Ecology – Energy flow through Ecosystems
Flow of energy
• Almost all activities of life are powered by energy
from the sun
• Energy moves through the communities of
ecosystems in a continuous one-way flow
• Nutrients constantly cycle and recycle in a
circular flow within ecosystems
• Energy enters ecosystem through photosynthesis
• Autotrophs or producers – convert solar energy
into organic molecules (food); become the basis
of the food chain
• Heterotrophs or consumers – acquire energy by
eating other organisms
• Amount of life an ecosystem can support depends on how
much solar energy the producers are able to convert into food
– primary productivity
 Gross primary productivity – total amount of energy
converted into the products of photosynthesis
 Plants use 10 – 70% of their gross productivity for their
own energy needs
 Net primary productivity – amount of energy stored (what is
left after the plant’s own cellular respiration) that is
available to consumers
 Measured in units of energy (calories) stored per unit
area in a given period
 Also measured in biomass – dry weight of organic
material
 Productivity of an ecosystem is influenced by many factors
Trophic Levels
Ecological niche – each species occupies it’s
own unique niche which encompasses all
aspects of it’s way of life – includes:
• Organism’s physical home or habitat
• Physical environmental factors necessary for
survival (range of temp it can withstand, pH
of soil, amount of moisture it needs, etc)
• What it eats and what it is eaten by – trophic
level
• Organism’s role in ecosystem – it’s
“occupation”
Trophic levels represent the levels through which energy flows as it
passes from the producers to the consumers in an ecosystem
•
“feeding level”
•
Relationship between what an organism eats and what it is
eaten by
1. Producers – autotrophic organisms that make food
2. Consumers – heterotrophs – from several trophic levels:
a. Primary consumers – herbivores – eat producers
b. Secondary consumers – eat primary consumers
(carnivores) eat other consumers
c. Top carnivore – top of food chain
d. Consumers may eat at different levels
e. Omnivores – eat producers and consumers
f. Scavengers – consumers that eat organisms recently
killed by other consumers (crows and hyenas)
3. Detritus feeders and decomposers – help
decompose and return nutrients to
atmosphere, soil and water


Detritus feeders – small animals and protists
that break down molted exoskeletons, fallen
leaves, dead bodies (ex. Earthworms, mites,
nematodes, pillbugs)
Decomposers (saprophytes) – fungi and
bacteria
• Trophic levels can be studied by looking at food chains –
each step in a food chain represents a trophic level
• Natural communities have food webs rather than simple
food chains – all of the possible food chains intertwined
Transfer of energy through trophic levels is
inefficient
• Each level only passes approx 10% of the
energy on to the next level (10% Law) – Why?
 Some of the energy is used for growth and
maintenance of organism itself
 Some of the energy is lost as heat during
metabolic processes
 Some of the energy is locked in chemical bonds
that consumer cannot break (cellulose)
• Less and less energy is available to
subsequent levels
• Transfer between trophic levels can be studied through
ecological pyramids
1. Pyramid of energy – shows maximum energy (productivity)
at the base and steadily diminishing amounts at higher
levels
2.
Pyramid of Numbers – number of individuals at each
trophic level
 Generally decreases as energy decreases moving up
each level
• Pyramid of Biomass – shows amount of
biomass at each trophic level
Ecology – Human Impact
• Biological magnification – process by which toxic
substances accumulate in increasingly high concentrations
in progressively higher trophic levels – ex. DDT is
dangerous because:
 Decomposers cannot readily break it down into
harmless substances (not biodegradable)
 It is fat soluble (not water soluble) and tends to
accumulate in the fatty tissues of animals
 Because of inefficient energy transfer between
trophic levels, herbivores eat large quantities of plant
material, carnivores eat larger amounts of
herbivores, etc. leading to biological magnification
 Higher trophic levels (top carnivores) have highest
concentrations in their tissues
 DDT continues to accumulate in predator’s body
through out it’s life
As humans have moved toward using fossil
fuels for energy, acid rain and global
warming have become major global issues
Acid rain – the US discharges 30 million
tons of sulfur dioxide into the atmosphere
each year
• 90% of sulfur dioxide in atmosphere
comes from human industrial activities
• Nitrogen oxide is also released from
vehicles, power plants and industry
• Acid rain or acid deposition (deposition of both wet or dry
acid)
• Sulfur dioxide and nitrogen oxide combines with water vapor
in the atmosphere to form sulfuric acid and nitric acid
• Acid often falls hundreds or thousands of miles away
(pollutants carried by the wind) dissolved in rain (snow, fog)
or as microscopic dry particles
• Acid eats away statues, buildings, damages trees and
crops, kills life in lakes
• Lakes become too acid to support life
• Acid rain washes away essential nutrients and kills microbes
that recycle nutrients
• Toxic metals (aluminum, lead, mercury, cadmium) dissolve
easier in acid rain and run into lakes and streams –
accumulates in fish leading to biological magnification
Global Warming
• As we burn fossil fuels, we release
increasing amounts of CO2 into the
atmosphere – since 1850, CO2 in the
atmosphere has increased more than 25%
 Deforestation (cutting of tens of millions
of acres of forest each year) also
increases CO2 in atmosphere
 Most in tropics, rain forests are burned
adding CO2 to atmosphere
Carbon Cycle
• CO2 has the ability to trap heat – acts very similar
to the glass in a greenhouse – allows solar energy
in and absorbs and holds the energy as heat –
greenhouse effect
• Effect is compounded by other greenhouse gases
(methane, chlorofluorocarbons or CFCs, water
vapor and nitrous oxide)
• Greenhouse effect is a natural process, allows life
on earth
• Human activities have amplified the
greenhouse effect leading to global warming
• each decade is showing record high average
temps that parallel the rise in atmospheric
CO2 and methane
levels
• Scientists predict a rise of 1.5o to 4.5o C in
average world air temps by end of 21st
century
• Last ice age was only 5o C lower than
present but that increase led to ocean
levels rising and moving inland by about
100 miles and great changes in species
composition
Consequences of Global Warming
• Sea levels will rise as polar ice caps and glaciers
melt – flood coastal cities and wetlands (breeding
grounds for many species of bird, fish, shrimp,
crabs – may become extinct)
• Shift in global distribution of temps and rainfall –
possibly leading to disruption of agriculture
• May have profound affect on distribution of tree
species – may wipe out hardwood forests of
eastern US
• May increase tropical disease-carrying organisms
like mosquitoes
• Global warming video
The Precautionary Principle
• Says that preventative action should be taken
now to reduce carbon emissions and greenhouse
gas production before it is too late
• Those who wish to continue producing excess
greenhouse gases should prove that there are no
harmful effects before continuing
• Some people argue against measures to combat
global warming because there is no absolute
proof that the greenhouse effect is harmful
• Counter argument is that by the time there is
proof, there will have already been catastrophic
consequences to the environment