We have tipped the scales towards people and livestock, reducing the share of wild mammals.
IIf you weighed all the mammals in the world, what fraction of this figure, known as biomass– including wild animals? As of 2020, they accounted for approximately 5 percent of the biomass of all mammals, up from about half in 1850, according to the study. paper recently published in the magazine Natural communications. As human populations have exploded over the past two centuries, our hunger for land and natural resources has radically changed the composition of the world's mammals.
Although scientists often track species extinction as a key indicator of biodiversity, the authors write that “this indicator only partially reflects the global state of wildlife.” Meanwhile, measuring creature biomass offers “an integrative global view of species groups while answering a very simple curiosity-driven question about the ubiquity of life.”
Pets currently outweigh wild mammals tenfold, putting significant pressure on natural resources. Increased demand for livestock significant quantities of water, land and feed. Livestock also makes some contribution 12 percent global greenhouse gas emissions.
The researchers also analyzed the biomass of wild marine mammals, which has declined by about 70 percent since 1850 due to the rise of industrial whaling and “extensive” hunting pressure in the 19th and 20th centuries. But after 1986, when the International Whaling Commission declared a moratorium on industrial hunting of large whale species such as the blue whale and humpback whale, the biomass of wild marine mammals began to recover. Such information is missed when looking only at species extinctions, write the authors of the new study, since only about 2 percent of marine mammal species have been recorded as extinct since the 1850s.
To arrive at these biomass estimates, scientists from Israel and the United States used extensive demographic data on human and livestock populations. But they are faced with a lack of data on wild mammals and acknowledge that their estimates have limitations. The team reviewed the literature to obtain historical population estimates for some species, and for species of wild land mammals for which there are no records, they “assume that their biomass has remained constant since 1850.” To estimate the biomass of wild marine mammals, they used a model based on population estimates and catch data.
While these biomass estimates are “imperfect,” the authors hope they can serve as a basis for future conservation efforts and tilt the global scale toward previous efforts.
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Main image: fir0002 / Wikimedia Commons.
