Extinction cascades

Current species extinction rates are at unprecedentedly high levels. While human activities can be the direct cause of some extinctions, it is becoming increasingly clear that species extinctions themselves can be the cause of further extinctions, since species affect each other through the network of ecological interactions among them. There is concern that the simplification of ecosystems, due to the loss of species and ecological interactions, increases their vulnerability to such secondary extinctions. It is predicted that more complex food webs will be less vulnerable to secondary extinctions due to greater trophic redundancy that can buffer against the effects of species loss.

In other words more complex food webs are likely less vulnerable to extinction cascades because there is a greater chance that other species can step in and buffer against the effects of species loss. Researchers from the University of Exeter used communities of plants and insects to experimentally test this prediction. The removal of a parasitoid wasp species led to secondary extinctions of other, indirectly linked, species at the same trophic level. This effect was much stronger in simple communities than for the same species within a more complex food web. 

The study results demonstrate that biodiversity loss can increase the vulnerability of ecosystems to secondary extinctions which, when they occur, can then lead to further simplification causing run-away extinction cascades. 

In case you want to read and learn more about the interesting discussions relating to extinction cascades I recommend a blog post that I found particularly helpful. Another good source of information is - in case you have access to TREE - a review article (the figure to this post I took from this article).