Miriam at The Oyster’s Garter offered a nice discussion about fragile ecosystems and human intervention.   She uses Macquarie Island (located between Antarctica and Australia) as an example (based on an article in the New York Times).  She writes:

Like on many isolated islands, the native birds evolved without predators and live in burrows.  Introduced cats were eating the birds and running amuck. So researchers embarked on an intensive cat-elimination program…  The only problem is that there [were] also introduced rabbits and introduced plants. With no more cats, the rabbits bred like rabbits and ate all the native plants. Introduced plants took over the bare slopes and prevented the native birds that this was all supposed to help in the first place from nesting in the best burrowing sites. 

Human intervention, then, changed the landscape (before on the left, after on the right):

(Of course, human intervention had also shaped the landscape on the left. )

This before and after picture is useful for thinking about the interaction of humans with their environment, the way in which humans are part of ecosystems, and the difficulty of figuring out how to manage environments once we’ve taken on the role of custodian.

(Image from Discover magazine.)