  A detailed analysis of three species-rich ecosystem food webs has shown that
they display scale-free distributions of connections. Such graphs of
interaction are in fact shared by a number of biological and technological
networks, which have been shown to display a very high homeostasis against
random removals of nodes. Here we analyse the response of these ecological
graphs to both random and selective perturbations (directed to most connected
species). Our results suggest that ecological networks are extremely robust
against random removal but very fragile when selective attacks are used. These
observations can have important consequences for biodiversity dynamics and
conservation issues, current estimations of extinction rates and the relevance
and definition of keystone species.
