Friday, February 03, 2012

Resolving Ecosystem Complexity

Dr. Os Schmitz wrote Resolving Ecosystem Complexity with the aim not of solving the entire nexus of ecological problems, but of trying to disentangle the Gordian Knot. The book slices through ecology from individual behavioral tradeoffs to ecosystem nutrient cycling rates. Individuals must balance tradeoffs between eating and being eaten, so that behavioral responses to predators ripple through an ecosystem to change overall species evenness and NPP.

Schmitz first lays out a distinction between ecosystems that are absolutely resource limited and those that are relatively resource limited, citing the work of Andrewartha and Browning (1961) as well as implicating stress-gradient theories used in biogeographic studies. If herbivores are absolutely limited by the availability of resources (time, food) then a unit reduction in their numbers will not have an effect on plants because another individual will simply step in to take the place of the missing individual. On the other hand, if herbivores are relatively limited, they could eat quite a lot more if predation pressure were decreased.

Schmitz insists on treating ecosystems as (at minimum) three-level systems, because every level is limited by the availability of nutrients in the level below it and the risk of predation from the level above. Schmitz does not limit his treatment to traditional community trophic interactions however, because his individual-focussed approach shows that individual behavioral responses can be as important as population changes.

For example, when herbivores alter their behavior (phenotypic plasticity)(link to evolutionary ecology) in environments with predators, different plants can grow and different ecosystem structures can develop. He calls this the Landscape of Fear theory.

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