Can t-tests be used to compare ecological indices from different sampling sizes?

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SUMMARY

The discussion centers on the statistical comparison of ecological indices derived from plant species occurrences across varying transect lengths in coastal dunes. José A Macedo poses a question regarding the appropriateness of using t-tests to compare two groups of beaches (erosive and non-erosive) based on these indices. Participants emphasize the need to understand the nature of the indices, specifically noting that they are species co-occurrence indices calculated using presence/absence data in 0.5 m segments. The consensus suggests that standardizing transect lengths may be necessary for valid statistical comparisons.

PREREQUISITES
  • Understanding of t-tests and their application in ecological studies
  • Familiarity with ecological indices, particularly species co-occurrence indices
  • Knowledge of data collection methods in ecological research
  • Basic statistical analysis skills using software such as R or Python
NEXT STEPS
  • Research the implications of using t-tests for ecological data comparisons
  • Learn about methods for standardizing transect lengths in ecological studies
  • Explore the calculation and interpretation of species co-occurrence indices
  • Investigate alternative statistical methods for comparing ecological indices across different sampling sizes
USEFUL FOR

Ecologists, statisticians, and researchers involved in biodiversity studies, particularly those comparing ecological indices across varying sampling conditions.

macedo
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Hello everyone

I would like that you may help me with this following question:

I have data from plant species occurrences from 30 sites (10 beaches with 3 replications for each one; 6 beaches not in erosive process; 4 in erosive process) in coastal dunes vegetation.
At each site I have made data collection along one transect (so all the 30 transects have different lengths and sometimes very different (namely between beaches), the smaller with 8 m and the bigger with 130 m).
I have calculated different ecological indices which gave me naturally 30 different values for each site.
Now, I grouped the 10 beaches in two groups (2 different environmental conditions: erosive beaches (12) and not erosive beaches (18)).
May I compare the two groups with all the data (with all the complete transects) with a t-Test or I have to previously to cut to a common length to all the 30 transects in order to compare statistically the data?
Thanks you for your attention
Sincerely
José A Macedo
 
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macedo said:
Hello everyone

I would like that you may help me with this following question:

I have data from plant species occurrences from 30 sites (10 beaches with 3 replications for each one; 6 beaches not in erosive process; 4 in erosive process) in coastal dunes vegetation.
At each site I have made data collection along one transect (so all the 30 transects have different lengths and sometimes very different (namely between beaches), the smaller with 8 m and the bigger with 130 m).
I have calculated different ecological indices which gave me naturally 30 different values for each site.
Now, I grouped the 10 beaches in two groups (2 different environmental conditions: erosive beaches (12) and not erosive beaches (18)).
May I compare the two groups with all the data (with all the complete transects) with a t-Test or I have to previously to cut to a common length to all the 30 transects in order to compare statistically the data?
Thanks you for your attention
Sincerely
José A Macedo

I think we need to know what the nature of the indices are.

CB
 
hello
Thanks for the message. The indices are species co-occurrence indices (null models) calculated with presence/absence of species in each 0.5 m.
Thank you again
Jose
 

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