Challenges to ecosystem management and some implications for science and policy

The ecosystems and biota we see today represent the evolution of life over a period of almost four billion years. Over the past several hundred million years the diversity of life has changed markedly as a result of evolutionary and other forces. Environmental fluctuations have led to changes in ecosystems and biota. Over the past 15 million years or so many regions of the planet have become more arid and this has led to changes in their constituent biota. As a result of changes in climate over the past two million years, glaciers have expanded and retreated a number of times. This has resulted in major expansions and contractions in the range of biota and ecosystems such as estuaries, forests and savannas. While these fluctuations have affected biological diversity, the rate of change has often been sufficiently gradual to allow organisms to adapt. They have, for example, been able to evolve, migrate and persist in refugia as a response to unfavourable conditions. While natural environmental changes and calamities have at times destroyed ecosystems and many organisms, populations of many species have survived and evolutionary processes have continued.