Humanity’s footprint threatens the Tree of Life
By: Rikki Gumbs
Our relationship with biodiversity is complicated. Global social and economic systems are supported by the benefits provided by biodiversity, yet our extraction of natural resources and conversion of natural habitats to human-modified landscapes is continually depleting Earth’s ability to support human life.
The conversion of natural habitats to agricultural and pasture lands is the leading cause of global biodiversity loss, with agricultural lands dominating more than 40% of Earth’s land surface. Worryingly, humanity’s expanding footprint is now directly impacting at least three quarters of the planet. We therefore set out to determine the extent to which human pressures are encroaching on regions of the planet containing the greatest concentrations of irreplaceable biodiversity.
The impacts of human activities are evident on the once-forested peaks of Mount Bamboutos, Cameroon. Image credit: Arnaud Tchassem
In its purest sense, biodiversity is living variation – the differences among and within individuals and species, their genes and traits, and the ecosystems they comprise. One fundamental measure of biodiversity is phylogenetic diversity: the amount of evolutionary history—the branches of the Tree of Life—represented by a single species or sets of closely related species. Each branch has a length, measured in millions of years, and we can count these branch lengths to quantify the uniqueness of, and diversity across, species.
We used the reptilian Tree of Life to identify regions of the planet that hold most irreplaceable reptilian phylogenetic diversity – branches of the tree that cannot be found anywhere else. We found that almost three quarters of the areas containing the largest concentrations of irreplaceable diversity are located in areas under high or very high human pressure. This overlap is much greater than we would observe if human pressure were distributed at random across the planet. Equally disconcerting is the fact that just 5% of these areas are experiencing low or no human pressure.
The overlap of human pressure and the most important regions for evolutionary history of reptiles. Grid cell colours indicate the intensity of human pressure and are restricted to the regions with the greatest concentrations of irreplaceable evolutionary history. Adapted from Gumbs et al. 2020, Nature Communications
When we looked at all terrestrial vertebrates (amphibians, birds, mammals and reptiles), we discovered that amphibians and reptiles are particularly evolutionarily unique and restricted to high pressure regions, whereas birds and mammals are more widely distributed and less unique. Worryingly, many of these amphibians and reptiles comprise the ~8,000 species in our study with Data Deficient IUCN Red List assessments. On average, Data Deficient species are comparable in both their evolutionary uniqueness and exposure to intense human pressure to threatened species and many species likely require urgent conservation attention.
Globally, we found Humanity’s activities threaten close to 50 billion years of terrestrial vertebrate phylogenetic diversity. However, this calculation included only those species for which we have adequate extinction risk information, which means it is almost certainly an underestimation. Twelve of the twenty snakes and lizards we identify as priorities, based on their evolutionary uniqueness and exposure to human pressure, lack sufficient extinction risk data; these twelve species alone represent more than 500 million years of unique evolutionary history about which we know very little.
The Purple Frog (Nasikabatrachus sahyadrensis), a secretive species that spends almost its entire life underground, is one of many highly evolutionary unique species threatened by humanity’s increasing footprint. Image credit: Sandeep Das.
We are still learning the true extent to which our activities are encroaching on natural habitats and threatening Earth’s most unique and important biodiversity. Our findings indicate that the magnitude of humanity’s impact on the natural world is incomprehensibly large and threaten the most irreplaceable areas and species on the planet.
However, it is not too late to change the course we are on to avoid even greater impacts. On the ground conservation efforts to conserve the some of the most evolutionary unique and threatened species are already underway, and evidence suggests that even small increases in the global protected area network can lead to large gains in conservation impact. If we work together to reduce our impacts on the natural world and conserve our natural habitats and species, we have the opportunity to avert the loss of an incredible amount of irreplaceable biodiversity.
Publication Authors: Rikki Gumbs, Claudia L. Gray, Monika Böhm, Michael Hoffmann, Richard Grenyer, Walter Jetz, Shai Meiri, Uri Roll, Nisha R. Owen, James Rosindell
