Three major attributes are used to define an ecosystem’s “health”: organisation, productivity and resilience. Organisation of an ecosystem is to do with how diverse the ecosystem is. As an ecosystem gets more diverse it becomes stronger due to having a larger pool of species to contribute to each role that is vital in the upkeep of the system.

To help explain why increased biodiversity results in a healthy ecosystem, we used the example of the re-introduction of wolves to Yellowstone Park in 1995–6.

The re-introduction of wolves to Yellowstone Park has largely been linked with dramatic changes in the landscape, but most crucially in ways scientists didn’t even think were possible. The biodiversity was hugely increased. Direct and indirect changes were observed, resulting in rivers changing direction; beaver, grizzly bear, eagle and raven populations increasing, among many others; increased heights and richness of berry-producing shrubs; and elk populations decreasing.

Wolves were a natural part of Yellowstone Park until the last official killing in 1926 and were re-introduced to keep the elk population under control. This had become overly large directly as a result of the absent wolves. While other changes in animal populations put strains on the park’s ecosystem (increasing coyote numbers pushed down pronghorn antelope numbers), the rise of the elks was the biggest contributor to the deteriorating conditions of the park. By 1997, Yellowstone contained “some of the worst overgrazed willow communities in the West”.

This example of the re-introduction of wolves highlights a crucially important concept: the addition or removal of just a small number of species leads to non-linear changes to the ecosystem. The extermination and consequent re-introduction of just a single species (out of many thousands) in Yellowstone caused widespread and deep rooted changes throughout the park. 

The same “delicate balance” also exists on the skin. When it is upset, organisms not associated with pathogenic behaviour can become damaging to the system/host. The elk, when regulated by wolves, pose a lessened threat, but as soon as they aren’t restricted by wolf predation, they become “pathogenic” to the ecosystem. Their numbers swell and, without wolves to scare them off, overgrazing occurs resulting in more pressure on cottonwood and aspen, among other plants, but most importantly stands of willow, on which beavers depend during the winter. The beaver communities use tall-willow and aspen for food and dam building materials. The loss of beaver dams results in increased erosion, and the loss of habitats for many creatures, including fish, amphibians, otters, moose, mink, wading birds and more. 

Using this one specific example we can relate the role of elk—out of proportion in numbers due to the wolves’ demise—to that of a pathogenic skin microbe, opportunistically becoming so to the host (i.e., the skin) once the very delicate balance is disturbed.

In order to observe whether the diversity of microbial species on the skin was a reliable indicator of healthy or damaged skin, our research looked at the diversity on skin untouched by modern cosmetics.

And the conclusion was that the less exposed communities were to western practices, the higher the skin diversity, which is clear evidence of an environmental factor in the developed world damaging skin. For the first time we proposed benchmark values of diversity against which we can measure skin to determine how healthy it is. This gives us the ability to be able to predict which people are more likely to be prone to skin ailments, and start to test whether cosmetic ingredients and products are a main cause of problem skin.