Associations between Epiphytic Orchids and Their Hosts and Future Perspectives of These in the Context of Global Warming

Round 1

Reviewer 1 Report

The authors of this study have surveyed a large number of tree species in Nepal along an elevational gradient to determine patterns in epiphytic orchid diversity. This is a very large dataset, and thus I think important to have the results published. However, the presentation of the results is confusing. The authors should be clearer about the difference between the total orchid species richness found on each plant species, the orchid species richness on each host species compared at a particular level of rarefaction, and the number of orchid species significantly associated with each host species. There also needs to be more information in the methods about how the trees that were surveyed were selected. It also needs to be clearer whether the altitudinal bands presented in this paper are based on the authors own surveys or are derived from the literature. The Discussion could also be more interesting if you talked more about which host species are generalists (hosting many orchid species but with no significant associations) vs. specialists (only hosting orchid species that significantly associated with them). You also talk about protecting orchid species from climate change, but don’t say anything about how someone would actually go about doing that. Any thoughts? Finally, there are some very interesting speculations about the host plant functional traits associated with supporting a more or less diverse orchid community. Is it possible to extract values for some of these functional traits from the literature? That would allow you to formally test which functional traits are most important in this context, which would greatly increase the impact of the paper.

Line 16: Insert “a” before “significant”

Lines 76-77: There needs to be more details about the study methodology. How were the study trees chosen? How many individual trees and species of trees were surveyed in each region?

Line 89: 75 individuals seems like a high cutoff. My guess is that you could have used more of the dataset.

Line 106: Insert “the” before “vegan”

Line 110: Do you mean per 20 host plants?

Lines 119-123: So you considered a species to be present in all altitudinal bands between the lowest and highest sites at which you observed the species? I thought in lines 85-87 you said that you got the altitudinal distributions from other sources. I think you could be clearer on what you are doing in this section.

Lines 125-137: The most recent IPCC report projects warming of 1.4-4.4°C by 2100. Thus, 5°C is an extreme expectation for global warming. Unless you have downscaling data that indicate greater than average warming in Nepal, I would include a more moderate (e.g., 2.9°C warming) scenario in your analysis.

Lines 140-142: This is confusing. I thought that the Phi coefficient was being estimated for each host species-orchid species pair, whereas here it sounds like there is a single Phi coefficient for each host species. Based on Figure 1, I think it is a separate Phi coefficient for each host species-orchid species pair, so I think what you mean is that there were 30 host species with at least one Phi coefficient greater than 0.2. If this interpretation is correct, then the hosts with the most orchid species have 12 orchids significantly associated with them, but might have more total orchid species recorded on them somewhere in the dataset. Whether the top hosts have 12 orchids that associate with them at all vs. 12 orchids that associate with them significantly gives a very different impression of how this community is structured, so it is important to be clear which of these two scenarios is occurring.

Lines 153-158: This is again a very confusing way to word your results. You only included trees with at least 75 individuals surveyed, so when you rarify your data to only 20 individuals, you are actually presenting orchid species counts that are lower than the total orchid species richness recorded on each host tree. Since you refer to the numbers from the rarefaction curves as the number of species they “potentially host” is makes it sound like they are larger than the number of species that you actually find on them, especially when you contrast it with the “actual numbers recorded in the previous paragraph.” In reality, you haven’t shown the total number of hosted orchid species up to this point in either figure, and those numbers would be higher still. You need to be much clearer about what each set of numbers truly represents.

Lines 163-164: You again refer to the “actual numbers of species of orchids hosted” when you mean the “number of orchid species significantly associated with a given host species”. You have it correct in the figure caption, so I’m not sure why you have it incorrect in the main text.

Lines 183-185: What was the total elevational range covered by your study. I know that it covered 4400 m, but did that start at sea level? Also, it is unclear if these altitudinal ranges are specifically from your surveys or what you found in the literature.

Line 184: Change “was” to “were”

Lines 189: I thought you were doing 100 m elevational bands, but this in only 50 m.

Figure 5: Is this all tree species or only host tree species? The caption says all tree species, but the legend says only host species. I think you also have a problem at the right side of the graph, where I believe black dots are covering up white dots, making it unclear if orchid richness is zero or one. The number of host plant species in the 1800-1900 m interval also seems strangely low. Is there a huge turnover in the host species community in this interval? If not, then why is the curve so jagged here rather than being close to smooth, with the number of host species in this interval being close to the number in the intervals just above and just below?

Line 214: Here you call Lagerstroemia parviflora and Litsea monopetala as the host species with the narrowest elevational range, whereas previously (Line 189) you said that Madhuca longifolia had the narrowest elevational range.

Line 217: Why don’t you say anything in the Discussion about the relationship in Figure 3? There is a lot of information here about which host species are generalists (host many orchid species, but none of them to a significant degree) vs. specialists (all the orchid species they host are significantly associated with them). The specialist species would be the ones with the largest positive residuals (farthest above the line) and the generalists would be the ones with the largest negative residuals (farthest below the line). Do you see any interesting patterns when contrasting these two sets of species?

Line 218: This section has a number of interesting hypotheses about why certain host species support higher (or lower) orchid diversity. Would it be possible to make this a formal analysis, comparing functional traits to orchid diversity to see which host species functional traits are most important for supporting a rich orchid community? That would make this a much more impactful paper.

Line 221: What do you mean by “nature”?

Author Response

We have addressed all the comments in the new manuscript and answered all the questions in the file attached here.

Author Response File: Author Response.docx

Reviewer 2 Report

This paper addresses a very interesting topic and makes use of what appears to be a very detailed and valuable dataset. However, as written there is unfortunately insufficient information in the Methods to be able to evaluate the paper in a meaningful way. In addition, there appear to be numerous errors or inconsistencies in the presentation of the results, making them hard to interpret.  A new version of the paper that provides much more information on the methods and clarifies the results would provide an interesting contribution.

Specific comments:

In the Introduction it is worth mentioning that there are other factors demonstrated to influence epiphyte abundance, including host characteristics such as bark rugosity, bark water holding capacity, nutrients in stemflow and throughfall, tree architecture (beyond height) etc (even though you didn’t focus on these).  Some of these are mentioned in the discussion, which is good.

The abstract states that, “The epiphytic orchids differed in their associations with different host plants  depending on abiotic and biotic factors.” This is not shown in the results.

The methods need much more detail and justification:

How was the vegetation sampled? The authors refer to another paper but this needs to be described clearly here or it is impossible to evaluate the paper.  For ex. was this information recorded in transects? What dimensions? How were they placed? Etc.

How were orchid species identified if they were not flowering? Were only adults identified?

Please also describe how this paper relates to, but is different from Timsima et al, 2016.

Please describe how the phi coefficient is calculated specifically, and please justify it’s use here.

If the trees were different sizes then the number of trees is not necessarily a good proxy for area. Please justify this.

There are inconsistencies and lack of clarity in the results:

Fig1. Does this show, for each host, the number of orchid species for which the phi coefficient is >0.2? Or just the number of species recorded per tree, as mentioned in the text? Please make this clear.

The authors state: “There is a significant positive correlation (P = 0.004, R2 = 0.246) between the actual numbers of species of orchids hosted by the 30 host species depicted in Figure 2 and the numbers predicted by the rarefaction analysis if 20 individuals per host species are considered (Figure 3).  But figure legend for Fig 2 says it represents, “The number of species of orchids significantly associated, in terms of the Phi coefficient (Φ), with a given species of tree”. Presumably this is different than the total number of species on a given tree species, because some orchid species will have phi coefficients <0.2 for that tree species.  Rather Fig 3 seems to indicate the relationship between the number of orchid species significantly associated with a given tree species and the total number of species found on it Please clarify.

The authors state “Biologically, the results of the rarefaction analysis are very similar to what we observed in the field”. Please provide this evidence in an appendix

Fig 3: The y axis is incorrectly labelled - it is not the phi coefficient in itself, which ranges from -1 to 1. Please rename

Fig 4:  Please title this more clearly. Based on the discussion, this appears to be the total number of orchid species observed across all individuals?

If so, this is just a species-area relationship as mentioned in the discussoin. It would be interesting to test this at the tree level – i.e. do the most abundant trees have the highest number of orchid species (looking at # of orchid species present per individual tree).  This would need to be interpreted in light of differences in size.

Please explain what each dot represents in Figures 3 and 4. Presumably in both figures each dot represents a different tree species. But then why are there so many more dot in Fig 4?

Discussion:

“A high number of species of orchids were associated with tall trees (such as Shorea robusta).” Please show the data for this in an appendix. There is no information presented on tree height.

Also given that tree size varies with elevation, then any relationship between size and richness should be examined at each elevation.

Fig 3 shows that host trees that have more significant associations with specific orchids also have a number of orchid species on them.  This figure is not interpreted in the discussion. Please interpret this - is this because most orchids had specific associations? Or?

The English is acceptable.

Author Response

We have addressed all the comments in the new manuscript and answered all the questions in the file attached here.

Author Response File: Author Response.docx

Reviewer 3 Report

The submitted manuscript is of high quality in general. Just some minor problems were found by me during the evaluation process.

The title is good, by well representing the content of the manuscript.
I recommend to revise the abstract. For instance, add p-values (and, if it is needed, other statistical indicators) in places, where the authors write "significant(ly)" or they say about differences (are they significant or not?) or if the authors write higher/lower/other issues.
The list of key words looks good for me.

The section Introduction is well written by highlighting the relevance of this research subject, representing the background of the research, and by presenting the main aim and research tasks of the paper. For me, this section is very good.

The section Material and Methods is written generally well, but some corrections are needed. For instance, I strongly recommend to not standardize Latin names of plants according to local sources or publications but according to the international and permanently developing database POWO for both epiphytes and host plants.
At the same time, the research design and framework of the analysis are being described quite well and in details. This is very good for maintaining the repeatability of the research. Moreover, most approaches are supported by references confirming the relevance of the used methods.
Therefore, the section Material and Methods is very well in general.

The section Results looks quite well. All graph plots were made in good quality (resolution). But I recommend to correct the figure captions to make them self-explaining, i.e. each figure caption should have information, where and when the analysed (presented) data were obtained, for instance, "in Nepal, 2016-2011" can be added to the figure captions of the used figures.
The statistical treatments look to be good and representable.
The results on the relationships between all tree species and all epiphytic orchids along altitudinal gradients look to be especially interesting, in my opinion. Indeed, such results can be obtained only in such areas, as Nepal, where a wide altitude range can be occurred. 
But the subsection "3.3. The effect of temperature increases on the number of plant species" is especially unclear for me. In particular, it is unclear, how threatenness of species is being assessed, i.e. how one species are considered threatened, while other species are considered non-threatened by temperature (by the way, I would call it "weather conditions" instead of "climate changes" as it is given in Material and Methods)? I recommend to add this information on the calculation approach in Material and Methods and more detailed information, why one species are threatened by temperature but other not?

The section Discussion is written quite well. All explanations and discussions are supported by references. But I strongly recommend to pay attention to the formatting of in-text citations. According to MDPI rules, the references should be presented as numbers in quadrate brackets in order of their mentioning in the main text. However, some in-text citations are formatted as "Author(s)-Year". These inconsistencies should be corrected during the revision stage.

Finally, the section Conclusions is quite general and non-concrete. Please, revise the section by adding more implications from the results obtained in this study to be more concrete and closer to data revealed in Nepal in 2006-2011.

But, despite my comments and suggestions, the study is well written, in my opinion.

Author Response

We have addressed all the comments in the new manuscript and answered all the questions in the file attached here.

Author Response File: Author Response.docx