-->PONE-D-26-07315-->-->Trap tales: The influence of red alder stand conditions and forest fragmentation on family-level beetle bycatch diversity-->

PLOS One

Dear Dr. Carroll,

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I've received comments from three reviewers. Based on their assessments as well as my own, I believe that your manuscript may be suitable for publication with a moderate level of revision. I agree with you (as do all the reviewers) about the information value of insect trap bycatch, and so I applaud you for undertaking this effort. I think the main criticism that emerges from the review comments is that you need to provide a fuller account of the methodological limitations of the study in your Discussion. You should also reexamine your conclusions, some of which should probably be tempered due to these limitations. Additionally, some aspects of your manuscript would benefit from clarification -- please look to the specific comments for guidance in that regard. Again, the reviewers and I see the merits of your manuscript, and because it is well-written and organized overall, I would be happy to reconsider it if you make the necessary changes.

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Additional Editor Comments:

L17: insert comma after "diversity"

L81: should be "promotes" instead of "promote"

L202-203 ("...and dead if foliage was absent for deciduous trees ..."): This implies that the stands were inventoried in leaf-on conditions. Was that the case? I would indicate in the text.

L208-211: So, in retrospect, would a different plot configuration have been better? For example, three smaller fixed-area plots at each location. Or would the result have been essentially the same? This is primarily a point for discussion (i.e., plot configuration matters, perhaps especially with small sample sizes).

L289-292: I agree that it makes sense to prioritize minimizing false negatives.

L345: use "spp." instead of "sp."

L349: replace "comprising" with "comprised of"

L376-378: Did the five sites differ noticeably in the main drivers of fragmentation? For instance, MK was the most remote but had a moderate level of forestry-related fragmentation. Were any of other sites similar? (Another point for discussion.)

L385-387: See previous comment. Did BL have any forestry activity?

L388-392: I do worry somewhat that five sites are not sufficiently representative of the landscape diversity. (Again, a point for discussion.)

L459-465: I'm not sure we can put too much stock in these results. 60% of the traps were in sites where there were no dead red alders recorded in the forest plot, so they're all represented as zeros even if there was some variation in dead red alder presence within the larger area. Again, in retrospect, would you have been better served by a different inventory plot configuration?

L478-479: I think we can put more stock in these results, given the between-site variation.

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Reviewers' comments:

Reviewer's Responses to Questions

-->Comments to the Author

1. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented. -->

Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #3: Partly

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-->2. Has the statistical analysis been performed appropriately and rigorously? -->

Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #3: Yes

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-->3. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.-->

Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #3: Yes

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-->4. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.-->

Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #3: Yes

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-->5. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)-->

Reviewer #1: I have a few separate comments for the authors:

- Redo the abstract. Specify exact numbers, not abstract words.

- The introduction lacks information about beetle baits based on beer, sugar, ethanol, and other agents. See such publications (https://doi.org/10.1134/S0013873824010056; https://doi.org/10.1007/s10841-017-9965-3; https://doi.org/10.1649/0010-065X-74.4.763; https://doi.org/10.3390/insects15060420) and give their analysis separately.

- Why weren't the beetles identified before the species?

- Why do I need Figure 2? It shows nothing and is of very poor quality.

- Make a conclusion

Reviewer #2: I enjoyed reading the manuscript about beetle family diversity in red alder ecosystems. It is well written and structured. Methods and analyses seem very solid.

I appreciate the authors’ use of bycatch from existing insect traps for ecological analysis. I agree that bycatch deserves ethical consideration and can be a valuable and cost effective source of data for many ecological research questions.

I also recognize the limitations of this sampling method. Because these traps are designed mainly to catch flying, terrestrial insects, some beetle families are likely underrepresented or missed entirely. For example, mostly ground dwelling or flightless groups, such as Carabidae, are unlikely to be sampled well using this approach.

I therefore suggest adding a clearly defined paragraph or section that explicitly discusses the limitations of the study and of this sampling method. Although these limitations are mentioned briefly, especially in the first paragraph of the Discussion, I think they should be stated more clearly and in a more structured way. This would improve transparency and help readers better understand how broadly the results can be interpreted.

Regarding the first paragraph of the Discussion, I suggest revising it substantially. Much of the information presented there seems more appropriate for the Results section. For example, the Discussion repeats which beetle families were captured as bycatch, even though this information is already presented in the Results and Table S2. The Results section already reports the total number of beetles and families captured, as well as the most abundant families. The Discussion would be stronger if this repetition were reduced and the focus shifted toward interpretation, including methodological limitations such as possible taxonomic biases in sampling.

I also have a question about the field measurements. Were all stand level metrics collected by the same researcher? If not, how was observer bias addressed? This is especially relevant for measurements such as DBH, where small differences among observers could affect the results. Clarifying this would increase confidence in the reliability of the field data.

The authors use single predictor models to assess the relationship between stand conditions, fragmentation metrics and beetle diversity. While this approach is useful for exploratory analyses, it does not allow assessment of the relative importance of predictors or their effects after accounting for correlations among variables.

Could the authors clarify why multivariate models were not used, for example after checking collinearity among predictors? Including multiple predictors in a single model (with standardized coefficients) would allow direct comparison of effect sizes and help identify which variables have the strongest associations with richness or diversity.

If the intention is not to rank predictors, this limitation should be stated more explicitly. It would also be helpful to clarify whether single predictor models were compared (e.g. using AICc), and what conclusions can reasonably be drawn from such comparisons.

Reviewer #3: The study makes a relevant and timely contribution, particularly given the limited ecological research on Alnus rubra–dominated systems. By focusing on beetle diversity in red alder ecosystems, the authors address a clear knowledge gap in a habitat increasingly affected by disturbance and fragmentation. The use of beetle bycatch from ethanol-baited traps is both efficient and cost-effective, effectively leveraging existing monitoring efforts targeting ambrosia beetles. This approach aligns well with contemporary trends in integrative and low-impact biodiversity assessment.

The study is grounded in a clear, hypothesis-driven framework linking stand conditions to habitat and resource availability. The inclusion of ecologically meaningful variables—such as deadwood, forest continuity, and structural heterogeneity—represents a notable strength, particularly given their well-established importance for saproxylic beetles. Furthermore, the application of appropriate statistical models demonstrates awareness of the distributional properties of count data (e.g., overdispersion), thereby enhancing analytical rigor.

However, several methodological and conceptual limitations should be considered when interpreting the results.

A primary concern is the limited taxonomic resolution. Identification restricted to the family level substantially constrains ecological inference: it obscures species-specific responses to stand conditions and fragmentation, reduces sensitivity to subtle changes in biodiversity, and may mask contrasting trends within families. This limitation is particularly critical in Coleoptera, where ecological differentiation within families can be considerable. In the same context, the use of Shannon diversity at the family level may inflate perceived diversity patterns and obscure biologically meaningful variation occurring at finer taxonomic scales.

Sampling bias associated with the trap type represents an additional limitation. Ethanol-baited multiple-funnel traps selectively attract specific ecological guilds, particularly xylophagous and saproxylic taxa. As a consequence, the resulting dataset is not representative of the entire beetle community, with underrepresentation of non-attracted groups (e.g., herbivorous or ground-dwelling taxa). Therefore, conclusions regarding beetle diversity should be interpreted as reflecting trap-biased assemblages rather than the full community.

The relatively small number of study sites (five forests) further limits statistical power and the generalizability of the findings. It also constrains the ability to disentangle potentially correlated environmental variables. In addition, the possibility of pseudoreplication should be explicitly addressed, particularly if multiple traps within sites are not appropriately accounted for in the analytical framework.

Temporal limitation is another important issue, as sampling was conducted in a single year (2024). This restricts inference about interannual variability and limits the robustness of conclusions about fragmentation effects. Beetle assemblages are known to exhibit substantial temporal fluctuations driven by climatic and stochastic processes.

Although fragmentation is included as a predictor, the use of relatively simple metrics (e.g., connectivity, patch size) may not fully capture landscape complexity. Key processes such as matrix quality, edge effects, and dispersal constraints may therefore be underrepresented, limiting causal interpretation. Relatedly, potential confounding between stand structure and fragmentation should be considered, as these factors are often correlated; without explicit control for collinearity, disentangling their independent effects may be difficult.

While the Discussion provides a thorough ecological interpretation of the observed patterns, the study's methodological limitations are only partially acknowledged and not consistently integrated into the interpretation. In particular, the implications of trap selectivity, family-level taxonomic resolution, limited spatial and temporal replication, and simplified habitat characterization remain underdeveloped. As a result, several conclusions—especially those referring broadly to beetle diversity and fragmentation effects—are stronger than warranted by the data. I recommend explicitly consolidating these limitations within the Discussion and aligning the scope of inference more closely with the study design.

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Reviewer #1: No

Reviewer #2: No

Reviewer #3: No

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Trap tales: The influence of red alder stand conditions and forest fragmentation on family-level beetle bycatch diversity

PONE-D-26-07315R1

Dear Dr. Carroll,

We’re pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it meets all outstanding technical requirements.

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Kind regards,

Frank H. Koch, PhD

Academic Editor

PLOS One

Additional Editor Comments (optional):

I've received comments from two reviewers, both of whom also evaluated your initial submission. The three of us agree that your revised manuscript is an improvement over the initial version. You clearly took some care in responding to the reviewer comments. In particular, I appreciate the additional text in the Discussion regarding your study's limitations, which in my view do not really diminish your findings nor your larger message about the value of bycatch.

Reviewers' comments:

Reviewer's Responses to Questions

-->Comments to the Author

1. If the authors have adequately addressed your comments raised in a previous round of review and you feel that this manuscript is now acceptable for publication, you may indicate that here to bypass the “Comments to the Author” section, enter your conflict of interest statement in the “Confidential to Editor” section, and submit your "Accept" recommendation.-->

Reviewer #2: All comments have been addressed

Reviewer #3: (No Response)

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-->2. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented. -->

Reviewer #2: Yes

Reviewer #3: Yes

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-->3. Has the statistical analysis been performed appropriately and rigorously? -->

Reviewer #2: Yes

Reviewer #3: Yes

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-->4. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.-->

Reviewer #2: Yes

Reviewer #3: (No Response)

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-->5. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.-->

Reviewer #2: Yes

Reviewer #3: Yes

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-->6. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)-->

Reviewer #2: (No Response)

Reviewer #3: The authors appear to have addressed all of the major concerns raised in my review. They have added clearer acknowledgments of the limitations associated with taxonomic resolution, trap selectivity, limited spatial and temporal replication, simplified fragmentation metrics, and potential pseudoreplication. They have also appropriately narrowed the interpretation of their findings to flying terrestrial saproxylic beetles and clarified that the study provides comparative insights rather than a complete assessment of beetle biodiversity. The revisions improve the transparency and balance of the manuscript, and the authors have adequately incorporated the requested methodological caveats into the Discussion.

I have no further major concerns. The manuscript has been substantially improved and is suitable for publication after these revisions. I recommend acceptance.

I also hope that, in the future, the authors will be able to process this valuable material further and achieve species-level identification, enabling a more detailed assessment of community composition and species-specific ecological responses. I wish them success in this important continuation of their work.

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-->7. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files.

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Reviewer #2: No

Reviewer #3: No

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