The Influence of Environmental Gradients on Ecosystem Stability

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Abstract
The dynamic behavior of ecosystems with spatially varying species characteristics may differ substantially from that of uniform systems with the same mix of species. If system behavior is to be correctly assessed, the spatial complexity must be treated in sufficient detail to account for the contribution of each significantly different part of the system to overall response. Systems along environmental gradients, one of the most common types of spatial heterogeneity, were evaluated in terms of the linear stability formalism. The more rapidly a perturbed system returns to equilibrium the more stable it is, and a normalized system time constant was developed as a measure of the dynamic properties which aid species in their persistence. This index of relative stability based on log-phase dynamics was strongly correlated with the behavior of a variety of systems. Diffusion equations [models] provide a useful representation of the ecosystem characteristics, especially system size, dispersal of seeds, symmetric and asymmetric distributions of growth and mortality. System stability depends not only on the nature of the parameters but also on the direction of the disturbance. Stability varies either directly or conversely with net productivity depending on whether the perturbation is negative or positive. Parameters related to productivity, including growth rate, mortality, system size, reproductivity and seed dispersal, and gradient steepness and curvature are discussed. Succession and competition are examined in plant and animal populations.