http://www.bioone.org/perlserv/?request=get-document&doi=10.1666%2F05008.1#I0094-8373-32-1-1-F01

Species extinction is a big topic of discussion these days. Whether global warming, habitat destruction, or other various sources are being pinned as the culprits, loss of biodiversity is indeed a serious issue that we are facing. However, what are the mechanisms driving this extinction cascade once a disturbance occurs and how do ecosystem parameters contribute to profiles of extinction throughout a food chain? The cited article attempts to create a testable model of species extinction in mass extinction events, using species richness, functional diversity, and trophic link distributions as parameters. Of course, defining these aspects in an ecosystem is a tough task in itself. Recent blog posts have cited papers addressing the issue of how interconnected some food chains actually are by defining mean distance between nodes.

Most mass extinctions do not involve direct destruction of species, but instead a bottom-up cascade of secondary extinctions as primary production is disrupted. However, one’s initial instinct to carry a linear relationship through the food chain through cause and effect relationships is not completely accurate. Assuming reasonable behavior, one would expect consumers to alter their interactions with remaining prey groups. In the presence of these conditions, which indeed is included in the model, there is a secondary, top-down stress on mid-level prey taxa. This can be easily seen in that if a predator feeds off a variety of prey, and one of the prey groups is reduced in number, the other groups increasingly become a source of food.

This model demonstrates that is impossible to know how a disturbance in primary production can effect a particular species without a nearly complete knowledge of their place in the food network. Species diversity, one would assume, would increase the stability of the system and its ability to hold up against mass extinction simply due to the fact that potential changes and concentration of food sources has less of an effect on each group if there are more of them. Thus, current species loss, especially at the extremely high levels witnessed in today’s world, serves not only to directly destroy current ecosystems, but make them much more vulnerable to potentially catastrophic disturbances.