Assessing the Risks of Extreme Droughts to Amphibian Populations in the Northwestern Mediterranean

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This is a well-written manuscript. The review is extensive and complete, including current knowledge on the ecological, physiological, and  demographic impacts of drought on amphibians of the North-Western Mediterranean across habitat types, including ephemeral ponds, permanent water bodies, lotic systems,  and terrestrial landscapes.   

I do not have opinion with the manuscript structure, but I think the manuscript is not that readable and hence can be improved. For example, some paragraphs is too long and can be separated into more paragraphs.  Moreover, some parts can be transformed into table or figure.

 

The following is my comment on the land-3754096 for your reference.

Amphibians are naturally vulnerable to drought stress because of their permeable skin. understanding Amphibian population response is critically important under climate change, in which drought is predicted to occur more frequently, particularly in the North-Western Mediterranean Basin—one of Europe’s most climate-sensitive regions. This justifies the need to Assess "the risks of extreme droughts to amphibian 2 populations in the North-Western Mediterranean".

This review focus on the direct effect of on physiology and demography of amphibians, and the indirectly effect via drought impact on ephemeral ponds, permanent water bodies, lotic systems, and terrestrial landscapes. The manuscript is well written, and is logically complete and well organized.

However, I have server comments below.   

Specifically, 1)Introduction is fine and fully addresses the need of the review. However, it should a brief introduction to the diversity of amphibians in the region. 

2). General susceptibility of the amphibian community to drought, 
in this section, the figure 1 and 2 are not in need, since this review aims to address the amphibians response to drought, and overemphasizing drought itself is not neccessary. Providing a background for drought is enough. Instead, it would be much better to additionally provide a conceptual diagram showing the ways drought affecting amphibians survival and reproduction, and population size. 

3. Potential effects of extreme droughts
There are a little repetition in response of amphibians among the subsections, and hence this section can be condensed somewhat.  Moreover, the figure 3 includes the outbreak disease, which is little reviewed in this section. I suggest removing removing it because section 4 details it in a figure. 

4. Emerging diseases and drought
Despite different diseases, they share some similar response to drought. Thus, this section can also be largely condensed. 

In general, this reviewer is timing and a nice addition to global change biology.

   

Author Response

Comments 1: 

This is a well-written manuscript. The review is extensive and complete, including current knowledge on the ecological, physiological, and  demographic impacts of drought on amphibians of the North-Western Mediterranean across habitat types, including ephemeral ponds, permanent water bodies, lotic systems,  and terrestrial landscapes.  I do not have opinion with the manuscript structure, but I think the manuscript is not that readable and hence can be improved. For example, some paragraphs is too long and can be separated into more paragraphs. Moreover, some parts can be transformed into table or figure.  

Response 1: 

We thank the reviewer for their positive assessment of our manuscript. We appreciate the suggestion to improve readability, and we have revised the text accordingly by splitting some of the longer paragraphs. Regarding the recommendation to transform certain sections into tables or figures, we agree that visual formats can enhance clarity and accessibility.

In response to this, and also considering Reviewer 2’s suggestion to include further analysis or synthesis, we have moved Suppl. Table 1 to the main text as Table 1. This table presents a preliminary, semi-quantitative assessment of the relative vulnerability of amphibian genera based on key life-history traits known to influence resilience to drought.

Our assessment is based on expert judgment and seven ecological and biological variables linked to population persistence under more frequent or prolonged drought conditions. Each variable was scored from 0 to 2 according to its contribution to drought sensitivity, and the scores were summed to generate a final susceptibility index ranging from 0 to 10, to ensure interpretability.

Along with a revision to the text, we hope that including this table in the main body of the manuscript improves its structure and contributes to the overall readability.

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript presents a comprehensive review of the ecological, physiological, and demographic consequences of increased drought on amphibian species. The authors have conducted a thorough literature review and the manuscript is rich in information and references. However, what I think is lacking is an actual attempt at a critical data analyses, and the manuscript looks more like a well-referenced summary piece, rather than a scientific study. The manuscript does not sufficiently address knowledge gaps, literature inconsistencies, or unresolved questions, it just lists what is known on its subject in almost an encyclopaedic fashion. This impression is strengthened by the fact that the relevance to the study region of much of the cited literature is not discussed at all, and at times the reader struggles to make a connection. Several themes are repeated throughout the manuscript, with overlapping references and phrasing (e.g., hydroperiod effects and plasticity). The section dealing with diseases is especially descriptive, with virtually no attempt at analyses for the stated study region of the manuscript (i.e., the North-Western Mediterranean); at least the relationships between the different factors (i.e., temperature, immune system, microbiome, etc.) should be mapped more clearly.

At several points throughout the manuscript I struggled to understand why the authors have included the information, and why they think it is relevant to their study:

Figure 1: This figure appears to be just a partial copy of figure 5 from Twomey et al. 2025, is this really necessary? I don't think this is good practice.

Figure 2: It is unclear how this figure and the values it presents are related to the more local context of the study.

Suppl. Table 1: How was this susceptibility (0-10) established? There is no cited reference and the authors do not explain their approach in the text.

Suppl. Table 2: It would be better to cite each study in reference to the species in question, rather than the currently presented citation of "1-14", so the reader knows which study provides data for which species.

Overall, I recommend major revision, in which the authors provide a more critical analysis of available literature instead of a simple (albeit comprehensive) summary, and do not copy figures from already published studies. They also must clarify the geographic applicability and relevance of the cited references to their specific study region.

Author Response

Comments 1: 

The manuscript presents a comprehensive review of the ecological, physiological, and demographic consequences of increased drought on amphibian species. The authors have conducted a thorough literature review and the manuscript is rich in information and references. However, what I think is lacking is an actual attempt at a critical data analyses, and the manuscript looks more like a well-referenced summary piece, rather than a scientific study.

The manuscript does not sufficiently address knowledge gaps, literature inconsistencies, or unresolved questions, it just lists what is known on its subject in almost an encyclopaedic fashion. This impression is strengthened by the fact that the relevance to the study region of much of the cited literature is not discussed at all, and at times the reader struggles to make a connection. Several themes are repeated throughout the manuscript, with overlapping references and phrasing (e.g., hydroperiod effects and plasticity).

Response 1: 

We thank the reviewer for their thoughtful comments. It is important to clarify that our intention was to produce a traditional narrative review, rather than an original research paper or a systematic review with meta-analytic components. We acknowledge that some reviews are designed to critically analyse biases in the literature or to address knowledge gaps explicitly; however, our primary aim was to consolidate and synthesize existing knowledge on how increasing drought frequency and severity might affect amphibians in the North-Western Mediterranean, across ecological, physiological, and demographic dimensions.

Given the scarcity of empirical data specific to the North-Western Mediterranean region, we chose to structure the manuscript as a comprehensive reference tool. To address knowledge gaps, we included also a lot of relevant studies from other regions that, while not always geographically aligned, provide useful insights or comparable ecological contexts. In this sense, we believe that compiling and organizing this otherwise fragmented information into a coherent and accessible resource offers clear value for both researchers and conservation practitioners working on amphibians under increasing drought pressure. Otherwise, we believe that producing a paper focused primarily on highlighting biases and knowledge gaps—given the topic and the geographic scope of the review—would likely result in a fragmented and difficult-to-read manuscript. In fact, in some cases, the number of unknowns in the region may largely outweigh the available knowledge, which would limit the usefulness of such an approach.

Regarding the comment on repetitiveness, we recognize that some concepts—such as hydroperiod or plasticity—reappear in different sections. This was a deliberate choice, as their ecological relevance varies depending on the context. For instance, drought-induced hydroperiod shortening has different consequences for species persistence in ephemeral ponds than in streams, and it also interacts differently with factors such as disease dynamics or reproductive strategies. We have revised the text to reduce unnecessary overlaps and clarify these contextual distinctions where needed. We also took note of the suggestion to better highlight knowledge gaps and the relevance of cited studies to the study region.

Nevertheless, we agree on the value of identifying patterns and generating new insights from the reviewed literature. For this reason, and in light of Reviewer 1’s comments, we decided to include Supplementary Material 1 as a main table. This table offers a comparative framework of species’ potential susceptibility to drought, synthesizing multiple life-history traits relevant to population resilience.

Comment 2:

The section dealing with diseases is especially descriptive, with virtually no attempt at analyses for the stated study region of the manuscript (i.e., the North-Western Mediterranean); at least the relationships between the different factors (i.e., temperature, immune system, microbiome, etc.) should be mapped more clearly.

Response 2: 

Similarly to the previous remarks, we appreciate the reviewer’s comment and agree that the section on emerging diseases could benefit from some additional discussion, especially regarding lack of knowledge. One of the main limitations we faced when addressing this topic is that most existing studies on pathogens such as Batrachochytrium salamandrivorans (Bsal), B. dendrobatidis (Bd), and Ranavirus have been conducted in temperate or montane environments, where drought is not yet a major environmental driver. In contrast, studies explicitly addressing how increased drought interacts with disease dynamics—especially in amphibian communities of Mediterranean ecosystems—are still scarce. This represents a significant knowledge gap, which perhaps should be more evident in our review.

Although some experimental studies have explored the role of individual factors (e.g., temperature effects on host immunity or microbiome composition), integrative studies assessing their combined effects on disease outcomes in real-world settings remain very limited. The biology and transmission pathways of pathogens like Bsal are only beginning to be understood, and our capacity to predict how they will respond to environmental change—especially under Mediterranean drought scenarios—is still unknown. We have revised the disease section to make these limitations more explicit.

Comment 3: 

At several points throughout the manuscript I struggled to understand why the authors have included the information, and why they think it is relevant to their study.

Response 3:

Given the broad scope and complexity of the topic, we have aimed to develop each section by progressively building the connection between drought and its potential ecological, physiological, or demographic effects on amphibians. For each variable or process discussed, we have attempted to explain its relevance and justify its inclusion in relation to drought-driven impacts on amphibian populations and communities. Since the comment does not specify which sections or examples were perceived as unclear, we have revised the whole text to improve the manuscript’s clarity and coherence and will revise the corresponding parts accordingly.

Comment 4: 

Figure 1: This figure appears to be just a partial copy of figure 5 from Twomey et al. 2025, is this really necessary? I don't think this is good practice.

Response 4:

We chose to include this figure because it clearly illustrates that the amphibian community in our study area is among the most susceptible to extreme drought, as shown in Twomey et al. (2025). Our intention is obviously not to mislead or incur in any form of malpractice. To avoid any ambiguity, we explicitly cited the source in the figure caption and in this new version we have even clarified that the image is directly reproduced from Figure 5 of the referenced work.

We believe this approach is totally open, and thus transparent and respectful of the original authorship. Altering the figure (e.g., changing proportions or colors) and labelling it as "based on..." could introduce further concerns or misinterpretation, potentially raising even more serious ethical issues.

Nevertheless, to ensure full compliance with the journal’s policies, we have contacted the editorial board for guidance. Should the use of the original figure be deemed inappropriate, we are fully prepared to remove it from the manuscript, but Creative Commons licence in the related article indicates: You are free to: Share: copy and redistribute the material in any medium or format for any purpose, even commercially.  Adapt: remix, transform, and build upon the material for any purpose, even commercially.  https://creativecommons.org/licenses/by/4.0/

Comment 5: 

Figure 2: It is unclear how this figure and the values it presents are related to the more local context of the study.

Response 5: 

We acknowledge the reviewer’s concern and appreciate the opportunity to clarify. Figure 2 is based exclusively on data from Supplementary Tables 1 and 2 in Eekhout et al. (2025), but filtered to include only studies explicitly conducted within the geographical scope of our study, i.e., the North-Western Mediterranean Basin. Specifically, we retained only data referring to Portugal, Spain, France, Italy, and Switzerland. We excluded countries such as Germany and the United Kingdom, as no relevant studies were available for those areas in the source material.

In Supplementary Table 1 of Eekhout et al., each study is associated with the region or subregion where it was conducted, along with the time period covered. Supplementary Table 2 provides the predicted percentage changes in specific water resource categories for the period 2050–2100, under both low and high greenhouse gas emission scenarios. Figure 2 summarizes these data for the relevant countries, presenting mean values and 95% confidence intervals across studies per resource type and scenario.

We believe this figure is relevant to the local context of our study because it integrates climate-driven projections of hydrological changes specifically for the North-Western Mediterranean region, which directly frames our analysis of amphibian vulnerability.

Comment 6:

A: Suppl. Table 1: How was this susceptibility (0-10) established? There is no cited reference and the authors do not explain their approach in the text.

Response 6: 

[Suppl. Table 1 is Table 1 in this new version]

We thank the reviewer for this observation. To our knowledge, there are currently no published studies quantifying the susceptibility of amphibian genera—or species—to drought in the North-Western Mediterranean. With this in mind, we aimed to provide a preliminary, standardized assessment of the relative vulnerability of different genera based on key life-history traits known to influence amphibian resilience to increasing drought frequency and intensity.

Our approach was based on expert judgment and a set of seven ecological and biological variables that are directly related to the probability of population persistence under prolonged or more frequent drought conditions. Each variable was scored from 0 to 1 or 2, depending on its relative contribution to drought sensitivity. These scores were then summed to produce a final susceptibility index ranging from 0 to 10, to allow for an easily interpretable scale.

The variables and scoring criteria used are as follows:

    Larval period: 0 = a few weeks; 1 = up to 3–4 months; 2 = ≥5 months

    Breeding season: 0 = autumn, winter, or year-round; 1 = spring; 2 = summer

    Reproductive strategy (timing): 0 = prolonged; 1 = explosive

    Reproductive strategy (flexibility): 0 = flexible; 1 = fixed

    Pond permanency preference: 0 = ephemeral; 1 = temporary; 2 = permanent

    Longevity: 0 = short (<10 years including immature stage); 1 = long

    Clutch size: 0 = large; 1 = small

We acknowledge that this is a semi-quantitative approach, aiming to minimize subjectivity by creating the scoring criterions. Thus, this index should not be interpreted as a definitive measure of vulnerability, but rather as a tool to visualize and compare general susceptibility patterns across genera in the region.

We have now added this explanation to the caption of Table 1, and we also include a graphical representation of the results to aid visualization in the supplementarymaterial.

Comment 7: 

Suppl. Table 2: It would be better to cite each study in reference to the species in question, rather than the currently presented citation of "1-14", so the reader knows which study provides data for which species.

Response 7:

Done. We have cited each study to match each species, and we have added more references which describe susceptibility to emergent pathogens.

Comment 8:

A: Overall, I recommend major revision, in which the authors provide a more critical analysis of available literature instead of a simple (albeit comprehensive) summary, and do not copy figures from already published studies. They also must clarify the geographic applicability and relevance of the cited references to their specific study region.

Response 8: 

We appreciate the reviewer’s comments and the opportunity to clarify these points, regarding the figures:

- Figure 1 is not original. We have explicitly and properly cited the original source to acknowledge this. We believe it is very useful in the manuscript, as previously discussed, and it was partially reproduced to facilitate comprehension and provide spatial context. As said in previous comments, we have contacted the editorial committee regarding this practice.

- Figure 2 was created by extracting and synthesizing data from the supplementary materials of Eekhout et al. (2025). Although the compilation of data to create the figure is not ours and therefore is properly cited, the figure itself is tailored by subsetting studies and data relevant to our study region.

- Figures 3 and 4 are original to this study. Figure 4 was inspired by the conceptual framework presented in Blaustein et al. (2018, https://www.mdpi.com/1424-2818/10/3/81), which is also properly cited, but expands upon their model by including additional levels of interaction relevant to our research.

We hope these clarifications address the reviewer’s concerns.

Reviewer 3 Report

Comments and Suggestions for Authors

The article is well-organized and clearly explains why it is so important to study the effects of extreme droughts on amphibian populations in the North-Western Mediterranean. The introduction and subsequent sections provide a clear context, making it easy to follow the flow of the content. However, I believe more attention should be given to habitat loss and fragmentation, as it is also a factor contributing to the global decline of amphibians. The topic of climate change and drought in the Mediterranean is highly relevant these days, especially with the increasing frequency of these events. The article highlights an urgent conservation issue, contributing to the knowledge of how climate change impacts biodiversity, particularly amphibians. Additionally, the article offers a thorough review of the current scientific literature on the effects of drought, incorporating a variety of studies on amphibian populations. This provides a broad perspective on the topic and becomes a valuable resource for future research. The inclusion of how emerging diseases, such as chytridiomycosis and ranavirosis, are affected by drought conditions adds an important dimension to the review. Understanding how these diseases interact with environmental stressors like drought is crucial for developing effective conservation strategies. The article mentions that local species are adapted to survive in temporary arid conditions, but the discussion on how these species might adapt to the increasing frequency and intensity of droughts is somewhat speculative. Further exploration of these species' adaptability, including genetic factors, would offer a clearer insight into their future survival. Although the article highlights the threats posed by droughts and diseases, it lacks a detailed discussion on how to mitigate these issues. I believe they should expand a bit more on the topic of habitat loss, as while climate change is mentioned, without habitat, it is impossible for many species to survive.

Author Response

Comments 1: 

The article is well-organized and clearly explains why it is so important to study the effects of extreme droughts on amphibian populations in the North-Western Mediterranean. The introduction and subsequent sections provide a clear context, making it easy to follow the flow of the content. However, I believe more attention should be given to habitat loss and fragmentation, as it is also a factor contributing to the global decline of amphibians. The topic of climate change and drought in the Mediterranean is highly relevant these days, especially with the increasing frequency of these events. The article highlights an urgent conservation issue, contributing to the knowledge of how climate change impacts biodiversity, particularly amphibians. Additionally, the article offers a thorough review of the current scientific literature on the effects of drought, incorporating a variety of studies on amphibian populations. This provides a broad perspective on the topic and becomes a valuable resource for future research. The inclusion of how emerging diseases, such as chytridiomycosis and ranavirosis, are affected by drought conditions adds an important dimension to the review. Understanding how these diseases interact with environmental stressors like drought is crucial for developing effective conservation strategies. The article mentions that local species are adapted to survive in temporary arid conditions, but the discussion on how these species might adapt to the increasing frequency and intensity of droughts is somewhat speculative. Further exploration of these species' adaptability, including genetic factors, would offer a clearer insight into their future survival. Although the article highlights the threats posed by droughts and diseases, it lacks a detailed discussion on how to mitigate these issues. I believe they should expand a bit more on the topic of habitat loss, as while climate change is mentioned, without habitat, it is impossible for many species to survive.

Response 1:

We thank the reviewer for the insightful and constructive comments. In response, we have added a new brief and final section titled "5. Mitigation", which specifically addresses potential strategies to mitigate the effects of extreme droughts on amphibian populations. This includes actions at multiple spatial scales—from large-scale interventions such as aquifer recharge and environmental flow regulation, to mid- and small-scale approaches such as habitat restoration, creation of new breeding sites, microhabitat enhancement, and climate-resilient management practices. This way we expand the discussion on the dimension of direct habitat loss by drought and water overexploitation, and emphasize the need to incorporate these considerations into conservation planning. This new section aims to offer a small set of feasible conservation responses which, since they largely relate to habitat, we hope it aligns with the reviewer’s valuable suggestions.

 

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

The authors have mostly addressed my comments and the more important aspects have been substantially improved - theerfore, I think the manuscript could be accepted in its present form.

Author Response

Dear reviewer,

Thanks very much for yur suggestions.

Sincerely Yours

Albert Montori and Eudald Pujol