More than one-third of all vertebrate species on Earth are now being used by humans, according to new research by scientists from Dalhousie University and institutes around the world. Almost 40 per cent of those exploited vertebrate species are now threatened.
The findings, published today in Communications Biology, suggest that people have a much broader impact on biodiversity, taking up to 300 times more prey species and causing outsized impacts on natural ecosystems. As a result, the ecological roles these overexploited species perform in ecosystems are under threat from human use.
“Human beings have gradually occupied a super-sized ecological niche and our ability to manage our impacts has not kept pace with that growth," says Boris Worm, Ocean Literacy Ambassador for the Ocean Frontier Institute and a professor with Dalhousie University who co-authored the report.
"A niche is a species' ecological operating space – where it lives, what it feeds on, essentially the conditions it needs to survive. The point here is that humans use many, many more species than any other vertebrate – we have a super-sized niche."
The international team of scientists from 14 institutions analyzed human ‘use’ data for 45,000 vertebrate species, including most known fish, mammals, birds, reptiles and amphibians. Whereas other top predators kill almost exclusively for food, ‘human predators’ have much more varied uses for their prey species. For land vertebrates, for example, the researchers were surprised to find that capturing terrestrial animals for the pet trade outnumbered food uses almost two to one.
“Comparing humans to other species like us, we have emerged as the planet’s most extraordinary predator, doing things that other predators do not. This includes commonly killing or capturing for reasons other than feeding themselves, as well as endangering thousands of prey species simultaneously," says co-author Chris Darimont of the University of Victoria and Raincoast Conservation.
Risks of overexploitation
The research also gives new insight into the risks of overexploitation, both from killing prey and live capturing them for the pet trade. Overexploited species tend to have different attributes – like large body size and a plant-based diet – compared with those not exploited or exploited sustainably. Indeed, the researchers find that humans are threatening a diverse and ecologically distinct set of species. Losing these species and the unique and potentially irreplaceable roles they play can bring deep changes to ecosystems.
How can humans continue to hunt and fish without endangering species and their roles in ecosystems? The research team recognizes that subsistence hunters and fishers can have more sustainable long-term relationships with the animals they use, which can help us to reimagine our relationship with animals. But more indiscriminate forms of use, such as some highly industrialized fisheries and unregulated capture of pets from the wild, are still dominant and require urgent attention from policymakers to limit their negative impacts.
“The unnatural selection of animals by human predators could lead to a range of repercussions across ecosystems. From the potential loss of large seed-dispersers such as the Helmeted Hornbill, to megaherbivores such as the Black Rhino, to migratory predators such as large sharks," says Rob Cooke of the UK Centre of Ecology and Hydrology.
How to manage or constrain such impacts has been the topic of recent negotiations under the Convention on Biological Diversity, aiming to halt and reverse species loss globally. This research identifies species that are not only overexploited but also have outsized ecological influence globally. These species can be prioritized in conservation action plans that consider not only specific species but also the broader ecosystem-level implications of species loss.
Concludes Dalhousie’s Boris Worm: “The good news is that humanity now sharply recognizes our destructive tendencies, and there is a real attempt to use the best available science to get things right, here in North America, and around the world. This makes me hopeful for the future of life on Earth.”
Senior Research Reporter
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