Regarding invasibility (factors that determine
the susceptibility of an ecosystem to invasion), evidence from many
studies, including palaeoecology, modern observationalstudies and
experimental work at different scales (mainly small plots) shows
that susceptibility/resistance of systems to invasion fluctuates
markedly over time and space due to changing climatic conditions,
disturbance, nutrients, availability of mutualists, and the
availability and abundance of propagules to initiate and sustain
invasions. Invasibility must thus be considered probabilistically
rather than deterministically. Even areas currently thought to be
resistant to invasion will probably be invaded as increased
propagule pressure and elements of global change alter key
processes in the system. A related aspect is the link between
native species richness in a system and its capacity to accept new
invaders.
Below-ground biodiversity and its role in
maintaining ecosystem functioning and integrity, is a new field of
research.
There is growing evidence that invading mplant
species alter this diversity and may affect ecosystem functioning
and resource pools in ways that are not well understood.