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In nature, larger species assembly appears more stable, while May's
random-assembly model proves the opposite is true. This study
experimentally tests whether addition of a species stabilizes
host-parasitoid laboratory systems. As a measure for stability of the
systems, dominant Lyapunov exponents (LEs) were estimated by fitting
nonmechanistic (LENNS model, incorporating neural networks) and mechanistic
nonlinear models to the population dynamics data. Both approaches showed
that addition of the parasitoid, Heterospilus prosopidis, increased the LEs
to be slightly positive values, indicating the species addition
destabilized the system to become chaotic. Sensitivity analysis further
revealed that the high searching efficiency and short handling time of the
parasitoid primarily contributed to the destabilization. When the other
parasitoid species was added to a host-Heterospilus system, the system was
stabilized, or LEs decreased. The two contrasting results indicate that it is not the number of species that determines the stability of species assembly but the identity of the species to add to. The data analyzed in the present study were provided by Drs. S. Utida and M. Shimada. |