Relative Efficiency of Pitfall Trapping vs. Nocturnal Hand Collecting in Assessing Soil-Dwelling Spider Diversity along A Structural Gradient of Neotropical Habitats

Round 1

Reviewer 1 Report

The manuscript “Relative efficiency of pitfall trapping vs. nocturnal hand collecting in assessing soil-dwelling spider diversity along a structural gradient of neotropical habitats” contains original and useful data. The authors compare the efficiency of the nocturnal hand collecting (NHC) with the passive pitfall trapping for collecting soil-dwelling spiders in the Neotropics. They conclude that NHC with experienced researchers is generally more efficient than pitfall sampling (especially in simpler, less structured, habitats e.g. garden, orchard and forest edge). However, the authors also caution that combination of multiple sampling techniques is required to capture the “entire” biodiversity of Neotropical spiders.

The authors wrote a good manuscript with balanced introduction and a solid discussion. Methods are technically sound and clearly written with minor issues that have to be clarified. I think the authors have the evidence to support their conclusions and I mostly have minor comments. However, I noticed one potentially major issue with the study design and I hope the authors can clarify it:

Throughout the manuscript you are focused on sampling of soil/ground–dwelling spiders via pitfall traps and NHC and comparing method efficiency. Why then collect araneids and tetragnathids via NHC as they are obviously not ground-dwelling spiders? If you include orbweavers (or any other non-ground-dwelling spider) into the analyses, that will influence your diversity indices. And using such indices you then discuss that NHC yielded higher diversity (e.g. in orchard) of ground-dwelling spiders, which I think might be problematic.

If my interpretation of your manuscript is correct then I suggest that either you adjust the manuscript (distancing yourself from strict ground-dwelling spider focus) or reanalyze relevant data or really carefully justify why you included non-ground-dwelling spiders to “compare the efficiency of two widely used sampling techniques, pitfall traps and NHC, to capture taxonomic and functional diversity of soil-dwelling spider assemblages along a broad gradient of tropical habitats in French Guiana (lines 88-90 in MS and many other parts of the MS where you emphasize focus on ground-dwelling spiders)”.

I know that addressing the above issue might require a considerable amount of work but I think it can be done. Therefore, my suggestion to the editor is to accept the manuscript after a revision.

 

Please see additional, mostly minor comments, below:

Lines 128-129: So your pitfall traps covered 25 m² within the 250 m² area in each of the four habitats? How large was the NHC sampling area, across the whole 250 m²? There were 25 pitfall traps in each plot?

Line 132: … six person-hours per plot.

Line 134: … nighT-time …

Line 134: … sampling leaf litter … Was there leaf litter in garden in orchard? Some additional details in the entire 2.2. Sampling protocol section would be appreciated e.g. NHC details (did you collect spiders only up to the certain height, did you only collect spiders that were visible or did you actively turn over stones, dig ... did you collect all spiders or target taxa…)

Line 157-158: “The 25 pitfall traps per habitat were pooled to make pitfall samples comparable to one hour NHC per habitat”. I checked the reference [6] and I can’t clearly make the connection. Maybe an additional sentence will help readers understand better.

Lines 177-178: How many of those spiders were actually adults and how many were “big enough” juveniles?

Line 214 (Figure 2): Incorporate the absolute numbers of morphospecies to this chart. Relative abundances with a small number of morphospecies plotted on a bar chart can be highly misleading.

Author Response

Please see the attachment

 

Author Response File: Author Response.docx

Reviewer 2 Report

This is a fine paper in an area that is poorly studied and therefore I think this paper an important contribution to evaluating ecological collecting methods in tropical ecosystems. Comparatively low capture numbers and difficulties to appropriately account for differences taxonomically were overcome by looking at functional groups. Trait-based approaches are becoming more and more relevant in ecological studies and therefore this paper considers modern developments in the area.

The introduction is sound and lists the key papers in the area. Methods and result sections require, in my opinion, some fine-tuning (see below), but the discussion is appropriate in length and contents.

In the methods section I would want to see two aspects dealt with more clearly: 1) I can not quite grasp how 'nocturnal hand collecting' in leaf litter was actually done. Did the scientist just comb through litter, or just react to moving animals they say, including eye-shine? Or did they actually collect litter, for example into trays to sieve through it? A bit more detail would help, remembering that the methods part should allow exactly repeating the experiment. 2) I am still not quite sure how juveniles were treated that could not be identified. No unidentified specimens are listed in the results (which I think they should). One of the intriguing aspects of pitfall traps are that they largely (or to a higher degree than any other method including NHC) catch mature males due to higher reproductive activity. Hence, pitfall trap generally catch a larger percentage of identifiable spiders, an aspect that is not discussed in this paper. Looking at the low capture numbers overall, it would be great to add this aspect to the study.

Otherwise I have little to criticise (please find minor comments in the attached manuscript file), congratulations on a fine effort!

 

Comments for author File: Comments.pdf

Author Response

Please see the attachment.

Author Response File: Author Response.docx