From Robert D. Holt, in the latest issue of Nature (a ten year perspective exercise into some major science area by leading scientist)*:
The greatest practical challenge facing ecologists over the next decade is that much of what we wish to study may vanish before we can really fathom it. The planet is increasingly dominated by ersatz ecosystems — human-sculpted landscapes occupied by haphazard assemblies of introduced species and tolerant natives. These are legitimate objects of study, but there are considerable practical, aesthetic and moral costs of losing natural ecosystems before we can even fully document and understand them.
*Nature 463, 26-32 (7 January 2010) doi:10.1038/463026a;