PONE-D-23-00796Insect decline in countries of Central and Western Europe - Drivers and pressures of Carabidae and Lepidoptera population and biodiversity trendsPLOS ONE

Dear Dr. Baden,

Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process.

This manuscript has been now evaluated by two expert reviewers. Both of them find the work valuable and interesting, but have several concerns with it current presentation. Reviewer 1 requires higher clarification regarding the approach, the drivers and pressures. Reviewer 2 thinks that it should be clearer that this review focuses on agricultural landscapes, and that the discussion is quite long with much of the text focusing on ‘data limitation, quality etc’, whereas the interpretation of the findings should come more to the forefront. I concur with these comments and therefore invite the authors to conduct a deep revision of the manuscript. If the authors are interested in revising the manuscript, they should adjunct to the revised manuscript a response letter in which all the comments of the reviewers have been answered point-by-point.

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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

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

Reviewer #1: N/A

Reviewer #2: N/A

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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

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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

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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 carefully read the manuscript “Insect decline in countries of Central and Western Europe - Drivers and pressures of Carabidae and Lepidoptera population and biodiversity trends”. The manuscript presents an exhaustive review on “The drivers and pressure behind insect decline based on long term monitoring data” of a specific region of Europe.

Although there are many studies reporting no significant changes in insect numbers, there is clear a significant bias against publishing papers about non-significant findings. Therefore, as the authors discussed, it is difficult to evaluate insects’ trends based on literature review. However, this work is more related to the identify the drivers and pressures reported in the literature to the different reported trends (i.e. decreasing vs. increasing). The authors used a useful a conceptual model (DPSIR) to disentangle several drivers and pressures influencing different states (insect individuals, populations and communities and their habitats). I enjoyed reading this well-written manuscript integrating data of an important amount of long-term studies and very illustrative figures on the pressures and drivers behind insect trends.

Major comments:

1-The title of the paper specifies that the work is related to “population and biodiversity trends” but in different parts of the manuscript it seems that the analyses are only related to evaluating population trends (Abstract L. 37-39; Introduction L. 84-87 and L. 91-92; Discussion L. 391). However, it is clear that they evaluated several parameters which do not measure population change (e.g. species richness, diversity indices, distribution). My main concern on the authors’ approach is analysing together the drivers and pressures of the trends in parameters measuring many different ecological facets of populations and insect communities. Although the approach could be useful to identify the major reported drivers and pressures of insect biodiversity trends, analysing together all these parameters difficult the possibility of evaluating their real impact on populations and communities. Clearly, in a specific location, contrasting trends could occur with respect to different parameters (e.g. increase in insect abundance but a decrease in insect diversity or increase in range size distribution of a species but a decrease in the population sizes). In any case, I think a discussion on the evaluated parameters and how they measure insect biodiversity should be incorporated in the manuscript. Also, I would like to see a justification of why differentiating between abundance measured by indices and “number of individuals”. It seems weird to use the term DPSIR model when the authors did not evaluate the “Impact” neither the “Response”. I may incorporate in the model and the Figure 1 which facet of insect biodiversity is the pressure affecting (which is measured by the different parameters). In fact, Table S5 report the trends separated by the different parameters. I may include this table in the manuscript.

2-As the authors mention in the manuscript, climate change is one of the most studied drivers to interpret insect’s trends and can imply several pressures to insects but only climate warming was included in Figure 1 (and climate change is not included as a driver in the figure). Therefore, I would like to see which specific pressures driven by climate change (i.e climate change in general in Table S3 = 38 studies) have been evaluated in the study region, including climate extremes, increased climate variability, water stress and which of them have been reported to have an impact on the habitat and/or on the organisms.

3-The pressure “weather/climate in general” (n=19) was classified as “climate” together with climate change pressures (“climate change in general”, “climate cooling” and “climate warming”). I expect that inter-annual weather/climate variability to be responsible of population fluctuations in insect but climate change to drive the long-term trends. Then, it seems incorrect to place in the same group (even including it as a pressure) the natural climate variability and the climate change pressures (e.g. long-term warming trends). I do not see in Table S4 which studies have analysed or mentioned the different pressures or which parameters they measured.

4- I would like to see in the introduction or the methods a paragraph about the study region. Why is this region interesting for evaluating insect trends (e.g. more data than other regions)? Why could be the particularities of the situation of insects in the study region? I expect that countries of Central and Western Europe with high population densities (e.g. compared to USA or Canada) are highly impacted by human activities (e.g. agriculture).

Minor comments:

Abstract:

- L. 19. I may say here that most of the long-term reported trends are from regions of USA and Europe. Now it could seem that these trends have been reported only in specific regions of Europe.

-L. 27. I may include the name of the order (Coleoptera) after Carabidae.

-L. 30. Change “environmental stressors” by “related factors”.

L. 36-37. I’m not sure here if I understand what do you refer for “intrinsic changed related to insect species or the environment”. Could you clarify it?

Introduction:

-L. 75. How a stressor could reduce competition? Do you mean that a stressor reducing the population numbers of some taxa decrease the competition with other taxa which can their populations?

Methods:

- L. 190. I do not like the use of “organism” as a synonym of “specie”s or vice versa.

Results:

L. 235-236. Could you include the number of publications by country?

L. 373. I’m surprised that forestation led to increasing biodiversity trends in Lepidoptera in the study region. At least in the Mediterranean region, there are some examples that the ecological succession from grasslands to scrublands and forests are related to declining trends in Lepidoptera. I guess forestation in degraded habitat could have a benefit on Lepidoptera? Could you tell me which are the publications reporting the positive effect of forestation in insect trends?

Discussion:

L. 494-495. Species richness (i.e. number of species) is a quantitative parameter.

Figures and tables:

-Figure 1: I’m not an expert on ecological resilience but I think this concept is more related to communities or populations than to organisms. In L. 165 it is mentioned “resilience of species”.

-Table S3: A more detailed legend is required.

-Table S4. Include pressures tested or mentioned.

Reviewer #2: Review: Rumohr et al. ‘Insect decline in countries of Central and Western Europe – Drivers and pressures of Carabidae and Lepidoptera population and biodiversity trends, to be considered for publication in the journal PLoS ONE.

Reviewer’s interpretation of the work: The authors performed a literature review on carabid beetle and butterfly trends (datasets of at least 6 years) in agricultural landscapes of south and western Europe. They identified increasing/stable/decreasing/unknown trends in various parameters (abundance, richness, etc.) and linked these to drivers, pressures and states (using the DPSIR methodology and presenting alluvial diagrams). Trends were mostly negative (i.e., a decrease in the insect parameter), but positive trends were also observed. Drivers were primarily anthropogenic, primarily agriculture, climate, nature conservation activities, urbanisation, etc. Results are discussed in detail, also with a focus on data quality and potential pitfalls in their study.

Specific comments:

The title is pretty long, and it seems that there is even a suggested ‘subtitle’. Why not simply use a modified subtitle as the main title, and remove the main one: Drivers and pressure behind insect decline in western Europe based on long-term monitoring data

L25. ‘drivers and pressures’ Later on in the article, these terms were described to have different levels of confidence, depending on whether they were tested or inferred. Make this clear in the Abstract.

Since Carabidae and Lepidoptera are at different taxonomic levels, I would state here (but no need to do this throughout the manuscript): Carabidae (Coleoptera) and Lepidoptera…

L28. ‘…data for at least 6 years…’ I presume (based on what comes later) that this is not 6 consecutive years, but rather data spanning at least 6 years, correct? For instance, could the data include a study that was performed in year X and then only again in year X + 6?. Also, later on the authors told us that they focused their work on agricultural landscapes (L87 & Table S1). This needs to be made clear in the Abstract.

L46-7. Another citation that can be used here is:

Declining diversity and abundance of High Arctic fly assemblages over two decades of rapid climate warming

Loboda, et al. Ecography https://doi.org/10.1111/ecog.02747

To be fair, there are also opposite findings (or at least findings of no change), that the readers should be made aware of:

No net insect abundance and diversity declines across US Long Term Ecological Research sites

Crossley et al. Nature Ecology & Evolution volume 4, pages 1368–1376 (2020)

L89-95. In the sentences above the objectives, the authors emphasised that the work is performed in the agricultural landscape of C and W Europe, but the objectives do not emphasise this. It definitely should come to the forefront here.

L116. I may have missed it, but what is the timespan of your literature search?

L130-1. Were the Carabidae also evaluated ‘in general’ and as specialists, generalists, etc.?

Table S2, S3 – state that these were obtained from your literature review, referring to Table S4

Table 1. Provide a more descriptive title. For instance, what do you mean by ‘pressures discussed in total’, ‘important pressures discussed in total’? Do you mean total amount of pressures/important pressures discussed in the papers?

Table S5 seems quite important/interesting. I would present it in the text, rather than the supplementary material.

L266-8. I find this sentence difficult to understand. Please rewrite.

L280. No need to cite Figure 2a an b here. You’re talking about alluvial diagrams in general. Or you could simply state Figs. 2a, 3a, 4a, 5a, and then Figs. 2b, 3b, 4b, 5b.

L286 onwards. Carabidae decreasing/increasing trends & Lepidoptera decreasing/increasing trends. There’s a lot to digest here. I recommend the authors provide a summary paragraph above these sections, summarising the main findings. Perhaps dealing with decreasing trends first (both taxa), and then increasing trends (both taxa). Then go into the nitty-gritty of each of the 4 sections.

L336-9. It is fascinating that for increasing trends (carabids), there is considerable statistical evidence, while for decreasing trends (carabids), there is so little (and mainly presumed). Any reason for this huge discrepancy? I see that this is discussed in the Discussion.

Figure quality should be improved.

Discussion. Make it clear early on that this study focused on agricultural landscapes. It may not be surprising that agricultural activity/intensification/extensification were often an important driver in the trends observed. In other landscapes (semi natural to natural, urban, etc.) there may be different prominent drivers of insect decline/increase.

L396 onwards. Apart from publication bias, the authors also need to discuss the confidence in these trends, since many were not supported by statistical analyses but were presumed. I see this is done later on in the Discussion, but perhaps also briefly mention it here.

“Discussion of methods”. I recommend that this section be placed at the end of the Discussion, perhaps together with “Knowledge gaps and future research needs”. The reader might be more interested to read the interpretations of your findings first, and then later on be made aware of the potential methods issues/pitfalls and knowledge gaps, etc.

L428-436. Not sure if this Google scholar vs. other courses text is needed. Perhaps some of this is common knowledge?

L439-49. The text here can go with the “Discussion of methods” etc. (see my comment above on this). At this stage, the reader wants to read the interpretation of your findings. In fact, so too are the next two paragraphs. The interpretation of your findings mainly starts in L471.

Knowledge gaps, etc. An additional action would be to have more statistical evidence of the trends observed. As the authors have (L555 onwards), much of this is based on ‘presumption’.

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Reviewer #1: No

Reviewer #2: No

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Drivers and pressures behind insect decline in Central and Western Europe based on long-term monitoring data

PONE-D-23-00796R1

Dear Dr. Baden,

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.

Within one week, you’ll receive an e-mail detailing the required amendments. When these have been addressed, you’ll receive a formal acceptance letter and your manuscript will be scheduled for publication.

An invoice for payment will follow shortly after the formal acceptance. To ensure an efficient process, please log into Editorial Manager at http://www.editorialmanager.com/pone/, click the 'Update My Information' link at the top of the page, and double check that your user information is up-to-date. If you have any billing related questions, please contact our Author Billing department directly at authorbilling@plos.org.

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Kind regards,

Amparo Lázaro, PhD

Academic Editor

PLOS ONE

Additional Editor Comments (optional):

The reviewer suggested the relocation of the section entitled "Parameters measured" to the methods section. The authors may consider this suggestion; both locations could be adequate

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 #1: All comments have been addressed

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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 #1: Yes

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

Reviewer #1: N/A

**********

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 #1: Yes

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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 #1: Yes

**********

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 #1: I appreciate the effort made by the authors for improving the manuscript following my suggestions and adresing my inquires. At this step I only would like to propose relocating the section titled "Parameters measured" (or potentially renamed as "Community and population parameters considered") to the methods section where it would be more contextually suitable.

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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.

If you choose “no”, your identity will remain anonymous but your review may still be made public.

Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy.

Reviewer #1: Yes: Pau Colom

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