This is an advance summary of a forthcoming article in the Oxford Research Encyclopedia of Environmental Science. Please check back later for the full article.
Ever since the expansion of early humans across the planet, biodiversity has been impacted by our activities, although the scales of biodiversity impact and primary mechanisms of action have changed over time.
Biodiversity is defined here as variation among living organisms, both within and between species. It is maintained by a balance between processes that generate variation and those that cause its loss. A concern for modern humans is that our activities are driving rapid losses of biodiversity, which outweigh by orders of magnitude the processes of biodiversity generation. The net biodiversity losses could have significant impacts on human wellbeing in both current and future generations.
Within species, biodiversity is reflected in genetic, and consequent phenotypic (e.g. morphological), variation between individuals. Genetic diversity is generated by germ line mutations, genetic recombination during sexual reproduction, and immigration of new genotypes into a population. Across species, biodiversity is reflected in the numbers of different species present and also, by some metrics, in the evenness of their relative abundances. At this level, biodiversity is generated by processes of speciation and by immigration of new species into an area.
In terms of biodiversity losses, there are processes that cause roughly continuous low-level losses, but there is also strong evidence from fossil records for transient events, in which exceptionally large losses of biodiversity have occurred. These major extinction episodes are thought to have been caused by various large-scale environmental perturbations such as volcanic eruptions, sea level falls, climatic changes, and asteroid impacts. From all these events, biodiversity has shown recovery over subsequent calmer periods, although the composition of higher level evolutionary taxa can by altered significantly.
In the modern period, biodiversity appears to be undergoing another mass extinction event, driven by large-scale human impacts. The primary mechanism of biodiversity loss caused by humans has changed over time. Even in the Pleistocene, early humans were thought to be partly responsible for species extinctions through hunting of large megafauna, and such exploitation continues into the present era. In addition, clearing of land for human agriculture and urbanization has been a major factor in driving biodiversity losses through loss of species’ habitats. Increasingly, additional pressures such as invasive species and climate change have the potential to cause biodiversity losses. It is worth noting that human activities may also lead to increases in biodiversity in some areas through species introductions and climatic changes (e.g. particularly Arctic areas), although these overall increases in species richness may come at the cost of loss of native species.
These changes to biodiversity, comprising in many cases the overall loss of genetic diversity and species richness at a local level, have the potential to have substantial impacts on human wellbeing. A wide range of species may be necessary for the provision of ecosystem services such as pollination, pest control, and decomposition. The importance of biodiversity becomes particularly marked, however, over longer time periods and, in particular, under varying environmental conditions. Here, biodiversity (both genetic and species-level diversity) provide resilience of ecosystem services. Limiting losses of biodiversity is likely to be important for maintaining the wellbeing of humans in current and future generations.