Peer review of: An excess of niche differences maximizes ecosystem functioning (2020)



Reviewers' comments second round 
 
Reviewer #2 (Remarks to the Author): 
 
I have read the revised manuscript by Godoy and colleagues, and again I am struck by the 
elegance and importance of this paper. The authors have done an outstanding job responding to 
comments on the previous version. 
 
I have one general thought, which may and may not be worth mentioning in the discussion part of 
the results & discussion section. Often there is an assumption that ecosystem function, as 
conceived from classic experiments, is tied to coexistence mechanisms or not impacted by 
diversity. But I think there is a third option, species contributions to function that do not 
necessarily depend on the underlying coexistence mechanism but could still be impacted by 
diversity. For example, pollination support where a species contribution to pollinator support would 
depend upon the relative dissimilarity to other community members, e.g., timing or colour or size, 
which is likely to be disconnected from coexistence. Take for example two communities completely 
structured by neutral dynamics, one has 4 grass species and the other has 3 grasses and 1 
flowering forb. Pollination function would be much higher in the latter and the probability of 
including relatively unique species increases with diversity. All this to say, that there might be a 
subset of functions that are just never linked to coexistence. 
 
Minor: 
Fig. 1 and 2: increase the font size and symbol size. Also, avoid red and blue, because of colour 
blindness. Google “colour blind palette” for optimal colour matches. 
 
 
 
Reviewer #3 (Remarks to the Author): 
 
After reading the new version of ms NCOMMS-19-35084A I consider that most of my concerns 
have been satisfactorily addressed or rebutted. My overall evaluation of this contribution is still 
very positive. There is still one concern regarding my previous comment on whether the increase 
in function can be attributed to the additive, independent effects of stabilizing and equalizing 
mechanisms, or by their joint effect so that function increases with “excess niche differentiation”. I 
like that the authors have resorted to the evidence and conducted new analyses, in this case 
Mantel tests. They find that niche differentiation is not as correlated with function as excess niche 
differentiation. Why not conduct an equivalent analysis using fitness differences vs. function? 
Assume you have two variables, one that is not correlated (niche differences) with a third 
(function), and a second (fitness differences) that is. Then, the sum (or difference, in this case 
excess differentiation) of both variables is expected to be correlated with the third. I would like to 
see if this is not the case. 
Regarding the same issue, I like the new title “Ecosystem functioning is maximized when niche 
differences are larger than required for stable coexistence” better than the previous one. This is 
strictly true, although it still sounds to me like there is a qualitative divide between “larger that 
required” or “smaller”, while we all concur that function increases gradually with stability (=excess 
differentiation, even if it is negative). I would prefer something than conveys the idea more 
clearly, although this is just a matter of opinion..