Transcript Energy Flow

Energy Flow
• Energy flows INTO an ecosystem as
sunlight
• This is converted into chemical energy
by autotrophs
• It is then passed to heterotrophs in the
organic compounds as food
• It will eventually leave the ecosystem as
heat
Energy flow
• Chemical elements are cycled between the
biotic and abiotic environment BUT
• Energy cannot be recycled so an ecosystem
must be powered by a continuous influx of
new energy from an external source
• Therefore energy flows THROUGH an
ecosystem whilst matter CYCLES
Trophic structure
• In biological ecosystems there exists a
hierarchy of organisms defined by the way in
which they obtain energy from their
surroundings
• This is the ecosystems TROPHIC STRUCTURE
• The trophic structure of the ecosystem
determines the route of energy flow and
chemical cycling
• This can be shown in a FOOD CHAIN which
shows the individual populations from each
trophic level
Producers
• Ultimately support all the other organisms
• Are the Primary producer
• Manufacture their own organic molecules (energy
containing nutrients)
• Mostly are photosynthetic creating organic molecules
from energy from sunlight
• Mainly plants but also algae and some protocists
Terrestrial: plants
Oceanic:
Phytoplankton (algae/bacteria)
Shores:
multi-cellular algae and aquatic plants
Consumers
• These are heterotrophic
• Directly or indirectly depend on photosynthetic
output by primary producers
• Obtain their energy containing nutrients by
consuming other organisms
• Includes all animals and fungi as well as some
bacteria and protocists
Primary Consumers
• Herbivores
• Consuming primary producers (plants and
algae and other photosynthetic organisms)
• Many also consume dead matter also
Terrestrial: mostly insects, snails, plant parasites and
some vertebrates (grazing mammals, birds)
Aquatic:
zooplankton (including heterotrophic
protocists), small invertebrates and some
fish
Sea-shores: multi-cellular algae and aquatic plants
Secondary and Tertiary
Consumers
Secondary Consumers:
Carnivores that eat herbivores (primary
consumers)
Tertiary Consumers:
Carnivores that feed on other carnivores
(secondary consumers)
Decomposers
Detrivores
•Animals that eat detritus.
•digest much of the material, but unable to digest
cellulose/lignin in plant cell walls but do break them
down
Saprophytes
• Mircobes (fungi and bacteria) that live on detritus.
• Digest it by extracellular digestion, and then absorb
the soluble nutrients.
• Can completely break down any organic matter
(including cellulose and lignin) to inorganic matter
such as carbon dioxide, water and mineral ions.
Light
Producers
Primary consumers
Decomposers
Death
Secondary Consumers
Tertiary consumers
Heat Energy
Top consumers
Heat
Energy
Energy Loss
• As energy flows through each trophic level
much is lost before it is consumed by organisms
at the next level
• Herbivores only eat a small fraction of plant
material produced and cannot digest all of it,
some will be passed unprocessed in the faeces.
• Of the energy they do take up, only a small
percentage would be used for growth and
available for the next trophic level.
Energy Loss
• The rest is used in cellular respiration which
degrades food molecules to inorganic waste
products and heat
• Carnivores are slightly more efficient at
converting food into biomass (because meat is
more easily digested than vegetation)
• But often secondary consumers use more
energy for cellular respiration., decreasing the
amount available for the next trophic level
Ecological Efficiency
This is the percentage of energy transferred
from one trophic level to the next
Efficiencies vary greatly among organisms from
5% to 20%
Therefore 80 to 95% of available energy is not
transferred to the next trophic level
This is often represented in pyramids of biomass
Ecological Efficiency
Some animals are more efficient at converting
energy into organic matter than others. Why?
• Large or small
•Homeothermic or Poikilothermic
•Carnivore or herbivore
•Young or old
98 %
Light
Producers
2%
10 %
Primary consumers
10 %
Decomposers
Death
Secondary Consumers
10 %
Tertiary consumers
Heat Energy
10 %
Top consumers
Heat
Energy
Pyramids of Energy
•
In general as you go up a food chain the size of the
individuals increases and the number of individuals
decreases.
•
Pyramids of energy are always pyramidal (energy cannot
be created), and always very shallow, since the transfer
of energy from one trophic level to the next is very
inefficient
•
The "missing" energy, which is not passed on to the next
level, is lost eventually as heat.
Pyramid of Energy
Tertiary Consumer
Secondary Consumer
Primary Consumer
Producer
Pyramid of Numbers
• The simplest way to compare different triophic
levels.
• These show the numbers of organisms at each
trophic level within a food chain
• The width of the bars represent the numbers,
or the bars may be purely qualitative
• Pyramids of numbers are most often triangular
(pyramid shaped- hence the name) shaped, but
can be almost any shape.
Advantage:
Allows us to overcome trying to compare the
numbers of organisms of varying sizes
Typical carnivore pyramid of
numbers
Owls
Mice
Snails
Grass
Single large producer
Owls
Blue tits
Caterpillars
Tree
Parasitic pyramid of
numbers
Parasites
Aphids
Rose bush
Parasitic wasp
Butterfly larvae
Nettle plant
Pyramid of Biomass
• These convey more information, since they consider
the total mass of living material (i.e. the biomass) at
each trophic level
• When measured the biomass is dry mass (since water
stores no energy) measured in kg m-2
• This can be found by drying and weighing the
organisms at each trophic level, or by counting them
and multiplying by an average individual mass.
• Pyramids of biomass are always pyramid shaped, since
if a trophic level gains all its mass from the level
below, then it cannot have more mass than that level
(you cannot weigh more than you eat). Except for ONE
exception!
• The "missing" mass, which is not eaten by consumers,
becomes detritus and is decomposed
Numbers vs Biomass
Birds
Ladybirds
Aphids
Rose bush
Pyramid of
numbers
Pyramid of
biomass