Shannon Diversity Index - Do you need the same species across sites to compare?

[Emma_Holman]

Hello,

I comparing fish diversity from the years 2013 to 2018 in a freshwater river system. There are however different species present in some years. Can I still use the Shannon Index to compare diversity? I have attached my calculations below.

Thank you!

 

[katxt]

Yes you can. How will you actually compare them?

 

[Emma_Holman]

Well the index for from 2013 to 2018 can be seen to drop which indicates overall diversity is decreasing over time? Is a stats test required to see if they’re significant?

 

[katxt]

You could do a regression of diversity onto time and see if the p value for the slope is less than 0.05.

 

[Emma_Holman]

What type of regression would you suggest is best to use? I'm analyzing my data on SPSS.

 

[katxt]

Put the year and diversity into two columns. Analyse, Regression, Linear. Make Year the independent variable and Diversity the dependent variable. Then look for the p value in the output anova table or the coefficients table