Evolutionary responses to environmental change: trophic interactions affect adaptation and persistence

Mellard et al. 2015 Evolutionary responses to environmental change: trophic interactions affect adaptation and persistence. Proc Roy Soc B 282: 20141351.

Effect of niche width on herbivore (solid red line), plant with herbivore (dotted green line), and plant alone (dashed blue line); under smaller (top) and greater (lower) temperature change. Moral of the story: bifurcations matter, people.

Effect of niche width on herbivore (solid red line), plant with herbivore (dotted green line), and plant alone (dashed blue line); under smaller (top) and greater (lower) temperature change. Moral of the story: bifurcations matter, people.

Lynsey McInnes

Lynsey Bunnefeld

‘We have an urgent need to understand and predict the response of individual species as well as whole communities and ecosystems to global change. However, the most commonly employed methods for predicting the response of species to climate change do not explicitly incorporate all fundamental ecological and evolutionary processes that may be major determinants of species responses to climate change.’

Haven’t we all read (and written) statements like that before?! Seems like we are missing a lot: dispersal ability, intraspecific variation, adaptive capacity, species interactions. These are all important issues to incorporate into predicting species’ responses to climate change. Different people take on different aspects and you get the crazies that try to model everything in one go and there is not a single study that does not have to resort to a suite of simplifying assumptions. And each study inevitably finds that their chosen issue IS important. What to do? It all sometimes feels completely overwhelming, as if the only worthwhile reaction is to shrug our shoulders and just wait and see what elements will be important and what not.

Meh. In the spirit of curiosity though and taking a step back from all the grimness, studies such as this one – a modelling study considering the different ways interactions between a plant and a herbivore could impact their responses’ to a changing environment – are, quite simply, interesting problems to tackle.

No doubt the authors could have set things up differently, included different assumptions or different parameters, but, from my limited knowledge of such studies, they appear to cover a broad parameter space and uncover a bunch of interesting responses. E.g., if plant and herbivore traits are correlated, their impacts on each other depend on their relative niche widths and initial conditions of the environment. To a big degree. This is cool stuff. Sobering, but cool. I love the line where they let slip that adding in a carnivore could change things further still!

Do you know what I would like to see though? I would like these authors, or other modellers, to make me a program or a package where I can play around with my own parameter combinations, perhaps from my chosen species or set of species, and make my own plots and response curves. Because I am not an expert in modelling like these guys are, I find myself having to believe what they say and the setup that they have chosen. I have faith that its probably fine, but it would be fun and informative to play around and recreate these plots and make my own. I think the more people that are comfortable (biologists and non biologists alike) with these kinds of analyses, the easier it will be to convince people that tipping points exist, that interactions matter, that responses are going to be quirky, but might be predictable sometimes. I think we need to get our hands much dirtier still. Do such tools exist?

Will Pearse

I always say a modelling exercise is only worthwhile if it tells you something you couldn’t have predicted at the outset. I find it hard to believe I could have guessed that the presence of a herbivore could so profoundly alter the evolution of a plant species, and so, while I would be lying if I said I followed all of it, I enjoyed this paper.

We say it very casually all the time, but predicting changes in species under climate change is all the more terrifying because we have no idea how those species will interact with each other in the future. Studies like this are very sobering to me, since things can get incredibly complex with only two actors. By complex, I mean switch-points that lead to different optima, because anything non-linear with some sort of tipping-point scares the goodness out of me. I have no idea how we could hope to empirically (and analytically) determine what would happen if there were another trophic level or additional herbivore/plant in this system. Perhaps arguments can be made for motifs (regularly repeating units of interactions) making things easier to model, but to be honest I’m sceptical. Grouping 300 interacting species into 10-30 different groups and then modelling those might be easier, but I’m not sure it would be easy. I’m happy to be corrected!

The authors discuss how pushing the plant towards a colder niche would badly-prepare it for climate change. I wonder if the number species we find doing ‘the wrong thing’ (leaving aside model slips!), which we sometimes attribute to species interactions, could be due to shifts like this. If a population is pushed into a particular region of parameter space, then I suppose the only thing to do is make the best of it. What if the ‘wrong move’ is only sub-optimal when we view things solely through the lens of climate? Maybe climate’s only part of the picture…


About will.pearse
Ecology / evolutionary biologist

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