PARENT SESSION
Oral Session #77: Biodiversity and Ecosystem Function II.
Presiding: G. Chong
Thursday, August 8. 9:00 AM to 11:30 AM. Coconino Meeting Room, TCC.

Parsing complexity in the complexity - stability debate.

Puth, Linda^*,1, ¹ University of Wisconsin, Madison, WI

ABSTRACT- Despite the mass of research exploring the effects of complexity on community and ecosystem stability, there is little consensus on the magnitude or direction of these effects. Much of this confusion stems from disparity in the meaning of the terms complexity and stability. While dividing the general term stability into resistance and resilience has rendered it more precise, an analogous treatment of complexity has yet to occur. Here, I parse complexity into two fundamentally distinct components and test the effects of changing each in an experimental setting. Complicatedness is elaboration at a single hierarchical level, and hierarchical organization is elaboration of hierarchical levels. An example of complicatedness is species number in the same trophic level, while an example of hierarchical organization is number of trophic levels in a food web. I created artificial communities composed of eleven species of green algae and perturbed them with two different types of species additions. The addition of green algae served as the complicatedness treatment, the addition of Daphnia pulex served as the hierarchical organization treatment, and the addition of both tested interaction effects. Repeated measures ANOVA showed that changing hierarchical organization had significant effects on primary producer biomass, ammonium, soluble reactive phosphorus and total nitrogen, while changing complicatedness had significant impacts only on Shannon-Wiener diversity. These results suggest that reducing the complexity-stability debate to the diversity-stability debate may be an unwarranted simplification.

KEY WORDS: complexity, stability, complicatedness, hierarchical organization