Transcript Energy Flow Through Ecosystems

Energy Flow Through Ecosystems
• The ultimate source of energy for biological
processes is the sun.
• In other words, the basis of living systems is the
solar energy captured through the lightdependent reaction of photosynthesis.
• The use of energy to manufacture living
material is called productivity.
Productivity Definitions
• Primary productivity- the rate at which energy is
bound by photosynthesis. It is often measured in
kcal/m2/year.
• Gross production- the amount of production before
metabolic costs (the energy required to sustain life) are
subtracted.
• Net production- the amount of production after
metabolic costs (respiration) are subtracted.
• Biomass- the amount of living material present at a
given time. It is measured in g/ m2.
Trophic Levels
• Energy captured by plants is passed along to other organisms as plants are
consumed by them. These organisms are in turn consumed by other organisms.
• Food chain- the steps in this transfer of energy.
• Trophic level- each step in this transfer.
– Primary producers (autotrophs)- the organisms that form the base of the
food chain. They include photosynthetic organisms and organisms that
derive energy from chemical compounds (chemoautotrophs).
– Primary consumers- organisms that eat primary producers. All organisms
that eat other organisms are heterotrophs.
– Secondary consumers- organisms that eat primary consumers.
– Tertiary consumers (top carnivores)- organisms that eat primary and
secondary consumers.
– Decomposers- organisms that break down the remains of other organisms.
Trophic Efficiency
• In nature, food chains interconnect to form food webs. For
example, more than one kind of animal may eat the same plant.
• Only about 1% of solar energy is captured by living organisms.
• From 30-75% of gross primary production is used in metabolic
activities.
• Due to such metabolic costs, only about 10% of the energy at one
trophic level is incorporated into net production at the next level.
• When the activities of decomposers (bacteria and fungi) are
taken into account, trophic efficiency is much greater than 10%,
however.
The Energy Pyramid
• If a figure is constructed of the
amount of energy at each
trophic level, the figure appears
as a pyramid. This is due to the
metabolic losses in energy that
occur at each level.
• Primary producers form the
wide base of the pyramid,
primary consumers form the
next layer, and secondary and
tertiary consumers form the
apex of the pyramid.
• Not only energy, but also
numbers of individuals in the
trophic levels tend to follow a
pyramid shape.
Measuring Primary Productivity
• Measuring production involves harvesting and
weighing biomass produced/ unit time. In the case of
plants, underground portions must be considered in
measures of productivity.
• Factors that influence primary productivity include
temperature, intensity of sunlight (which varies
seasonally), and the age of the community.
• As communities such as forests age, productivity may
increase at first, but as they reach old age
productivity may decline.
Comparisons of Community Production
Community Climate
Kcal/m2/yr
Desert
Arid
400
Lake
Temperate
2,400
Deciduous
Forest
Temperate
4,800
Tropical
Rainforest
Tropical
20,000
Cropland
Temperate
8,800
Salt marsh
Temperate
12,000
Freshwater
marsh
Temperate
17,000
Generalizations about Community
Productivity
• The tropics have among the most productive systems,
in part because incident solar radiation is greater
toward the equator.
• The most productive temperate systems are marshes.
Nutrients are continually brought in and wastes are
flushed out as water moves through them.
• Deserts and oceans are among the least productive
systems. Little water in deserts and few nutrients in
open oceans are responsible. Thus, 80% of the Earth’s
surface is covered by the least productive systems.