Terrestrial Species

Declining biodiversity is a major environmental problem everywhere on Earth, including developed regions such as Western Europe and the USA. European leaders have recognized this and set the target of halting biodiversity loss by 2010, under the EU Strategy for Sustainable Development that was adopted by the European Council in 2001. World leaders agreed upon a substantially less ambitious goal at the 2002 World Summit on Sustainable Development in Johannesburg, South Africa: to significantly reduce the current rate of biodiversity loss by 2010. The practical challenge for both goals is to measure the rate of change in biodiversity, to determine whether the decline is slowing or has stopped. This relates to the task of defining, in operational terms, what biodiversity is. The causes of biodiversity decline must be understood in order to devise effective countermeasures. None of this can take place without the participation of society at large, who have to be convinced about the importance of biodiversity if there is to be any real hope of implementing meaningful measures. So what is biodiversity? The cynical answer is: everything that is good in nature. This captures the point that biodiversity is not a simple concept, has never been since its conception (Wilson & Peter, 1988), and never will be. The official definition is: “The variability among living organisms from all sources, including, inter alia, terrestrial, marine and other aquatic ecosystems and the ecological complexes of which they are part; this includes diversity within species, between species and of ecosystems” (Convention on Biological Diversity, 1992). My personal interpretation is that there is no biodiversity loss in a particular landscape when there is no obvious decline in the abundances of large numbers of species living in that landscape. This is based on the observation that a range of species with diverse ecological requirements accurately reflects the state of the environment. It acknowledges that population sizes fluctuate for natural reasons, but in the absence of great environmental changes, entire communities of species would not be expected to exhibit a trend towards lower abundances, ultimately leading to regional, national and global extinctions. This notion of biodiversity loss simplifies the issue by focusing on population sizes, but as every biologist knows, viable populations cannot be maintained without a sufficient habitat— and their habitat is not sufficient if habitat loss and fragmentation are the primary cause of biodiversity decline. On the other hand, an abundance of species in a certain landscape or habitat does not necessarily indicate that there is no threat to biodiversity; many of these species may already be threatened if their environment is insufficient to maintain their numbers and diversity in the long term.