PCLM-D-25-00327

Regional risk shifts to monarch butterfly migration due to climate change

PLOS Climate

Dear Dr. Ureta,

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Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. Does this manuscript meet PLOS Climate’s publication criteria?>

Reviewer #1: Partly

Reviewer #2: Partly

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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 (please refer to the Data Availability Statement at the start of the manuscript PDF file)??>

The PLOS Data policy

Reviewer #1: No

Reviewer #2: Yes

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4. Is the manuscript presented in an intelligible fashion and written in standard English??>

Reviewer #1: Yes

Reviewer #2: No

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Reviewer #1: This paper examines the potential for the presence of milkweeds in North-Central Mexico to draw monarchs from the migrating population and for those monarchs to engage in reproduction and possibly establish a resident population. Depending on how extensive this phenomenon is, it could reduce the size of the migrating population. The question the authors address is how this potential for milkweeds in N-C Mexico to harbor monarchs might change under a couple of climate change scenarios.

To address this question there are a number of other questions to address:

1) What milkweed species are currently growing in N-C Mexico along the migratory route during the migratory period (October-November)?

2) At any time of the year are there milkweeds present that could support monarchs, making it possible to have a resident population?

3) What are the observations of eggs and larvae (ELM) on milkweeds in N-C Mexico and at what times of the year?

4) What are the ecological niches of each of the milkweed species in N-C Mexico? What species die back in summer or winter?

5) How would conditions under the climate models shift milkweed distributions in the future?

6) What is the ecological niche for monarch eggs and larvae and what are the conditions under which they could not persist as a resident population (eg probability of consecutive temperatures below freezing)? How can ELM make it through the winter or make it through the summer?

I don’t think the authors adequately answered these questions.

Question 1 – no information

Question 2 - It’s not just whether there is an occurrence record for a particular species, but species die back at certain times so you have to know if a particular species is available. You would have to know something about the abundance of the species to know whether it could support a monarch population.

Question 3 -Line 81 They refer to georeferenced records of ELM. Presumably these are records of someone observing eggs or larvae on milkweeds. This is an important data set because it would tell us when and where and on what milkweed species. We don’t see that data set. The authors say they will make the data available once the paper is accepted but we need to know something about the data set to evaluate its worth. How many data points are there. How many milkweed species. Perhaps a frequency distribution of occurrences on different milkweed species. And the authors seem to include in their analysis all of Mexico rather than focusing on N-C Mexico along the migratory route, which is most relevant. We don’t know if this data set would answer Questions 3 without seeing it. What would a map showing the location of these observations and at different times of year look like?

Question 4 – how are the ecological niches determined for each species?

Question 5 – The authors use models to predict conditions in the future. We need to know the answer to Question 4 to get at possible distribution changes.

Question 6 – How do you use the records of an observation on a milkweed to develop the ecological niche for ELM? There are data on the ideal temperatures for larval development and the temperature extremes that would kill larvae.

In the analysis of future change, they say: “Climate change

projections indicate contrasting potential reductions of 40% and 8% in suitable habitat by 2070, under the CanESM5 and MPI-ESM1-2-HR, respectively.” But then go on to say “This trend suggests that monarchs may increasingly establish reproductive resident populations in northeastern to central Mexico rather than reaching their overwintering sites.” If there is a reduction in suitable habitat wouldn’t that REDUCE the likelihood of establishing resident populations?

Specific comments:

Figures – the location of the MBBR should be indicated

Abstract -There is empirical observation …. – there is no study that shows that (see 35-37)

14-15 Not relevant -delete

35-37 Reference 22 does not provide empirical evidence local breeding

38 plantings rather than plantations

52 Texas and Mexico – what can be said about people planting A. curassavica or C. gigantea in Northern Mexico and whether there has been pushback on that practice?

162-163 how did you determine relevance?

165 what data were used to determine monarch preference for different milkweed species?

208 in the Northeast

283-290 this is just a repeat of what is in the Introduction - delete

355-356 Yes, we need data!

368 lay eggs on species

Reviewer #2: The manuscript highlights regional risk shifts to monarch butterfly migration due to climate change and uses habitat suitability modeling to evaluate the impacts of two nonnative milkweed species on the future on monarch butterfly residency/winter breeding in northern Mexico and Texas - the primary migratory route in and out of the overwintering colonies in central Mexico. While this is an interesting paper, I feel that the overall presentation of the introduction and discussion are lacking or at least not comprehensive enough to provide the necessary background/sufficient literature review - especially as it concerns the two nonnative plants. There is a growing body of research on the potential impacts of these nonnantives n monarch breeding, residency. I feel that the introduction does not provide the appropriate depth necessary to effectively set up the rest of the manuscript. Similarly, the Discussion is somewhat insufficient as well. While the authors try to provide a broad overview of impacts to the monarch, this is done at the detriment of providing more depth regarding the primary topic of the manuscript - the impact of these nonnantive milkweed family plants under under global change. Just as an example, there is research (Faldyn, M.J., Hunter, M.D. and Elderd, B.D., 2018. Climate change and an invasive, tropical milkweed: an ecological trap for monarch butterflies.) that looks at how the use of Asclepias currassavica and their cardenolide concentrations change under warming temperatures and how this will potentially negatively impact the monarch. I would encourage the authors to significantly revise these manuscript sections to more fully provide the detail needed for the reader and to appropriate set up their argument.

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Reviewer #1: No

Reviewer #2: No

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Regional risk shifts to monarch butterfly migration due to climate change

PCLM-D-25-00327R1

Dear Dra. Carolina Ureta,

We are pleased to inform you that your manuscript 'Regional risk shifts to monarch butterfly migration due to climate change' has been provisionally accepted for publication in PLOS Climate.

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Best regards,

Jennifer Lee Wilkening, Ph.D

Academic Editor

PLOS Climate

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Additional Editor Comments (if provided):

Reviewer Comments (if any, and for reference):