The Combined Effects of Multiple Invasive Species on Persistence of Imperiled Pahrump Poolfish

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

 

Dear Editor,

Thank you for giving me the opportunity to review the manuscript. I appreciate the effort the authors have put into this study.

Overall, the manuscript is well-prepared. The abstract and introduction are clear and sufficient, effectively outlining the study's objectives and providing necessary context. However, I have a few questions and suggestions regarding the methodology section, which I believe would enhance the clarity and comprehensiveness of the paper. My detailed comments are as follows:

1. Line 81: Please remove the extra 'a' at the beginning of the sentence.
2. Line 88: The Confidence Interval is mentioned as 9%, which seems incorrect. Please verify and correct it.
3. Line 111: The term "production of juveniles" is unclear. Does this refer to the growth or reproduction of the species? Please clarify.
4. Line 118: Including an explanation for the observed crayfish deaths would be beneficial for better understanding.

Additionally, I suggest the following improvements:

• Experimental Set-Up: Including an image of the experimental setup would greatly improve the manuscript's clarity. Alternatively, you could provide a simple table summarizing the species names, numbers, and replicates for easy reference.
• Line 121: How were the fish fed during the study? Was it done manually (by hand) or using automated food-dropping machines? This information is missing and should be included.

The rest of the paper is well-written. The results and discussion sections are comprehensive, and the findings are appropriately addressed.

Thank you for the opportunity to review this manuscript. I hope my comments are helpful to the authors in refining their work. Please feel free to contact me if further clarification is needed.

Author Response

REVIEWER #1
Dear Editor,
Thank you for giving me the opportunity to review the manuscript. I appreciate the effort the authors have put into this study. Overall, the manuscript is well-prepared. The abstract and introduction are clear and sufficient, effectively outlining the study's objectives and providing necessary context. However, I have a few questions and suggestions regarding the methodology section, which I believe would enhance the clarity and comprehensiveness of the paper. My detailed comments are as follows:
1. Line 81: Please remove the extra 'a' at the beginning of the sentence.
Incorporated. Lines 78-80 in revised version.

2. Line 88: The Confidence Interval is mentioned as 9%, which seems incorrect. Please verify and correct it.
This section was re-vised as we added in the original unpublished mark-recapture data into this version. We have clarified that confidence intervals are 95% - line 224 in the revised version.

3. Line 111: The term "production of juveniles" is unclear. Does this refer to the growth or reproduction of the species? Please clarify.
Restated as: “Further, two previous experiments consistently showed that mosquitofish effectively eliminated juvenile poolfish [28,37].” Lines 168-169 in revised version.

4. Line 118: Including an explanation for the observed crayfish deaths would be beneficial for better understanding.
Incorporated. Added the following: “Crayfish deaths were likely due to aggression among conspecifics as inferred from missing appendages on dead crayfish, and by active feeding by live crayfish on dead conspecifics.” – lines 177-179 in revised version.

Additionally, I suggest the following improvements:
1. Experimental Set-Up: Including an image of the experimental setup would greatly improve the manuscript's clarity. Alternatively, you could provide a simple table summarizing the species names, numbers, and replicates for easy reference.
Incorporated. Table 1 added which includes mesocosm treatments and their respective species composition. Lines 207-210 in revised version.

2. Line 121: How were the fish fed during the study? Was it done manually (by hand) or using automated food-dropping machines? This information is missing and should be included.
Incorporated. We have indicated that fish were fed BY HAND and also specified the amount of food provided for crayfish. Lines 182-185 in revised version.

The rest of the paper is well-written. The results and discussion sections are comprehensive, and the findings are appropriately addressed. Thank you for the opportunity to review this manuscript. I hope my comments are helpful to the authors in refining their work. Please feel free to contact me if further clarification is needed. Thank you for your recommendations.

Reviewer 2 Report

Comments and Suggestions for Authors

Dear Dr. Paulson and Stockwell,

multiple invasive species are common in many ecosystems, and effects or impacts on native species may accumulate or strengthen. However, impacts may strongly depend on the species and the ecosystem itself. In your study, you excluded the ecosystematic effects, which is an appropriate approach. Please do clearly discuss this potential restriction.

In your discussion, you may add some further effects of (multiple) invasions which may impact native species. There are numerous studies of synergistic effects or restricting effects among invasive species. The "novelty" of your approach is the inclusion of a third species, which is native. This is not sufficiently investigated, as you clearly state. Please focus and discus this fact in a much stronger way.

All other comments are included in the pdf file.

Comments for author File: Comments.pdf

Author Response

REVIEWER #2

Line 2: “Experimental populations” - This term is unclear, I would not use it in the title. Incorporated. Term is removed from title.

Line 17: “do non-experimental mesocoms exist? What is an experimental mesocosm?” Good point, rephrased as “ We also report the results of mesocosm experiment where we tested individual and combined effects of invasive Red Swamp Crayfish, Procambarus clarkii, and Western Mosquitofish, Gambusia affinis, on experimental populations of Pahrump Poolfish, Empetrichthys latos” - Lines 22-25 in revised version.

Lines 20-22: “make clear that this is something like the basis to test if there is a difference on native poolfish survival/recruitment if 1 or 2 species invade a system”

We revised this section as follows: “Survival rates were near 100% for adult poolfish in allopatry but were significantly lower for the other two treatments; poolfish were sympatric with crayfish (~53%), and when poolfish were sympatric with both crayfish and mosquitofish (~55%). In allopatry, poolfish produced over 90 juveniles per mesocosm, but about 65 juveniles per mesocosm when poolfish were sympatric with crayfish, but this difference was not significant. However, juvenile production plummeted to near zero when poolfish were sympatric with both crayfish and mosquitofish.” Lines 25-31 in revised version.

Lines 27-28: “active management: a total removal is not realistic and you have not tested what effect a reduction of invasive species density would have”. Incorporated. We have changed the goal to detection and control of invasive species. Lines 31-33 in revised version.

Lines 44-45: Please clarify, the difference and peculiarities of multiple simultaneous invasions” “important for what?” AND “ what is the reason if they are ‘important’ or not?” Removed this sentence.

Lines 46-51: please give some details for both to clarify the differentiation between individual and synergistic effects: Thank you the paper we cited did not discriminate between these two effects. Revised to make the interactive effect more concise. Line 50-54 in revised version.

Lines 60-62: “please give some data to exemplify the strength of the decline” Rephrased to clarify that these impacts have included the extirpation of local fish populations. “A wide variety of invasive predators have been directly associated with the extirpation of numerous fish populations in the southwestern United States [14-18].” Lines 63-64 in revised version.

Lines 68-72: “give example for “endemic species” Rephrased as: “These impacts have been attributed to predator naiveté of endemic fishes, which evolved in depauperate communities. Specifically, endemic fishes are hypothesized to have lost anti-predator traits as they evolved in simple systems with limited predation, thus making them vulnerable to invasive predators [14-16, 19-20]. – Lines 66-70 in revised version.

Lines 79-82: “Understanding the possible interactions of both Western Mosquitofish and Red Swamp Crayfish is critical for resource management because both of these non-native species a are listed as the greatest threat to the various endemic fishes in the Southwestern US [32].” - threat: details: new parasites, agonistic interactions, predation???

Incorporated. Clarified that both species are considered non-native predators. Lines 78-80 in revised version.

Lines 82-83: “The co-invasion of Red Swamp Crayfish and Western Mosquitofish have been associated with the decline of two refuge populations of the Endangered Pahrump Poolfish, Empetrichthys Latos.” “Why”
We have added the population monitoring data which were originally cited. This new section provides the context and motivation for the mesocosm experiment. Lines 129-154 and 213-241 in revised version.

Line 90: “Give some basic information on your studied species: time of first introduction, max. TL, age structure of the population(s), type of reproduction etc” We have added a background section to the manuscript, that provide information on the history of the various refuge populations. We have also added additional information on Poolfish life history. Lines 92-126 in revised version.

Line 97: – Materials & Methods: “please introduce some words, how you measured the juvenile production” Incorporated. We added in a sentence to provide explicit definitions for our response Variables of adult survival and juvenile production. Lines 187-189 in revised version.

Line 106 – Is “randomized block design” a known term. Randomized block designs are commonly used in field experiments, with the number of blocks reflecting the number of replicates.

Lines 111-112: “Each block of three tanks was replicated seven times for a total of 21 experimental tanks, arranged in a linear sequence.” “What does this mean?” Deleted “arranged in a linear sequence”.

Lines 129-132: Used ANOVA for what? Explain Tukey HSD; Rephrase 2nd sentence. Why are parametric results reported. We re-phrased this section as suggested. Lines 190-192 in revised version.

Line 149: Treatments sharing at least one letter were not significantly different (p > 0.05). Show test. The revised section describes the pairwise tests. Lines 190-192 in revised version,

Lines 151-154: Was this mosquitofish juvenile production? We have clarified that this was Poolfish juvenile production. Lines 187-189 in revised version.

Lines 159-160: Move to methods. We have kept this section here, because it is a post hoc test which was only conducted because we observed high variation in adult survival.

Lines 164-167: “indicate and summarize the meaning of this result” Added the following sentence: “This finding suggests that the crayfish predation on adult poolfish resulted in the reduced production of poolfish juveniles.” Lines 270-271 in revised version.

Line 174: “Fig 2 + 3 are highly comparable. Please delete one and give the results in the text” Figure 2 showing the number of juveniles was mistakenly inserted twice. The revised version has the correct figures which are renumbered due to the addition of the new section on population monitoring. In the revised version, Figure 4 is the number of juveniles produced per mesocosm, and Figure 5 is the relative number of juveniles per surviving adult poolfish per mesocosm.

Lines 191-192: Please explain – give more details. We reworded this section as follows: “The combined effects of both crayfish and mosquitofish effectively eliminated the production of poolfish juveniles. It is noteworthy, that similar work has shown mosquitofish to virtually eliminate poolfish juvenile production [28,37]. Thus, this experiment did not reveal emergent effects [1] of the combination of these two predators.” Lines 321-324 in revised version.

196-205: Move this section to the introduction. In the revised version we have added the population monitoring data. This new section provides the context and motivation for the mesocosm experiment. Lines 129-154 and 213-241 in revised version.

Line 206-214: Move this section to the introduction. The revised version no longer has this section.

Lines 216-218: Due to what? This section was removed from the revised version.

Lines 224-226: what impacts? We removed this section as applying our findings to explain the historic extinction of a closely related species was a reach. Thanks for the comment.

Lines 227-229: “Impacted by what? We rephrased this sentence to make it clearer. “Overall, this study, combined with previous mesocosm experiments [28,37], demonstrates that non-native predators can have negative effects on Pahrump Poolfish populations.” Lines 344-346 in revised version.

Reviewer 3 Report

Comments and Suggestions for Authors

Authors provided a detailed study on the combined effects of invasive species on the endangered species Empetrichthys latos. In general, the ms is well written, and I consider the basic premise, method developed and questions asked by this study as valuable and interesting. In specific, the abstract clearly states the context, the purpose of the study, the main results and the implication of the results. Statistical techniques used are the appropriate for comparative analyses. Results are clear, very well presented, and are in line with the discussion and the purpose of the study. Tables and figures are also well presented and titled. The discussion is detailed enough and the scope of the manuscript are well supported by references to previous studies, adding depth and context to the discussion.

Minor comments

While the discussion is comprehensive, it occasionally reiterates results without expanding on their broader ecological implications. More emphasis on management strategies or lessons for other ecosystems would strengthen the section.

Also, the authors could provide some lines regarding the limitation of the study due to the artificial nature of the experiment, which may limit the applicability of results to natural ecosystems with more complex interactions.

Last but not least, the authors should reduce the amount of the high wording dublication in the manuscript.

Thus, I recommend a minor revision of the manuscript especially enhancing the depth of the discussion.

Author Response

REVIEWER #3. Authors provided a detailed study on the combined effects of invasive species on the endangered species Empetrichthys latos. In general, the ms is well written, and I consider the basic premise, method developed, and questions asked by this study as valuable and interesting. In specific, the abstract clearly states the context, the purpose of the study, the main results and the implication of the results. Statistical techniques used are the appropriate for comparative analyses. Results are clear, very well presented, and are in line with the discussion and the purpose of the study. Tables and figures are also well presented and titled. The discussion is detailed enough and the scope of the manuscript are well supported by references to previous studies, adding depth and context to the discussion.

Minor comments

While the discussion is comprehensive, it occasionally reiterates results without expanding on their broader ecological implications. More emphasis on management strategies or lessons for other ecosystems would strengthen the section.

We have expanded the paper by reporting population monitoring data. . Lines 129-154 and 213-241 in revised version.

Also, the authors could provide some lines regarding the limitation of the study due to the artificial nature of the experiment, which may limit the applicability of results to natural ecosystems with more complex interactions.

We have added in a paragraph that discusses the limitations and relevance of mesocosm experiments for protected species, where ecosystem experiments are not feasible. Lines 334-343 in revised version.

Last but not least, the authors should reduce the amount of high wording duplication in the manuscript. Thus, I recommend a minor revision of the manuscript especially enhancing the depth of the discussion.

We have made moderate revisions throughout the manuscript to reduce duplication.