Correlation among Stabilities and their Causes in Modeled Ecological Communities

Abstract:

The relationship between the complexity and stability of ecological systems has long been a focus of theoretical ecology. As the concepts of complexity and stability have been enriched and extended, the debate over the relationship between complexity and stability has also continued. One recent and important development was the incorporation of interaction types as an important factor; another has been the recognition that ecological stability can be defined in different ways, and the connection between these has been a focus of recent effort.

We establish a general dynamic model for hybrid ecological communities, based on an intuitive concept of consumer-resource interaction (a fundamental aspect of ecological communities). Different interaction types such as antagonism and mutualism, emerge naturally according to the choice of consumer-side and resource-side conversion rates (two important parameters of the consumer-resource interaction). The general consumer-resource dynamic model also involves the ‘handling time’ of resource species by consumer species, which provides a nonlinear functional response among species. We define three different aspects of ecosystem stability for comparison: ‘persistence’ as the fraction of surviving species at equilibrium, ‘resilience’ as the rate at which the system returns to equilibrium after a small pulse perturbation, and ‘fragility’ as the probability of sudden shifts as continuous external pressures are applied.

We found explicit correlations among fragility, persistence and resilience conditioned by interaction types and strengths, and the handling time:
(i) while increasing the strength and proportion of mutualistic interactions leads to a sharp (step-like) increase of fragility, it also results in more persistent and resilient communities (and vise versa); (ii) Increases in the handling time of species has a negative overall effect on fragility but a positive effect on persistence; these relationships are weakened with decreasing strength and proportion of mutualistic interactions.

Finally, we have used multi-objective optimization to compute the optimized proportion of interaction types, values of interaction strengths and handling times which results in optimized stability, as a trade-off between fragility, persistence and resilience.