Biogeography has been on my mind of late, in part stimulated by thinking about the work we’re writing up on the frequency of wind versus animal pollination in plant communities in different parts of the world that I mentioned in one of my earlier Brazil posts. André has added more communities to the data set following some field work in Uruguay, and we are collaborating with Bo Dalsgaard and his colleagues in Denmark on analysing how historical and contemporary climates may have shaped the patterns we’re seeing. It follows on neatly from the previous work Bo has done on climate and hummingbird-flower interactions. I’ll report back when we have more to say.
The other reason for thinking about biogeography is that a couple of recent scientific reports have captured my attention. The first dealt with new fossil discoveries of species related to that enigmatic South American bird the hoatzin (Opisthocomus hoazin). The report can be read here but in summary, the evidence suggests that the bird family to which hoatzins belong was once much more widespread and may have originated in Europe. Hoatzins are not the only such example: hummingbirds, which are also currently restricted to the Americas, were found in Europe in earlier times, according to reports from back in 2004 and more recently in 2007. It appears that contemporary biogeography may not reflect past biogeography for some (perhaps most?) groups of species.
As a lesson in contemporary biogeography, it’s often been pointed out that the famous Vera Lynn song The White Cliffs of Dover falls short in its scientific accuracy:
There’ll be bluebirds over
The White Cliffs of Dover
Tomorrow, just you wait and see
Bluebirds are members of the genus Sialia, a group of three species which do not naturally occur in Britain, in fact are not present in Europe at all. So you’re not likely to hear them singing in southern England. But perhaps the genus was present in the distant past? Who knows? In the meantime we may have to change the lyrics to the song. Unless the writer was predicting what might happen in the future when continental drift means that Europe and the Americas will be much closer together.
The other report that caught my eye was of an interesting study that has compared plants and birds in cities across the globe, and looked at how urbanisation reduced the diversity of the native species compared to non-urban areas nearby. However I do hope that the lead author was being misquoted when she said that: “Owing to the fact that cities around the world share similar structural characteristics – buildings, roads etc – it is thought that cities share a similar biota no matter where they are in the world”. She goes on to say that they had discovered that some species: “are shared across cities, such as pigeons and annual meadow grass, but overall, the composition of cities reflects the unique biotic heritage of their geographic location”. Well yes, of course: any of our undergraduate students taking the second year module in biogeography could have told you that! As a serious hypothesis to test it lacked rigour: few tropical birds and plants could survive in temperate-zone cities, for example. There’s more to the study than just this, of course, as you can see from the abstract. Nonetheless it was an odd statement to make in my view.
The Wikipedia definition of biogeography that I linked to at the beginning of this post is perhaps a little limited in its scope: “the study of the distribution of species and ecosystems in geographic space and through geological time” doesn’t cover the species interactions that have been a focus of my research, for instance. Perhaps “macroecology” fits it better, though (as I’ve mentioned before) there’s been a lot of debate in the scientific literature about where biogeography ends and macroecology begins, or whether the two are synonymous. My own view is that the two overlap considerably, but that macroecology is bringing a lot of new tools and approaches to the study of organisms at large spatial scales. Whether that warrants the definition of a different discipline is debatable, but like all such debates (e.g. the difference between ecology and natural history as recently discussed on the Dynamic Ecology blog) it provides us with a way of reassessing our own views on the work we do, which is always a good thing.