Biodiversity collapse causes extinction.

Civilization, and even the fate of our species, is utterly dependent on proper global ecosystem functioning. Ecosystem functioning, including primary productivity, the biogeochemical cycles, and the network of trophic mutualistic and antagonistic species interactions that compose the food chains, is the fabric of life—a fabric that is translated by humans as ecosystem services (e.g. [28,39]). The vast literature on the biodiversity–ecosystem function relationship and the significance thereof in terms of services to humanity has focused its attention on the consequences of changes in the diversity of (mostly) plant species or genetic variants on four major types of ecological processes: (i) provisioning, such as crop yield, fodder yield, wood production, medicines and medicine models; (ii) regulating, such as biocontrol, pollination and nutrient cycling; (iii) support services such as primary productivity; and (iv) cultural services, such as inspiration, and education (see a classic review in [40]; also [39]). Biodiversity–ecosystem function studies focused on animals are more limited, but some reviews make such relationship evident too, including services such as crop pollination and pest control, seed dispersal, litter decomposition, carbon cycling, carrion and dung removal, soil erosion control, animal forage provisioning, and zoonosis risk regulation (see reviews in [30,41]). What all this implies, in practical terms, is that the millions of years of plant and phytoplankton cumulative photosynthesis; the tens of millions of soil organisms that transform dirt into fertile soil, decompose the bodies of dead organisms and contribute to nutrient recycling; the wild and domesticated plants, animals (both terrestrial and aquatic) and fungi that for millennia have fed and currently feed the human population (i.e. we all eat biodiversity); the communities of animals that maintain plant reproduction and genetic diversity, as well as those animals that regulate the abundance of disease hosts and vectors; the thousands of plants, fungi, other microorganisms and animals that have provided and continue to provide medicine or medicine models; the physical protection due to ecosystem ‘structures’ such as mangroves and coral reefs from extreme weather events; and the increasingly appreciated significance of the inspirational, educational and emotional benefit derived from our contact with biodiversity constitute the life-support systems for humanity (see a recent review in [18]). In a different perspective, ecosystem services have been examined in economic terms (see a major review in [42]), and several researchers have attempted to calculate the value of nature's services in a variety of ways. Among these would be the cost of infrastructure that needs to be developed to substitute for the services of, for example, protective coastal ecosystems, and the price of water treatment plants that can play the role of wetlands in filtering contaminants [43]. Similarly, one estimate is that without mangroves flood damage in tropical coastal areas would increase by more than 16% or $US82 billion annually. However, we emphasize that the fundamental value of ecosystems in the intersection culture–ecosystem functioning lies in that the value of our life-supporting systems ‘is essentially incalculable’ [18]. This short review makes it evident that humanity cannot survive in the absence of biodiversity and ecosystem functioning, which, as we have discussed above, we are increasingly degrading. Furthermore, the prospect of Homo sapiens being present when the normal recovery times following a mass extinction occur is simply unrealistic. Finally, it is imperative to appreciate that all these aspects of human dependence on biodiversity—the intersection between human culture and ecosystem services—occur at the level of the populations of the myriad species and functional groups present where human populations are present. Therefore, it is crucial that we examine the impact of the human enterprise on the myriad populations of plants, animals, fungi and microorganisms.