PONE-D-25-32694A bioavailable 87Sr/86Sr isoscape of Mongolia: implications for the reconstruction of past human and animal mobilityPLOS ONE

Dear Dr. Le Corre,

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Both reviewers recommend minor revisions to your manuscript. I believe the paper is a solid and well-executed piece of scientific work, and I likewise recommend only minor revisions.

My only comment to the authors is to carefully review the recent literature on Sr isoscapes, as other studies have applied machine learning models in this context and may warrant acknowledgment.

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6. We noted in your submission details that a portion of your manuscript may have been presented or published elsewhere. [This manuscript includes previously published ⁸⁷Sr/⁸⁶Sr data from archaeological sites (Table 2, Table S2, Figure 6), which are compared to the isoscape predictions as an example of application. While several of these studies also aimed to assess local vs. non-local origins of individuals, they relied on point-based local baselines (e.g., fauna, plants) specific to each site. In contrast, our study uses these same ⁸⁷Sr/⁸⁶Sr values to evaluate a novel, spatially continuous isoscape model. The aim is not to reinterpret the archaeological data per se, but to demonstrate the potential of the isoscape for assessing the origin of archaeological material and to evaluate the isoscape’s predictive accuracy. As such, this does not constitute dual publication.] Please clarify whether this [conference proceeding or publication] was peer-reviewed and formally published. If this work was previously peer-reviewed and published, in the cover letter please provide the reason that this work does not constitute dual publication and should be included in the current manuscript.

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Reviewers' comments:

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Comments to the Author

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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: Yes

Reviewer #2: Yes

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

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Reviewer #1: Yes

Reviewer #2: Yes

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Reviewer #1: Yes

Reviewer #2: Yes

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5. Review Comments to the Author

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Reviewer #1: The authors present a wonderful study: 1) the goals are well-defined; 2) the methodological approach is robust, formally exploring alternative machine learning algorithms (RF and EML) to build strontium isoscapes; 3) the results are extensive and clearly described and analyzed; and 4) the discussion is warranted by the baseline presented in this paper and the inferences are both conservative and interesting. An additional merit of the paper is the public availability of all the data, analytical procedures and codes utilized to develop the paper. Hence, this research is fully and easily replicable.

I don't have signficant suggestions and strongly recommend its publication in PLos One.

Reviewer #2: General comments

This paper presents an impressive number of 87Sr/86Sr samples for an understudied region of the world. This contributes greatly to the ongoing efforts to create bioavailable strontium isoscapes around the world, thank you! Thank you also for providing the variables in a downloadable format as well as all the code used in this study.

The manuscript itself was easy to read and has a nice clear structure. The thorough explanation of the modelling methods employed is appreciated. I have only minor comments (specific ones below), and only have a few slightly larger (but optional suggestions) to the authors. These larger suggestions are more interest on my account that requirements for the paper!

In the Introduction (lines 132 – 152) as you can’t see the dates of references it is a little confusing the order of the environmental data collection, perhaps add the order of these studies into the text.

In Methods (line 228), you mention that notably the predicted bedrock 87Sr/86Sr is included. Why is that notable and what difference can this potentially make to the model output?

In Methods (line 279), you state that the EML model accounts for spatial auto-correlation between samples. My questions for this statements were does spatial autocorrelation hold for Sr given distinct boundaries between geological units? Does the appearance (or not) of spatial autocorrelation influence the results of EML model? RF does not take into account the closeness of sampling sites, but does EML? Consider adding a sentence or two addressing this, if it makes sense!

In Results, (lines 307 onwards), it isn’t very clear which data is being used for each of the model iterations, consider making that clearer.

Specific comments

Line 93, line 136, line 143, line 233 – Capitalise the Sr on 86Sr

Line 110 – perhaps define where is High and Central Asia

Line 145 – capitalise B on Bronze Age

Line 156 – “exceeding locally 4000m” is odd phrasing, perhaps “Mongolia has an average elevation of 1500 m, with some regions exceeding 4000 m.”

Figure 1 – a lot of specific regions/mountain ranges etc are mentioned in the preceding and later paragraphs, perhaps add these to Fig 1 to make it clearer for the reader to follow. The blue dots are also a little difficult to see, perhaps a slightly darker blue would be easier?

Line 253 – should it be tree not three?

Line 487 – capitalise the Sr on 87Sr

Line 318 - Perhaps “but reaches RMSE = “ instead of “but allows to reach RMSE”

Line 319 – Perhaps reword to “The EML has similar performance compared to the RF model”

Line 377 – over is not needed in “spanning over less”

Line 504 – “without relying on a real” instead of relying to

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Reviewer #1: Yes:  Ramiro Barberena

Reviewer #2: No

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A bioavailable 87Sr/86Sr isoscape of Mongolia: implications for the reconstruction of past human and animal mobility

PONE-D-25-32694R1

Dear Dr. Le Corre,

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Federico Lugli, Ph.D.

Academic Editor

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