Bird communities losing their redundancy and risking collapse

Humans have been altering the natural world for centuries. But how, exactly, this is impacting wild animals and plants is a key question still not fully understood.

On the one hand, it could be argued that the animals that survive in human-dominated environments are more resistant to change as they have already survived massive upheavals. It would therefore seem likely that they might act as something of a buffer to wider collapse.

But a new paper has shown how bird communities responding to human impacts are perhaps not quite as resilient as previously thought. The research has found that the reduction in the diversity of birds heavily impacts their functional redundancy as, for example, there are fewer species of seed-eating birds. This would mean we are entering a period where further human pressures can no longer be absorbed.

Dr Patrick Walkden is one of our researchers working to assess the state of bird biodiversity around the world. Working alongside colleagues, they have published their results in the journal Nature.

“We’ve been saying for a long time that we can afford to lose a few species here and there, but it has now got to the point where actually we can no longer afford to lose any more,” says Patrick. “We’ve sort of reached that limit of our insurance, so to speak, and we’ll pay at the end of it.”

The breakdown of natural fail-safes

The study looks at what is known as functional redundancy in the natural world, focusing specifically on birds.

At its core, the concept of functional redundancy basically means that a system has multiple failsafes that can all do the same thing. This means that if one part of that system were to fail, another part would be able to fill in and stop the system from falling apart.

In practice, functional redundancy manifests itself within biology in many ways, from DNA to brain networks. We also see it playing out in ecosystems around the world.

A forest, for example, might have multiple species of birds that all eat fruit. In the process of eating the fruit, the birds will then spread the plant’s seeds throughout the forest, helping to propagate not only the food that the birds rely on but the woodland as a whole.

But if one of these birds were to go extinct, then it wouldn’t necessarily cause the forest ecosystem to collapse, as the seeds of the fruit might be dispersed by another species. This helps to buffer the environment from major disturbance.

In order to see how resilient this process is in the wider world, Patrick and his colleagues took the data from almost 3,700 species of birds and mapped them onto over 1,200 sites around the planet that have been recently altered by human activities.

This might include, for example, turning what was once a forest into agricultural land, or converting coastal scrub into urban sprawl.

“In theory, when there’s environmental perturbation, the species that survive are the ones that are resilient to that environmental change,” explains Patrick. “What we found was that there are two ways that can then go.”

“In the face of more environmental change, then these systems could actually be more resilient because species now living there are the survivors of the change. But this paper finds, which is kind of counterintuitive maybe, is that actually these ecosystems are less resilient, less stable and more at risk from those future perturbations.”

This is because that previous functional redundancy has already been cleared out, meaning that additional pressures effectively finish the job.

“It really is a further loss of stability and resilience, and if we continue to apply anthropogenic pressures globally these systems are at risk of collapse.”

With a rapid increase in the rate of human activity changing the natural world, there is a very real concern that we are now approaching that tipping point. The easiest way to counter this would be to reduce those human pressures by, for example, making more room for the natural world within our own spaces.

It could also involve giving a helping hand to species that have already gone extinct to restore some of that lost functional diversity.

Professor Joseph Tobias, from the Department of Life Sciences at Imperial College London and a senior author on this latest study, says, “With land-use change accelerating worldwide, our study highlights the urgency of managing and preserving functional diversity to ensure that future ecosystems continue to function in ways that help to support human life and economic stability.”

But it is not only the human pressure of land use change that is impacting birds. They are also starting to feel the brunt of other impacts, such as the ever-worsening climate change. In order for these species to survive, it will take a collective action to protect and preserve the natural world on which we all rely for survival.