On Biodiversity There are two kinds of biodiversity: Functional diversity: the different functional groups of organisms that are represented in a system. Response diversity: the range of different response types available within a functional group. Biodiversity matters because: 1. Biodiversity affects the health of an ecosystem. When some of the functional species are missing, an ecosystem can experience an undesired regime transition. For example, the Caribbean reefs and the Great Barrier reefs along the east coast of Australia are in different health conditions although both have subjected to overfishing by humans.  In the Caribbean, several functional groups of coral are missing or represented by only a handful of species, which leads to the decline of hard corals and the dominance of fleshy seaweed. Compared with the Caribbean reefs, the Great Barrier reefs had a relatively rich suit of species to begin with and are in better condition. 2. Biodiversity affects the resilience of an ecosystem. When the range of different response types is larger, the service provided by a functional group is likely to be sustained over a wider range of conditions, and the system has a greater capacity to absorb disturbances, which happen from time to time in all ecosystems. Intuitively, the more species in an ecosystem, the higher the chance that some of them will survive disturbances. 3. Biodiversity affects the services that an ecosystem offers to humans. For instance, if the Great Lakes were dominated by Asian Carps, it would provide much less values to human lives than thriving with all kinds of fish. 4.   Biodiversity is important for aesthetics. The world is definitely more interesting for humans with more species. 5.  Biodiversity may affect the productivity of an ecosystem. More species are likely to increase the primary production of an ecosystem due to the complementary functions of the species and more effective utilization of lights and nutrients. In summary, biodiversity matters because it plays an important role in the functioning of an ecosystem, and we humans reply heavily on the functioning of an ecosystem. If an ecosystem crashes or transits to a different regime, it can no more provide the services people need, and we will be in great trouble. Therefore, the research of biodiversity is important. The more so, because we are dramatically reducing biodiversity. However, the current focus of biodiversity research on the relationship between the richness of plant species and primary productivity in short term is of less importance although relevant, not to say that they are also flawed. It is more meaningful to study the functions of the species in the system and understand the interactions and interdependences between them. Then, we can know better how species loss can affect the functioning of the system, and whether it will lead to crash or regime transition of the ecosystem in the long run. Instead of measuring some properties of the ecosystem and plotting their relationships with the number of species, a system approach will be more useful. Along with empirical studies, theoretical research and modeling with a focus on long term functioning of ecosystems can make a contribution.
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