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After reviewing this new version, I consider that the manuscript has been improved with the corrections suggested by the reviewers and is ready for publication.
[# PeerJ Staff Note - this decision was reviewed and approved by Patricia Gandini, a PeerJ Section Editor covering this Section #]
Thank you for submitting the revised version of your manuscript "Population size and structure of Grant’s gazelle and lesser kudu in Geralle National Park, Southeastern Ethiopia". In this new version, the manuscript shows important and valuable improvements that bring it closer to a final version. However, one of the reviewers considers that the manuscript still has weak points that should be improved before publication.
According to the reviewer, the manuscript remains disorganized for publication because the hypotheses underlying the research are not specified and the results are not arranged in a logical order. The reviewer also considers that the manuscript is written inconsistently and not all citations are cited correctly or included in the bibliography. Some minor comments are also noted throughout the manuscript.
This manuscript continues to be too disorganized for publication. In particular, the hypotheses underlying the research are not specified, the results are not laid out in a logical order, the manuscript is inconsistently written, and not all citations are correctly cited or included in the bibliography.
This work is primary research, but the research questions and hypotheses are not well-defined, it is difficult to judge the validity of the methods because the methods are not described in sufficient detail.
It is difficult to judge the validity of the findings based on the information provided in the manuscript.
Major comments
We appreciate the authors’ efforts to make changes recommended in the previous review, but we still have major comments that we would like the authors to address:
1. This manuscript lacks testable hypotheses which are central to the writing of a scientific paper, even for an observational study like this. In our reading, there are at least three potential hypotheses that can be answered with the data and study design presented by the authors, focusing on i) seasonal variation in density and abundance, ii) how habitat influences density and abundance and iii) how both play out across different feeding guilds of herbivores. If the authors make these changes, most of the writing will change and minor comments listed below may be redundant.
2. Previously, we also highlighted issues with data analysis and the presentation of results. The authors have improved this section, but they still need to do a better job at guiding the reader on which result was obtained by which analysis and from which variables. Rather than explaining the software used to get density, the authors should explain the underlying processes of calculating density. To elaborate on this, distance sampling is a well-established method for estimating density and irrespective of the software used for analysis, it follows the same underlying process which has major outputs that are important to report. These include i) detection probability, ii) effective strip width, iii) population density, and iv) model selection criteria, all of which may vary based on the number and type of covariates. Furthermore, when reporting results, providing readers the effect size and direction of the effect is of the utmost importance. For example, the density of kudus during wet season averaged X (95% CI: x – y; p < 0.001, test stats, and degrees of freedom) more than the density during dry season. The authors should also strive to separately present methods, results, and discussion for kudus and grants gazelles parallel to the earlier presentation of each hypothesis (i.e., one paragraph for seasonal variation, another for variation within different habitats, etc.). See Augustine 2010 for an example study on how to write methods and results sections for a similar study (https://doi.org/10.1111/j.1365-2028.2010.01207.x).
Minor comments:
3. L48-49: This claim is incorrect. A quick search will show that there are other species in the genus Gazella (search “Gazella” in the Mammal Diversity Database: https://www.mammaldiversity.org/explore.html). Further the authors should recheck all the references and ensure that they actually report the claims they reference here.
4. L53-55: Please confirm that this sentence is true. There has been speculation for subspecies but not a different species, Butynski and Dejong also talks about this, page 39; https://www.researchgate.net/publication/379329141).
5. L95: When the authors mention something in the introduction (for example, human population pressure), it gives an impression it will be measured or inform study design, but this is not true here. The authors should think about the value of each sentence and its contribution to testing their hypotheses.
6. L102 -105 repeats L105 -109 and should be deleted since second part is written more clearly than the first.
7. L147-150: The authors should include this information only if it affects the design of the study and is included in the testing of hypotheses. Otherwise, it should be removed.
8. L154 -180: unless required to, there is no need to add the categories (reconnaissance and sampling design)—the authors should combine them under “data collection”. Saying we laid transects according to the available habitat (grassland, bushland etc) already implies the authors did some reconnaissance, and it is also part of study design. The authors also do not need to include a formula for determine transect length if they eventually offset the difference using the transect length. This only increases confusion by leading readers to ask what the purpose of using a formula was in the first place? Why was b = 3, what is l0 and n0? Generally, how did this equation lead to transect of different lengths (2.3 to 6.8 km)?
9. L188- 193: Whenever the authors mention equipment, they should represent it as (Model, City of the company, and Country of origin). For example, we used a smartphone (Sony Xperia Z1, Tokyo, Japan)
10. L 178-180: if a GPS was used to navigate the transect, wouldn’t natural markings be a bit redundant?
11. L 185- 187: The authors should include a reference for the “believed active period”
12. L 189 -193: Which transects were walked and which ones were conducted on motorbike, etc? This should be stated clearly, for example, we walked transects in wooded areas and used motorbikes for open grassland. However, the authors need to state whether using different methods affected animal behavior and how, and how this may impact detection functions.
13. L 181-324: As mentioned earlier, distance sampling is a well-established method for estimating density and has important major outputs that are important to report comprehensively. I would suggest that the authors look at other papers that have used similar methods and follow the common formats. With a quick search, here are 2 examples: https://doi.org/10.1007/s11284-007-0394-8, https://www.jstor.org/stable/3784635?seq=1. This comment should be read alongside major comment #2.
14. L264-274: We commend the authors for following the standard reporting methods by displaying test statistic, degrees of freedom and p-value, but the results could be presented better. The most important thing about presenting results is giving the effect size and directions of the effect for example the density of kudus during wet season averaged X (95% CI: x – y; p < 0.001, test stats, and degrees of freedom) more than the density during dry season. The sentence habitat vs. season does not give much information on what is going on. L267-268 also shows DF = 9, but the authors reported 4 habitats and 2 species (8 groups total). These numbers do not add up. This comment should be read alongside major comment #2.
15. L375,448,456: (Tomillo 2016) this in-text citation is missing in the reference section and other in-text citations are inconsistent.
This work provides valuable information on the population density of two species of gazelles. One reviewer only has minor comments, while the second reviewer considers that there are major comments. Given this, I would like to see a major revision dealing with all the comments. Please revise paying particular attention to the more critical comments, especially in all the editorial details, clarify much more the methods and objectives of the study, trying to tie closely with the results obtained. The clarification of a study hypothesis also helps enormously in the approach of the study. It is also necessary to expand the statistical details that support the results. Both reviewers make a series of observations directly about the manuscript that I ask you to specifically address each of them.
Please be aware that we consider these revisions to be major, and your revised manuscript will probably have to be re-reviewed.
**PeerJ Staff Note:** Please ensure that all review and editorial comments are addressed in a response letter and that any edits or clarifications mentioned in the letter are also inserted into the revised manuscript where appropriate.
**Language Note:** The review process has identified that the English language must be improved. PeerJ can provide language editing services - please contact us at [email protected] for pricing (be sure to provide your manuscript number and title). Alternatively, you should make your own arrangements to improve the language quality and provide details in your response letter. – PeerJ Staff
=There is a need of editorial works
=Uniformity in the usage of text citations based on the rule of the journal is required
=Professional article stricture is in a standard
= The results are self-contained and sufficient.
=The research is within the aim and scope of the journal
=The research questions well addressed showing the existing gap of the studied subject
=Investigation of the research is more technical and ethical
=The methods described with sufficient details and information
=The findings is novel and stated clearly
=Statistically sound
=The conclusion well stated by supporting the findings
The topic is interesting and well written with sufficient findings and analysis. However, the author needs to address the concerns raised in the word document with a track-changes. Besides, there is a need of editorial works throughout the whole document.
The writing is largely vague and ambiguous. In-text citations are often missing from the biography. The manuscript is disorganized, and some of the authors' conclusions are beyond the data and analyses presented in the manuscript. More details are provided in section 4.
This research is original and fits the aims and scope of the journal. The research questions are clear, but often articulated poorly. The writing obscures the ability of reviewers to evaluate the methods, but some concerns are still apparent. The methods need to be much more clearly described. More details are provided in section 4.
We have significant concerns about the validity of the findings, but further explanation by the authors may address these concerns. More details are provided in section 4.
Major comments
1. The stated aims of the study (“To this end the present study attempts to answer research questions such as, what is the exact population size of N. granti and T. imberbis at GNP?, as proxy for exact global population estimate. What is the future population prospect of these two species?”) do not align with the data and analyses presented in this manuscript. The data provided by this study can be used to provide reasonable local population estimates of the two antelope species (part 1 of question 1 above) but cannot be used as a proxy for global populations for the two species presented (part 2 of question 1). With such localized study, one can only make inference to the population studied. While predicting future prospects for this population is possible (question 2 above), the study design, data collected, and analysis method are not designed to answer this question.
2. The methods used for analyses need to be described much more clearly. The authors have failed to clearly state the methods used for analysis and instead often simply list technical terms related to the software packages they used. For example, a few methods used in the manuscript including ANOVA and Poisson regression models (Lines 215) have been listed without an explanation of why these methods were chosen and have also been stated incorrectly. In addition, presentation of the results often do not follow standard methods and could be improved.
3. Because there were no explicit hypotheses, the manuscript writing has no logical flow and is thus hard to follow and understand. In general, the manuscript should start by broadly introducing the study topic, then the paragraphs that follow should aim to address each question/hypothesis to be tested, carefully addressing possible outcomes for each. For example, how are densities expected to change between season, species, and across different habitat types? The sections subsequent to the introduction should then follow this structure in parallel.
Minor comments
4. Throughout the manuscript, there are consistent grammatical issues that impede reader comprehension. The authors should carefully review the writing and if possible, seek a reviewer that can help improve its readability.
5. Line 35: Ungulates are herbivores so African ungulates or African herbivores would equally suffice.
6. Line 39: the in-text reference used here is missing in the References section and so are many other references, including in lines 354, 363, 385, 448, etc. Other references are not in the correct format, including lines 385, 394, 465, etc. The authors should correct these according to the journal’s format.
7. Line 51: This abbreviation should be spelled out before it is used.
8. Lines 94-97 has been repeated in the methods section. I would suggest leaving this kind of information and any description about the study area for the methods section, under the study area subsection.
9. Lines 138-140: Much of this information could be removed without affecting information content.
10. Lines 157-158: It is unlikely that QGIS was used to locate transects. Do the authors mean QGIS was used to plot selected transects onto the study area map? If so, the authors should reference the map (Fig 2) where this is shown.
11. Lines 167-171: It is unclear as to whether the authors walked the transect, cycled, or used a motorbike to conduct the survey. If a motorbike was used, a speed of 6km/h seems too low—from personal experience, motorbikes stall at such low speeds.
12. Lines 173-177: Six people with experience were involved in the survey, does this exclude the field assistant that needed training?
13. Lines 185-188: For clarity, the authors should split the methods based on the species that they were applicable to.
14. Lines 196-201: This section could be removed without affecting information content. In addition, instead of simply stating they used R software, the authors should mention the exact package(s) used and provide a citation for each. Similarly, the authors should more completely describe how each was used—for example, what was the role of QGIS here?
15. Lines 206-209: Again, any abbreviation should be stated first in full. It is also hard to understand what analysis is actually being done in this section. It would help to further describe the underlying methods that are being performed and why they were used.
16. Lines 210-211: The authors should ensure each statistical decision is explained. For example, why was the perpendicular distance grouped or ungrouped?
17. Line 215: These are two separate statistical analysis methods that also seem to have appeared from nowhere without explanation as to how they are relevant. It would help for the authors to provide reasons for why a certain method was chosen over others.
18. Lines 221, 230, 231: the term “interaction” has a different meaning than used here. The word the authors may be looking for in this case may be “association”. Similarly, are transect lengths always used as offset or used to find effective strip width? In any case, if this was deliberate, the authors should state why offsets were chosen as a method.
19. Line 228: When presenting results, the authors should use effect size and direction of the effect as the topic of their sentences. The authors should strive to follow standard ways of presenting statistic by stating the statistical test used, the value of the test statistics, and P-values, throughout this section. See https://onlinelibrary.wiley.com/doi/epdf/10.1111/j.1469-185X.2007.00027.x.
20. Lines 234-237: This should be moved to the methods section. To avoid overly convoluted sentence this could be written as “We fitted quasipoisson regression to reduce overdispersion”.
21. Line 257: Detection probability (Pâ) scales from 0 to 1 or could be represented as a percentage, but the units here are unclear. It would help to explain how the authors arrived at the value stated. Similarly, whenever a value X±Y is given, they should be followed by what each value represents (e.g., the mean estimate for kudus was 3.5 ± 1.9 (SE)).
22. Line 264: This statement leans more towards resource selection, which is beyond the scope of this study. Grant gazelles occurred in low densities in habitats x and y would be more appropriate.
23. Line 274: The authors need to provide a reason for truncation. Truncations are used to define a limit in which detection is impossible. In open grassland, detection could be well over 150 meters.
24. Line 275: When a graph is mentioned, it should be followed by the figure number that shows what is described.
25. Lines 282 and 285: Fig 4a and 4b show frequency distribution curves for sight distances that look like normally distributed curves. This shape is unusual for distance sampling data, which has underlying assumptions that animals closest to or on the transect are detected with certainty and as the distance increases, the detection probability decreases with species-specific variation expected based on the size of species and habitat. Since this distribution violates that assumption, an explanation for why it appears in the authors’ data should be given.
26. Line 303: The authors should state exact associations between dependent and independent variables. “Main effects model” could mean anything.
27. Line 320: While this statement might be true, the species discussed here are not rare nor vulnerable. Just stating estimation of population is a prequisite for better management of the species could suffice.
28. Lines 329-330: Population viability is beyond the scope of this project—this has a specific meaning with higher standards of evidence than provided in this manuscript. A healthy population perhaps could suffice, but the authors also need to elaborate on this.
29. Lines 333-340: The authors should be careful to make inferences only supported by their data. This study did not incorporate data on movement of Grant’s gazelle in and out of the protected area nor influence of grazing on the densities of the two species. Similarly, when reporting and comparing studies that have somewhat similar results, the authors should state that their findings are consistent to those other studies rather than stating that their results support them.
30. Line 343: Bushland and grassland are incorrectly written.
31. Lines 359-361, This statement leans more towards resource selection, which is beyond the scope of this study. Grant gazelles occurred in low densities in habitats x and y would be more appropriate. See comment 22.
32. Lines 370-371: Population viability is beyond the scope of this project. A healthy population perhaps could suffice but you also need to elaborate on this (see comment number 28).
33. Lines 377-380: While poaching might be an issue, the data provided here cannot be used to make this claim nor was it subject for this study. The authors should delete this claim. See comment 29.
34. Lines 405-407: Were kudus expected to be in open grassland in the first place? Species survey designs are generally guided by the species biology, and kudu are browsers well-known to inhabit relatively dense vegetation. The authors should give an explanation for their sampling design for kudu including a habitat they are unlikely to be found.
35. Lines 415-417: I would recommend that the authors delete these sentences or explain them better. The authors should instead consider explaining how age affects population growth: what would it mean for the population if it was largely composed of only adults, females, or had no juveniles? The authors can then discuss this in the context of the different mating strategies.
36. Line 431: The sentence on this line is incomplete.
37. Lines 460-461: This information is also good but to make such claims, the authors need to have designed their study in a way that accounts for the density of predators. See comment 29.
38. Line 471: Population viability is beyond the scope of this project. A healthy population perhaps could suffice but the authors also need to elaborate on this. See comment 28.
39. Lines 483-491: The authors mentioned 6 people participated in data collection, but it is unclear if these are the same people they acknowledged or if there were other people not mentioned. Similarly did the 6 people include the three authors? The authors should clarify.
40. Fig 1: The quality of these maps could be improved. Maps should be exported with a DPI of at least 300.
41. Fig 2: In the map, the vegetation has been classified into four categories: bushland, grassland, savanna, and woodland. Savanna is a broad term that could encompasses all the others, so the authors should clarify what is meant by this category. Additionally, while it is possible to lay straight transects, in savanna grassland, it is highly improbable that all transects were straight. The author should give an explanation how this was achieved—did they clear vegetation along the transect line, walk around vegetation, etc.
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