Geology Reference
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introduced three herbivore species which, unlike Lovelock's earlier daisy-eaters, be-
haved more like real predators by largely ignoring rare prey and feeding mostly on the
commonest daisy species. I manipulated the complexity of my food webs by changing
the number of daisy species eaten by each herbivore. In the simplest food webs, each
daisy was assigned only one randomly selected herbivore out of the three as its predator,
whilst in the most complex food web each daisy was eaten by all three herbivores. The
stage was set for a Gaian exploration of the complexity-stability debate.
One dull winter's day whilst working at my computer at Schumacher College in
Devon, I programmed the most complex food web, and prevented the herbivores from
eating any daisies until almost a quarter of the way through the run as a control. With no
predation, the model rapidly settled into its usual stability with constant populations of
two dominant daisy species and constant global temperature. Then I set the herbivores
loose, and running amok as much as equations can, they followed their mathematical
destiny and decimated the two abundant daisy species, thereby opening up space for the
many other species previously present only as seeds in the rich soil. The herbivores had
abolished a floral tyranny of the minority, replacing it with a massive and permanent in-
crease in daisy diversity as species of all albedos flourished, each at a low but constant
abundance, with none overly dominant. The astonishing thing was that all of this had
virtually no effect on the planet's overall temperature that displayed itself as a stable flat
line on my computer screen, seemingly oblivious to the convulsions and upheavals go-
ing on amongst the populations of daisies and herbivores.
Then I programmed a low-complexity food web, in which each daisy species was
eaten only by a single randomly selected herbivore. As before, I began by holding
the herbivores in check and watched as two daisy species again reached high constant
abundances and as the global temperature reached a constant level. Then the herbivores
were set free. To my utter amazement, the stability vanished, replaced by wild rhyth-
mical oscillations of temperature, daisies and herbivores. These effects were repeated
for most solar luminosities and random connectance patterns. Tightly coupled feedbacks
between complex biological communities and the non-living environment had stabilised
both global climate and population dynamics in my model Gaian ecosystem
(Figure
dominant daisies and restored stability. Modelling such as this, combined with extens-
ive evidence from the field, supports Elton and MacArthur's early intuitions that more
complex communities are indeed, in general, more stable.
