Interpopulation Variability in Dietary Traits of Invasive Bleak Alburnus alburnus (Actinopterygii, Cyprinidae) Across the Iberian Peninsula

Round 1

Reviewer 1 Report

Dear Authors,

I will concern only about the discussion.

1. Lines: 232-233 I don't understand "Thus, planktonic Crustacea were very important for bleak in the River Saône, although Diptera larvae and detritus (i.e. benthic food items) were more consumed"?
2. Did you analyze the food base for bleak in each river (e.g. benthic macroinvertebrates, alga, sediment deposit)?
3. Did you observe shifts in the fish diet with its age?
4. Did you measure water velocity or water temperature in each habitat/river site/ country? We can expect different thermal conditions between France and Spain. Water temperature has a strong influence on fish metabolism and food digestion.
5. What was the bed geo/morphology in selected habitats?
6. Why did you electro-fish so many habitats and bleak is preferring mainly lentic ones according to the literature?
7. Why restrict bleak as invade species in Spanish waters if most habitats are lentic and regulated? Native fish species will recolonize rivers if natural habitats will be restored....

The above problems should be included in the discussion.

 

 

 

 

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

Review of Latorre et al Inter-Population Variability in Dietary Traits of Invasive Bleak Alburnus alburnus (Actinopterygii, Cyprinidae) across the Iberian Peninsula (WATER)

 

This study investigates the dietary traits of the bleak, a cyprinid which is an important invasive species in the Iberian Peninsula. Results were compared between invasive and “reference” (native range) populations. The main conclusions, that there are wide inter-population differences in diets, is potentially valuable information for biodiversity scientists and conservation managers. The manuscript is well-written. However, I find the study to be lacking essential information about resource availability. I also find that the conclusions about latitudinal gradients cannot be supported. I therefore cannot recommend publication.

 

Specific comments:

 

Line 63 – Delete “however and”.

 

Line 72 – Please concatenate fresh waters – “freshwaters”.

 

Line 165 – It appears that no measurements of food availability were taken. This is unfortunate because an animal’s diet is obviously constrained by the resources that are available. Without this information is it impossible to know how much of the variation in food occurrence or ingested mass is due simply to resource availability and how much is due to inherent population differences. For this reason, most studies measure the availability of resources and calculate feeding selectivity (e.g. De Los Ríos Méndez et al., 2019).

 

De Los Ríos‐Méndez, J., Kanamori, G.A. and Landaeta, M.F., 2019. Lunar influences in the diet habits and selectivity of larval clingfish Gobiesox marmoratus. Journal of fish biology, 95(3), pp.833-846.

 

Line 285 – I have two problems with the statement about the latitudinal gradient. First, this result is not clearly shown in any figure or table. Second, and more important, it should not be possible to say anything about latitudinal gradients with so few locations. The sample size and latitudinal range is simply too small.

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

The study contrasts the diet composition of bleak in five Iberian rivers (where the species is invasive) and one reach in the Saône river (where the species is native). River reaches with similar general characteristics were selected (regulated) and a total of 1200 fish/stomach contents were examined. A substantial inter-population variability in dietary descriptors was found and linked to the species successful establishment in Iberia.

The ms. is well conceived and written and could be of interest to the readers of Water.  

I made just a few comments that could be used to review the ms.

Lines 111-114. The authors state that “Moreover, the year 2019 is considered to have been hydrologically ‘average’ in the study areas [19,20]. As a result, the effects of particular dry or wet years on dietary traits are avoided within our study, which allows the data to be considered representative for this species in the invaded Mediterranean region of Europe.”. Although hydrology is pivotal shaping the riverine environments, other factors are also important (e.g. nutrients). Therefore, I would remove the last part of the last sentence, i.e. “which allows the data to be considered representative for this species in the invaded Mediterranean region of Europe”.

Lines 306-307. Are most Iberian endemics “specialized to narrow trophic niches” or highly plastic to account for the natural variability in Iberian rivers?   

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

thank you the Authors for explanations to my requests.

 

Reviewer 2 Report

I have re-reviewed this manuscript which has been revised through a scattering of additional statements and the insertion of several extra references. Unfortunately, these additions do nothing to address the major flaws highlighted in my first review, particularly the omission of data on food availability and the lack of statistical support for major conlusions claimed in the manuscript. I still cannot recommend publication.