How much, or rather how little, redundancy can we afford to lose without pushing the system to the edge of some irreversible and catastrophic change? This is the central question evaluated in this article. Giulio A. De Leo and Simon Levin article looks at the different aspects one must explore to value ecosystem integrity and health. To evaluate ecosystems health and integrity one must look at "links among biodiversity, ecosystem functioning, and resilience; and to stress and distinguish the effects of natural and anthropogenic disturbance" according to De Leo and Levin. .
The authors" state instead of focusing on a single species we should take a holistic look at ecosystems. De Leo and Levin use an example of the American chestnut and how the introduction of blight eliminated it from the North American forest. Once the chestnuts were wiped out another species took its place in the canopy and the forest did not experience any significant productivity change. De Leo and Levin argue that the loss of diversity weakens the forest to adapt to catastrophic changes on longer time scales. This is one aspect of ecosystems integrity. They are stating that many aspects should be taken into consideration when managing ecosystems. .
Some other aspects that managers must take into consideration when evaluating ecosystems integrity are keystone species and functional groups. De Leo and Levin say that more attention should be paid to groups of species (guilds) rather than individual species. They stress that "the loss of species within a guild may reduce the long-term resilience properties of the system, and may lead to noticeable change in short-term system dynamics." We must look ahead and ask the question: What effect will this have on the ecosystem in 50 or 100 years? .
Another feature to evaluating ecosystems integrity is the role of ecological redundancy. Ecological redundancy is fundamental in maintaining an ecosystem's ability to withstand stress and catastrophe.