Climate envelope modelling reveals intraspecific relationships among flowering phenology, niche breadth and potential range size in Arabidopsis thaliana

Banta et al. Ecology Letters 15(8): 769-777. Climate envelope modelling reveals intraspecific relationships among flowering phenology, niche breadth and potential range size in Arabidopsis thaliana

Easy to forget that Arabidopsis thaliana doesn't just live in laboratories! Via Wikimedia

Easy to forget that Arabidopsis thaliana doesn’t just live in laboratories! Via Wikimedia

Lynsey McInnes

Lynsey McInnes

You guessed it, this was another of my choices. I found it a while back and was intrigued over the approach the authors would take. In brief, the paper looks at whether genotypes underlying (or rather, linked to) flowering time generate significantly different niche models (and by extensions niches) and thus can they (the authors) provide evidence that there are intraspecific differences in niche and niche breadth. A. thaliana is a great species to use to ask this question, it is an exceedingly well-known model organism and has a wide distribution.

The conclusions of the paper are far from surprising, with such a wide distribution and with known flowering time variation, it was inevitable that the authors would find evidence of intraspecific variation in niche dimensions. Nevertheless, this is really important to show! There is a whole market devoted to niche models and projections of range change due to climate change that almost exclusively treat species as a single entity. Oops. This is clearly too simplistic for species beyond a certain range size (and yes people kind of know this already). Papers like this (and the Razgour et al. paper we covered earlier) demonstrate this well. Phew.

Now here comes the issue. This paper was only possible because it builds on a ton of A. thaliana research. For instance, genetic variation in flowering time was already known and the underlying loci already characterised. The authors state themselves that defining coherent populations that might be expected to have significantly different niches to each other is really difficult (they probably could not have emphasised this enough!). Populations are rarely closed entities. They circumvent this problem here by going straight for a crude single locus genotype definition. How would you make your population buckets without this additional data? Can you? Is movement among populations (with their specific local adaptations) something that might save chunks of a species range? Probably.

If niche models don’t die a death completely, their next incarnation is going to be models which incorporate not only intraspecific variation, but also connectivity among these chunks (this is going to have to involve dispersal among spatially discrete chunks and degree of genetic exchange among co-occurring genotypes). For such models to be successful and have ‘conservation relevance’ a lot more crosstalk is going to be needed among (macro)ecologists and landscape geneticists/phylogeographers (yay, that’s me!).

This paper is a great start and I look forward to seeing developments in the field that enable it to be useful for non-model organisms (perhaps with no genetics), using multi-locus genotypes, integrating additional ecological traits, adding depth to our understanding of how populations interact to make up a range and ultimately, one day, far into the future, what a realised niche is relative to a fundamental one?

Will Pearse

Will Pearse

A lot is said about model systems in evolution and ecology, and I think papers like this, where model systems for which we have a lot of information are used to answer questions in related fields, are great.

I wear my love of phylogeny and niche conservatism on my sleeve, but that doesn’t mean I don’t appreciate a good demonstration of intraspecific variation when I see one. Flowering time should be variable in a species that spans so much of Europe, because it’s exposed to such different environmental conditions. Whether ability to adapt to novel conditions, or the general constraints that mean the species has to vary its flowering time, are as variable within the species is a slightly different question. I’ve been spending some time thinking about the inheritance of species’ potential for intraspecific variation, and I’m not entirely sure I can come up with a bullet-proof way of deciding what should, or shouldn’t, show such variation. I’d be interested to know if you can!

When I saw figure 4, which shows that earlier-flowering genotypes have larger potential ranges, I was very happily sold. I’m often somewhat nervous when I read a paper involving niche modelling or species distribution models, simply because the things seem so damn hard to get right. Therefore that the authors found any kind of relationship (albeit one with some scatter) is extremely impressive, and indicates they’ve really found something cool. The extremely tight relationship between niche breadth and potential range size is less surprising to me, both from existing theory (that the paper cites), and from the definition of niche breadth itself. A species has a higher niche breadth if “different habitats are equally suitable” (p. 772) based on the MaxEnt suitability scores for each cell, and the potential range is also defined from the MaxEnt predictions which, presumably, incorporate habitat suitability. Thus I’m not so surprised that the relationship between these two things are so strong, because I think they’re related to one-another; that doesn’t make the conclusions any less valid, but it did leave me hoping (as the authors themselves mention) that someone will be able to quantify observed range occupancy for these genotypes. If I’ve missed something obvious about the above, please do let me know – I’m no niche modeller for sure!


About will.pearse
Ecology / evolutionary biologist

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