimilarity. Based on Sorenson’s index, how similar or dissimilar would you say the communities present at the sites were?

7- Did you expect this result before the data were collected?

8- What possible explanations would you suggest to account for your results?

9- What do you conclude about the impacts on species composition due to environmental disturbance? What actions might be taken to restore some of the ecological conditions that might be lacking at the disturbed site?

10- T-test Results:

Species Richness: t value:              significance:
Species Diversity: t value:              significance:

If either of your findings were significant at the .01 level, you have shown that the difference in either species diversity or species richness between the disturbed and the native site was substantiated.

If neither of your findings was significant, it could be that you have not yet collected enough samples to adequately represent any potential differences. A second possible explanation is that the two sites were not significantly different enough environmentally from each other. There could be additional explanations. What explanations do you think are most plausible?

11- If you repeated this study with more time to carry it out, how would you change the design of the study in order to get a more accurate picture of the diversity present in disturbed and undisturbed sites?