ECOSYSTEMS 139
the nonliving (abiotic) components
(air, water, soil minerals) were
linked together by nutrient cycles
and energy flows. This entire
system—the ecosystem—was
the central ecological unit.Producers and consumers
Lindeman’s research showed how
an ecosystem is powered by a
stream of energy from one organism
to another. The organisms can be
grouped into discrete “trophic levels”
(feeding levels)—from producers
(plants and algae), which absorb
energy in the form of sunlight to
make food, to consumers (animals).
“Primary consumers” are the
herbivores that eat the plants;
“secondary consumers” are animals
that eat the herbivores. Each trophic
level depends on the preceding one
for its survival. At the same time,
dead material accumulating from
each stage is broken down by
decomposers, such as bacteria and
fungi, and materials in the form of
nutrients are recycled back to feed
plants and algae.Measuring
productivityLindeman’s trophic-dynamic
theory helped to clarify the
idea of ecosystem productivity,
which ecologists had previously
defined in rather vague terms.
The productivity of a plant
or animal is measured by its
growth in organic material,
or biomass. This is never equal
to the organism’s energy
input, because the conversion
of solar energy into leaf in the
case of plants, or the conversion
of food into flesh in the case of
an animal, is never 100 percent
efficient. Some energy is
released as heat, most of which
is lost via respiration—an
essential aspect of metabolism
in all living things.
Warm-blooded animals lose
a lot of heat when their body
temperature is much higher
than that of their surroundings.
All animals also lose energy
when they excrete urine. In
addition, not all the material
in an animal’s food can be
digested in its gut, and the
material that is expelled as
feces represents unused
chemical energy.This thermal image of an
elephant shows how some of the
animal’s heat is lost. Both its body
temperature and its manure are
warmer than the surroundings.See also: Ecological niches 50–51 ■ Nonconsumptive effects of predators
on their prey 76–77 ■ The food chain 132–133 ■ The ecosystem 134–137Lindeman also demonstrated how
some of the energy at each trophic
level is lost as waste, or converted
into heat when organisms respire.
By combining the results of his own
study with data from a wide range
of other sources, he was able to
build a picture of this system as it
worked in Cedar Creek Bog.
British ecologist G. Evelyn
Hutchinson, considered to be one
of the founding fathers of modern
ecology, was Lindeman’s mentor at
Yale University. He recognized the
importance of his student’s work to
the future development of ecology,
and he lobbied for Lindeman’s
paper to be accepted. Lindeman,
who had always suffered from ill
health, died in 1942 from cirrhosis
of the liver at the tragically young
age of 27, just four months before
his trophic-dynamic paper—now
seen as a classic in its field—was
finally published. ■Boneworms are deep-sea creatures
that feed on the remains of animals
such as whales. They grow “roots” to
break down the bones, thereby recycling
nutrients from the dead material.... biological communities
could be expressed as
networks or channels through
which energy is flowing and
being dissipated...
G. Evelyn HutchinsonUS_138-139_Energy_flow_through_ecosystems.indd 139 17/12/2018 14:33