Statistical mechanics of ecosystems

Although common ecologists' knowledge has been that the larger the
biodiversity of an
ecosystems the more stable it is, a result of Robert May in the beginning of
the 70s pointed
in the oposite direction. May studied the stability of randomly generated
ecosystems
and found that the larger the biodiversity the smaller the set of the stable
ones. For a
decade experimental data seemed to confirm this result. However, the
improvement
of these data and the appearance of assembly models threw away May's result
indicating
that the selection occurring while building the ecosystem leads to the
assembly of a
stable community resistant to invasions. In this work we propose a
simplified model
of an ecosystems that permits us to study the whole assembly process. Such a
process
generates a finite Markov chain containing all ecosystems connected through
invasion.
Studying the chain we prove that indeed the assembly process makes the
ecosystem
more and more resistant to invasions and drives it to an asymptotic robust
state.
Moreover, such an state is independent on the ecosystem history. In this
talk I will
describe the model and discuss its properties as well as possible extensions
and the
insight they will allow us to gain.
(http://ifisc.uib.es/~damia/JoseCuesta/assembly_model.ppt.gz)