The Ecology Book

150

IT IS THE CONSTANCY

OF NUMBERS

THAT MATTERS

ECOLOGICAL RESILIENCE

T

he capacity for ecosystems

to recover following a

disturbance—such as a

large fire, flood, hurricane, severe

pollution, deforestation, or the

introduction of an “exotic” new

species—is known as ecological

resilience. Any of these impacts

can upset food webs, often

dramatically, and human activity

is responsible for an increasing

number of them.

Staying resilient

Canadian ecologist Crawford

Stanley Holling first proposed the

idea of ecological resilience to

describe the persistence of natural

systems in the face of disruptive

changes. Holling argued that

natural systems require stability

and resilience, but—contrary

to what previous ecologists had

assumed—these are not always

the same qualities.

A stable system resists change

in order to maintain the status quo,

but resilience involves innovation

and adaptation. Holling wrote

that natural, undisturbed systems

are likely to be continually in a

transient state, with populations

of some species increasing and

others decreasing. However, these

population changes are not as

important as whether the whole

system is being fundamentally

altered. The resilience of a system

can be described either by the time

it takes to return to equilibrium

after a big shock or by its capacity

to absorb disturbance.

One example that Holling studied

was the fisheries of the Great Lakes

in North America. A large tonnage

of sturgeon, herring, and other fish

was harvested in the early decades

of the 20th century, but overfishing

dramatically reduced the catches.

Despite subsequent controls on

fishing, populations in the Great

Lakes did not recover. Holling

IN CONTEXT

KEY FIGURE

Crawford Stanley

Holling (1930 –)

BEFORE

1859 Charles Darwin

describes the interdependence

between species as an

“entangled bank.”

1955 In the US, Robert

MacArthur proposes

a measure of ecosystem

stability that increases as

the number of interactions

between species multiplies.

1972 In contrast with

MacArthur, Australian

ecologist Robert May

argues that more diverse

communities with more

complex relationships may be

less able to maintain a stable

balance between species.

AFTER

2003 Australian ecologist

Brian Walker works with

Crawford Holling to refine

the definition of resilience.

Ecosystems are dynamic—

constantly changing and

inherently uncertain, with

potential multiple futures ...

Crawford Stanley Holling

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