Ecosystem Organization: Mutualism and Cybernetics or Plain Darwinian Struggle for Existence?

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Abstract
The ecosystem theories of the Odum school are based on the premise that the observed order in ecosystems is unlikely to arise by chance from Darwinian struggles for existence. However, Hairston et al. (1960; HSS) showed, a quarter of a century ago, that such emergence of order from exploitative interactions guided by short-term maximization of individual fitness, is not at all unlikely. The originmal HSS hypothesis conflicts with well-documented cases of resource limitation in herbivorous populations and with the recurring strong impacts exerted by these populations on the vegetation. However, this conflict is only apparent. HSS explained why the world is green and why there can be an abundance of forage that is not consumed. This observation does not refer to steppe and tundra environments, which are green for only a few weeks and where there is an obvious shortage of forage during the unfavorable season. The limitation of grazers by resource depletion in such environments and the strong impacts of herbivory on the vegetation are, in fact, straightforward consequences of the exploitation view in HSS, applied to relatively unproductive ecosystems. The same reasoning, applied to still more barren environments, predicts that these should be passively harsh (in the sense of White 1978), with grazers being limited by resource shortage but having only marginal impact on the vegetation. This extension of the logic in HSS, preliminarily proposed by Fretwell (1977) and formally analyzed later (Oksanensen et al. 1981), creates predictions that are in good agreement with the results of competition experiments and grazer-exclosure experiments and with the aberrant vegetation of grazer-free islands in cold regions.