Habitat Fragmentation Affects Richness—A View Through a Metacommunity Lens

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Comments

In the context of the biodiversity crisis, the change in landscapes has been proposed as a main cause of biodiversity loss. However, it is not clear how landscape structure affect biodiversity patterns. The present study attempts to advance on the role of landscape structure on metacommunity diversity, specifically the effect of habitat fragmentation on species richness. Apart from the theoretical contribution, its results also could have impacts on management and conservation strategies. I think the study has a big potential but, first, I think it needs to solve some problems. In this line I have some comments that I detail below and hope that could improve the study.

 

1. The introduction lacks a general framework of metacommunities; how the metacommunity mechanisms that determine diversity are affected or modulated by the fragmentation effect that is proposed. The introduction needs more framework and support about the effect (positive or negative) of fragmentation on richness. How fragmentation affect metacommunity process. In addition, in my opinion is very short the presentation of the main problem. The hypothesis should emerge from the introduction, and not should be a section apart from the introduction. Please, could you explain in more detail what you call as “effective dispersal”. 

 

2. I think the “Approach” point (1.2) could be incorporated in the Methods section. The metacommunity model should be more explicitly presented. Maybe a conceptual figure explaining the metacommunity model could help to understand it. The differences with previous models that authors emphasize are ok, but after the proposed model was presented.

 

3.  It has been recognized that the heterogeneity in patch connectivity promoted higher levels of species richness (see for example Savary et al 2024; Borthagray et al 2023). Landscapes with the same amount of area, resources or energy, only differing in landscape configuration could harbor different levels of richness. Thus, I wonder if the change in the size of habitat-- mosaic of small habitat—could be correlated with a higher gradient in habitat connectivity. I know that is not the aim of this article, but I think it should be considered unless in the discussion. 

Savary, P., J.-P. Lessard, and P. R. Peres-Neto. 2024. Heterogeneous dispersal networks to improve biodiversity science. Trends in Ecology & Evolution 39:229-238. 

Borthagaray, A. I., D. Cunillera-Montcusí, J. Bou, I. Tornero, D. Boix, M. Anton-Pardo, E. Ortiz, T. Mehner, X. D. Quintana, S. Gascón, and M. Arim. 2023. Heterogeneity in the isolation of patches may be essential for the action of metacommunity mechanisms. Frontiers in Ecology and Evolution 11.

 

4. Landscape and habitat connectivity is an important component, that needs more explanation through all the manuscript. 

Line 77: How was patch connectivity monitored?

Lines 107-108: “Landscape connectivity was a function of proximity of suitable patches..” How is the spatial arrangement of patches in the different landscapes. I don’t understand how patch connectivity was measured. Maybe a plot with the three landscapes structure could be presented.

specific landscape features

In Line 126, it is said that: “Individuals of species arriving on a patch incompatible with their requirements cannot use its resources – such species lose energy until they find a suitable patch.” In this context, individuals of species arriving on a patch incompatible, cannot use those patches for energy supply, but they can use them to move, like a steppingstone patch, to achieve a suitable patch. That scenario is considered herein, since for connectivity could be important.

Line 172: Please explain: “The degree of connectivity generated in a landscape involved assessing the fraction of patches that were immediate neighbors to at least one patch of the same suitability.” This refers to a degree centrality. Please, explain in detail how connectivity was estimated, and if authors refer to landscape or patch connectivity.

Line 230: “the patterns associated with connectivity are weak..” however I think the way connectivity was estimated could be biased the result.

 

5. Some details of the model should be presented. i) How many individuals per species in a patch are; ii) the model starts with a uniform distribution of species?

 

6. Dispersal is associated with the random choice of an individual to move or reproduce; thus, dispersal limitation is not considered in the model. If the direction of movement is random, why authors mention in Line 234 “the ability to disperse”. Moreover, I think the model is not spatially explicit as it is presented.

 

7. Line 169: The landscape richness is the response variable from the metacommunity model. Is it gamma diversity? O how it was estimated?

Author Response

Please see the attachment. Many thanks for the most useful suggestions and questions!

JM and JK

Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

In this work, the authors explored how habitat fragmentation per se affect species richness at the landscape scale. In general, this manuscript emphasizes the hot topic in conservation ecology. However, when I read this study, I find there are many problems that require the authors to address before we can assess it completely:

1. In abstract, "because of smaller population sizes and increased isolation of habitat patches". I think because smaller, isolated patches leads to smaller population sizes and therefore greater extinction risk. Isn't it? Please clarify it.

2. In abstract, "although the circumstances remain unclear or incomplete." In fact, there have been some mechanisms proposed to explain why many small patches can harbor more species than few large patches when controlling for the total habitat amount. Thus, I would say "the circumstances remain elusive".

3. In abstract, "in fragmented habitats of different patch sizes" should be "in fragmented landscapes consisting of multiple patches of varying size"

4. For graphical summary, I don't think it reflect the topic in this study. You should indicate the both landscapes have the same total habitat area, and then plot species richness against mean patch size or habitat fragmentation per se (while not patch size).

5. In Introduction, line 36, please delete "predictable".

6. Line 38, please write it in more detail, for example, observations that many small patches can harbor higher species richness than few large patches at the same total habitat area, were quite frequent...

7. Why did you make subsections in Introduction: 1.1. Question and 1.2. Approach. You can directly put in the final paragraph  of Introduction.

8. I don't think the authors made a good literature review in Introduction, thus I would suggest them making a thorough review for this topic. 

9. In Figs 3 & 5, please indicate the slopes therein.

10. There are many minor errors in language, thus I would strongly ask the authors to correct throughout this ms.

11. In Discussion, "For example, (Guo et al. 2023) examined food webs with competition-colonization tradeoffs among basal species, omnivores, and other secondary consumers and found that habitat loss would lead to predictable topology changes in species loss." , where "(Guo et al. 2023)" should be written as "Guo et al. (2023)". There are several places having such problem, please correct them. You stated that Guo et al. (2023) can predict topology changes, which I disagree. In contrast, C-C tradeoffs among basal species yield complex food web topological structures, which are actually highly variable and unpredictable. 

11. In Discussion, please discuss more about your novel work by comparing to others. 

Overall, I would ask the authors to check the ms thoroughly, as there are many minor problems in this work. 

Comments on the Quality of English Language

There are many minor points in language that require the authors to correct (see my comments above).

Author Response

Please see the attachment. Many thanks for the great tips and suggestions!

 

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

I think the authors have already addressed all my comments sufficiently, thus I would recommend it for publication in Diversity.