Energy in Ecosystems II
IB syllabus: 2.1,
AP syllabus
Ch. 4
Syllabus Statements
• The non-living, physical factors that influence the
organisms and ecosystem—such as temperature,
sunlight, pH, salinity, and precipitation—are termed
abiotic factors.
• An ecosystem is a community and the physical
environment with which it interacts.
• The trophic level is the position that an organism occupies in
a food chain, or the position of a group of organisms in a
community that occupy the same position in food chains.
• • Producers (autotrophs) are typically plants or algae that
produce their own food using photosynthesis and form the
first trophic level in a food chain. Exceptions include
chemosynthetic organisms that produce food without
sunlight.
• Feeding relationships involve producers, consumers and
decomposers. These can be modelled using food chains,
food webs and ecological pyramids.
• Ecological pyramids include pyramids of numbers, biomass
and productivity and are quantitative models that are usually
measured for a given area and time.
• In accordance with the second law of thermodynamics,
there is a tendency for numbers and quantities of
biomass and energy to decrease along food chains;
therefore, the pyramids become narrower towards the
apex.
• Bioaccumulation is the build-up of persistent or nonbiodegradable pollutants within an organism or trophic
level because they cannot be broken down.
• Biomagnification is the increase in concentration of
persistent or nonbiodegradable pollutants along a food
chain.
• Toxins such as DDT and mercury accumulate along food
chains due to the decrease of biomass and energy.
• Pyramids of numbers can sometimes display different patterns;
for example, when individuals at lower trophic levels are
relatively large (Inverted pyramids).
• • A pyramid of biomass represents the standing stock or
storage of each trophic level, measured in units such as grams
of biomass per square metre (g m–2) or Joules per square
metre (J m-2) (units of biomass or energy).
• Pyramids of biomass can show greater quantities at higher
trophic levels because they represent the biomass present at a
fixed point in time, although seasonal variations may be
marked.
• Pyramids of productivity refer to the flow of energy through a
trophic level, indicating the rate at which that stock/storage is
being generated.
• Pyramids of productivity for entire ecosystems over a year
always show a decrease along the food chain.
vocabulary
•
•
•
•
•
•
Abiotic factor
Biomass
Biotic factor
Ecosystem
Standing crop
Trophic Level
Ecosystems
• Are communities and their
interactions with the
abiotic environment
Ecosystem Components
2 parts
– Abiotic – nonliving components
(water, air, nutrients, solar energy)
– Biotic – living components
(plants, animals, microorganisms)
Biota
Terrestrial Ecosystems
Aquatic Life Zones
• Light penetration
• Sunlight
• Water currents
• Temperature
• Dissolved nutrient
concentrations (especially N
and P)
• Precipitation
• Wind
• Latitude (distance from equator)
• Altitude (distance above sea level)
• Suspended solids
• Salinity
• Fire frequency
• Soil
Significant abiotic factors
What abiotic factors effect this
Aquatic food chain?
The abiotic influence
• Species thrive in different physical
conditions
• Population has a range of tolerance for
each factor
• Optimum level  best for most individuals
• Highly tolerant species live in a variety of
habitats with widely different conditions
The Law of Tolerance: The existence, abundance and distribution of a
species in an ecosystem are determined by whether the levels of one or
more physical or chemical factors fall within the range tolerated by
that species
Lower limit
of tolerance
Few
organisms
Abundance of organisms
Few
organisms
No
organisms
Population Size
No
organisms
Upper limit
of tolerance
Zone of
Zone of
intolerance physiological stress
Low
Optimum range
Temperature
Zone of
Zone of
physiological stress intolerance
High
Abiotic factors may be Limiting
Factors (2.6.1)
• Limiting factor – one factor that regulates
population growth more than other factors
• Too much or too little of an abiotic factor
may limit growth of a population
• Determines K, carrying capacity of an area
• Examples
– Temperature, sunlight, dissolved oxygen
(DO), nutrient availability
Techniques to measure abiotic factors
• Terrestrial
– Light intensity or insolation (
lux) – light meter; consider
effect of vegetation, time of
day…
– Temperature (°C) –
themometer; take at different
heights, points, times of day,
seasons…
– Soil moisture (centibars) –
tensiometer or wet mass dry
mass of soil; consider depth of
soil sample, surrounding
vegetation, slope…
• Aquatic (specify marine or
fresh)
– Salinity (ppt) – hydrometer;
consider role of evaporation
– Dissolved Oxygen (mg/L) – DO
meter, Winkler titration;
consider living organisms,
water circulation,
– pH – pH probe or litmus paper;
consider rainfall input, soil and
water buffering capacity
– Turbidity (FTU) – Secchi disk
or turbidity meter; consider
water movement,
Techniques (2.2.2)
•
For any of them you should know the
following
1. What apparatus is used for measurement
and its units
2. How it would vary or be used to measure
variation along an environmental gradient
3. Scientific concerns about its implementation
4. Evaluation of its effectiveness or limitations
Terminology and Roles of Biota
• Producers (Autotrophs) – Through
photosynthesis convert radiant to chemical
energy (energy transformation)
• Consumers (Heterotrophs) – Must consume
other organisms to meet their energy needs
– Herbivores, Carnivores, Omnivores, Scavengers,
Detritivores
• Decomposers – Break down organisms into
simple organic molecules (recycling
materials)
Food chains and Food webs
• Food chain  Sequence of organisms each of which
is the source of food for the next
• Feeding levels in the chain  Trophic levels
–
–
–
–
–
–
First trophic level = producer
Second trophic level = consumer, herbivore
Third trophic level = consumer, carnivore
Highest trophic level = top carnivore
Arrows indicate direction of energy flow!!!
Decomposers are not included in food chains and webs
• For complexity of real ecosystem need food web
which shows that individuals may exist at multiple
trophic levels in a system (omnivores)
Figure 53.10 Examples of terrestrial and marine food chains
Local examples
Trophic Level
Estuary system
Everglades habitat
Producer
Turtle grass
Phytoplankton
Primary Consumer
Grass shrimp
Zooplankton
Seconday Consumer
Pin fish
Blue gill
Tertiary Consumer
Spotted Sea trout
Bass
Quarternary Consumer
Osprey
Racoon
6th trophic level
Aligator
Food Web
• Summarizes the trophic relationships of a
community through a diagram
• Food chain  web, once a given species
enters the web at multiple trophic levels
• Most consumers are not exclusive to one
level (ex. we are omnivores)
Figure 53.11 An antarctic marine food web: Identify the trophic levels
Antarctic pelagic (open ocean) community found in
seasonally productive Southern Ocean
1. Zooplankton: dominant herbivores in Antarctic are
euphausids (krill) and herbivorous plankton called
copepods
2. The zooplankton are eaten by carnivores including
penguins, seals, fish, baleen whales
3. Carnivorous squid feeding on fish and zooplankton
are important link in food web
4. Seals and toothed whales eat squid
5. During whaling years humans became top predators
in the system
6. Entire food web depends on phytoplankton 
photosynthesizing microorganisms obtaining energy
from the sun
Food Webs
•
Food webs are limited by the energy flowing
through them and the matter recycling
within them
• Ecosystem is an energy machine and a
matter processor
1. Autotrophs: make their own food (plants
algae & photosynthetic prokaryotes)
2. Heterotrophs: directly or indirectly depend
on photosynthetic output of primary
producers
Producers
• Transform energy into a usable form
• Starting form may be light energy or
inorganic chemicals
• Turned into organic chemical energy
• This is the form that is used at other
trophic levels
Photoautotrophs
Consumers
• Heterotrophs: get energy from organic
matter consumed
• Primary, Secondary & Tertiary consumers
• Herbivores  primary consumers, eat
plant material e.g. – termites, deer
• Carnivores  other consumer levels, eat
animal material e.g. eagles, wolves
• Omnivores  consumers eating both e.g.
bears
Figure 53.0 Lion with kill in a grassland community
Decomposition
• Decomposers obtain energy by breaking
down glucose in the absence of oxygen
• Anaerobic respiration or fermentation
• End products = methane, ethyl alcohol,
acetic acid, hydrogen sulfide
• Matter recycling  inorganic nutrients
returned to producers
Decomposition Process
Detritus feeders
Bark beetle
engraving
Long-horned
beetle holes
Carpenter
ant
galleries
Decomposers
Termite and
carpenter
ant
work
Dry rot fungus
Wood
reduced
to powder
Time progression
Mushroom
Powder broken down by decomposers
into plant nutrients in soil
Consumers or Decomposers
• Detritivores = get their energy from detritus,
nonliving organic material  remains of dead
organisms feces, fallen leaves, wood
• May link producers to consumers
– Dung beetles, earth worms
• Saprotrophs = feed on dead organic material by
secreting digestive enzymes into it and absorbing
the digested products
• Producers can reassimilate these raw materials
– Fungi (mold, mushrooms), bacteria
Energy in living systems
• Food chains, webs and pyramids,
ultimately show energy flow
• Obey the laws of thermodynamics
• Obey systems laws – input, transfer,
transformation, output
Thermodynamics Review
Universal laws that govern all energy changes in the
universe, from nuclear reactions to the buzzing of a bee.
The 1st law: Energy can be transferred and transformed but
not created or destroyed
a)
–
–
Energy flow in the biological world is unidirectional:
Sun
energy enters system and replaces energy lost from heat
Energy at one trophic level is always less than the previous level
The 2nd law: Energy transformations proceed spontaneously
to convert matter from a more ordered, less stable form, to a
less ordered, more stable form
b)
-
Energy lost as heat from each level
Energy at one level less than previous because of these lossed
Energy Flow in Communities
• Energy unlike matter does not recycle through a
community  it flows
• Energy comes from the sun
• Converted by autotrophs into sugars
• Amount of Light energy converted into chemical
energy by autotrophs in a given time period  Gross
Primary Production GPP
• The amount to pass on to consumers after plants have
used their share  Net Primary Production NPP
• NPP = GPP - R
The Source of All energy on Earth
is the …
Figure 3-10
Page 52
Energy emitted from sun (Kcal/cm2/min)
15
10
Visible
Light is
The usable
Energy
5
0
0.25
1
2
Wavelength (micrometers)
2.5
3
What is the sun?
• 72% hydrogen, 28% helium
• Temp and pressure high so H nuclei fuse to
form He releasing energy
• Fusion energy radiated as electromagnetic
energy
• Earth receives 1 billionth of the suns Energy
• Most reflected away or absorbed by
atmospheric chemicals
Energy to Earth
• 30% solar energy reflected back into space by
atmosphere, clouds, ice
• 20% absorbed by clouds & atmosphere
• 50% remaining
– Warms troposphere and land
– Evaporates and cycles water
– Generates wind
• < 0.1% captured by producers for photosynthesis
• Energy eventually transformed to heat and trapped
by atmosphere “Natural Greenhouse Effect”
• Eventually reradiated into space
So if sunlight in = sunlight +
heat out
What state is the system in?
Stable Equilibrium
Summary of solar radiation
pathways
• Incident radiation comes in, it is then…
– Lost by reflection (ice caps) and absorption (soil,
water bodies)
– Converted from light to chemical energy
(photosynthesis in producers)
– Lost as chemical energy decreases through
trophic levels
– Through an ecosystem completely converted
from light energy into heat
– Reradiated as heat back to the atmosphere
Energy Flow II
• Energy measured in joules or kilojoules
per unit area per unit time
• Energy conversion never 100% efficient
• Some energy lost as heat
• Of visible light reaching producers, only
1% is converted to chemical energy
• Other levels are 10% efficient – only
assimilate %10 of energy from previous
level
Figure 54.1 An overview of ecosystem dynamics
Energy Flow and Food webs
• Biomass = the total dry weight of all
organisms in one trophic level
• Usable energy degraded with each
transfer
– Loss as heat, waste, metabolism
• % transferred = ecological efficiency 
ranges from 5-20%
• More trophic levels = less energy available
at high levels
If that loss happens at every trophic level think about how much
energy is lost.
Makes the lower trophic levels most efficient in terms of overall
energy available in the system
Energy Flow through Producers
• Producers convert light energy into
chemical energy of organic molecules
• Energy lost as cell respiration in producers
then as heat elsewhere
• When consumers eat producers energy
passes on to them
• In death organic matter passes to
saprophytes & detritivores
Energy Flow through Consumers
•
•
•
Obtain energy by eating producers or other
consumers
Energy transfer never above 20% efficient,
usually between 10 – 20%
Food ingested has multiple fates
1. Large portion used in cell respiration for
meeting energy requirements (LOSS)
2. Smaller portion is assimilated used for growth,
repair, reproduction
3. Smallest portion, undigested material excreted
as waste (LOSS)
Figure 54.10 Energy partitioning within a link of the food chain
Energy flow through Decomposers
• Some food is not digested by consumers
so lost as feces to detritivores &
saprophytes
• Energy eventually released by process of
cell respiration or lost as heat
Construct and analyze
energy flow diagrams
for energy movement
through ecosystems
• Trophic level boxes are
storages – biomass per
area (g m-2)
• Energy Flow in arrows –
rate of energy transfer
(g m-2 day-1)
Energy values in KJ m-2y-1
Often the size of the boxes and arrows is proportional to their
amount
Using Pyramids to express
ecosystem dynamics
© 2004 Brooks/Cole – Thomson Learning
Energy
Input:
1,700,000
kilocalories
Incoming solar energy
not harnessed
1,679,190
(98.8%)
Energy
Transfers
Waste,
remains
20,810
(1.2%)
Producers
4,245
Metabolic heat,
export
3,368 13,197
Herbivores
Top carnivores
21
Carnivores
Herbivores
383
3,368
720
383
2,265
Carnivores
90
21
Top
carnivores
5
272
16
Decomposers,
detritivores
Energy Output
Total Annual Energy Flow
20,810 + 1,679,190
1,700,000 (100%)
Decomposers/detritivores
Producers
20,810
5,060
Pyramids
• Graphic models of quantitative differences
between trophic levels
• By second law of thermodynamics energy
decreases along food webs
• Pyramids are thus narrower as one ascends
– Pyramids of numbers may be different  large
individuals at low trophic levels – large forests
– Pyramids of biomass may skew if larger
organisms are at high trophic levels  biomass
present at point in time – open ocean
Losses in the pyramid
• Energy is lost between each trophic level,
so less remains for the next level
– Respiration, Homeostasis, Movement, Heat
• Mass is also lost at each level
– Waste, shedding, …
Pyramids of Biomass
• Represents the standing stock of each
trophic level (in grams of biomass per unit
area g / m2)
• Represent storages along with pyramids of
numbers
How do we get the biomass of a trophic
level to make these pyramids?
• Why can’t we measure the biomass of an entire
trophic level?
• Take quantitative samples – known area or volume
• Measure the whole habitat size
• Dry samples to remove water weight
• Take Dry mass for sample then extrapolate to entire
trophic level
• Evaluation  It is an estimate based on assumption
that
– all individuals at that trophic level are the same
– The sample accurately represents the whole habitat
© 2004 Brooks/Cole – Thomson Learning
Pyramids of Biomass
Abandoned Field
Ocean
Tertiary consumers
Secondary consumers
Primary consumers
Producers
Pyramids of Numbers
• Needs sampling similar to Biomass and
therefore has the same limitations
• Also measures the storages
© 2004 Brooks/Cole – Thomson Learning
Pyramids of Numbers
Grassland
(summer)
Temperate Forest
(summer)
Tertiary consumers
Secondary consumers
Primary consumers
Producers
Pyramids of productivity
• Flow of energy through trophic levels
• Energy decreases along the food chain
– Lost as heat
• Productivity pyramids ALWAYS decrease
as they go higher – 1st and 2nd laws of
thermodynamics
• Shows rate at which stock is generated at
each level
• Productivity measured in units of flow
(J / m2 yr or g / m2 yr )
Figure 54.11 An idealized pyramid of net production
Figure 54.14 Food energy available to the human population at different trophic
levels
Efficiency of trophic levels in relation to the total energy
available decreases with higher numbers
But efficiency of transfer always remains around that 10% rule
Take an Economic Analogy
1. If you look at the turnover of two retail outlets
you can’t just look at the goods on the shelves
• Rates of stocking shelves and selling goods
must be known as well
2. A business may have substantial assets but
cash flow may be limited
3. So our pyramids of Biomass and numbers are
like the stock or the assets and our pyramids
of Productivity are like our rate of generation or
use of the stock
How does pyramid structure effect
ecosystem function?
1. Limited length of food chains
•
•
•
Rarely more than 4 or 5 trophic levels
Not enough energy left after 4-5 transfers to
support organisms feeding high up
Possible exception marine/aquatic systems
b/c first few levels small and little structure
2. Vulnerability of top carnivores
•
•
•
Effected by changes at all lower levels
Small numbers to begin with
Effected by pollutants & toxins passed
through system
Effects II: Biomagnification
1. Mostly Heavy metals & Pesticides
•
•
Insoluble in water, soluble in fats,
Resistant to biological and chemical degradation,
not biodegradable
2. Accumulate in tissues of organisms
3. Amplify in food chains and webs
4. Sublethal effects in reproductive & immune
systems
5. Long term health effects in humans include
tumors, organ damage, …
Water
0.000002 ppm
Phytoplankton
0.0025 ppm
Herring gull
124 ppm
Herring gull eggs
124 ppm
Zooplankton
0.123 ppm
Lake trout
4.83 ppm
Rainbow smelt
1.04 ppm
Practice Problems
• The insolation energy in an area of rainforest is
15,000,000 cal/ m2/day. This is the total amount of sun
energy reaching the ground. The GPP of the producers
in the area, large rainforest trees, is 0.0050 g/cm2/day
and 25% of this productivity is consumed in respiration.
By laboratory tests we found that 1 gram of rainforest
tree contains 1,675 calories of energy.
•
A. What trophic level are the trees considered? (2
point)
•
B. Calculate the NPP of the system. (5 point)
•
C. Find the efficiency of photosynthesis. (5 point)
•
D. If a monkey population eats the fruit from the
trees how many square meters of forest will each
individual need to feed in if they require 400 calories
each day?
Practice
• Create a food web for the following FL
organisms
largemouth bass, panther, racoon, white tailed
deer, bullfrog, shiner (small fish), water
beetles, zooplankton, phytoplankton, marsh
grass, rabbit, water moccasin, dragonfly,
duckweed, egret, wood duck,
Human
Blue whale
Sperm whale
Killer
whale
Elephant
seal
Practice:
Crabeater seal
Identify the trophic levels
In the food web
Leopard
seal
Emperor
penguin
Adélie
penguins
Petrel
Squid
Fish
Carnivorous plankton
Herbivorous
zooplankton
Krill
Phytoplankton
• http://www.indianriverlagoon.org/stats.html