Biodiversity has “intrinsic value” – or value for its own sake – but it also has significant value in all cultures for the things that it provides: food, medicine, building and craft materials and spiritual, cultural and aesthetic services. Less obvious, but just as important, are the services that allow natural and human-altered ecosystems (such as agricultural and urban landscapes) to function properly – regulating the climate, soil fertility, and the outbreak of pests and diseases. Some level of biodiversity – the exact amount is at this stage unknown – is a necessary condition for the delivery of ecosystem services, but it is especially important for maintaining functional ecosystems. The value of ecosystem services can sometimes be expressed in monetary terms but these estimates are very contentious, and are not the only way of expressing importance. Value can, for instance, be measured in terms of other aspects of human well-being, such as health, security or good social relations.
Ecosystem services depend not so much on the absolute number of species present, but on the diversity of the functions performed by different members of the ecological community. The preservation of the natural biodiversity of an area and genetic diversity of crop species can enhance resistance to invasion by pests and diseases thus reducing agricultural losses. Planting a variety of crop species and varieties, and preserving their wild relatives, increases crop resistance to pests and diseases and thus the probability of meeting food needs. Ethiopia and the Upper Nile are recognized as global centres of crop plant genetic diversity. Agro-biodiversity farming practices can enhance biological control and reduce the dependency and costs associated with biocides in monocropping systems. Similarly, natural and semi-natural ecosystems, both terrestrial and marine, appear to be more resistant to IAS if the number, types and relative abundance of native species are preserved.
Biodiversity can provide pollution detoxification and control. Certain aquatic and marine organisms provide water filtration services that significantly reduce the impacts of pollution on water quality. For example, the hydrological processes in wetlands, and particularly the slowing down of water-flow by vegetation and the creation of anaerobic zones, bring about the deposition of heavy metals from streams and rivers, reduction in nitrogen loading through denitrification, and reduction of pathogens through predation by other microorganisms. Well-vegetated watersheds significantly reduce the volume of sediment flowing down rivers. Protecting the ecosystems and organisms that provide such services is generally far more cost-effective than the alternative of building and operating water filtration plants. In the context of the oceans, some marine microbes can degrade toxic hydrocarbons such as those released in an oil spill, providing valuable pollution processing services.
Ecosystem biodiversity – both terrestrial and marine – influences climate at local, regional and global scales. The type and distribution of habitats and the functional diversity of terrestrial plants influence the reflection of incoming radiation from the sun back to space, evapotranspiration, air temperature, fire regime and carbon sequestration, all of which influence climate. It has been suggested that human-induced changes to the vegetation in the semi-arid Sahel has contributed to decreased precipitation since the 1970s and to desertification. Marine biodiversity plays a major role in climate regulation, particularly through its effects on nitrogen cycling and carbon sequestration. If there were no life in the ocean, transfer of carbon dioxide from the atmosphere to the sea floor would cease, and atmospheric carbon dioxide levels would rise.
Recreational and spiritual values
People of all cultures and income levels value the cultural, spiritual, religious, educational and aesthetic benefits of biodiversity . Traditional societies express these values in the form of sacred species, ecosystems and landscapes, while urban and developed societies express this in the form of protected areas and heritage sites. Many religions attach spiritual values to ecosystems or components of ecosystems, such as trees, hills, rivers or groves. Loss or damage to ecosystems can therefore harm social relations by, for example, impeding religious and social ceremonies that bind people. Biodiversity also has intrinsic value for many people: it is valued as an end in itself, apart from any use value that it provides to people.