Linking Life-History Traits, Ecology, and Niche Breadth Evolution in North American Eriogonoids (Polygonaceae)

Pink (Japanese) knotweed Persicaria capitata from Wikipedia

Lynsey McInnes

Lynsey McInnes

Another micro/macro choice from me. Surprise!

I liked this paper. I thought it was a thoughtful attempt to address a specific question that is bypassed by many a macroevolutionary biologist. The authors want to tease apart whether they can explain patterns across species in niche breadth and rate of niche breadth evolution by looking below the species level (given that niche breadth is really not a good ‘species-level’ trait).

Now, bridging the micro to macroevolutionary divide might be expected to require multiple data points per species to get a measure of intraspecific variation. The authors sidestep this by using measures of climatic tolerance to characterise niche breadth, reasoning that evidence for local adaptation in plants is common and a broad niche necessarily comes about through intraspecific variation. I kind of agree, but do wonder what other ways intraspecific variability could be/might need to be quantified.

They find that perennials have higher rates of niche breadth evolution while annuals have higher rates of niche position evolution. In essence, they put this down to perennials inhabiting more variable, colder and higher environments and annuals specialising in more stable environments. Perennial species thus do better with a broad niche as there are always some adaptations floating around the species to deal with the different conditions thrown on them. Annuals on the other hand have evolutionary speed on their side to pop out a new species when needs be (so that across species niche position change is more rapid). The authors concede that some of their reasoning is (very thoughtful) conjecture although the story they build up is a convincing one.

The authors state themselves that to understand what mechanisms underlie these variations across life-history strategies needs more evidence. One place to start would be looking for confirmation of local adaptation across populations of each species and to find out the genetic mechanisms underlying this. Another would be to fill out the phylogeny to see if sampling gaps are biasing the story. From the phylogeny it looks like perenniality is pretty clustered on the tree, how clustered? And what is missing? Do the independent origins of perenniality have the same kind of niche breadth? What are the problems with using this kind of niche modelling approach? How much broader a niche could these species persist in if they had the opportunity?

I wonder what other systems this type of approach would be good for? Is variance in climate experienced within the range a good measure of intraspecific variability? It obviously captures something but how correlated is it with range size?  Have we just shifted the question of how life history strategies affect range size to how do they affect a convoluted measure of range size? This might be a good thing, but it might also be dangerous if niche breadth/climatic tolerance is not the main driver of range size variation (saying that, it probably often is).

A lot to think about.

Will Pearse

Will Pearse

This is an interesting paper; the methods are very through, and I enjoyed the focus on the evolution of intraspecific variation.

I like the idea that annuals, by hiding in the seed bank, can avoid adverse environmental conditions and this have a narrower niche breadth. The pedant in me is tempted to argue that this dependence on the seed bank will require specific adaptations and an extension of the niche, but I don’t think that’s tremendously important. If true, this hypothesis suggests that climatically stable regions (the tropics) should show less annual vs. perennial variation. I also wonder whether an annual spending longer underground has fewer effective generations and so a reduced capacity for evolution.


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