Ecosystems as Systems

An interconnected web

An ecosystem’s organisms and physical surroundings interact. Changing one part can affect many others, so an intervention needs to be assessed across the system. Sometimes restraint is useful; sometimes active management is necessary. The question is what the intervention changes and how those effects spread.

For instance, in areas that are prone to forest fires, the local fire department may attempt to put out every single fire they hear about as soon as possible, regardless of size. In fire-adapted ecosystems, suppressing every fire can disrupt an important ecological process. Some fires have benefits as well as destructive effects. Burning dead plants releases the nutrients they contain back into the soil, helping to fertilize the next generation of plants. Fires cut through the thickest areas of plants, letting sunlight through to reach new areas.[1] Depending on the ecosystem and the fire, they can also suppress some invasive species or diseased plants.[2]

Perhaps most importantly, regular small fires burn up accumulating plant matter. Where frequent, low-intensity fire is part of the ecosystem, suppressing it can allow fuel to accumulate and contribute to more severe fires.[3]

Conservation efforts can also focus too narrowly on individual animals while overlooking the habitats they need. Both African elephants[4] and Asian elephants[5] depend on suitable habitat and protection from threats to wild populations.

Preserving habitat allows elephants to live and breed in the wild. Captive breeding, including artificial insemination, addresses a different part of the problem. Artificial insemination can produce offspring[6] but can be expensive.[7] Its success does not itself preserve the habitat those animals would need outside captivity.[8] Captive programs also need to address welfare, including space, social relationships, and survival of offspring.[9] The relevant comparison is how each program contributes to sustaining populations, rather than simply how many animals it produces.

Protecting individual organisms and protecting the relationships that sustain a population are connected tasks.

« Economic systems are, of course, complex structures, in which the pattern of interactions resembles a web. This means that the dominant party in one interaction may well be the subordinate in another. Control thus diffuses through the ecosystem, generally from entities with high energy demands to those with more modest requirements. The ability to adapt to, or at least to accommodate, the power structure remains the ticket to success for all players—dominants and subordinates alike—regardless of how much influence an entity wields. » — Geerat Vermeij

There is no size restriction on ecosystems. Isolated puddles in rocks have their own ecosystems, but so too does the ocean. Matter and energy move across ecosystems. Animals migrate, pollen blows around, and water can transport a variety of species or materials to other systems. Very few ecosystems are completely closed. Long-distance migration of many species ties ecosystems together.

Species differ in how strongly they affect an ecosystem. A keystone species has an effect disproportionate to its abundance. Its loss can cause large changes in other populations and in the structure of the ecosystem, even if the whole system does not collapse. The name comes from zoologist Robert T Paine, who compared them to the special stone known as a keystone, that is used at the top of an arch to ensure its structural stability. Without the keystone, the arch would collapse. It is a small component, but everything else depends on it. Keystone species can be hard to identify, as they may only be present in low numbers or may not be highly visible species. Identifying a keystone species requires evidence about the effects of its presence or absence, including changes observed when its numbers fall.

It is common for keystone species to be predators (organisms that eat other, usually smaller, organisms) as they play a crucial role in maintaining the numbers of their prey. Predators tend to be present in relatively small numbers compared to their prey. In other cases, herbivores (organisms that eat plants) are important for maintaining the levels of certain plants, thereby keeping the habitat in a favorable state for other organisms. Some species have reciprocal relationships in which the loss or reduction of one would harm the other and the effects would ripple out to the rest of the ecosystem. So, in general the value of keystone species is dependent on their ability to either provide what other species need to survive or to control population levels.

An example of a keystone species is the sea otter, which lives in kelp forests. Sea otters eat sea urchins, which in turn eat kelp. If there are enough sea otters in the ecosystem, they prevent the numbers of sea urchins from getting too high. Where otters strongly control urchins, losing them can allow urchins to overgraze kelp. Kelp loss then affects the other species using the forest and the carbon stored in it. The strength of this cascade depends on local conditions and other predators; it is not a claim that every kelp ecosystem depends entirely on otters.[11]

Finally, ecosystems aren’t static. The internal dynamics are constantly changing as the system adjusts to and recovers from disturbances. Some ecosystems are robust, others more fragile. Some have a high capacity for resistance, which is the tendency of a system to remain close to its equilibrium state. It takes a significant disturbance to affect these ones. Resistance is contrasted with sensitivity, describing those systems for whom very weak disturbances can have a profound effect.

Resilience concerns a system’s capacity to recover or retain its functions after disturbance. Recovery speed is one useful measure, alongside the scale of disturbance it can absorb. A system may change readily yet recover quickly, while another may resist change but struggle once pushed beyond a threshold.

This is why ecosystem is such a useful mental model. The parallels with human organization are clear. Our family units tend to function as their own system and so can our teams at work. But we are also part of the larger ecosystems of our cities or organizations, and people can move across ecosystems with ease, bringing change and challenge.