How nature spreads risk (and we don't)
Lessons from ecosystems for a world obsessed with efficiency
Last week, I argued that we’ve built a fragile society. We’ve optimised so much that our systems work brilliantly — right up until they don’t. When shocks hit, the impacts can be catastrophic. The global financial crisis made that clear. And the cost of fuel at the pump right now is a timely reminder.
Natural ecosystems face similar uncertainties, extremes, and surprises. But many of them persist for centuries. One reason is that they don’t optimise around a single best strategy. In variable environments, systems persist by spreading risk across multiple dimensions.
Before turning back to what this means for society, let’s look at four ways nature actually does this.
1. Across genes and species
Diversity in and of itself helps ecosystems hedge against uncertainty.
The greater the diversity of genes in a population, the more likely it will bounce back from unexpected shocks. Extreme events like floods, droughts or heatwaves can selectively remove particular genotypes. If some persist, the population can rebuild from within rather than starting from scratch.
Species within a community provide the same resilience. We call this the portfolio effect. Just like investing in a diverse portfolio of stocks and shares buffers investors from unexpected shocks, the more species a system supports, the more stable it will be in response to ups and downs in the environment.
This is because species respond in different ways to change — what we call response diversity. As a result, their populations don’t all rise and fall at the same time. When you average across them, these asynchronous dynamics smooth out the variability, making the aggregate measure of the system (e.g. overall abundance or biomass of all life in the system) more stable.
In some cases, species fluctuate in opposite directions — declines in one are offset by increases in another. These compensatory dynamics further stabilise the system, but they’re not required for the overall buffering effect to emerge.
Each species in an ecosystem performs many functions — pollination, carbon sequestration, nutrient cycling, predation, water filtration. These are what ultimately lead to ecosystem services — things like clean water for drinking, food, medicine and so on. In a system with high functional redundancy, when a species is lost from the system, another fills its role. The functioning of the system is resilient to ups and downs in the environment.
Diverse systems don’t avoid shocks — they avoid failing all at once.
2. Across space
Ecosystems do not operate in isolation. We’ve learned over recent decades just how interconnected life is. What happens in one ecosystem is the result of processes operating at a range of scales. Species move in and out of habitats, resources are exported across boundaries, and nutrients are brought in from elsewhere.
Once we begin to consider these spatial dynamics, we start to see how crucial the spatial mosaic of the landscape is for resilience of ecological systems. For instance, the idea of source-sink metapopulation dynamics (metapopulation = collection of populations) emphasises how some habitats are sources of recruits (where reproduction is possible) and others are sinks (where species are not able to reproduce for some reason or another). In this case, source populations top up the sink populations. We see this here in our local rivers where nonnative trout prey upon native galaxiid fishes in sinks that are fed by trout-free source populations.
When we begin to modify landscapes, much of the natural resilience mechanisms are removed. That’s why the Single Large Or Several Small (SLOSS) debate has raged on in ecology for decades (is it better to have one big patch of forest or lots of small ones?). For rivers, it’s important to allow them space to move — not just for flood risk protection but also for providing habitat variability and connections to the floodplain, all of which help species find places to hide during flood events or rare their young.
Intact connections among diverse ecosystems enables them to remain resilient in the face of variability.
3. Across time
Species don’t just respond to the environment in the moment — they store up gains, they delay responses, they wait. Species have a suite of inbuilt mechanisms that help them cope with unpredictability in the environment.
Some build up seed banks that lie dormant in the soil for years, then spring into life when the conditions are right. Desert landscapes that look lifeless can erupt into life almost overnight.
Others produce dormant life stages. Short-lived species may produce eggs or larvae that pause development until conditions improve. Many zooplankton rely on these “time capsules” to persist through droughts.
And species can store up the gains made during good times to get through the bad. This so-called storage effect is prominent in desert annual plant communities, where species trade off competitive ability and drought tolerance resulting in some plants growing better during wet years, others in dry years.
And finally, long life spans of course buffer species from bad times. If they can just hold tight and withstand the bad times, then offspring will come during the good. Not every year needs to be good — far from it.
Time, in other words, is another dimension across which risk is spread.
4. Across strategies within organisms
Many of the previous dimensions involve organisms with strategies that enable them to maximise their risk spreading. In particularly variable environments, species have evolved numerous ways to spread their risks.
One evolutionary strategy is to separate their life stages among systems. For instance, many freshwater insects have an aquatic juvenile stage and terrestrial adult stage, so they spread their risk among different places. Mayflies that emerge from streams become food for riparian birds, bats and insects, but often only for a day or two, so they minimise their exposure to terrestrial predators. Salmon prioritise egg and juvenile survivorship over adult survivorship by travelling inland to spawn.
Unlike salmon, rainbow trout spread risks by adopting different life history strategies. Some individuals remain in freshwater their entire life cycles, while others migrate to sea and return as steelhead. This partial migration spreads risk across environments. River and ocean conditions don’t vary in the same way or at the same time, so when one strategy performs poorly, such as during a heatwave or a poor year at sea, the population can persist.
Finally, while you expect massive hatches of mayflies across the United States in systems that have highly predictable river flow regimes, New Zealand insects avoid putting all their eggs in one basket to avoid catastrophe during one of the many unpredictable floods they experience.
These examples of bet‑hedging highlight how species spread risk across time when the future is unpredictable. Instead of betting everything on one strategy, these species spread their chances across different futures.
At this point, it might seem that risk spreading is only relevant in highly variable systems. This isn’t necessarily the case.
Even systems that are strongly tied to environmental rhythms have slack
The establishment of riparian cottonwood seedlings in the US southwest appears at first to be something of a magic act. These cottonwood species have evolved in the presence of highly predictable river flows, where floods fall predictably within a small window during spring each year. In the Colorado River basin, most of the precipitation falls as snow, gets locked up during the winter and all released as spring temperatures melt the snow. This creates a highly predictable rhythm that species have evolved to capitalise on.
Cottonwood do this by releasing their seeds during that spring snowmelt window. But for seedlings to establish, a number of criteria need to be met: the flood has to fall within the window in which cottonwood release their seeds, it has to be large enough to inundate the floodplain, and the water has to recede at the right rate — too fast and the roots of the seedlings can’t keep up with the receding moisture, too slow and they sit in water.
But, here’s the key thing. While this looks like a system that is fragile because of how tightly dependent the species is on a highly predictable environment, there’s always buffer built into natural systems. In this case, it’s that cottonwood don’t need seedlings to establish every single year. They are, of course, long-lived species, so they can afford to go long periods without juvenile recruitment. In fact, we’ve found a recruitment event about every seven years was about the sweet spot when designing river flows to support diverse communities.
This looks like a system balanced on a knife‑edge. In reality, persistence comes from buffers operating across time and strategy. Failure can come in most years without collapse.
In sum, nature doesn’t eliminate risk — it distributes it across genes, species, space, time, and strategies.
The ecological mechanisms are fascinating, but the even more interesting question is how they can be applied to societal problems. Below, I explore each one and what it means for how we grow food, maintain supply chains, manage water, and strategise businesses — for paid subscribers.
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