Climatic niche shifts between species native and naturalized ranges raise concern for ecological forecasts during invasions and climate change

Early & Sax (in press). Global Ecology and Biogeography DOI: 10.1111/geb.12208. Climatic niche shifts between species native and naturalized ranges raise concern for ecological forecasts during invasions and climate change

regan_niche_shifts

Come to America – fame, fortune, and the chance for a fresh niche! Figure 3 from Regan & Sax.


Lynsey McInnes

Lynsey Bunnefeld

I like this paper a lot. It plays to all my new found interests in, what I like to call, intelligent macroecology. It takes a small subset of species (50 or so plants that are native to Europe and naturalised in the United States) and conducts a suite of well thought out analyses on them in order to ascertain if there are any general patterns in niche shifts following facilitated expansion of the native range. Sure, not all European plants naturalised in the US have been looked at, but that doesn’t matter one bit.

Early & Sax draw heavily on comparisons with another recent study by Petitpierre et al. who showed that multiple large range agricultural weed species show little evidence for niche shift following range expansion. In contrast, Early & Sax find plenty of evidence for major changes in niche position and niche breadth (alongside evidence of species with little or no niche shift).  They argue that Petitpierre’s dataset is unlikely to be representative of the majority of species which are range-restricted and have little history of human-assisted movement into a broad niche space. So, while this study does not refute their findings, it does expand them to provide a more nuanced picture of potential outcomes.

I am as guilty as the next person of glibly stating that range limits are mostly climatic at the macro scale and that, although biotic interactions probably play a role, its 100% fine to base conclusions and indeed policy on the idea that the niche that species are currently realising would be similar anywhere on the globe. This paper and a suite of others are rapidly kicking down this argument. Small scale transplant experiments and other comparative datasets are indicating time and again that a species’ realised niche is delimited by much more than just climate.

This is, of course, a problem for the massive field of predicting species’ responses to climate change.  Species are commonly expected to move, adapt or perish in the face of an altered climate regime. In fact, they might also be able to tap into an ability to occupy a wider or different niche without evolving new adaptations. Conversely, if other species ‘get there first’ they might lose niche space to a novel competitor.

These findings are both really interesting from a how do macro niches work in principle perspective as well as a what on earth is going to happen in the very near future perspective. I think they argue for an ecosystem or community (however you might choose to define either of those concepts) wide perspective. If biotic interactions or historical contingencies or even landscape barriers are really influencing the niche space that many species are currently occupying, we have no hope of predicting how species will respond to climate change (because don’t get me wrong, climate still has a major influence on occupiable niche) if we don’t also consider how species are influenced by the actions of others. Sounds simple, but it probably isn’t.

I don’t know much about network analysis at all, but it seems like this is the way forward (see last week’s post too). At the most broadest scale, one could look for the primary species with which the focal species interacts within its range, one can also focus on similar species found surrounding the focal one’s range that might be playing a similar role and thus excluding the focal one from range expansion. I think it is crucial to think more broadly than phylogenetically-close relatives but also look for functionally-similar species. And of course add in trait variation of all involved parties through space and time. Of course.

In conclusion, a great paper that adds to the growing voice among macroecologists that climate alone just won’t cut it. Not even for just understanding how spatial diversity patterns come about, let alone for conservation of these patterns into the future.


Will Pearse

Will Pearse

This paper deserves some attention. Using a quite amazing dataset, the authors (Regan has posted on PEGE!) looked at the native and introduced ranges of plants. They found that species’ introduced ranges often extend beyond the conditions of their native range (which they term niche shift).

Isolating when species distribution models fail because they don’t account for non-stationary processes like dispersal is a really, really important thing to do. Dispersal ability is the problem that a lot of people bring up time and time again – interestingly, dispersal ability had no correlation with species’ niche shift. However, time since introduction did, and the explanation given for that (time for humans to spread the species) is essentially dispersal limitation. I think another thing at work here is release from biotic controls – species evolve in a regional community, and when they get into an area with a radically different biotic community (…when they’re spread around more by us…) biotic limitations are relaxed and they can tolerate more novel environmental conditions. I think I just re-regurgitated some Ricklefs, but with maybe less of an emphasis on pathogens. The most range-restricted species seemed to show the greatest increase; assuming this isn’t some sort of artefact (lesser range –> more likely to detect increase) then I think these species should be more limited by species interactions.

Which brings me to what I think is the part of the paper most likely to annoy people – that we might have over-estimated species range change under climate change if we assume everything is niche limited. I think we almost certainly have, but I would caution that range expansion in a completely different continent is different from range change at home. Leaving aside the arguments above about species co-evolving, under climate change the entire community is being stressed, whereas in an introduction/invasion the new species is both the invader and the sole novel stressor. Moreover, there is a lot of variation in these results,: I find it quite harrowing that while the authors were able to explain some of the variation in niche shift they couldn’t explain it all. Put frankly, we still don’t know what’s going to happen to species’ ranges under climate change, and (to me) that’s terrifying.

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About will.pearse
Ecology / evolutionary biologist

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