Download Nutrient and Energy Transfer (Lecture 6)

Physiological Ecology
Outline
 Introduction
 Evolution
to Ecology
and Natural Selection
 Physiological
 Behavioural
Ecology
Ecology
Physiological Ecology
 study
of species’ needs and tolerances
that determine their distribution and
abundance
 species
need lots of things: e.g.,
carbon, nitrogen, amino acids, etc.
– we will discuss species needs and
tolerances with regards to ENERGY
Physiological Ecology
 Nutrient
and Energy Transfer
 Endothermy
and Ectothermy
 Climate
 Current
Climate Change
Physiological Ecology
 Nutrient
and Energy Transfer
 Endothermy
and Ectothermy
 Climate
 Current
Climate Change
Nutrient and Energy Transfer
Ch. 6.1 – 6.6, Bush
Outline
 Basics
of energy
 Photosynthesis
 Trophic
Levels
 Efficiency
of Energy Transfer
Outline
 Basics
of energy
 Photosynthesis
 Trophic
Levels
 Efficiency
of Energy Transfer
Forms of Energy

Fuel (chemical bond energy):
– nutrients, such as carbohydrates
– needed for everything a species does
– e.g., growth, movement

Heat:
– needed for all chemical reactions
– by-product of reactions

Light:
– needed by plants to create fuel
Energy transfer
Energy source

The ultimate energy
source for (most) life
on earth is the sun
Outline
 Basics
of energy
 Photosynthesis
 Trophic
Levels
 Efficiency
of Energy Transfer
Photosynthesis
 What
is it?
 Chlorophyll,
 Variations
 The
a necessary pigment
in photosynthesis
fate of carbohydrate
Photosynthesis

Synthesis of
carbohydrates from
CO2 and water

Sunlight acts as
energy source

O2 is a by-product
In Chemistry notation…
Energy from sunlight + CO2 + H2O 
CH2O + O2
Chlorophyll, a necessary pigment
Pigments absorb light energy
Pigments absorb light energy between 400-700 m
-energy in this range is termed
Photosynthetically Active Radiation (PAR)
Why are leaves green?

Pigments cannot
absorb light in the
green wavelength
region
The “Green Gap”
Why are some plants not green?

Chlorophyll is
missing from some
cells, making the
reflectance of other
pigments visible
Fall colour

the production of
chlorophyll requires
sunlight and warm
temperatures

in many plants,
chlorophyll production
stops in fall and other
pigments become
visible
Why is chlorophyll necessary?

Other pigments pass on the
energy they absorb to a
chlorophyll molecule

When chlorophyll is in an
energized state, it is able to turn
light energy into chemical bond
energy

This chemical bond energy
passes through a number of
different molecules and then rests
within a carbohydrate (glucose)
molecule
Variations in photosynthesis
 C3
photosynthesis
 C4
photosynthesis
 CAM
photosynthesis
CO2 must enter though stomata

stomata (sing., stoma)
are tiny holes on the
undersides of leaves

CO2 enters and
moisture is released

In hot, dry climates, this
moisture loss is a
problem
CO2 is turned into sugar with
RUBISCO

RUBISCO (short for
Ribulose-1,5-bisphosphate
carboxylase) is the most
important enzyme on Earth

O2 has an inhibitory effect
upon photosynthesis
because it makes RUBISCO
perform
PHOTORESPIRATION
instead
C3 photosynthesis
– CO2 enters passively so
stomata have to be open
for long periods of time
– Majority of plant species
use this variation of
photosynthesis
– C3 plants experience high
rates of:
 water loss in hot, arid
regions
photorespiration
where O2:CO2 ratio is
high
C4 photosynthesis
– Have a special enzyme that
actively pumps in CO2 and
delivers it to RUBISCO enzyme
so:
 (1) stomata do not have to
be open for long
 (2) photorespiration is
reduced
– Energetically costly
– 1-4% of plant species use C4
photosynthesis.
– used by species that live in hot,
sunny environments with low CO2
 E.g. tropical grasses
The global distribution of C4 plants in
today's world

C4 grasslands (orange)
have evolved in the tropics
and warm temperate regions
where C3 forests (green) are
excluded by seasonal
drought and fire.

C3 grasses (yellow) remain
dominant in cool temperate
grasslands because C4
grasses are less productive
at low temperatures.
CAM photosynthesis
– open stomata at night
when the air is cool and
more humid, thereby
reducing water loss
– store the CO2 in tissues
to be used during the day
– storage space is a
potential constraint, thus
many CAM plants are
succulent (e.g. cacti)
Unrelated species with similar physiology
-Photosynthetic pathways
show CONVERGENT
EVOLUTION
-CAM found in at least 12
different families
-Recent studies say C4
has independently
evolved over 45 times
in 19 families of
angiosperms
Cacti (Americas)
Euphorbia (Africa)
Why photosynthesize?

sugars created from
photosynthesis are
necessary for:
– chemical reactions
– plant functions
– e.g., conduction
of water and
nutrients up the
stem
– growth (biomass)
Outline
 Basics
of energy
 Photosynthesis
 Trophic
Levels
 Efficiency
of Energy Transfer
Energy transfer
Two types of organisms

Autotrophs (producers)
– organisms which can manufacture their own food
– e.g., plants

Heterotrophs (consumers)
– “other feeders” – organisms which must consume
other organisms to obtain their carbon and energy
– e.g., animals, fungi, most protists, most bacteria
Trophic Levels

Tropic level refers to how organisms fit in
based on their main source of nutrition
– Primary producers
 autotrophs (plants, algae, many bacteria, phytoplankton)
– Primary consumers
 heterotrophs that feed on autotrophs (herbivores,zooplankton)
– Secondary, tertiary, quaternary consumers
 heterotrophs that feed on consumers in trophic level below
them (carnivores)
– Detritivores
 bacteria, fungi, and animals that feed on decaying organic
matter
Trophic levels examples
How many trophic levels?
Exceptions to the rule?

Carnivorous plants
capture and digest
animal prey

They are able to grow
without animal prey,
albeit more slowly

~600 spp. of
carnivorous plants
have been described
Food chains versus food webs
chain – the pathway along which
food is transferred from trophic level to
trophic level in an ecosystem
 Food
web – the feeding relationships in
an ecosystem; many consumers are
opportunistic feeders
 Food
Food chains versus food webs
Food chains
Food web
Outline
 Basics
of energy
 Photosynthesis
 Trophic
Levels
 Efficiency
of Energy Transfer
The energy budget

The extent of photosynthetic activity sets the
energy budget for the entire ecosystem

Of the visible light that reaches
photosynthetic land plants, 1% to 2% is
converted to chemical energy by
photosynthesis

Aquatic or marine primary producers (algae)
convert 3-4.5% - this difference accounts for
why aquatic and marine food chains tend to
be longer
Efficiency of Producers
One difference among ecosystems
is their reflectance. Broadleaf
forests reflect up to 20% of visible
radiation. Conifer forests reflect
only about 5%.
Ecosystems with low leaf area (e.g. deserts)
absorb very little light. Conifer forests with
very high leaf area index can absorb almost
95% or more of the “incident light”
Coniferous versus deciduous forest
Efficiency of photosynthesis

Of the energy that is
actually absorbed
by chloroplasts, at
best about 20% is
converted into
sugars
Plant biomass – a fraction of total
energy

Of the solar energy
that is converted
into organic
molecules in
photosynthesis,
about 40-50% is lost
in the processes of
respiration
Primary productivity

Gross Primary Productivity (GPP):
– total amount of photosynthetic energy captured in
a given period of time.

Net Primary Productivity (NPP):
– the amount of plant biomass (energy) after cell
respiration has occurred in plant tissues.
NPP
=
plant growth/
unit area/
unit time
GPP
–
total photosynthesis/
unit area/unit time
Plant respiration
Secondary Productivity
productivity – the rate at
which consumers convert the chemical
energy of the food they eat into their
own new biomass
 Secondary
Pyramid of productivity
 Energy
content of each trophic level
 Pyramid
has large base and gets
significantly smaller at each level
 Organisms
use energy for respiration
so less energy is available to each
successive trophic level
Productivity pyramid
Calculating Ecological Efficiency
 Lindeman
Efficiency:
-can be seen as the ratio of assimilation
between trophic levels
= energy (growth + respiration) of predator
energy (growth + respiration) of food species
Simplifying Ecological Efficiency
 Production
Efficiency:
-can be seen as the ratio of biomass production
between trophic levels
= energy (growth + respiration) of predator
energy (growth + respiration) of food species
Calculating efficiencies
e.g., grasshopper:
Efficiency:
=1,000 J / 10,000 J
=10% efficient
Efficiencies
 Herbivores
are generally more efficient
than carnivores (7% versus 1%)
 Ectotherms
are more efficient than
endotherms (up to 15% versus 7%)
The “Lost” energy
 First
Law of Thermodynamics:
– energy cannot be created or destroyed it
can only change form
 Second
Law of Thermodynamics:
– as energy changes form it becomes more
disorganized. I.e., ENTROPY increases
Energy quality index:
– light>chemical bond>movement,heat
What happens to the rest of the
energy?

used to do work (cell
processes, activity,
reproduction)

“Lost” as heat (entropy)

not consumed or not
assimilated:
decomposers
eventually get this!
Detritivores and decomposers
Summary

Virtually all energy comes from the sun; this energy
is never destroyed, it just changes form

Photosynthesis converts light energy into chemical
energy

All other trophic levels depend on photosynthesis for
life

Organisms vary in their ability to extract energy from
the trophic level below them but most efficiencies are
below 15%, leaving much for detritivores