OCBILs & YODFELs

 

I recently stumbled upon the OCBIL theory. In the words of Hopper (2009): “OCBIL theory aims to develop an integrated series of hypotheses explaining the evolution and ecology of, and best conservation practices for, biota on very old, climatically buffered, infertile landscapes (OCBILs). Conventional theory for ecology and evolu- tionary and conservation biology has developed primarily from data on species and communities from young, often disturbed, fertile landscapes (YODFELs), mainly in the Northern Hemisphere.” As a geomorphologist, and in particular a biogeomorphologist interested in coevolution of landscapes, biota, and soils, the OCBIL-YODFEL contrast is extremely interesting—mainly because it implies a key role for landscape age, stability, and geomorphic disturbance regimes in the development of ecosystems and evolution of biodiversity patterns.

The basic line of reasoning is that the geomorphic setting of OCBILs results, through natural selection, in biotic assemblages that differ fundamentally in their traits from biotas evolving in YODFELs. This has implications for biodiversity and conservation strategies (Hopper’s primary concern). The antiquity and relative lack of disturbance (particularly by glaciations) of Gondwanan remnants of the southern hemisphere has long been noted by geomorphologists such as Rowl Twidale, T.R. Paton, Geoff Humphries, Cliff Ollier, and Colin Pain to result in many landform, soil, and regolith characteristics that differ markedly from what is typically found in Eurasian and North American settings. The latter have been much more frequently disturbed, directly or indirectly, by glacial/interglacial cycles during the Quaternary. In particular, the geologically old, relatively flat, dry, unglaciated landscapes of Australia and southern Africa have produced geomorphology, in the sense of scientific practice as well as the landscape itself, quite different from the dominant European and North American views. The geomorphologists mentioned above are or were all based in Australia for most of their careers, and Hopper, not surprisingly, is also an Aussie (a biologist, he was a student of Twidale’s).

It is not surprising that areas with large differences in landforms, climate, and soils would produce different ecosystems and evolutionary trajectories. However, as the burgeoning literature of biogeomorphology and niche construction shows, this is not only a matter of organisms adapting to environmental constraints. This is a two-way street, with biota also influencing landforms and soils. Further, factors such as longer time periods between major disturbances such as glaciations and volcanic eruptions, and persistence of more-or-less consistent climates, greatly increases the number of possible evolutionary trajectories.

Thus far, OCBIL theory has taken some long-recognized ideas from geomorphology and pedology and applied them to evolutionary and conservation biology and ecology. Many of the evolutionary adaptations of OCBIL plants identified involve biogeomorphic engineering, such as sand-binding roots and clay mineral synthesis. Thus there is a great opportunity for new insights into coevolution of biota, landforms, and soils.

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Hopper, S.D., 2009. OCBIL theory: towards an integrated understanding of the evolution, ecology and conservation of biodiversity on old, climatically buffered, infertile landscapes. Plant & Soil 322: 49-86. 

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