Natural biodiversity loss
Biodiversity Loss
By John P. Rafferty
Biodiversity, or biological diversity, is a term that refers to the number of genes, species, individual organisms within a given species, and biological communities within a defined geographic area, ranging from the smallest ecosystem to the global biosphere. (A biological community is an interacting group of various species in a common location.) Likewise, biodiversity loss describes the decline in the number, genetic variability, and variety of species, and the biological communities in a given area. This loss in the variety of life can lead to a breakdown in the functioning of the ecosystem where decline has happened.
The idea of biodiversity is most often associated with species richness (the count of species in an area), and thus biodiversity loss is often viewed as species loss from an ecosystem or even the entire biosphere (see also extinction). However, associating biodiversity loss with species loss alone overlooks other subtle phenomena that threaten long-term ecosystem health. Sudden population declines may upset social structures in some species, which may keep surviving males and females from finding mates, which may then produce further population declines. Declines in genetic diversity that accompany rapid falls in population may increase inbreeding (mating between closely related individuals), which could produce a further decline in genetic diversity.
The primary drivers of biodiversity loss are influenced by the exponential growth of the human population, increased consumption as people strive for more affluent lifestyles, and reduced resource efficiency.
Even though a species is not eliminated from the ecosystem or from the biosphere, its niche (the role the species play in the ecosystems it inhabits) diminishes as its numbers fall. If the niches filled by a single species or a group of species are critical to the proper functioning of the ecosystem, a sudden decline in numbers may produce significant changes in the ecosystem’s structure. For example, clearing trees from a forest eliminates the shading, temperature and moisture regulation, animal habitat, and nutrient transport services they provide to the ecosystem.
Natural biodiversity loss
An area’s biodiversity increases and decreases with natural cycles. Seasonal changes, such as the onset of spring, create opportunities for feeding and breeding, increasing biodiversity as the populations of many species rise. In contrast, the onset of winter temporarily decreases an area’s biodiversity, as warm-adapted insects die and migrating animals leave. In addition, the seasonal rise and fall of plant and invertebrate populations (such as insects and plankton), which serve as food for other forms of life, also determine an area’s biodiversity.
Biodiversity loss is typically associated with more permanent ecological changes in ecosystems, landscapes, and the global biosphere. Natural ecological disturbances, such as wildfire, floods, and volcanic eruptions, change ecosystems drastically by eliminating local populations of some species and transforming whole biological communities. Such disturbances are temporary, however, because natural disturbances are common and ecosystems have adapted to their challenges (see also ecological succession).
Human-driven biodiversity loss
In contrast, biodiversity losses from disturbances caused by humans tend to be more severe and longer-lasting. Humans (Homo sapiens), their crops, and their food animals take up an increasing share of Earth’s land area. Half of the world’s habitable land (some 51 million square km [19.7 million square miles]) has been converted to agriculture, and some 77 percent of agricultural land (some 40 million square km [15.4 million square miles]) is used for grazing by cattle, sheep, goats, and other livestock. This massive conversion of forests, wetlands, grasslands, and other terrestrial ecosystems has produced a 60 percent decline (on average) in the number of vertebrates worldwide since 1970, with the greatest losses in vertebrate populations occurring in freshwater habitats (83 percent) and in South and Central America (89 percent). Between 1970 and 2014 the human population grew from about 3.7 billion to 7.3 billion people. By 2018 the biomass of humans and their livestock (0.16 gigaton) greatly outweighed the biomass of wild mammals (0.007 gigaton) and wild birds (0.002 gigaton). Researchers estimate that the current rate of species loss varies between 100 and 10,000 times the background extinction rate (which is roughly one to five species per year when the entire fossil record is considered). In addition, a 2019 report by the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services noted that up to one million plant and animal species are facing extinction due to human activities.
