In the book ‘The Theory of Ecological Communities’ by Mark Vellend speciation is one of the four high-level processes explaining local community patterns and dynamics. Mark discusses the influence of regional species pools and speciation rates on local diversity. In many temperate and tropical locations speciation has happened in situ over evolutionary timescales, but the Arctic is different. Here, long-term dynamics are controlled by glacial and inter-glacial cycles. More than twenty thousand years ago at our field site Qikiqtaruk – Herschel Island, there probably was no island at all and instead just the terminus of the Laurentide ice sheet.
What determines regional richness today at least for plants in much of the Arctic is the distance to glacial refugia and time since de-glaciation. Here on Qikiqtaruk, we are located pretty much right at the edge of Beringia – the unglaciated region in the Yukon, Alaska and Eastern Siberia during the last ice age. We are also close to one of the northern most extents of the treeline around the circumpolar Arctic, such that the boreal forest species pool is only about 100 km away. This means that potentially species diversity will be higher here than in other similar environmental conditions in other parts of the Arctic.
If we are thinking about the diversity of other species, most of the birds are migratory here and spend their winters thousands of kilometers farther south, some as far south as the neotropics or even the southern hemisphere. What determines local avian diversity is therefore migratory dynamics. Presumably Arctic bird species did not speciate here in the Arctic, but in their winter ranges and then over time explored further and further northward breeding grounds.
We have enjoyed tag team birding with Cameron Eckert, Yukon Parks biologist, and hearing about or seeing the regular rare sightings of birds outside of their normal ranges from the Calliope hummingbird, tufted puffin, short-tailed shearwater to the gyrfalcon that we documented ourselves as it came through camp. The bird species pool is a dynamic one, with more and more sightings of southern birds blowing up on the winds of storms. It is good to reflect on communities of species that are far more mobile than the perennial tundra plants that we study.
At the end of August, we conducted an additional protocol as a part of the International Tundra Experiment to document the size of the tundra plant species pool around our long-term monitoring plots. By tromping around in concentric circles we were able to identify 36 additional species within 100 m of our plots. These species could be invading into the ecological communities in the future. The closest observed new species were Parrya naudicaulis, a pretty brassica a mere 2 m away from the ‘Herschel’ vegetation plots and a Papaver radicatum, a lovely bright yellow poppy about 5 m away from the Komakuk vegetation plots.
It is very likely that new species will be entering into the plots in the future, but perhaps also likely that other rare species within the plots will disappear over time – representing the dynamics between dispersal, ecological drift and local extinction. But overall will these plots become more diverse as the growing seasons continue to lengthen and the permafrost-related cryoturbation disturbances decrease? With one major species invasion in the first 18 years of the ecological monitoring programme, perhaps increasing diversity is the prediction that I would make for these plant communities.
Very slowly over time in these perennial plant communities, evolutionary selection is occurring and perhaps new species are forming in situ adapting to the changing environmental conditions. One of the goals of Team Shrub’s research is to identify how much local adaptation occurs between populations of shrub species along large elevational gradients and to test whether Arctic shrubs have genetically limited growth rates and canopy heights relative to the same species growing further south. Perhaps we are observing speciation in action – though we probably won’t be around to see the outcome of natural selection in the Arctic, unless we will???
By Isla and Gergana
This blog post was written on Qikiqtaruk-Herschel Island in the Western Canadian Arctic as part of Team Shrub’s island book club, aiming to read and discuss Mark Vellend’s 2016 book “The Theory of Ecological Communities” while we are out in the field, right next to the communities we study. Team Shrub are a group of plant ecologists who often work in high-latitude tundra ecosystems on topics in community ecology.
The team’s book club discussions are summarised in four blog posts:
- Qikiqtaruk Book Club Part I: Ecological communities in the Arctic
- Qikiqtaruk Book Club Part II: Selection in the Arctic
- Qikiqtaruk Book Club Part III: Speciation, drift and dispersal in the Arctic
- Qikiqtaruk Book Club Part IV: Theory and high-level processes in the Arctic