surrounded by ocean but also
“islands” of distinct habitat
surrounded by a very different
environment—is so important
in ecology. In the US in the 1960s,
Edward O. Wilson and Robert
MacArthur discovered key factors
determining species diversity,
immigration, and extinction on
islands. James Brown later did
similar work on animal populations
in isolated patches of forest ridge in
California. Such work has showed
how to identify species most at risk
of extinction due to isolation.Stability and resilience
One major contribution to the
understanding of ecosystem
dynamics was the concept of the
evolutionarily stable state. In the
1970s, British biologist John
Maynard Smith used the termevolutionarily stable strategy (ESS)
to describe the best behavioral
strategy for an animal competing
with others living in its vicinity.
This strategy depends on how the
other animals behave and is
determined by the animal’s genetic
success—if it makes the wrong
decisions, it will not live long and
cannot pass on its genes. The
overall balance between the
evolutionarily stable strategies of
all the animals in an ecosystem is
called the evolutionarily stable state.
Canadian ecologist Crawford
Stanley Holling introduced the idea
of resilience—how ecosystems
persist in the wake of disruptive
changes such as fire, flood, or
deforestation. A system’s resilience
can be seen in its capacity to absorb
disturbance, or the time it takes to
return to a state of equilibriumafter a trauma. Ecologists now
understand that ecosystems can
have more than one stable state,
and that resilient systems are not
always good for biodiversity.
When the populations of many
species are declining or becoming
locally extinct, ecologists are once
more focusing their attention on
ecosystem resilience. Many,
including French ecologist Michel
Loreau, believe that if diversity in
an ecosystem is reduced, the whole
system will be less likely to resist
major impacts such as the effects of
climate change. Today, Loreau and
others are working toward finding a
new general theory that can
explain the relationship between
ecosystem biodiversity and
resilience in order to understand
and combat the effects of today’s
environmental challenges. ■ECOSYSTEMS
1976
Hal Caswell proposes
a “neutral” theory
of biodiversity, suggesting
that competitors are often
equal, and chance plays
the deciding role in
what does or doesn’t thrive.Crawford Stanley
Holling uses the
term ecological
resilience to show how
ecological systems
survive change.1973
Robert MacArthur
examines the
biodiversity of
isolated communities
in The Theory of
Island Biogeography.1967
1972
John Maynard Smith
defines his
Evolutionarily Stable
Strategy (ESS) theory
in On Evolution.2000
Scientists at the
Biodiversity and
Ecosystem Function
conference in Paris
examine how the
loss of species
impacts ecosystems.131
2015
A study of grassland plants
suggests that biodiversity
increases an ecosystem’s
resistance during
and resilience after
climate events.1980
Robert Paine coins the term
“trophic cascade” after his
field experiments show the
effect on an ecosystem
when a keystone species
is removed.US_130-131_Ch_5_Ecosystems_Intro.indd 131 22/11/2018 17:50