Life on the Wire—Plant Growth on Power Lines in the Americas

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Title: Life on the wire –plant growth on power lines in the Americas

 

General comments: Overall the manuscript is concise and provides a comprehensive overview of the conditions under which epiphytes grow on power lines across the Americas. It also provides a list of species commonly found on different sites. Overall, the paper is well-written and enjoyable to read.

 

I have a few suggestions that may help improve the manuscript:

 

Figure 3 compares the elevational distribution and climatic variables of the growing site with the overall elevation and climate of the Americas. It would be helpful to clarify what is meant by “climate of the Americas” or “The Americas” as mentioned in the legend. Is this meant to represent the expected climate at the particular site? For example, ~35% of wire plants are found at elevations of 0-500 m, compared to ~70% expected at these sites across the Americas? Clarifying this point would be helpful.

 

Discussion: Organizing the discussion into sections could improve readability, as the current format reads as a series of paragraphs without clear topic sentences. Authors might consider organizing it as follows:

 

1.  General patterns of epiphyte distribution on power lines,

2. Tillandsia dominance on power lines

3. Reproductive patterns for living in the wire

4. Conclusions

 

Minor comments:

The information about singleton species is interesting and I was wondering if the authors could expand on which elevation sites these species are found? Are they more commonly found at higher elevations? This information might be available in the supplementary material, but I did not find it easily accesible. For instance, are species like Aechmea organensis, Brassavola nodosa, Catopsis sessiliflora, Tillandsia fasciculata, T. exserta, and T. makoyana, etc primarily found in rural areas, or do they prefer areas with higher precipitation, higher elevations, and lower temperatures?

 

Line 134: Consider replacing the word “important” with “successful in terms of growth”

 

Line 148: Consider replacing the word “important” with “abundant”

 

Final thought: How long can T. recurvata survive on a wire? These observations are likely dependent on whether the electrical company clear them when they become a nuisance. However, if left undisturbed, are we talking about years of growth under these conditions? It is interesting to consider whether T. recurvata may be found more frequently on wires than trees in the future due to deforestation and urbanization.

Author Response

Thanks for the positive feedback. Here is our response to your suggestions:

Figure 3 compares the elevational distribution and climatic variables of the growing site with the overall elevation and climate of the Americas. It would be helpful to clarify what is meant by “climate of the Americas” or “The Americas” as mentioned in the legend. Is this meant to represent the expected climate at the particular site? For example, ~35% of wire plants are found at elevations of 0-500 m, compared to ~70% expected at these sites across the Americas? Clarifying this point would be helpful.

We actually describe exactly this in lines 167 - 176, which is also the reason for the discussion about Amazonia. what we did is be even more explicit in MM, so that there should be no more doubts.

Discussion: Organizing the discussion into sections could improve readability, as the current format reads as a series of paragraphs without clear topic sentences. Authors might consider organizing it as follows:

1.  General patterns of epiphyte distribution on power lines,
2. Tillandsiadominance on power lines
3. Reproductive patterns for living in the wire
4. Conclusions

Thanks for this suggestion. We actually tried to do this, but in the end deleted the subheadings again. So we would rather leave it the way is was

Minor comments:

The information about singleton species is interesting and I was wondering if the authors could expand on which elevation sites these species are found? Are they more commonly found at higher elevations? This information might be available in the supplementary material, but I did not find it easily accesible. For instance, are species like Aechmea organensis, Brassavola nodosa, Catopsis sessiliflora, Tillandsia fasciculata, T. exserta, and T. makoyana, etc primarily found in rural areas, or do they prefer areas with higher precipitation, higher elevations, and lower temperatures?

As stated in the caveats one should not put too much trust in the exact numbers. The Aechmea, for example, is mentioned in a paper, but without abundance - maybe there were several individuals. So we think any detailed analysis would be premature, but we do hope that our paper will produce a lot of observations in iNaturalist and even some papers detailed analyses.

Line 134: Consider replacing the word “important” with “successful in terms of growth”

Line 148: Consider replacing the word “important” with “abundant”

both changed as suggested

Final thought: How long can T. recurvata survive on a wire? These observations are likely dependent on whether the electrical company clear them when they become a nuisance. However, if left undisturbed, are we talking about years of growth under these conditions? It is interesting to consider whether T. recurvata may be found more frequently on wires than trees in the future due to deforestation and urbanization.

We would say as long as on a a tree. We cited the Wester/Zotz paper which compared growth and survival of T. flexuosa. This was over one year, but this could be future study over a longer period

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript is well structured and deals with a very interesting aspect of epiphytes that rarely receives attention from botanists or is mentioned at the time of collecting specimens. The methods are clear and the results and discussion provide original and relevant information that can be the starting point for detailed studies on the topic. I am attaching the manuscript with some comments and would only suggest to the authors, if possible, to include more images, particularly of some of the most representative and also the less common species, that grow on power lines.

Finally, I would like to mention that although unfortunately I do not have photographic evidence, I have observed plants of Tillandsia circinnatioides Matuda, T. ionantha Planch., and T. mitlaensis W. Weber & Ehlers growing on power lines, in some locations in Mexico.

Comments for author File: Comments.pdf

Author Response

First, thanks for the very positive reception of our paper

1) several edits marked in the submitted file - all changes made as suggested

2) inclusion of more images - the majority of images are from others and the resolution of the iNaturalist files is typically not sufficient fora publication. We did, however, add one more observation to Figure 1, so that at least one species of Tillandsia is shown now.  Moreover, in the supplement we give the ID of all observations - so please have a look at any pic that seems interesting!

Reviewer 3 Report

Comments and Suggestions for Authors

Review Manuscript ID diversity-3179814 : “Life on the wire –plant growth on power lines in the Americas”

The manuscript addresses the occurrence of plants on cables and wires, a fact that is already known and recorded, but not exactly inventoried. The subject is interesting and there is poor literature on this mechanism, especially on whether this is a characteristic that could be related to an adaptive advantage of plants occurring in urban environments. In fact, this possibility was not discussed in the article, and although there is little bibliography on the subject, I think it should be hypothesized and discussed here. The text is well written, but some points need to be corrected and considered so that the article can be improved and published in Diversity.

Introduction

Page 2 – line 65:  The authors report the occurrence of plants from the Southern United States to Argentina and Brazil. It is not clear whether there are no reports from the rest of the world, or whether there is a limitation in data collection. This is discussed very briefly later, but I think it should be made clear in the introduction, even if it is not clear why this occurrence is only in the Americas.

Material and Methods

Some items should be better detailed. It was not clear how they identified that these species or genera were occurring in cables. From the iNaturalist photos? And the data obtained from the scientific articles?

Results

In Table 1, align the #obs column. Please standardize the citation of taxa. Why is a Vriesea not identified at the species level listed as Vriesea sp. and Tillandsia not? I imagine that "Bromeliaceae" was not identified as a genus. All of this must be reported in the legend.

Page 6 – line 162:  Figure 3 is not subdivided into a and b, please check. When you mention the preference of plants for lowlands and cite the Amazon as a justification, I wonder if in the entire distribution obtained on the map, there are other lowlands. It seems to me that this is not a good example, besides it seems like a topic for discussion and not results.

Figure 4 legend: T. balbisiana (red)  and not T. balbisiana (rot), right?

Page 8 – line 188:   “However, a wide geographical range is not a sufficient explanation for the success of that species, because T. usneoides has an even wider distribution, but its documented occurrence on power lines is quite limited.” I think this is discussion.

Page 9 – line 197:  “The average maximum size…”. Where are these results? It would be interesting to have a more complete table with this information. If they are not included, it should be marked as "data not shown".

Discussion

Page 9 – line 223: About the conspicuous gap in Amazonia: This gap in the Amazon occurs for Bromeliaceae. Could this be a bias? The paper by Zizka et al 2019 (DOI: 10.1111/ddi.13004) deals with the species richness of American Bromeliaceae, and this gap is again confirmed. Therefore, I think that this lack of occurrence data is related to this, which should be discussed more strongly.

The success on power lines was explained on page 9, starting at line 248, as being due to several factors, including the reproductive system and vegetative size. I think these are plausible hypotheses and are properly discussed. However, these data are not presented in the manuscript. No compilation of these data was made for the species listed in Table 1. This needs to be transparent in the discussion section. For example, the occurrence of Tillandsias that are cross-fertilized does not match the hypothesis. This is explained further, on page 10, line 277. I think it is necessary to improve this part, linking the pieces about the reproductive system, size, and so on.

Page 10 – line 281: Review the umlaut in aeranthos.

Page 10 – line 288: Why are all these authors cited?

Page 10 – line 289: What do you mean here? Please clarify this sentence.

Page 10 – line 301: “Thus, one should be cautious when interpreting differences in the regional numbers of observations as evidence for actual differences in the frequency of plants on power cables.” Regarding this sentence, I think it could be better discussed. In addition to the variation in the distribution of plants, as already mentioned in Bromeliads in the Amazon, there may also be a socioeconomic context involved. Could regions with lower rates record less? Have fewer wires and cables? All of this should be discussed and put into perspective.

 

 

Author Response

The manuscript addresses the occurrence of plants on cables and wires, a fact that is already known and recorded, but not exactly inventoried. The subject is interesting and there is poor literature on this mechanism, especially on whether this is a characteristic that could be related to an adaptive advantage of plants occurring in urban environments. In fact, this possibility was not discussed in the article, and although there is little bibliography on the subject, I think it should be hypothesized and discussed here. The text is well written, but some points need to be corrected and considered so that the article can be improved and published in Diversity.

R: Thanks for the positive reception. Please see the following for our response

Introduction

Page 2 – line 65:  The authors report the occurrence of plants from the Southern United States to Argentina and Brazil. It is not clear whether there are no reports from the rest of the world, or whether there is a limitation in data collection. This is discussed very briefly later, but I think it should be made clear in the introduction, even if it is not clear why this occurrence is only in the Americas.

R: Since we are not aware of any observation of plants or lichens of power lines outside the Americas (with the exception of introduced Tillandsias in Hawaii – which we do mention), there is no reason to analyse the unknown. One of us recently visited Japan and was intrigued by the many power lines that were devoid of anything. We now mention explicitly in the introduction that there available information suggests that this phenomenon is restricted to the Americas

Material and Methods

Some items should be better detailed. It was not clear how they identified that these species or genera were occurring in cables. From the iNaturalist photos? And the data obtained from the scientific articles?

R: We are a bit confused by this comment. We are very explicit that we reviewed more than 100,000 observations in iNaturalist – it is pretty obvious from the photo that a plant is growing on a power line. How should that be “detailed” – we are even very explicit about the quality issues, because the bromeliad expert Alfredo Cascante carefully reviewed each observation. All this is already stated. Moreover, we also cite all papers that deal with the phenomenon – the first authors is collecting the literature for 30 years. Although the probability of having missed a source in the gray literature is still non-zero, we are pretty confident that we covered it pretty well. Still, we have expanded our section on “caveats” in the discussion.

Results

In Table 1, align the #obs column. Please standardize the citation of taxa. Why is a Vriesea not identified at the species level listed as Vriesea sp. and Tillandsia not? I imagine that "Bromeliaceae" was not identified as a genus. All of this must be reported in the legend.

R: Thanks for pointing out these oversights. We have made the changes in the Table.

Page 6 – line 162:  Figure 3 is not subdivided into a and b, please check. When you mention the preference of plants for lowlands and cite the Amazon as a justification, I wonder if in the entire distribution obtained on the map, there are other lowlands. It seems to me that this is not a good example, besides it seems like a topic for discussion and not results.

R: The problem with a/b was also detected by another reviewer. Thanks. Similarly, the “Amazon issue” was also brought up by another reviewer (#4). We think that our interpretation is simply plausible, not more, but also not less. However, we have changed the wording in our brief discussion of this issue to emphasize that this is our suggestion. On the other hand, this should be obvious in a purely descriptive study. The important point is: this is just one of many starting points for interesting follow-up studies.

Figure 4 legend: T. balbisiana (red)  and not T. balbisiana (rot), right?

R: changed

Page 8 – line 188:   “However, a wide geographical range is not a sufficient explanation for the success of that species, because T. usneoides has an even wider distribution, but its documented occurrence on power lines is quite limited.” I think this is discussion.

R: we think that an occasional brief comment in the results is ok and would like to keep it as it is

Page 9 – line 197:  “The average maximum size…”. Where are these results? It would be interesting to have a more complete table with this information. If they are not included, it should be marked as "data not shown".

R: Sorry for the confusion. These are literature data. This is now stated explicitly.

Discussion

Page 9 – line 223: About the conspicuous gap in Amazonia: This gap in the Amazon occurs for Bromeliaceae. Could this be a bias? The paper by Zizka et al 2019 (DOI: 10.1111/ddi.13004) deals with the species richness of American Bromeliaceae, and this gap is again confirmed. Therefore, I think that this lack of occurrence data is related to this, which should be discussed more strongly.

We now include a brief reference to the Zizka et al 2020 paper

The success on power lines was explained on page 9, starting at line 248, as being due to several factors, including the reproductive system and vegetative size. I think these are plausible hypotheses and are properly discussed. However, these data are not presented in the manuscript. No compilation of these data was made for the species listed in Table 1. This needs to be transparent in the discussion section. For example, the occurrence of Tillandsias that are cross-fertilized does not match the hypothesis. This is explained further, on page 10, line 277. I think it is necessary to improve this part, linking the pieces about the reproductive system, size, and so on.

R: we are afraid that we cannot do much better. There is no compilation in Table 1, because our argument is based on sketchy data of a few species

Page 10 – line 281: Review the umlaut in aeranthos.

R: Species names are based on wfo and we use that spelling

Page 10 – line 288: Why are all these authors cited?

R: Thanks for pointing this out – it is just a formatting issue – these are the authors of this particular paper. It is now changed to Leal et al

Page 10 – line 289: What do you mean here? Please clarify this sentence.

R: we added an introductory sentence to this paragraph.

Page 10 – line 301: “Thus, one should be cautious when interpreting differences in the regional numbers of observations as evidence for actual differences in the frequency of plants on power cables.” Regarding this sentence, I think it could be better discussed. In addition to the variation in the distribution of plants, as already mentioned in Bromeliads in the Amazon, there may also be a socioeconomic context involved. Could regions with lower rates record less? Have fewer wires and cables? All of this should be discussed and put into perspective.

R: Yes, there are limitations of this study that were not explicitly mentioned in the submitted ms. We added a few sentence in the discussion

Reviewer 4 Report

Comments and Suggestions for Authors

The paper addresses a fascinating and eye catching, very special  aspect of the ecology of epiphytes. This fact and the good, innovative  idea to approach the diversity and distribution of "wire plants" with the iNaturalist data provided by citizen scientists make the paper and its results scientifically relevant,  interesting, and thus to my opinion well worth publishing.

The list of detected plants on wires is new and widens very much the knowledge about species in this curious habitat. Also the distribution data presented are very interesting   .

Weaknesses are, that the study does not get deeper in the analysis of the presented data, but this will mean another, much more extensive investigations. Some relevant questions to get deeper in would be e.g.:
- role of the tank/non tank habit for success in this habitat. One would postulate, that only the grey Tillandsias (and related genera) with their capability to grow in all directions are really capable of colonizing this habitat. It would be important to get deeper in the question, whether the tank forming species that were found are growing there because of special, rare peculiarities at their growing spot (like the discussed case of Wehrauhia)
- the importance of details of the habitat (isolated or not) is dicussed very briefly and surely would be worth to study further. But this is not possible with the approach of the presented study
- missing of wire plants in the Amazonian. The presented map documents this clearly - a very interesting information. This topic is also briefly discussed, but the discussion leaves one unstisfied. The following questions come up: i) is the iNaturalist recording from Amazonia comparable to the other areas, or generally, what biases could play a role in the lack of data from this area; ii) does the lack of records from Amazonia (if valid) not strongly support the hypothesis, that only "gray Tilandsias" and relatives are the only ones really capable of growing on wires. These plants are missing or rare in Amazonia. A comparison of distribution areas opf the most important wire species with the map given in the paper would probably make this evident.

However, in spite of its limits, the presented study is innovative and provides important new data and I thus strongly recommend it for publication.

Author Response

Thanks for the positive reception. You come up with a number of interesting questions about “wire plants”, but as you yourself mention the approach taken in this study limits our capacity to answer them. However, we can only emphasize that our paper will certainly motivate others to “fill the gaps” or, if gaps are real and not artefacts of sampling, try to investigate the underlying reasons.

Reviewer 5 Report

Comments and Suggestions for Authors

This is an interesting contribution to the knowledge of plants (and lichens) found in urban environments, associated with structures created by humans, most of which naturally occur as epiphytes.

However, I believe attention is needed regarding the delimitation of the groups studied, as, generally speaking, the study primarily focuses on plants, with lichens appearing only incidentally in the text. Lichens are mentioned in the abstract, listed among the species in the results, and referenced only three times in the discussion, but none of these references effectively discuss their occurrence in this type of environment. There is no mention of lichens in the introduction, which is entirely focused on vascular epiphytes.

In my view, this occurs because, in fact, the study represents a systematic data survey on Bromeliaceae occurring on electric wires, following a consultation of the iNaturalist database specifically for records of this family and their respective citations in the literature. The other families of vascular epiphytes and lichens themselves seem to be included in the work only because there is some mention in the literature or because the authors made their own field observations. However, there was no application of the same method for data collection from the consulted photo database. Although we know that Bromeliaceae are indeed the group of plants (epiphytes) most represented or likely to occur on electric wires, this method of sampling from the database seems to have biased this relationship even further. Would a search on iNaturalist for species from other families yield different results than those already published in the specialized literature?

Several comments have been made in the text to clarify confusing points or to request changes that the authors deem relevant.

Comments for author File: Comments.pdf

Author Response

Lichens are mentioned in the abstract, listed among the species in the results, and referenced only three times in the discussion, but none of these references effectively discuss their occurrence in this type of environment. There is no mention of lichens in the introduction, which is entirely focused on vascular epiphytes.

In my view, this occurs because, in fact, the study represents a systematic data survey on Bromeliaceae occurring on electric wires, following a consultation of the iNaturalist database specifically for records of this family and their respective citations in the literature. The other families of vascular epiphytes and lichens themselves seem to be included in the work only because there is some mention in the literature or because the authors made their own field observations. However, there was no application of the same method for data collection from the consulted photo database. Although we know that Bromeliaceae are indeed the group of plants (epiphytes) most represented or likely to occur on electric wires, this method of sampling from the database seems to have biased this relationship even further. Would a search on iNaturalist for species from other families yield different results than those already published in the specialized literature?

1. your description is absolutely correct – we did not go systematically for anything but bromeliads – which meant reviewing more than 100,000 observations out of c. 110000 if we had not restricted our review to 10 years. We included the “bycatch” because we did not expect anything but members of this family. We are not aware of any reports of non-bromeliads, so a focus on bromeliads seems logical and arguably reflects their real importance. This is all clearly laid out in MM. Still, we have tried to be even more explicit in the revised version.

We are a little bit surprised by your criticism of our treatment of lichens. We report 3 observations of lichens. That is what we have. Not more, not less. We could have simply ignored that and not mentioned it to have a "neat" story. In contrast, we believe that it is a value to document this – “lichen” appears in the abstract and is a keyword, so the interested lichenologist or general naturalist has a chance to detect our work. On the other hand, we don’t see how to extend our treatment because there is not more to say than “there are a few lichens on power lines”. Our study is about what we know, but even more importantly about exposing gaps – gaps in the distribution of bromeliads which may be observational artefacts or gaps in our record of other organisms like lichens that may be found, if rarely, on power lines.  Would be a success if our study leads to observations of lichens on power lines popping up all over the Americas!

 

Several comments have been made in the text to clarify confusing points or to request changes that the authors deem relevant.

1. Thanks. We addressed all concerns. In most cases we simply made the suggested change, sometimes not – please see the following comments

l 127-29 here we explain how we assigned photosynthetic pathways to different species. This is clearly method of results presented, e.g., in Table 1

Photos of interesting observations. We document all observations in the supplement – so it should be straightforward for the reader to use the ID given in the supplement to have a look at any pic of interest

line 194 Do you doubt that we were able to see reproductive structures? If so, please have a look at the iNaturalist pictures

lin 197-99 sorry for the confusion. We did not explicitly specify that these values are literature values. This has been changed now

l 250 pollination – these plants are growing in a completely artificial setting. We are rather sure that, e.g., downtown San Jose is a less than ideal setting for pollinating insects

l 256 the role of attachment. These are just suggestions. We do not claim that we know the exact reasons

L262 we abbreviated this partially redundant section

Round 2

Reviewer 3 Report

Comments and Suggestions for Authors

I have carefully reviewed the authors' responses to my suggestions and questions. They have added and corrected almost all of the items I raised. I consider that the article is now more complete and stronger, and is ready for publication.

Author Response

Thanks!