Jason,
There are few things qualitatively different about any dispersal agent.
But, considering the impact and abundance of humans and their dispersal
agents these days, there is a quantitative difference. Also, there is a
qualitative difference at least in one respect. Dispersal is an evolved
trait (at least modified by evolution) while human-mediated dispersal
can disperse organisms that did not evolve to be good dispersers.
Thus, between the quantitative difference (increased dispersal rates,
greater dispersal distances due to humans) and the qualitative
difference (dispersal of comparatively "poor" dispersers due to humans),
the combined effects ONLY means a greater rate of introductions, often
of species that would never have dispersed by any other means, than ever
in the history of the planet.
But, besides that, there is no difference between dispersal agents and
events.
Cheers,
Jim
Jason Hernandez wrote on 11-May-10 21:48:
What, then, is the ecological difference between humans as a dispersal agent, and,
say, seabirds as a dispersal agent? When we study Hawaiian native plants, are we
not studying "how natural selection influenced organisms after their
introduction, or as a consequence of
the introduction of other species"? The system is still one of an organism having been
brought to some isolated location to which it could not otherwise have gotten on its own. The
whole study of island biodiversity is inherently the study of introductions of
"alien" species by various means, except in the case of continental islands formerly
connected to the mainland.
Jason Hernandez
East Carolina University
