Self-stabilization of the biosphere under global change: a tutorial geophysiological approach

Abstract

A 2‐dimensional extension of the simple Lovelock‐Watson model for geosphere‐biosphere feedback is introduced and discussed. Our enriched version also takes into account various pertinent physical, biological, and civilisatory processes like lateral heat transport, species competition, mutation, germination, and habitat fragmentation. The model is used as a caricature of the Earth System, which allows potential response mechanisms of the biosphere to environmental stress (as generated, e.g., by global warming or anthropogenic land‐cover change) to be investigated qualitatively. Based on a cellular automaton representation of the system, extensive calculations are performed. They reveal a number of remarkable and, partially, counter‐intuitive phenomena: our model biosphere is able to control almost perfectly the geophysical conditions for its own existence. If the environmental stress exceeds certain thresholds, however, life breaks down on the artificial planet via a first‐order phase transition, i.e., in a non‐reversible way. There is a close connection between self‐stabilizing capacity, biodiversity and geometry of habitat fragmentation. It turns out, in particular, that unrestricted Darwinian competition, which reduces the number of co‐existing species, is the best guarantee for survival of the artificial ecosphere as a whole.

Evolution and the Regulation of Environmental Variables

“…The next significant result to be repeated is that allowing albedo to mutate does not affect regulation, and may in some cases actually increase its range [4,5,6,7]. For this scenario we allowed albedo to take any value in the range [0.25, 0.75], corresponding to the full range from black to white.…”

“…We observed similar results to Lenton and Lovelock [10], in that regulation was observed to occur, but with a more gradual tailing in and tailing out than with the non-evolvable growth function. For completeness, we have also run the model with heat transfer between neighbouring patches [6], and found that the qualitative nature of the results is unchanged for all of the above scenarios. The exception is where the heat transfer is so efficient that there is no perceptible difference in temperature between patches; in this case there is no possiblity of a particular daisy species gaining a selective advantage over its competitors by altering its local temperature.…”

“…Our model is a cellular automata model in which patches are arranged in a 2-dimensional toroidal lattice (another CA Daisyworld model was presented by von Bloh et al [6], but in a different form and with different aims). Each patch may be barren (bare earth) or may contain a single species of daisy.…”

“…However, the simplicity of the original Daisyworld model means that it cannot answer questions about the compatibility of biotic regulation and evolution. To address these questions a number of extensions to the model have been presented [4,5,6,7,8,9,10], but it seems likely that the Daisyworld model has now answered as many questions as it is able to.…”

Towards understanding how surface life can affect interior geological processes: a non-equilibrium thermodynamics approach

“…Such observations can be seen as the starting point for the Gaia hypothesis which proposed that the Earth and its biota form a co-evolving, selfregulating system that is robust to perturbations (Lovelock, 1979). The initial Gaia hypothesis has developed with different studies considering it from different aspects such as evolution and natural selection (Lenton, 1998), theoretical ecology (von Bloh et al, 1997), dynamical systems (Lenton and van Oijen, 2002) and thermodynamics (Kleidon, 2004). It is now accepted that the possession of an atmosphere far from thermodynamic equilibrium is a sign of widespread life on Earth.…”