Response of the Zygopteran Community (Odonata: Insecta) to Change in Environmental Integrity Driven by Urbanization in Eastern Amazonian Streams

Round 1

Reviewer 1 Report

This paper analyses the effects or urbanization in aquatic communities, focusing on Zygoptera species abundance, biomass and the r or k related life histories.

Although I find the topic interesting, I think that this manuscript needs some extra work.

The introduction lacks a clear organization and some information relevant to the study is missing (see comments below).

Statistical analyses are unclear to me. I think the authors should give the accumulation curve and justify why there was no rarefaction of the samples previously to run the statistical test for differences in richness. Firstly, what was your response variable in this analysis? Also, I would like to know the number of streams in each category, as I am not sure that authors have enough sample size for the analyses. As they are analysing species richness, I think the anova test is not the best option, as Anova is based on the assumption of the response variable being a continuous numerical variable. Richness is not continuous, as it is an integer. Although some data transformation was performed, authors should be using a poisson distribution instead of a gaussian distribution for their data. 

About the correlation, as you are using temperature as a predictor, you should also control for the stream category, because I expect you´ll be catching more individuals with higher temperatures in all streams, and temperature is not a fixed variable across all day. Thus temperature per se is not a good predictor of the type of stream effect.

 

 

 

Abstract

Line 20. Why would air temperature affect community if the juveniles live in the aquatic part?

Line 21. Why less abundant species?

Line 23. Previously, you mention reference streams. I guess control sites are those reference streams. Please, be consistent with the terms across all manuscript and keep the same name for the same conditions.

Lines 25-27. This sentence is unclear to me. Please, explain the meaning of no “overlapping strategies, once r-strategies were places above k-strategists?”

Line 27. Same as above, preserved are control or reference streams?

 

Introduction

Lines 42-43. “once they are… “ do you mean because they are associated?

Lines 44-45. The loss of vegetation does not cause discharge of residential waste. Please, rephrase this to accurately describe the situation.

Line 58. The response to this change.

Lines 64-65. Do you mean community composition in relation to species richness and abundance?

Lines 66-67. What is a conservation status? Please explain what you mean by this.

Lines 69-71. Repetitive, please remove.

Lines 71-74. As you are going to analyse Zygoptera, please explain here a bit more about the ecology of this group.

Lines 75-76. This is also repetitive. Please re-structure your introduction to avoid repetitions and have a clear order.

Line 79. Include the name of the author

Lines 80-85. Please, explain what r strategists and k strategists are, and include references to studies that have analysed Zygoptera or Odonata communities in this regard, as a starting point for your study.

Lines 86-96. Please, before justify your hypotheses. What are altered or intermediate streams? Why do you expect intermediate streams to be ecologically stable? What do you mean by dominance of k-strategists? Why higher air temperatures favour abundant species and what do you mean by abundant species? The species that are favoured in any situation will always be abundant in that situation, by definition.

Lines 93-96. I think you should explain all this more in detail. For example, how the resource availability changes as how this is related to reproduction.

 

Material and Methods

 

Figure 1. Please, explain what is the meaning of high-low urban. Include a clear indication of the location of the metropolitan area. Also, I think you should include different symbols for reference and urban streams. I suggest to remove the Amazon biome figure here, as it is already in the general map, and include some detailed figure of the sampling scheme on a stream.

Lines 123-126. Large remnant of what? In your figure there are no stream inside conservation areas. Also, how did you select the 100m stretch in each stream?

Table 1 is missing. I cannot assess if the sampling was correctly distributed across the years, or there was a bias, for example, sampling all reference streams in 2015 and the rest on 2016.

Line 158. What is total size?

Lines 178. What do you mean by species abundance in here? Is it the sum of all individuals of all species or the number of species? Was it a pearson correlation with normality assumption? Also, why do you use a different significance value than the standard?

 

Results

Line 183. Please, explain what you mean by observed and estimated species. And explain in methods how you estimate the total number of species: chao index, jacknife?

Figure 2. I would prefer to see a curve for each stream category, as you are using those to compare your samples .

Table 1 is still missing to see the results of the sampling.

Figure 3. Please translate the figure to English.

 

Discussion

I think this section should be based on the results and at this point I do not have enough information about the methods and results to go into details here. However, on comment:

Lines 231-233. More abundant species are always those favoured by the environmental conditions, thus this is circular reasoning. Maybe you want to look at the specific characteristics that make some species more abundant under specific environmental conditions.

 

Author Response

Thanks for reviewer's comments.

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

Authors studied the effect of urbanization on the amazonian forest by studying the quality of the streams in the forest. Odonata abundance and biomass was used as the proxy to measure the health of the stream. 

Overall, the authors provided enough details of methods to understand the study. Although the manuscript was logically  written there were grammatical errors and inappropriate usage of words in some sentences. 

After minor corrections the manuscript could be accepted for publication 

Specific comments:

Line 79: Include the authors names for the article cited

Line 119: An explanation of the figure in the legend will help understand it better

Line 123: Provide an explanation in the difference in the number of sites

Line 128: Add a period

Line 155: What is the rationale for measuring only male species?

Line 183: Give a space between the numbers and the plus/minus sign

Line 209: Rephrase to “Total suborders sampled in”. Axes of the graphs need to be translated to English

Line 212: Change Anova to uppercase

Line 214: It is unclear when the authors metion “Once” in the sentence. Please rephrase accordingly.

Line 218: Include the correlation method used in the legend.

Line 222: Delete following

Line 236: Replace “departure” with “replaced with”

Author Response

Thanks for reviewer's comments.

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

I still think this is an interesting topic and I appreciate the effort that the authors have done to improve the text. I think some sections have greatly benefit from it. There are still a couple of caveats, that I include below.  

 

Detailed comments:

Introduction

Lines 37-40. This needs a reference. Check the United Nations reports.

Line 69. Maybe bioindicators instead of tools?

Lines 77-78. These curves refer to the community composition, right? Specify this.

Line 87. Predominance of organisms with…

Line 88. That are

Line 98. Your hypothesis V is repetitive with I. Remove it; it is not needed.

 

Methods

Figure 1. The changes in this figure have greatly improved it.

Line 135. Specify what you mean by similar environmental conditions, as the vegetation and the temperature where different among the streams.

Line 136. 2015.

Subsection 2.3. As you have five streams in each category, I guess you did this classification before going to sample the species to decide where to locate your sampling sites. If this is correct, I suggest to move this section above, so it makes more sense to the reader.

 

Results

Line 212 and below. Estimated species sounds a bit confusing. Change it by something like total estimated richness by jacknife.

Line 222. The add the units for the n values. Individuals?

Lines 228-232. Seeing the figure, I would not agree with the authors here. The statistical power of an Anova with such a SMALL sample size is very low (n=5 for each category). Thus, it is very difficult for the test to find statistical differences at the 0.05 level. A p value of 0.06 and the figure that shows that the confidence interval of the richness for altered streams does not overlap the mean value for intermediate or control streams suggests that, most likely, there is a difference in Richness that the test is not able to capture due to the low power. I recommend rewriting this point and add the explanation in the discussion, as your results actually point to a decrease richness in altered streams.

Lines 250-252.  Use points instead of commas in the numbers, including those in figure 4. Also a value of r = 0.59 does not mean that the correlation explains 59% of variation. The explanation power will be the r2 = 0.59*0.59 = 0.35, i.e. 35%. Please, correct.

 

Discussion

Line 259. “following” here sounds strange, I suggest changing it for “in accordance with previous studies (refs).

Lines 260-266. This result is interesting. It proves that the odonata community is very sensitive to alterations in the environment, thus your results support the idea that they are a good bioindicator for monitoring environmental change. I think you should highlight this idea in your discussion.

Lines 268-271. I completely disagree with this statement, as I explained above. Please, rephrase and at least acknowledge the limitations of your data to analyse this.

Line 306-307. I do not know what you mean here.

Author Response

Reviewer 1

Comments and Suggestions for Authors

I still think this is an interesting topic and I appreciate the effort that the authors have done to improve the text. I think some sections have greatly benefit from it. There are still a couple of caveats, that I include below.  

 

R: We thank the reviewer for reading and suggesting our manuscript and we are very happy that he liked our corrections. All the points mentioned by the reviewer are very relevant, and we agree with the highlighted points. Below we present the answer and the modifications of each observation point by point.

 

Detailed comments:

Introduction

Lines 37-40. This needs a reference. Check the United Nations reports.

R: Thanks for the correction. We made the change in the text.

Lines 37-40. Currently, 55% of the world’s population lives in urban areas, a proportion that might increase to 68% until 2050. Projections show that the gradual migration of the human population from rural to urban areas is congruent with the worldwide population growth, which could reach 2.5 billion until 2050 [55].

55. United Nations, Department of Economic and Social Affairs, Population Division (2019). World Urbanization Prospects: The 2018 Revision (ST/ESA/SER.A/420). New York: United Nations.

 

Line 69. Maybe bioindicators instead of tools?

R: Thanks for the correction. We made the change in the text.

Lines 69-79. “...which allows us to use them as bioindicators in different studies [22, 23].”

Lines 77-78. These curves refer to the community composition, right? Specify this.

R: Thanks for the note. However, the curve refers to the total abundance of organisms by the sampling unit versus biomass.

Line 87. Predominance of organisms with…

R: Thanks for the correction. We made the change in the text.

Lines 86-87. “The abundance curve would be above the biomass curve. There would be a predominance of organism with low biomass...”

Line 88. That are

R: Thanks for the correction. We made the change in the text.

Lines 88-89. “...but quite abundant, for example, species from the genus Ischnura that are abundantly found in altered Environments.”

Line 98. Your hypothesis V is repetitive with I. Remove it; it is not needed.

R: Thanks for the correction. We made the change in the text.

 

Lines 92-103. “In our study, we assessed the effects of urbanization in the Zygoptera community in the Brazilian Amazon. For that, we tested the following hypotheses: i) altered streams will have a predominance of organisms with fast growth and small biomass (r-strategists), in intermediate streams, r and k-strategist species will overlap, once these environments tend to be ecologically stable; iii) in control streams, there will be a dominance of k-strategists, with slow growth, less abundant and with high biomass; iv) urban expansion in Amazonian streams will cause loss of Zygoptera species richness. Our premise is that the suppression of natural vegetation maximizes the incidence of light in the water bodies, increasing the temperature and changing the availability of resources (e.g. Wood residues inside and outside the channel, oviposition and perching sites) so that the organisms there tend to invest more in reproductive success than in body growth in favor of their offspring [24,21].”

 

Methods

Figure 1. The changes in this figure have greatly improved it.

R: Thanks very much. We are grateful for all the suggestions made by the reviewer in the previous version.

Line 135. Specify what you mean by similar environmental conditions, as the vegetation and the temperature where different among the streams.

R: Thanks for the correction. We made the change in the text.

Lines 132-136. “Samplings were performed in 15 streams with different degrees of environmental disturbance, five from altered areas, five from the intermediate group and five from the control group. The streams selected were of small orders (first and second-order streams, according to Strahler's classification) with similar environmental conditions but with different degrees of environmental disturbance, for example, native vegetation cover and air temperature vary between treatments (see Subsection 2.3).”

Line 136. 2015.

R: Thanks for the correction. We made the change in the text.

Line 37. “Sampling was carried out during the dry season, from August to December 2014 and 2015.”

Subsection 2.3. As you have five streams in each category, I guess you did this classification before going to sample the species to decide where to locate your sampling sites. If this is correct, I suggest to move this section above, so it makes more sense to the reader.

R: Thanks for the suggestion. However, we would like to keep this explanation of the treatment classes that we have in our study. We believe that it is easier for the reader to understand the variation contemplated in our research.  In addition, we are also linking this part of the text with subsection 2.2.

Lines 32-36. “Samplings were performed in 15 streams with different degrees of environmental disturbance, five from altered areas, five from the intermediate group and five from the control group. The streams selected were of small orders (first and second-order streams, according to Strahler's classification) with similar environmental conditions but with different degrees of environmental disturbance, for example, native vegetation cover and air temperature vary between treatments (see Subsection 2.3).”

Results

Line 212 and below. Estimated species sounds a bit confusing. Change it by something like total estimated richness by jacknife.

R: Thanks for the correction. We made the change in the text.

Lines 212-213. “We collected 342 specimens, of 45 observed species and 70 ± 6.0 (mean ± confidence interval) total estimated richness by jackknife...”

Line 222. The add the units for the n values. Individuals?

R: Here, we add the number of individuals per family. The idea is to show which families are more abundant in our study.

Lines 228-232. Seeing the figure, I would not agree with the authors here. The statistical power of an Anova with such a SMALL sample size is very low (n=5 for each category). Thus, it is very difficult for the test to find statistical differences at the 0.05 level. A p value of 0.06 and the figure that shows that the confidence interval of the richness for altered streams does not overlap the mean value for intermediate or control streams suggests that, most likely, there is a difference in Richness that the test is not able to capture due to the low power. I recommend rewriting this point and add the explanation in the discussion, as your results actually point to a decrease richness in altered streams.

R: We thank you for your observation and for the opportunity to try to resolve any possible questions. We know that the smaller the number of samples, the greater the data's variation and that this can affect the results. Precisely for this reason, we tested the effect on richness using two methodologies, using Anova and with the comparison by the confidence interval inference. In both analyzes, the results were congruent, as both were not significant. We disagree with the reviewer when stating that there is no overlap of the intermediate treatment's confidence interval with the altered area. If you look at the y-axis of figure 3, the intermediate treatment's confidence interval starts at 33 and the average richness of the altered is 34 species. Therefore, the confidence interval of the intermediate overlaps the average of the altered. This overlap indicates that there is no significant difference between the two treatments. However, to try to meet the reviewer's suggestion, we inserted this question in the discussion, as can be seen below.

Lines 272-275. However, our study found no significant changes in species richness between treatments, but it is possible to observe a loss in species richness in altered environments. However, there was great variation within the treatments. For this reason, we indicate that new studies try to increase the number of samples of each type of habitat to try to reduce this variation.

Lines 250-252.  Use points instead of commas in the numbers, including those in figure 4. Also a value of r = 0.59 does not mean that the correlation explains 59% of variation. The explanation power will be the r2 = 0.59*0.59 = 0.35, i.e. 35%. Please, correct.

R: Thanks for the correction. We made the change in the text.

Lines 250-254. The hypothesis that air temperature would be a significant predictor for the Odonata order, since it would affect species abundance, was corroborated (r²=0.35; p=0.019). There was a positive relationship between the abundance of individuals and air temperature, suggesting an increase in temperature increases species abundance (Figure 03). The correlation explained 35% of the variation found in the data. 

Discussion

Line 259. “following” here sounds strange, I suggest changing it for “in accordance with previous studies (refs).

 R: Thanks for the correction. We made the change in the text.

Lines 259-260. Our results accumulate evidence that urbanization negatively affects Amazonian streams, in accordance with previous studies [4, 10].

Lines 260-266. This result is interesting. It proves that the odonata community is very sensitive to alterations in the environment, thus your results support the idea that they are a good bioindicator for monitoring environmental change. I think you should highlight this idea in your discussion.

R: Thanks for the correction. We made the change in the text.

Lines 259-277. “Our results accumulate evidence that urbanization negatively affects Amazonian streams, in accordance with previous studies [4, 10].   As we expected, biomass was higher than abundance in preserved environments, and abundance was higher than biomass in altered environments. Contrary to what we expected, the hypothesis that in intermediate streams, there would be an overlapping of r and k-strategists was not corroborated, once intermediate streams have shown a predominance of abundant species. Suggesting that, in these environments, the Odonata community is numerically dominated by organisms with r-strategy tendencies. This study has similar result similar with what was registered in the Brazilian Cerrado, where species with small body size were dominant in altered environments, reflecting the effects of anthropogenic change in streams [41]. On the other hand, following the patterns we expected, the abundance was positively affected by temperature, suggesting environments with increased temperature favor the most abundant Zygoptera species [45]. However, species richness of Zygoptera was not affected by urbanization, contrary to what we expected evidence that, depending on the type of land use, the morphological characteristics of Odonata may better respond to the effects of environmental changes. However, our study found no significant changes in species richness between treatments, but it is possible to observe a loss in species richness in altered environments. However, there was great variation within the treatments. For this reason, we indicate that new studies try to increase the number of samples of each type of habitat to try to reduce this variation. In general, here we can show that the Odonata community is very sensitive to changes in the environment, therefore, corroborate the idea that the Order's organisms are a good bioindicators to monitor the effects of urban expansion.”

Lines 268-271. I completely disagree with this statement, as I explained above. Please, rephrase and at least acknowledge the limitations of your data to analyse this.

R: Thanks for the correction. We made the change in the text.

Lines 272-275. However, our study found no significant changes in species richness between treatments, but it is possible to observe a loss in species richness in altered environments. Certainly, a larger sample and or maybe a more robust analysis would detect the effects of urban expansion on species richness.

 

Line 306-307. I do not know what you mean here.

R: Thanks for the comment. We agreed with the reviewer and we removed that part of the text.

Author Response File: Author Response.docx

Reviewer 2 Report

Thank you for including the suggestions and the concerns were all addressed.

Author Response

We thank the reviewer for reading and suggesting our manuscript and we are very happy that he liked our corrections.