Further thoughts on diversity and stability in ecosystems
Biodiv Sci. 2002, 10 (1):
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The idea that greater diversity leads to increased community stability has long been contentious as a result of lack of consensus over the meanings of both diversity and stability in empirical studies and unrealistic models of communities in theoretical studies. Diversity and stability can occur in each biological structure level in ecosystems. However, only species diversity and community stability were involved in most of previous studies, which might be another major reason that there is no consensus on the issue. This paper presents an exploration of the relationship between diversity and stability of community and population, attaching great importance to the biological structure level of ecosystems in which diversity and stability are examined. We conclude, firstly, that prior to investigation on the relationship between diversity and stability, the biological structural level of both diversity and stability should be clearly identified, and some terms with respect to both diversity and stability should be recognized, such as phenotypic diversity, population diversity, species diversity, community diversity as well as population stability, community stability, ecosystem stability, etc. Secondly, four major properties included under the concept of stability, i.e., resistance, resilience, persistence and temporal variability, all contribute to stability and yet may have very different relationships with diversity under different disturbance regimes. We redefine these properties of stability in terms of the characteristics of disturbances, dividing them into two types. Resistance and resilience are measurements of stability when ecosystems are disturbed by abnormal disturbances, such as fire, drought, grazing, attack by insects or diseases, invasion of exotic species, etc. Persistence and temporal variability are measurements of stability under normal environmental fluctuations. Thirdly, the dynamics of stability at a given level of ecosystem may be strongly influenced by the patterns of diversity within this level. For example, community stability may be favored by population diversity as well as phenotypic diversity, while population stability ultimately depends on phenotypic diversity. Finally, with the discussions of related issues on diversity and stability in both community and population, this paper holds that, under specific premises, diversity may give rise to stability. Additionally, an assembly interpretation model with respect to the long term debate over the issue on diversity and stability is proposed. We analogise diversity and stability as two assemblies, and three basic corresponding relations may exist among the elements between this two assemblies. The first two are efficient correspondence and inefficient correspondence. The former implies that diversity would lead to stability, the latter implies that it would not. The third relation is unknown correspondence. In this case, the properties underlying these corresponding relations are still unknown due to our limited knowledge. This simple model is promising to reconcile the long term dispute over the issue on diversity and stability.