Hello, I have a dataset of zooplankton abundance and I have to calculate a biodiversity index. I was thinking about the Shannon-Wiener.
Data of abundance per each species is calculated through an average between two replicate hauls. My tutor is saying I can't apply the Shannon-Wiener because I have an average instead of an absolute value. She's not an ecologist though, and she's not used to work with biodiversity indices. Do you think it's a problem that the dataset takes into account the average of the replicate hauls instead of the absolute value of abundance in order to calculate the Shannon-Wiener?
Hello Angelo; Since your two hauls were intended to sample one population the sum of each species abundances would satisfy the requirements of the SW index. I think that you can use the SW index for your analysis.
Best regards, Jim Des Lauriers
What is the reason for the two replicates? Why dont you take it as a "random effect" in a mixed model? Averaging loses a lot of information and perhaps is a practice that should have been abandoned a while ago.
Hello Angello, I think you could obtain one diversity value for each replica and then calculate the media value of those two diversity indices as a representative value of the diversity in each sample site. Or, maybe, report each value separately as representing the diversity. The diversity values should be similar if the data are a "good" replica. What do you think?
Wim Kaijser Federico Giri unfortunately i don't have access to each replica because i didn't do the sampling myself, it's open-access data coming from the CPR (continuous plankton recorder) and only the averaged values are available.
This is the CPR website: https://www.cprsurvey.org/
This is the link to download files: https://www.bodc.ac.uk/data/published_data_library/catalogue/10.5285/285d5ae7-934f-f7c4-e063-7086abc031fc/
The point of my tutor is this: in the dataset, there are values like 14.37 that are not counts, but come from an average and are standardized for a cubic meter to calculate the average abundance of a taxon per cubic meter. Because those are not raw counts, I can't use them for the Shannon-Wiener index. But I still have the same doubt James Des Lauriers brought up: if they sampled the same population, couldn't the averaged standardized values be used anyways? Does it really change that much if it's not raw counts?
Hello Angelo; Reading your second comment, I think that your tutor might be correct. Are all of the values in the dataset presented as "the average abundance of a taxon per cubic meter"? If so, you are attempting to measure relative abundances. As I read the requirements of the SW index...if ALL of the values are presented that way then you can still use the SW index.
Repurposing data this way is hazardous, particularly if you are the least bit uncertain about how the raw data were treated. Read the requirements of the test carefully and follow them exactly. Otherwise you'll get an answer but it may well be bogus. Lots of published studies have fallen into just such a trap. Best regards, Jim Des Lauriers
1. Ecosystem Health Assessment
- Biodiversity Monitoring: H' is used to assess the health of ecosystems, where higher diversity often indicates a healthier and more stable environment.
- Disturbance Impact Analysis: It helps measure changes in biodiversity due to disturbances like deforestation, pollution, or habitat fragmentation.
2. Comparative Analysis
- Spatial Comparisons: Comparing biodiversity across different ecosystems, such as forests, wetlands, or grasslands.
- Temporal Studies: Monitoring biodiversity changes over time, such as pre- and post-human interventions or natural disasters.
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