Time lags in ecological systems.

Abstract A model representing ten species in a four trophic level community is constructed by using Volterra's equations including time lags, and is solved numerically for some values of the parameters. Classical discrete and continuous time lags yield similar results; simulating with discrete time lags thus appears useful. Parasitic versus predatory structures are compared by measuring the amplitudes of oscillations and the time taken to settle down to equilibrium, and give the following qualitative conclusions for the model. An increase in the carrying capacity of a trophic level increases the destabilizing influence of time lag in that level, this increase is more marked in predatory structures. Time lags appear to cause more violent oscillations in species strongly linked to a predatory system than in weakly linked species. The oscillatory period increases in predatory systems as the time lag is moved to higher levels, while it decreases in parasitic systems.

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