The current loss and decline of animal species is contributing to the early stages of a sixth mass biological extinction event, says an international team of scientists, who warn of future impacts to ecological functions and human wellbeing.Two argus butterflies

Unlike previous extinctions, driven by natural planetary transformations or catastrophic asteroid strikes, the current die-off can be associated to human activity, according to the scientists who published their study in the journal Science.

Lead author Rodolfo Dirzo, a professor of biology at Stanford University in California, has described an era of "Anthropocene defaunation” (defaunation is used to describe the loss of both species and populations of wildlife). Dr Nick Isaac of the Centre for Ecology & Hydrology (CEH) is also one of the authors of the new paper, a review of scientific literature and data analysis.

Large animals – described as megafauna, which include elephants, rhinoceroses, polar bears and countless other species worldwide – face the highest rate of decline, a trend that matches previous extinction events. Their loss has wider effects, for example on surrounding landscapes and rodent populations which can destabilise other species and even human health.

But the scientists also detail a worrying trend in invertebrate defaunation. While the human population has doubled in the past 35 years, in the same period the number of invertebrate animals – such as beetles, butterflies, spiders, and worms – has decreased by 45 percent.

As with larger animals, this is driven mainly by loss of habitat and global climate disruption, and could have trickle-up effects in our everyday lives. For example, insects pollinate roughly 75 percent of the world's food crops, worth an estimated 10 percent of the economic value of the world’s food supply. Insects also play a critical role in nutrient cycling and decomposing organic materials, which helps ensure ecosystem productivity.

"We tend to think about extinction as loss of a species from the face of Earth, and that's very important, but there's a loss of critical ecosystem functioning in which animals play a central role that we need to pay attention to as well," Professor Dirzo said.

Long-term distribution data on moths and four other insect orders in the UK show that a substantial proportion of species have experienced severe range declines in the past several decades.

Nick Isaac, an ecologist within the Biological Records Centre at the Centre for Ecology & Hydrology, carries out research into abundance, distributions, diversity and extinction risk of species. The BRC provides a focus for the collation, management, dissemination and interpretation of species observations (biological records) in the UK and has also been at the forefront of developing methods to extract trends from such observations.

As well as Stanford and CEH, the other co-authors on the report are from the University of California at Santa Barbara, the Universidad Estadual Paulista (Brazil), Universidad Nacional Autonoma de Mexico and University College London.

Additional information

Stanford University issued a press release for this story.

Full paper reference: Dirzo et al, Defaunation in the Anthropocene, Science, 25 July 2014, Vol. 345 no. 6195 pp. 401-406. doi: 10.1126/science.1251817

Vanishing fauna: introduction to Science special issue

Biological Records Centre at CEH




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