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Thank you very much for addressing the reviewer comments. Both a reviewer and I are happy with the changes you have made. Your manuscript is ready for publication now.
[# PeerJ Staff Note - this decision was reviewed and approved by Patricia Gandini, a PeerJ Section Editor covering this Section #]
Revised manuscript is improved - I am happy for publication to go forward.
Revised manuscript is improved - I am happy for publication to go forward.
Revised manuscript is improved - I am happy for publication to go forward.
I am pleased with the efforts that the authors underwent to address all comments. I'm happy for the MS to be published.
Please expand your discussion on the limits of the conclusions given the short study period during only one year. This is an important factor for readers when considering the generality of the results.
[# PeerJ Staff Note: It is PeerJ policy that additional references suggested during the peer-review process should only be included if the authors are in agreement that they are relevant and useful #]
I have read the paper entitled “High variability in the attractiveness of municipally-planted decorative plants to pollinators” by Czaczkes, Breuss and Kurze. The scopes of this study are timely and interesting. I agree that it is very important to provide evidence-based guidance to cities that can help ameliorate the “planting plannings”, in a way that they can both satisfy the general public but also support local pollinators. This is an ongoing debate, and several municipalities are becoming more and more receptive to the information that researchers can provide, so I think having an increasing number of studies such as this one is important.
My main issue is with the Introduction. I think that more context about urbanization and pollinators should be given. As I specify below, cities can support a certain diversity of pollinators, but at the same time they have several constraints that filter species from a taxonomic and functional point of view. Including these aspects would better frame the importance of your study in the context of urban ecology studies. The last part of the Introduction could also benefit from rephrasing and some more detail, to better frame the aims and scopes. More details are given below.
The experimental design seems appropriate for the aims, although the scattered availability of some plants within the study sites did not allow precise and reliable information. The design is repeatable and could be applied in other contexts.
Data and code have been provided. Data analysis seems appropriate.
Conclusions are supported by the results.
I have only minor comments to improve the Methods, Results and Discussion sections that are addressed below.
SPECIFIC POINTS
INTRODUCTION
L33: I think “land USE” is missing
Paragraph L37-53: I think that the Introduction might benefit from more detail concerning the challenges that urbanization presents to insect pollinators. What you report is not incorrect, but you almost only report the (potential) positive effects of urbanization, while bypassing the serious threats that they present to pollinators. I agree that some kinds of urban environments can sustain and be very important for pollinator populations, as the work you cited shows, but at the same time urban areas are certainly not the best environments for all (or even most of) wild pollinators. It’s important to assess the context with which one compares urban areas, as showed by Wenzel et al. 2020 that you already cite, as urban areas may host diverse communities compared to some environments but not others, and it depends on the level of urbanization (Geslin et al. 2016 doi: 10.1002/ece3.2374; Fauviau et al. 2022 doi.org/10.1038/s41598-022-21512-w; Liang et al. 2023 doi.org/10.1111/ele.14277). Moreover, and I think this is very important to highlight, urbanization acts as an important filter of species related to functional traits. Only a subset of communities found in more natural areas usually can adapt or survive in urban areas depending on the combination of their traits (e.g., Hamblin et al. 2017 doi.org/10.1098/rsbl.2017.0125, Fauviau et al. 2022 doi.org/10.1038/s41598-022-21512-w; Weber et al. 2022 doi.org/10.1007/s10980-023-01755-2; Liang et al. 2023 doi.org/10.1111/ele.14277). Mutualistic interactions may also be significantly affected in urban areas, with changes in network structure and potentially negative effects on both partners (Baldock et al. 2015 doi.org/10.1098/rspb.2014.2849; Fisogni et al 2022 doi.org/10.1016/j.landurbplan.2022.104512; Sirohi et al. 2022 doi.org/10.1007/s11252-022-01290-z). I think more context on the balance between potentially positive and negative effects of urban areas would help to better frame your Introduction and also the importance of your work.
L56: I think you meant “nectaries”
L59: What do you mean with “chosen to be attractive”? That they were selected as potentially attractive species? I would suggest reformulate to clarify.
L69-72: just a personal preference, but I would remove the parenthesis from “such as” to “Chapman et al. 2023”. I think a simple comma before “such as” is enough, the sentence is clear enough with the examples reported outside a parenthesis.
L77-87: I find the last paragraph of the introduction a bit inconsequential and disconnected. I get the general point, but I think it should be restructured to present the rationale between your aims in a clearer way. In Lines 79-82 I got a bit lost with these two sentences. I am not sure what the different “it” refer to. I would suggest making the subjects explicit every time. Also, “highly attractive partner” to whom, the researchers, I guess? I think it’s also important to highlight that municipalities are not the only potential planters of attractive plants. They are important for public areas (please highlight this point), but private and common gardens may be very important too. Maybe it is easier to work with municipalities for several reasons which you may highlight, and that’s why they can be the primary partner for these kinds of studies. I think it’s important if you rework this last paragraph a little.
L84: “on A broad variety”
L85: add that the city is in Germany.
METHODS
L90: Table 1 is fine, and the descriptions of the surroundings of the study sites are helpful, but would it be possible to provide a map of the study sites? I think that visualizing your sites on a simple land-use map (or even on Google Maps, why not) would be even better. If you are able to do that, you could move this table in Supplementary Materials if needed.
L91: Remove “in” between ranged and from.
L92: Please also indicate in the parenthesis what you considered as morphogroup, i.e., species and cultivars.
L95-97: how many times each site was visited over this period? Please specify even if it can be inferred from the Raw Data table.
L96: In the Metadata to the Raw Data file, you report 9 AM - 12 PM for the morning sessions, while here you say 8-11 AM. Please modify which one is incorrect.
L99-104: I think more detail is needed here. You selected 11 public parks, so did you follow all of the flowering plants in those parks? What size are these 11 parks, I cannot find this information in the Raw Data file. In the same file, you report the “total_area_cultivars” in m2, but it does not say if it covers all or only part of the parks. Also, you talk about plants here, but it would be more correct to talk about flowers or flowering plants, because you only considered insects visiting open flowers.
L101: Maybe it’s more accurate to say “all insects visiting flowers in the quadrats”, as these are your observation units, rather than the area.
L102: I agree that 1 minute is longer than the 10 seconds used by Garbuzov et al. (which was basically a transect), but I wouldn’t say it’s an extended period for pollinator observations. It is very short, in fact. I get that you had a large area to cover and 1 minute was the longest you could spend at each quadrat, I would just suggest using a different phrasing.
L106-108: here and in the previous lines you talk about plants, not flowers. I see that in the Raw Data table you describe “coverage” as the entire plant, not just the flowers. Why? Didn’t you only considered insects visiting the flowers? You should clarify this point.
L109: afternoon rather than evening. Were these observations carried out on the same day, or on six (or any other number of) days throughout the 16/08 – 06/09 period? Please specify even if it can be inferred from the Raw Data table.
L116-119: STATISTICAL ANALYSIS. I appreciate the availability of the full code and analyses performed in the annex. Nonetheless, I think you should report here how you built the models (model type, response variables and predictors, random effect, error distribution). Just the basics to allow the reader to understand your analyses without the need for searching for them in an external file. I think this is a normal and necessary standard. Also, I saw that the model called ‘adjX’ in the ‘Wild bees’ part has all NAs for SE, z values and p-values. What happened here? Minor thing, annex S1 is called S2 in the supplementary files.
RESULTS
L121: like the point above this has been switched, annex S2 is called S1 in the supplementary files.
L130: by looking at Figure 2 right, Aster ageratoides is listed above Salvia yangii (which you compare in L140-141). Why are you citing (only) the latter?
L136: switch names of the annexes.
L139-142: because you later discuss this, I think it could be interesting to cite a few more examples of plants that were visited by insects other than honey or wild bees (which you analyse more deeply later), such as wasps, other flies and ants.
L141: close parenthesis after figure 2.
L145: what do you mean with “ecologically relevant topics”? I think that all flower visitors, not only bees, are very ecologically relevant! Especially because you show in Figure 2 that some plants host many flies, wasps, and ants.
L154-159: From Figure 3 it seems that Aster ageratoides, Erynginum planum and Campanula persicifolia are only visited by wild bees, not by “some” or “twice as many”. Maybe the numbers don’t allow reliable statistical analyses, but the data is striking. I would rephrase to clarify. The same is true for some of the less visited cultivars. It would be interesting to cite these plants too, as the focus of the paper is on all flowering plants found in your study sites.
DISCUSSION
L183: I don’t understand the reference to Table 1. It doesn’t show insects in relation to habitat, only habitat description. Please clarify what this overlap with other studies means.
L184: flowers (not flower).
L185-186: This is too simplistic. I don’t think that generalist necessarily equates to well adapted to urban environments. They are potentially able to cope with limited and highly variable food resources better than specialized bees (but if the right resources are there, specialized bees might as well be), which is different. There are many variables that may interact in determining why an insect can adapt to urban environments (food resource availability in space and time, nesting resources, heat resistance among others).
L193: disappointing (not disappointed).
L206: remove “gives”.
L214-215: There’s also the problem with multiple counting of the same individuals if insects are not sampled.
L222: The insect point of view is interesting. The plant’s perspective might be interesting too: more visitors do not always mean more (or more efficient) pollination. This might be less interesting from the city perspective, if they keep planting new individuals every year, but if they are willing to ensure self-sustenance of perennial species, this should be taken into consideration.
FIGURE LEGENDS
L431: cultivars (not cultivated)
RAW DATA and METADATA: “coverage_in_%” in the Raw Data table is not explained in the Metadata table. In addition, when describing “cultivar”, you say interacting with a cultivar, but I think it would be better to say visiting flowers, as that is what you actually considered.
Supplemental Table TS1: Header of the third column states “annual/perennial/shrubs”, but no shrubs are reported in the table. Instead, one Biennial is reported. Modify accordingly. I think Alcaltheae spp. should be Alcalthaea spp., and you wrote “peRRenial” in the same line.
This is an interesting piece of research exploring insect attractiveness to ornamental plantings in urban settings. The manuscript is clearly written. The introduction is clear and provides enough relevant background information by citing appropriate literature. The main aim of this research was to identify suitable ornamental plant species based on their ability to attract insects. Raw data and R script for analysis are given. The authors did not include the conclusion section. Figures need more work. Figures represent only the descriptive data, not the actual model outputs. For example, significant or non-significant values are not shown in any of the figures. In Figure 1, labels in the x-axis are not very clear and in Figure 2 the legend of the one graph is included within the other graph. I suggest authors make figures to represent the results appropriately and follow the guidelines.
Research work is within the scope of the journal and the research question is clear. The study was carried out in 11 parks located from central to the edge of the city which is commendable. To increase understanding, it is worth providing a list of plant species available in each location. The authors selected plant species with low replicates for analysis and were unable to draw firm conclusions as mentioned in lines 158-159 and Figure 2. I commend the authors for their extensive data set but the statistical analysis section needs more detail and re-organized. According to the given R markdown file, the authors wanted to organize the analysis based on four questions but they did not perform models adequately to address these questions. For example, no model was performed to check the effect of total patch area on insect visitation rates. Also, models are not properly described in the text. I suggest providing more detail including response variables, fixed and random factors, data distribution families, controlling zero inflation, residual diagnostics, etc. in each mixed effect model separately and clearly in the text.
The authors generated a new set of information by surveying plants on their ability to attract insects at a regional level. However, the authors reported only the visitation data in this study. It is required to improve the manuscripts reporting more findings. For example, the authors can think about including details of the behaviour of these insects on each plant species such as collecting nectar, pollen, or any other resources. Other than bees and flies, some insects like ants and beetles also visited some of the selected plants which is interesting. Providing details of insect behaviour on plants makes a clear idea of their involvement in pollination while enhancing the validity of findings. As data collection was done a few hours in the morning and afternoon separately in each location, authors can report how insect visitation changes over the time of day. This information could be other interesting findings and worth including in the manuscript. The authors did not provide a proper conclusion linked to the research question at the end.
These are my additional comments on this study.
Using the term “pollinators” is quite misleading as authors counted only insect visits, so my suggestion is to use “insect visitors” throughout the manuscript including the title.
Line 72 : remove additional bract given after Chapman et al., 2023.
In Figure 2 authors said that some plants, such as Blue Eryngo (Erynginum planum “Blaue Zwerg”), were not commonly planted, so may not be a reliable estimate. But this is the plant species received the most visits (> 5 visits/m²). A similar statement is given in lines 158 - 159. These statements impair the strength of the findings and I suggest authors consider plants with enough replicates in data analysis. Please provide any specific reasons for including those plant species (with no adequate replications) in the study.
In line 126, I suggest starting the paragraph with the most important finding “Plants differ significantly in their overall attractiveness (glmmTMB, Chiq=89.06, P < 0.0001)". Significant variations between plant species are not shown in Figure 2 or the text. Please also consider reporting statistics adequately (not just the P values) throughout the manuscript.
In Figures 2 and 3, insect visitation should be reported as visits m² m⁻¹
In lines 140 - 142, the authors mentioned that Salvia yangii and Aster ageratoides show almost identical overall attractiveness in terms of insect visitations per m² m⁻¹ (figure 2, Salvia yangii is dominated by honey bees, while wild bees are the most common visitors to Aster ageratoides. Please explain what you mean by “identical overall attractiveness” here. Similar visitation rates?
When citing figures in the manuscript please use abbreviations (fig.) in lines 124, 126, 140, 141 etc.
Please check the P value given in line 155 with the statistical output and make changes. It is better to provide other important statistics including estimates along with P values here.
As mentioned in lines 182 -183, I can’t see reporting insects in Table 1. It contains only study locations, GPS coordinates, and descriptions of surrounding locations. Please check it and make it more clear.
In discussion, the authors need to discuss findings in a way that focuses on the objectives of the study. For example, In lines 191-193, the authors mentioned that our results demonstrate that the current urban plantings do not support a diverse pollinator community. The majority of plants are attractive to honey and wild bees, but not attractive to most other groups, especially butterflies and beetles. Here it is a bit confusing whether authors need to identify pollinators or conserve insects.
1. Abstract Ln 16: I think you mean 130-fold difference, not increase
2. Abstract Ln 18: honey bees, which are not A conservation
3. Ln 30: are set, not is set
4. Ln 39: loss of DIVERSE floral resources
5. Please provide some more references for periods of dearth (i.e., Couvillon et al 2014 Plos One, Ohlinger et al 2022 Biol Letters). The latter looks at both nectar and pollen availability using waggle dance distances as proxy for availability.
6. Ln 83: these data, not this data
7. Ln 84 a broad variety
8. Ln 84 – why do you say broad variety of annual ornamentals. Seems to me you also worked with perennials (Ln 92)
1. Ln 96 – this is a short range of data collection and will obviously impact the abundance and diversity of insects that you witness. You deal with this a bit in the discussion (Ln 167, centered largely on bumble bees) but not really enough. When will many of your flower-visiting insects be out and about for your area?
2. Ln 191 – you cannot really say much about diversity with such a narrow (and very late) sampling range.
No comment
1. Ln 46: of course it’s not just low nectar flow that is a problem, as many non-Apis pollinators are focused more on pollen collection to feed to developing brood (as they do not need to make and store honey for overwintering).
2. Ornamentals may be bred to offer long periods of flowering availability, but even that won’t outlast a generalist, such as a bumble or honey bee, that needs floral resources for longer than any one plant is blooming. Honey bees for example forage from March – late October. There needs to be many plants, and many different plants, to cover that window.
3. Ln 48: Samuelson et al 2022 (J Applied Ecology) demonstrated positive impact of urban environments, as did Garbuzov et al 2015 (Urban Ecosystems)
4. Ln 222 – I enjoyed the discussion on cognitive traps
5. One thing you don’t deal with is any difference b/w annual and perennial, where as this is a big deal esp in terms of management. Imagine how much more work a municipality needs to put into a system requiring annual replanting, whereas perennials might only need some maintenance. There’s also a big cost difference. This will be important for municipalities if that is part of your target audience
6. Figure 3 interesting but not really discussed. Can you talk about it a bit in the discussion?
7. Actually, you don’t refer back to figures in the at all discussion. That might be helpful.
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