How biodiversity portfolio effects build ecosystem resilience

Climate change, disappearing habitats, invasive species and overfishing are all unrelenting pressures, with ecosystems worldwide continually bearing the consequences.

A new synthesis paper examines the question underlying this widespread damage.

What enables an ecosystem to withstand a major shock and continue operating – providing fish, clean water and the food webs relied upon by people and wildlife – rather than gradually falling apart?

Researchers at the Centre for Ecosystem Management say the answer lies in something that may seem counterintuitive: disorder. More precisely, it is the ecological complexity created by genuine variety.

The financial principle behind portfolio effects

Ecologists refer to this safeguarding form of variation as portfolio effects, and the financial-sounding name is deliberate.

A diversified investment portfolio can withstand one company collapsing because losses are offset elsewhere.

Ecosystems follow a comparable principle. Where species, habitats and ecological relationships are sufficiently varied and function across several scales simultaneously, the wider system can withstand a disruption that might otherwise overwhelm it.

The benefit goes beyond protection from catastrophe. The researchers found that portfolio effects can do more than steady a food web during disruption: they may also increase its productivity when conditions are normal.

Habitat heterogeneity helps transfer this effect upwards, extending it through trophic levels and across the physical landscape. As a result, stability established at one scale can strengthen stability in a completely different place.

“Ecosystem resilience is not just about having many species, but about maintaining the variation within and across scales that helps the individual organisms, species, and ecosystems persist and adapt,” said study lead author Kayla Hale.

Landscape and species variation

The difficult reality is that human activity often simplifies the very variation landscapes need in order to remain resilient.

Land conversion, the introduction of invasive species and intensive resource extraction all drive habitats and biological communities towards uniformity.

Once this uniformity takes hold, the buffering capacity normally supplied by portfolio effects begins to vanish with it, making ecosystems less predictable and more susceptible to genuine, long-term decline.

Differences between habitats are important because disturbances rarely affect an entire landscape equally. Patches that remain undamaged can support those experiencing pressure.

Variation among species and populations serves another purpose: it allows a community to reorganise under altered conditions while continuing to perform its role and produce the resources on which everything downstream depends.

These forms of variation do not operate separately. Instead, they strengthen one another, enabling an ecosystem to flex under pressure rather than fail.

“This work highlights biodiversity and habitat heterogeneity as a form of natural insurance,” Hale said.

“Protecting this variation helps maintain the capacity of ecosystems to respond to both expected and unexpected environmental challenges.”

Rethinking the purpose of conservation

These findings are not limited to the Great Lakes. They have implications for conservation strategy, ecosystem management and policy choices intended to preserve ecosystem services in a changing world.

The researchers maintain that safeguarding and restoring diversity across habitats, species and their interactions could be among the most effective available approaches for helping ecosystems keep up with global change.

Nor must existing damage be treated as irreversible.

The experts point out that focused management can rebuild resilience-supporting processes that have already been weakened. This means restoration must be considered alongside protection.

A different understanding of biodiversity

Ultimately, the research proposes a broader way to view biodiversity. Biodiversity is not merely worth protecting because it is attractive or because its loss feels inherently wrong.

It operates continuously and unobtrusively as insurance – the sort that an ecosystem calls upon only when circumstances go wrong.

The paper also argues that resilience is not a fixed quality that some ecosystems possess while others lack.

Rather, it emerges from diversity working across every scale at once, from an individual organism to a whole landscape.

By protecting that variation, ecosystems improve their chances of enduring whatever follows, anticipated or otherwise, while continuing to support the people and species that depend on them in the years ahead.