The self-organization of trophic structure in ecosystem models: the succession phenomena, trigger regimes and hysteresis

The self-organization of trophic structure in ecosystems during the course of biogenic succession was analyzed using the dynamic ecosystem model with two competing food webs of the type ‘producer–consumer–top predator’. Variants of the model with feeding-specialized and mixed-feeding consumers were considered. The ecosystem development was limited by one biogenic element, recycling in the system, with the total reserve of element MΣ. The biogenic succession was simulated by a slow increase of MΣ from zero to higher values, and after that by a gradual decrease back to zero. The different trophic structures, formed from the initial set of species were analyzed, and analytical conditions of their existence and stability were obtained. The total pool of element MΣ was found to be the key parameter, determining the development of food webs. It was shown analytically that each particular trophic structure, formed from an initial set of species exists and is stable within a strictly defined range of MΣ values; following the gradual increase of MΣ, trophic structures replace each other, thus forming succession series. In the ecosystem model with feeding-specialized consumers, the gradual development of trophic organization from primitive ‘one-species’ structure to the most complicated food webs was demonstrated, and two possible variants of succession series were revealed. In the system with mixed-feeding consumers more than 10 different variants of succession series were found, depending on the ecological parameters of the species. Specific trigger regimes were found, when two different trophic structures existed and were stable within one and the same range of parameters; the actual realization of a particular trophic structure was completely determined by initial values of biomasses of species. For succession series, which contained trigger regimes, a hysteresis phenomena was demonstrated: the successive changes in the trophic structures realized following the gradual increase of MΣ were not reproduced in the same order if MΣ was gradually decreased back to its previous values.