Toward a Hierarchical View of Ecological Interactions

The controversy between J. P. Grime and D. Tilman about the meaning of plant competition (either as a strategy associated to the capacity for capturing resources when in abundant supply, or to the ability to have a low resource requirement when in short supply) has stimulated the development of various competition models. Even if there is not so far a general agreement in theoretical ecology about the mechanisms by which plants interact, the variety of models reflects the variety of processes involved. It turns out that competition cannot be fully understood by considering processes in isolation. In particular, the balance between negative and positive interactions among plants within communities has been challenged. Empirical evidence suggests that competition is perhaps not so important in explaining species coexistence and dominance, especially in stressful environments and species-rich communities, in which facilitation appears to be an important driving force.

Only complex models may allow relating plant competition with other processes, such as facilitation, dispersal, allocation of nutrients among and within plants, interactions with microbial communities, habitat fragmentation, herbivory, pulses of resource supply, and disturbances.

Composition, structure, diversity, species turnover, resilience, and invasibility are all emergent properties of plant communities, which cannot be explained without a hierarchical view of the system. Ecological communities are hierarchically structured, and emergence of entities or properties requires the interplay between different spatiotemporal organization levels, including bottom-up and top-down influences. Cellular automata (e.g., the self-assembling model of modular plants) have proved to simulate competition effect as a bottom-up emergence in a two-level system. However, the modeling of multilevel ecological hierarchies in a constructive way is still only a promising challenge.

See also: Cellular Automata; Competition and Behavior; Competition and Coexistence in Model Populations; Competition and Competition Models; Forest Models; Gause's Competitive Exclusion Principle; Grassland Models; Growth Constraints: Michaelis-Menten Equation and Liebig's Law; Growth Models; Individual-Based Models; Limiting Factors and Liebig's Principle; Metapopulation Models; Neutral Theory; Plant Growth Models; Population and Community Interactions.

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