The role of phenology for determining plant-pollinator interactions along a latitudinal gradient
Does phenology explain plant-pollinator interactions at different latitudes? An assessment of its explanatory power in plant-hoverfly networks in French calcareous grasslands
Increased knowledge of what factors are determining species interactions are of major importance for our understanding of dynamics and functionality of ecological communities . Currently, when ongoing temperature modifications lead to changes in species temporal and spatial limits the subject gets increasingly topical. A species phenology determines whether it thrive or survive in its environment. However, as the phenologies of different species are not necessarily equally affected by environmental changes, temporal or spatial mismatches can occur and affect the species-species interactions in the network  and as such the full network structure.
In this preprint by Manincor et al.  the authors explore the effect of phenology overlap on a large network of species interactions in calcareous grasslands in France. They analyze if and how this effect varies along a latitudinal gradient using empirical data on six plant-hoverfly networks. When comparing ecological network along gradients a well-known problem is that the network metrics is dependent on network size . Therefore, instead of focusing on complete network structure the authors here focus on the factors that determine the probability of interactions and interaction frequency (number of visits). The authors use Bayesian Structural Equation Models (SEM) to link the interaction probability and number of visits to phenology overlap and species abundance. SEM is a multivariate technique that can be used to test several hypotheses and evaluate multiple causal relationships using both observed and latent variables to explain some other observed variables. The authors provide a nice description of the approach for this type of study system. In addition, the study also tests whether phenology affects network compartmentalization, by analyzing species subgroups using a latent block model (LBM) which is a clustering method particularly well-suited for weighted networks.
The authors identify phenology overlap as an important determinant of plant-pollinator interactions, but also conclude this factor alone is not sufficient to explain the species interactions. Species abundances was important for number of visits. Plant phenology drives the duration of the phenology overlap between plant and hoverflies in the studied system. This in turn influences either the probability of interaction or the expected number of visits, as well as network compartmentalization. Longer phenologies correspond to lower modularity inferring less constrained interactions, and shorter phenologies correspond to higher modularity inferring more constrained interactions.
What make this study particularly interesting is the presentation of SEMs as an innovative approach to compare networks of different sizes along environmental gradients. The authors show that these methods can be a useful tool when the aim is to understand the structure of plant-pollinator networks and data is varying in complexities. During the review process the authors carefully addressed to the comments from the two reviewers and the manuscript improved during the process. Both reviewers have expertise highly relevant for the research performed and the development of the manuscript. In my opinion this is a highly interesting and valuable piece of work both when it comes to the scientific question and the methodology. I look forward to further follow this research.
 Pascual, M., and Dunne, J. A. (Eds.). (2006). Ecological networks: linking structure to dynamics in food webs. Oxford University Press.
 Parmesan, C. (2007). Influences of species, latitudes and methodologies on estimates of phenological response to global warming. Global Change Biology, 13(9), 1860-1872. doi: 10.1111/j.1365-2486.2007.01404.x
 de Manincor, N., Hautekeete, N., Piquot, Y., Schatz, B., Vanappelghem, C. and Massol, F. (2019). Does phenology explain plant-pollinator interactions at different latitudes? An assessment of its explanatory power in plant-hoverfly networks in French calcareous grasslands. Zenodo, 2543768, ver. 4 peer-reviewed and recommended by PCI Ecology. doi: 10.5281/zenodo.2543768
 Staniczenko, P. P., Kopp, J. C., and Allesina, S. (2013). The ghost of nestedness in ecological networks. Nature communications, 4, 1391. doi: 10.1038/ncomms2422
Anna Eklöf (2019) The role of phenology for determining plant-pollinator interactions along a latitudinal gradient . Peer Community in Ecology, 100034. 10.24072/pci.ecology.100034
Revision round #22019-10-26
Decision round #2
All comments have been addressed and the manuscript reads well. There are only a few minor comments to address from one of the reviewers.
Reviewed by anonymous reviewer, 2019-10-13 20:29
Reviewed by Ignasi Bartomeus, 2019-10-23 19:38
Revision round #12019-03-14
Decision round #1
Thank you very much for submitting your preprint to PCI Ecology. Two reviewers have now commented on your preprint and they were both positive to the research questions and your scientific approach. I indeed do agree with this. But both reviewers also have some comments and suggestions of ways to improve your contribution.
When reading the preprint there were two issues I find crucial to address. First, I experienced that there was a lack of details regarding the description of SEM, and it seems like the authors assume the reader is already quite familiar with the methodology. I think this will usually not be the case. Therefore, I think it is necessary to add some text and go a bit deeper into explanations of this (this is also a comment from Reviewer #1). Second, to me (as for Reviewer #2) the connection to phenology seems a bit secondary As I see it there are to ways to address this; either make the connection to phenology much more clear and stronger in the text or to actually turn around the focus more towards the method on estimating probabilities of occurrence of interactions for informing models.
In addition to these comments the reviewers have additional suggestions that the authors should address in order to further improve their contribution. As such, I would like to invite the authors to submit a revised manuscript before a decision is made about a recommendation.
Anna Eklöf .