Since the age of the great explorations, the excitement of travelling to new parts of the planet has been unequally distributed among biologists. For those studying large plants and animals, every new region, every new continent would offer floras and faunas consisting of large numbers of new and exotic species. For those studying microbial life, wherever they turned their microscopes they kept finding more of the same. Why? The classical hypothesis is that the enormous population sizes of microbial species drive ubiquitous dispersal of these species, so that, as formulated by the Dutch microbiologist Baas Becking in the 1930, “Everything is everywhere, but, the environment selects”. Recent attempts to resolve the debate by searching for endemic species, or by exploring geographic patterns in genetic data, has stranded over taxonomic uncertainties and methodological disagreements.
Telford, Vandvik and Birks circumvent these problems by using regional biodiversity patterns to test the “Everything is Everywhere” hypothesis. To do so they combine new ecological theory developed for entirely different habitats and organisms (trees in tropical rainforests) with enormous databases on species distributions collected through decennia of climate- and environmental change research. They argue that if dispersal is ubiquitous, all regions should share one underlying richness-environment relationship, governed by the availability of species in the global species pool. If dispersal is limited, the global relationship should break down so that different regions end up with different richness-environment relationships. Specifically, they predict that there should be a matching between regional availability of a particular habitat, and the local diversity in that habitat. And that was exactly what they found: within each region the highest diversity was always found in the lakes with the most common pH-values.
This research has implications for the reconstruction of past environments: Transfer functions may for example not be as ‘transferable’ between regions as has previously been assumed. More generally, there are also implications for our understanding of global biodiversity patterns: Microbial species may not be as fundamentally different as the “Everything is Everywhere” hypothesis has suggested. This means that large-scale biogeographic patterns like endemism and vicariance (different species doing the same ‘job’ on different continents), which contribute a significant proportion of the global biodiversity of macrobial species, may be important among micro-organisms as well. Such patterns are just more difficult to spot through a microscope.
Read the story På høyden, 19.05.06: How many species are there on Earth?