Abstract/Summary

Human activities in the Anthropocene are influencing the twin processes of biodiversity generation and loss in complex ways that threaten the maintenance of biodiversity levels which underpin human well-being. Yet, many scientists and practitioners still present a simplistic view of biodiversity as a static stock, rather than determined by a dynamic interplay of feedback processes that are affected by anthropogenic drivers. Biodiversity describes the variety of life on earth, from the genes within an organism, to ecosystem level. However, this article focusses on variation amongst living organisms, both within- and between- species. Within species, biodiversity is reflected in genetic, and consequent phenotypic variation between individuals. Genetic diversity is generated by germ line mutations, genetic recombination during sexual reproduction and immigration of new genotypes into populations. 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 immigration of new species into an area. Anthropogenic drivers affect all these biodiversity generation processes, whilst the levels of genetic diversity can also feedback and affect the level of species diversity, and vice versa. Therefore, biodiversity maintenance is a complex balance of processes and the biodiversity levels at any point in time may not be at equilibrium. A major concern for humans is that our activities are driving rapid losses of biodiversity, which outweigh by orders of magnitude the processes of biodiversity generation. A wide range of species and genetic diversity could be necessary for the provision of ecosystem functions and services (for definition see Braat 2016); for example in maintaining the nutrient cycling, plant productivity, pollination and pest control that underpin crop production. The importance of biodiversity becomes particularly marked over longer time periods and in particular under varying environmental conditions. In terms of biodiversity losses, there are natural 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 be significantly altered. In the modern era, biodiversity appears to be undergoing another mass extinction event, driven by large-scale human impacts. The primary mechanisms of biodiversity loss caused by humans vary over time and by geographic region but include: overexploitation, habitat loss, climate change, pollution (e.g. nitrogen deposition) and the introduction of non-native species. It is worth noting that human activities may also lead to increases in biodiversity in some areas through species introductions and climatic changes, although these overall increases in species richness may come at the cost of loss of native species and with uncertain effects on ecosystem service delivery. Genetic diversity is also affected by human activities, with many examples of erosion of diversity through crop and livestock breeding or through the decline in abundance of wild species populations. Significant future challenges are to develop better ways to monitor both the drivers of biodiversity loss and biodiversity levels themselves, making use of new technologies, and improving coverage across geographic regions and taxonomic scope. Rather than treating biodiversity as a simple stock at equilibrium, developing a deeper understanding of the complex interactions— between environmental drivers, and between genetic and species diversity — is essential to manage and maintain the benefits that biodiversity delivers to humans, and to safeguard the intrinsic value of the Earth’s biodiversity for future generations.