Phylogenetic trait-based analyses of ecological networks

Rafferty, N.E., and Ives, A.I. Ecology (in press). DOI:10.1890/12-1948.1. Phylogenetic trait-based analyses of ecological networks

An animal and a plant, or a plant and an animal. They’re all in a phylogeny, somewhere, right? By Alvesgaspar (Own work) [GFDL or CC-BY-SA-3.0], via Wikimedia Commons

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Will Pearse

There are relatively few studies of ecological interaction networks that use phylogenetic information, and so this study, which no only does so but also suggests a new method for doing it, is great.

Anthony Ives is constantly developing new methods that are useful to eco-phylogeneticists and ecologists in general, and this paper is an excellent example. Phylogenetic linear mixed models are a way of simultaneously examining trait and phylogenetic information, and strike me as an extension of Ives’ earlier work with Matt Helmus. I love these methods; they allow us to answer questions we’re actually interested in (what determines species interactions) using phylogenetic and trait data. They don’t just look at a property of our data (like phylogenetic dispersion) and then force us to infer from that other properties of the system. My only criticism (which is better communicated by Nate Swenson) is we should go further – why collect phylogenetic information if we only use it to validate trait data? I, probably unfairly, want to shift the question to ‘what determines how species interactions evolve‘.

I think the interaction network literature is filled with cases of people trying to find unifying, abstract aspects of structure – motifs. I wonder if this is because the phrase ‘interaction network’ can cover so many kinds of interactions (pollinators, herbivores, competitors, etc.) in so many different taxa. Maybe eco-phylogeneticists can help, and there are over-arching phylogenetic patterns that can unify all these different systems and approaches. Every organisms on Earth fits into the Tree of Life somewhere, and that makes every single interaction network study, be it of bats or bell-flowers, comparable in some way. Which can only be a good thing!

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Lynsey McInnes

I was really excited about this paper when I chose it. Traits, phylogenies, my pet interest ecological networks! I have the feeling the paper is really good, but I have to say I struggled with it. I think I dove too quickly into the deep end. Maybe I should have gotten more comfortable with the network literature or the traits on phylogenies literature, but I still haven’t learnt to do things like that…

Across biological sub-fields, everybody knows that species’ interactions matter, but, at least in the fields I have most experience of, namely macroecology and macroevolution, explicitly incorporating the effect of species’ interactions (or making them the point of an analysis) is only a very recent development. I think this means that any advance is a good one (and I feel like we’ve mentioned this a number of times before on PEGE).  So, in that respect, this paper is neat. It takes a well-studied, tractable set of plant-pollinator interactions and attempts to parse out the reasons underlying the different communities: do traits or relatedness underlie them? The authors make the case that methods such as theirs can help predict how guilds of species will fare under climate change as  it allows them to anticipate whether phenological mismatch will take hold or whether, in the pool of the other guild, species exist that can match advancing phenologies. Admirable.

I guess the missing link as I see it can be surmised from the title of the paper – ecological networks. What about evolutionary responses? Is it necessary to consider that mismatches might be ameliorated by co-evolutionary responses to environmental change? Is the timescale too short? Will there be less pressure for evolutionary change if, for the plants for example within the pollinator pool there are species ready to pollinate them following their flowering advance. Perhaps teasing apart this additional potential response will be a feature of a subsequent paper from these guys.

I also wonder how space affects these patterns. How do patterns and expectations change as one investigates multiple populations across a larger region? How does local adaptation affect responses? What about variation in the available plants/pollinators across space? What about gene flow among populations? How might one go about incorporating traits, phylogeny and interactions with intraspecific variation and space? Is that too much to consider at once?