How well have we made use of what islands have to offer? In understanding patterns and controls of biological diversity, we have made substantia! progress. Research has moved from an early focus on cataloging and on biological oddities (the "dodo approach" described by Adsersen (1995)), through the development of dynamic approaches such as island biogeo-graphy, towards analytical and experimental approaches to understanding the pattern and nature of island diversity (Eliasson 1995, Footc 1995, Roughgarden 1995). At the same time, research has broadened from primarily species-level work to encompass biological diversity at the population and landscape scales as well (Kaneshiro 1995, Vitousek and Benning 1995), and to begin the effort to integrate our understanding across levels of organization. We are not far enough advanced in using the unique attributes of islands to understand ecosystem function, but with the recognition that certain types of islands (volcanic archipelagoes, coral atolls) offer an extraordinarily straightforward geochcmical background to ecosystem studies, we are beginning to make progress. However, in addressing the major concern of this paper - How do we evaluate the influence of biological diversity at the population and species level on whole-ecosystem function? - we have a long way to go.
We can think of interactions between diversity and ecosystem function in a number of ways, for which the following questions are important:
1. Does biological diversity affect the functioning of ecosystems when they are at or near steady state, in that under constant conditions highly diverse systems are more productive, retain more nutrients, etc., than less diverse systems?
2. Does biological diversity affect the response of ecosystems to environmental fluctuations or perturbations, such that highly diverse ecosystems are more resistant to change, or recover more rapidly following change, than less diverse ecosystems? 3. Does biological diversity affect rates of biological invasion or extinction, and do these in turn affect ecosystem structure and function? Note that we do not mean local invasion and extinction in terms of equilibrium island biogeography, but rather human-caused introductions from outside the regional biota, and global extinctions.
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