Goal functions in ecosystem and biosphere evolution

Although natural selection operates at the gene or individual level, a number of proposals, hypotheses and theories exist postulating the evolution of entities such as ecosystems, and indeed the entire biosphere. Further, there exist theories of evolution that are based not on the relative advantages (be they competitive or mutualistic) conferred on individuals, populations, or taxa, but on community, ecosystem, or biosphere-level goal functions, typically related to productivity criteria. A key question is why nature would seek to optimize energy flux or efficiency, biogeochemical cycling, or anything else. While development along some optimal pathway does occur, whether this is a rule, a tendency, or merely a possibility is not clear. This paper reviews theories of evolution and ecosystem development based explicitly or implicitly on goal functions. If the environment is conceptualized as a multidimensional resource space allocated among organisms, then only three assumptions are necessary for a developmental pathway toward increasing productivity: (1) higher rates of resource procurement and use are associated with ecological or selective advantages; (2) the environment is biologically saturated (or tending in that direction); and (3) the resource space is not contracting due to external abiotic forcings. This suggests that a tendency for evolution along a pathway toward maximum energy and/more matter fluxes, storages, transformations, or cycling does not require goal functions or natural selection operating at levels beyond the individual. Key research needs involve rigorous testing of these assumptions (particularly the first two), and the relative importance of, and relationships between, various notions of productivity.