The Impact of Breeding Yellow-Legged Gulls on Vegetation Cover and Plant Composition of Grey Dune Habitats

Round 1

Reviewer 1 Report

I have completed my review for ‘The impact of breeding Yellow-legged gulls on vegetation two cover and plant composition of grey dune habitats’, which is currently under consideration for publication in Diversity. Here, the authors characterized the effect of the Yellow-legged gulls on the vegetation cover and plan composition at some breeding sites. In addition, they compared two types of breeding colonies: an older colony (over 13 years old) vs. relatively new colonies (sites used for three years). They found that the gulls had greater impacts on the vegetation cover and composition in the older colony. I enjoyed reading the manuscript and believe it could be an essential addition to the interaction of wildlife and humans, an issue has received more attention throughout the literature. However, the manuscript has some issues that need further clarification.

Information about the colony site at each sampling location would be beneficial. The age of the colony is critical information. However, the number of breeding pairs and the colony's extension (surface) will allow a better idea of the impact of the gulls. New colonies may have lower gull density than older ones, so that the impact could be an interaction of time and gull density. Also, information about the timing of the breeding season would help.

The study sites are barrier islands, which they characterized by high dynamics. Do the three study locations have similar vegetation cover and composition? For example, what does a higher/lower proportion of tall vs. short vegetation cover mean in these dunes?

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 2 Report

Kia ora Diogo and team,

You have undertaken an interesting study on the response of vegetation to the presence of yellow-legged gull breeding colonies of different ages (3 and 13 years) across grey dunes on three islands in the Algarve.

I’m interested as to why you did not consider a comparison of plant communities across all the individual quadrats (n = 360). Species cover values for each quadrat could be ordinated to show the dissimilarity of the communities across the three islands and how this varies both inside and outside the colony sites (using hierarchical classification and indicator species analysis). This would also provide an indication of any possible trajectory for the 3 year old colony vegetation. The collected data has quite a lot of power that is not harnessed by simply comparing cover values of aggregated taxa for vegetation height.

There is not much information on the behaviour of yellow-legged gulls – where this species forages, what food resources are taken and subsequent nutrient load in their faeces, what is the breeding season etc. I think of interest would be any information on whether yellow-legged gulls have broad habitat requirements or even cultural memory for historic breeding sites? It might be worth including framing around the loss of much of the suitable habitat (can this be quantified – it is only inferred in the introduction) for yellow-legged gulls.

As it stands this article could be made more valuable by undertaking ordination to examine vegetation community patterns more robustly. Further a greater examination into the ecology of the taxa apparently affected would make for an important assessment of likely drivers and effect.

Specific comments:

Please italicise all scientific names.

The use of “squares” rather than “plots” is confusing when in the methods you also start talking about quadrats – could this be amended to change square to plot?

Across your seasonal sampling period did you notice any differences in flowering times between the “inside” and “outside” plots? I was wondering whether the different disturbance regimes and nutrient inputs were affecting phenology and potentially plant fitness?

Abstract line 1: “The establishment of Yellow-legged gull Larus michahellis present very large populations”… suggest change to: “The establishment of large populations of yellow-legged gull Larus michahellis”

Line 54: “Gulls can impact soil suitability” – what is meant by suitability here? Please be more specific; or, remove suitability as the sentence works without the word.

Line 63: what is meant by a stress-ruderal species? Confusing as in same paragraph you describe the increase in ruderal and decrease in stress-tolerant taxa.

Lines 63–64: “and the decrease of plant species with long life cycles” – expand on this a little more: why are stress-ruderal type species benefitting and taxa with long life cycles losing?

Line 75: “though this has not been addressed in previous studies” – how were patterns established in other studies, where they longitudinal – resampled over time?

Line 96: “which is listed in the Ramsar Convention” perhaps: “which is named as a wetland of international importance under the Ramsar Convention”

Line 105: “living” or “live” vegetation rather than “alive”

Line 147: delete “marginally”: you set your significance level α = 0.05 so this value is significant – marginally infers that p-values are a robust statistical approach.

Line 155: Medicago littoralis is a nitrogen-fixer – it is interesting that this species is becoming more competitive in an area of high-nitrogen. Does this plant normally succeed in eutrophic systems?

Line 155: are these two taxa more common on East Deserta Island than West DI and Culatra I? Space for time replacements and then inferring effect is challenging when different taxa occur in different factors in your design.

Line 189: does gull “stamping” have a strong effect on vegetation? Is there any other published work that might support the strong influence of physical movement of seabirds on vegetation? References from paragraph lines 203–213 could be included here.

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 3 Report

REV Diversity 532

This is a short but very interesting manuscript with an ecological relationship among seabirds (Gulls) and plants. I read it with interest. Manuscript is well written, sampling design is good. Although local-based, results are exhaustive and suggest some implications about the nest’s occurrence, the role of gulls in explain the plant distribution and the dynamic of gulls along the coasts. Theere are minor points that should be improved but I think that the ms deserves to be published on Diversity only after MINOR REVISIONS. Here below I reported some pits that should be added or corrected.  I like to re-read a further revised version of this good ms.

MINOR POINTS

Larus michahellis should be written in italic everywhere along the text (e.g. row 10).

Row 21. ‘Paronychia argentea’ and ‘Malcolmia littorea’ should be written in italic. Idem for ‘Suaeda maritima’ and ‘Helichrysum italicum’ (row 23).

In keywords, latin names should be written in italic.

Rows 40 and 41. In italic, Larus. See also rows 43,50 (Salmonella), 58, 72, 155, 162, 164, 166, 183, 184, 191, 200, 219 and everywhere.

In the sentences rows 62-72, see also, for rubbish transported inside nests: Marine Pollution Bulletin, 2020, vol. 150, 110682: Heterogeneous composition of anthropogenic litter recorded in nests of Yellow-legged gull (Larus michahellis) from a small Mediterranean island - ScienceDirect; https://doi.org/10.1016/j.marpolbul.2019.110682. Regarding the change in vegetation due to presence on Larus michahellis’nests, see ‘Alien-dominated plant communities’ syntopic with seabird’s nests: evidence and possible implication from a Mediterranean insular ecosystem’. Ethology Ecology & Evolution, 33(5), 543-552; https://doi.org/10.1080/03949370.2020.1870568. This last paper corroborated as stated by the authors. Ee also the paper of De La Peña-Lastra et al., 2021 on Catena, 199, 105115.

Row 100. Add possible references about the presence of gulls, locally (if existing).

Rows 103, 106 and 109. Please correct ‘m2’ (2 should be in apex).

Rows 227-229. Very interesting (ecological) results (‘the local vegetation dynamics of the grey dunes are associated with changes in the spatial distribution of breeding gulls’).

Finally, check everywhere for the scientific names of birds and plants (in italic font). Add the role of anonymous reviewers in the Acknowledgments.

I like to read a further version after revision.

Have a nice work.

Comments for author File: Comments.docx

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 4 Report

This study addresses the impact of breeding Yellow-legged Gulls on the vegetation cover and plant composition of grey dune habitats on some islands in southern Portugal. The study focuses on vegetation changes as a function of the number of years that yellow-legged gulls have been nesting in the same place.

It is a novel study because it studies their impact on grey dunes and is of interest for making decisions on the management of these areas.

My recommendation for future studies is that they should include soil analysis so that it is better supported. 

Comments for author File: Comments.pdf

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Round 2

Reviewer 3 Report

Manuscript has been largely improved. Now, it deserves to be published after these last very minor changes:

row 114. 'humid' or 'wet'?

rows 321-322: please, correct the font in Acknowledgments.

Have a nice work.

Author Response

# Reviewer 3

Manuscript has been largely improved. Now, it deserves to be published after these last very minor changes:

Re: Thank you very much for your revisions and suggestions. Please find our positive responses to the following comments. 

row 114. 'humid' or 'wet'?

Re: Changed to wet.

rows 321-322: please, correct the font in Acknowledgments.

Re: Done.