Geology Reference
In-Depth Information
of solar energy by increasing their cover of what little bare soil remains. But under a
very bright sun, with no more bare soil available, a small increase in solar energy extin-
guishes life with sudden rapidity. A similar event takes place in more complex versions
of the model in which daisies occupy a three-dimensional, spherical planet. It seems that
small disturbances at critical moments in the life of a self-regulating system can trigger
unexpected and sudden shifts into totally new system configurations. Could it be that
just an extra increment of pollution or habitat destruction could trigger an equally dra-
matic shift towards a new and potentially inhospitable climatic regime on our real Earth?
Lovelock's next move with Daisyworld was to run the model with many daisy spe-
cies, each with a slightly different albedo on a scale of almost pure black to pure white.
Once again, the model regulated temperature beautifully. When he added rabbits that ate
daisies and foxes that ate rabbits he expected to see wild fluctuations of temperature,
but to his immense surprise he found that this more ecologically complex world was re-
markably stable. My own work on Daisyworld, conducted with Lovelock as a guide and
mentor, involved using the model to explore the vexed question in ecology of wheth-
er more complex ecological communities— those with more species and more inter-
connections between species—are better able to recover from disturbances than simple
communities. This area of ecology, known as the 'complexity-stability debate', has been
of central concern to ecologists since the 1950s, when the pioneer ecologists Charles
Elton and Robert MacArthur suggested that more complex communities should be more
stable. Their reasoning was based on various lines of evidence, including the fact that is-
lands with fewer species seemed to be more vulnerable to invading species than species-
rich continental areas, that crop monocultures are more vulnerable to pest outbreaks, and
the apparent lack of insect outbreaks in species-rich tropical communities compared to
boreal and temperate communities.
This was the accepted wisdom for many years, until the Australian theoretical ecolo-
gist Robert May published the first mathematical analysis of this problem. May turned
Elton and MacArthur's insights, and the whole of scientific ecology, inside out by show-
ing that more complex communities were far more likely to collapse than simple ones.
Further modelling by May's successors did little to overturn these counter-intuitive res-
ults, and the controversy raged for about thirty years. Early on in my work on Daisy-
world I realised that it provided an interesting template for exploring this issue for the
simple reason that no one in the whole 60-year history of theoretical population eco-
logy had attempted to address the complexity-stability debate by modelling the feed-
backs between life and its non-living environment along the lines that Lovelock had de-
veloped.
With Lovelock's help, I created a new version of Daisyworld populated by 23 daisy
species along a gradually increasing gradient of albedo, from light to dark, and then
