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I would like to start a monitoring in different caves, compare caves of different age and length, and find out if there are any correlations between these factors and their diversity.

I was thinking to use the Shannon-Wiener diversity index and to use both pitfall traps and timed area search sampling methods. Can I get a single index value for each cave even if the methods are different?

And what about that caves which have stream or pools where the fauna can be very abundant? Even if I collect a sample of water, the abundance of certain species can be very high (e.g. copepoda).

Sorry for the banal questions but I have not experience with indices and statistics.


Clarification after comments:

I have about 20 caves to sample, I want to compare the fauna of these caves (richness and abundance). As I told they have differents lenghts, ages and others environmental features. Some of the caves have also streams or little pools (where I will take water samples to identify the fauna).

I have read some articles where the diversity indices were calculated using just one single methodology (traps or timed area search), and also for only one kind of fauna (acquatic or terrestrial).

The question is: Is there any methodology to get one single value of diversity index for each cave? (which considers both terrestrial and aquatic fauna). Or maybe in these conditions I can just get the number of species for each cave, without being able to compare their abundance?

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  • $\begingroup$ So if I understand you have cave with only pitfall and cave with only timed area search sampling methods ? $\endgroup$ – Nico Coallier Apr 6 '16 at 21:56
  • $\begingroup$ Not sure if you can read the answer that I wrongly deleted. No, I was thinking to use both method in each cave. The question is, can I get a single index value for both aquatic and terrestrial fauna? $\endgroup$ – Joseph Apr 7 '16 at 17:17
  • $\begingroup$ Why do you wanna do that ? $\endgroup$ – Nico Coallier Apr 8 '16 at 3:23
  • $\begingroup$ If I have two index values for caves which have both aquatic and terrestrial fauna, and just one value for others which have only terrestrial fauna, how can I compare them (in terms of abundance and richness)? $\endgroup$ – Joseph Apr 8 '16 at 14:21
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You could account for this in your statistical analysis. I'm assuming that you will collect terrestrial fauna the same way in every cave, and if there is a stream in a cave aquatic fauna will be collected in some standardized way as well. I'll also assume you'll have some other explanatory variables that you think may explain diversity, richness, or abundance. These could include cave temperature, length, depth, etc.

Calculate the Shannon-Weiner index for each cave using all species and abundances, whether they came from an aquatic or terrestrial sample. Then for you statistical model include whether a stream was present in a cave or not using a binary variable along with your other explanatory variables.

index ~ f(temperature, length, depth, stream)

In this example temperature, length, and depth are all continuous variables. Stream will be a binary variable (either 0 or 1, 1 meaning a stream was present). This will give you a measure of how much a stream contributes to diversity.

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