157
See also: Mutualisms 56–59 ■ Keystone species 60–65 ■ The ecosystem
134 –137 ■ Organisms and their environment 166 ■ Invasive species 270–273ECOSYSTEMS
environmental challenges. That,
he says, requires the integration
of community ecology (the study of
how species interact in ecosystems)
with ecosystem ecology (research
into the physical, chemical, and
biological processes that connect
organisms and their environment).Complex cycles
Scientists of both disciplines firmly
believe that biodiversity, especially
species and genetic diversity, is
an important driver of ecosystem
functioning. Ecosystems are
powered by an input of energy and
recycling of nutrients: plants and
animals grow, die, and decompose,
returning nutrients to the soil
and restarting the cycle. These
processes depend on the species
within the ecosystems, which in
turn depend upon one another as
they interact—as predators and
prey, for example. Many ecologists
argue that a large variety of
complementary species are needed
to keep an ecosystem working and
make it resilient to change. Others
say that a few key species may be
more important to stop ecosystems
from collapsing.When researching such issues,
ecologists have tended to use both
traditional observational fieldwork
and also sophisticated mathematical
models. More recently, research
has begun to incorporate the
manipulation of ecosystems
in a more controlled way, on plots
of land, for example, or within
closed systems housed in giant
greenhouselike facilities called
phytotrons. The experiments help
to establish what factors—such as
numbers of species, or species type
and dominance—affect ecosystems
in the long term. Their findings
show that the effects of biodiversity
on ecosystem functions are
complex. While the most diverse
ecosystems tend to be the most
productive, their success also
depends on climate and soil fertility.
There is more to be learned
about how plant diversity affects
soil processes, the role of microbe
biodiversity in the soil, and the
effects of mutualistic species, such
as flowering plants and pollinating
insects. Much has been achieved,
but questions remain, and the
unifying theory that Loreau is
seeking has still to be devised. ■Habitat fragmentation
Barro Colorado Island in the
Panama Canal of Central
America was formed in 1914,
when tropical rain forest was
flooded by damming, creating
an isolated fragment of forest
surrounded by water. Since
1946, the area has been
studied in detail by biologists
of the Smithsonian Institution
and elsewhere to determine
the effects of this habitat
fragmentation: species
diversity on the island has
declined, and top predators are
among the most vulnerable
species. In the US, studies of
habitat fragmentation and its
effects on diversity in the
Florida Keys led to Robert
MacArthur and E.O. Wilson’s
seminal Theory of Island
Biogeography (1967).
From such environments,
planners have learned
important lessons about how
to conserve species in isolated
patches of habitat—sometimes
in the midst of cities—that are
set aside as reserves. Barro
Colorado, and places like it,
have also provided vital
opportunties for study, where
ecologists can explore how
changing species diversity
affects the functioning of an
ecosystem at every level.Biodiversity loss... is likely
to decrease the ability of
ecosystems to resist the
effects of climate change.
Michel LoreauOne of the distinctive and
fascinating features of
ecological systems is their
extraordinary complexity.
Michel LoreauUS_156-157_Biodiversity_and_eco_system_function.indd 157 12/11/18 6:25 PM