Improving our knowledge of species interaction networks
Niche complementarity among pollinators increases community-level plant reproductive success
Ecosystems shelter a huge number of species, continuously interacting. Each species interact in various ways, with trophic interactions, but also non-trophic interactions, not mentioning the abiotic and anthropogenic interactions. In particular, pollination, competition, facilitation, parasitism and many other interaction types are simultaneously present at the same place in terrestrial ecosystems [1-2]. For this reason, we need today to improve our understanding of such complex interaction networks to later anticipate their responses. This program is a huge challenge facing ecologists and they today join their forces among experimentalists, theoreticians and modelers. While some of us struggle in theoretical and modeling dimensions [3-4], some others perform brilliant works to observe and/or experiment on the same ecological objects [5-6].
In this nice study , Magrach et al. succeed in studying relatively large plant-pollinator interaction networks in the field, in Mediterranean ecosystems. For the first time to my knowledge, they study community-wide interactions instead of traditional and easier accessible pairwise interactions. On the basis of a statistically relevant survey, they focus on plant reproductive success and on the role of pollinator interactions in such a success. A more reductionist approach based on simpler pairwise interactions between plants and pollinators would not be able to highlight the interaction network structure (the topology) possibly impacting its responses [1,5], among which the reproductive success of some (plant) species. Yet, such a network analysis requires a fine control of probable biases, as those linked to size or autocorrelation between data of various sites. Here, Magrach et al. did a nice work in capturing rigorously the structures and trends behind this community-wide functioning.
To grasp possible relationships between plant and pollinator species is a first mandatory step, but the next critical step requires understanding processes hidden behind such relationships. Here, the authors succeed to reach this step too, by starting interpreting the processes at stake in their studied plant-pollinator networks . In particular, the niche complementarity has been demonstrated to play a determinant role in the plant reproductive success, and has a positive impact on it .
When will we be able to detect a community-wise process? This is one of my team’s objectives, and we developed new kind of models with this aim. Also, authors focus here on plant-pollinator network, but the next step might be to gather every kind of interactions into a huge ecosystem network which we call the socio-ecosystemic graph . Indeed, why to limit our view to certain interactions only? It will take time to grasp the whole interaction network an ecosystem is sheltering, but this should be our next challenge. And this paper of Magrach et al.  is a first fascinating step in this direction.
 Campbell, C., Yang, S., Albert, R., and Shea, K. (2011). A network model for plant–pollinator community assembly. Proceedings of the National Academy of Sciences, 108(1), 197-202. doi: 10.1073/pnas.1008204108
 Kéfi, S., Miele, V., Wieters, E. A., Navarrete, S. A., and Berlow, E. L. (2016). How structured is the entangled bank? The surprisingly simple organization of multiplex ecological networks leads to increased persistence and resilience. PLoS biology, 14(8), e1002527. doi: 10.1371/journal.pbio.1002527
 Gaucherel, C. (2019). The Languages of Nature. When nature writes to itself. Lulu editions, Paris, France.
 Gaucherel, C., and Pommereau, F. Using discrete systems to exhaustively characterize the dynamics of an integrated ecosystem. Methods in Ecology and Evolution, 10(9), 1615-1627. doi: 10.1111/2041-210X.13242
 Bennett, J. M. et al. (2018). A review of European studies on pollination networks and pollen limitation, and a case study designed to fill in a gap. AoB Plants, 10(6), ply068. doi: 10.1093/aobpla/ply068
 Magrach, A., Molina, F. P., and Bartomeus, I. (2020). Niche complementarity among pollinators increases community-level plant reproductive success. bioRxiv, 629931, ver. 7 peer-reviewed and recommended by PCI Ecology. doi: 10.1101/629931
 Bastolla, U., Fortuna, M. A., Pascual-García, A., Ferrera, A., Luque, B., and Bascompte, J. (2009). The architecture of mutualistic networks minimizes competition and increases biodiversity. Nature, 458(7241), 1018-1020. doi: 10.1038/nature07950
Cédric Gaucherel (2019) Improving our knowledge of species interaction networks. Peer Community in Ecology, 100037. 10.24072/pci.ecology.100037
Reviewed by Nicolas Deguines, 2019-11-26 12:09
Revision round #22019-11-15
Decision round #2
Dear Ainhoa Magrach,
Your preprint, entitled Interaction network structure maximizes community-level plant reproduction success via niche complementarity, has now been reviewed again. The referees' comments and the recommender’s decision are shown on PCI site. As you can see, the recommender found your article interesting, but suggests a few (minor) revisions.
We shall, in principle, be happy to recommend your article as soon as it has been revised in response to the points raised by the referees, and in particular the second one. Once the recommender has read the revised version, he/she may decide to recommend it directly, in which case the editorial correspondence (reviews, recommender’s decisions, authors’ replies) and a recommendation text will be published by PCI Ecology under the license CC-BY-ND.
Alternatively, other rounds of reviews may be needed before the recommender reaches a favorable conclusion. He/she also might decide not to recommend your article. In this latter case, the reviews and decision will be sent to you, but they will not be published or publicly released by PCI Ecology. They will be safely stored in our database, to which only the Managing Board has access. You will be notified by e-mail at each stage in the procedure.
Thanks in advance for submitting your revised version. Yours sincerely, The Managing Board of PCI Ecology.
Reviewed by Nicolas Deguines, 2019-10-02 16:01
Reviewed by anonymous reviewer, 2019-09-04 21:23
Revision round #12019-06-17
Decision round #1
Recommendation: Major revision
This paper is well written and addresses interesting ecological questions. Yet, as stated by all reviewers, it deserves additional analyses and requires the writing to be more rigorous.
The R3 has made an impressive work by listing all locations at which the authors should add justifications and explanations for readers. Many other precisions are required to follow the study and make it fully reproducible. The R4 added the point of view of an experimenter and suggests to include more details on the measurements (be it in the supplementary materials).
R2 has mentioned the possible biases coming from the non-exhaustive sampling of the species network. This point may be generalized by the question of the possible biases of the study. How to reduce the uncertainty coming from all the possible co-variables? Elevation has been mentioned by reviewers, as well as other species (outside the most common plant sp.) or possible evolutionary effects. In addition, R4 reminds that wind-pollination and self-pollination may bias the study, and should be addressed or at least argued.
While R2 mentioned the danger to use the term “prediction”, which was not discussed in the paper, R1 mentioned the danger to use the term “mechanistic” when based on correlative studies. Authors have no choice but to remove these terms or to complete their analyses and provide all the details required to convince the readers. As an ecologist, I am also surprised that authors did not comment the possible autocorrelation between sites. Even with a 7km averaged inter-distance in a forested landscape, I guess we can easily hypothesize a partial redundancy between sites due to spatial links. Unfortunately, autocorrelation is one of the most difficult issues in statistics and in particular in GLM models (see Dorman et al. papers). Authors should mention this point, as some other limitations: in particular, GLM are assuming linear relationships whereas ecological relationships are often non-linear. Authors should probably control this issue too. Finally, one point I am particularly aware is that ecological networks are not static at all, although they are often hypothesized so. Even on a short term as in this study, networks may change their structure (not only their fluxes, but also species and species interactions involved) due to frequent local extinctions and invasions. Furthermore, what if a specific relationships is not stable (shifting from positive to negative for a while)? This observation is neglected by most ecologists today and should be at least commented in the discussion.
Overall, this paper seems to be a relevant attempt to include community analysis into more traditional species-centered studies. For this reason, it should be considered. But reviewers mentioned a large number of points that authors should address before recommendation. For this reason, on behalf of PCI ecology, I suggest a Major revision to be sent.
Best wishes. CG.