BIOL 4120: Principles of Ecology
Lecture 3: Adaptation to
Physical Environment: Light,
Energy and Heat
Dafeng Hui
Office: Harned Hall 320
Phone: 963-5777
Email: dhui@tnstate.edu
Topics (Chapter 3)
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3.1 Light is primary source of energy for the
biosphere
3.2 Plants capture the energy of sunlight by
photosynthesis
3.3 Plants modify photosynthesis in high water
stress environments
3.4 Diffusion limits uptakes of dissolved gases from
water
3.5 Temperature limits occurrence of life
3.6 Each organism functions best under certain
temperature
3.7 Homeothermy increases metabolic rate and
efficiency
Earth provides highly diverse
environments:
1.7 million known species now
All species have three common
basic functions
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Assimilation: acquire energy from external environment
Reproduction: to produce new individuals
Response to external stimuli: able to respond to both
physical (light, temperature etc) and biotic (predator etc).
All organisms acquire energy
• Energy obtained directly from an energy source by a living
organism is called autotrophy (autotroph)
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Plants are autotrophs, primary producers
So are certain bacteria like Thiobacullus ferrooxidans
• Energy obtained indirectly from organic molecules by a living
organism is called heterotrophy (heterotroph)
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All animals are heterotrophs, secondary producers
Some organisms can be a mixture like lichens where you have an
alga and a fungus living together
Autotrophs obtain solar energy through photosynthesis.
3.1 Light is the primary source of
energy for the biosphere
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All life requires energy to
sustain itself
With very few exceptions,
all life on earth is
dependent on solar
energy
Life on Earth exists
because it’s fitness is
optimal for the
environment created by
solar energy
Shortwave
longwave radiation
Earth is a balanced ecosystem in term of
solar energy inputs and outputs
Light is the primary source of
energy for the biosphere
PAR:
photosynthetically
active radiation
400-700 nm
Light absorption
spectra of plants
Light absorption spectra of
algae
Ulva: sea lettuce, shallow water
Porphyra: red alga, deep-water
3.2 Plants capture energy of
sunlight by photosynthesis
Photosynthesis (review)
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All life is built on a framework of
carbon atoms
The ultimate source of carbon for
organic molecules is CO2
CO2 is transformed into organic
molecules by plants (photosynthesis).
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Photosynthesis is the process by which the
Sun’s energy (shortwave radiation) is used to
fix CO2 into carbohydrates (simple sugars)
and release O2
Photosynthesis begins with light reactions
• Absorption of light energy by chlorophyll (a
pigment molecule)
• Conversion of the light energy into ATP (adenosine
tri-Phosphate) and NADPH (Reduced form of
nicotinamide adenine dinucleotide phosphate)
Photosynthesis continues with the dark reactions
• Incorporation of CO2 into simple (organic) sugars
using the energy provided by ATP and NADPH
• Carboxylation is catalyzed by the enzyme rubisco
(ribulose biphosphate (RuBP) carboxylaseoxygenase)
C3
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The Calvin cycle (C3 cycle) initially
fixes CO2 into 3-PGA
(phosphoglycerate)
This cycle is called Calvin-Bensen
cycle, or C3 cycle. Plants employing it
are known as C3 plants
RuBP: Ribulose biphosphate
Rubisco: ribulose biphosphate
(RuBP) carboxylase-oxygenase
3-PGA: phosphoglycerate
G3P: glyceraldehyde 3-phosphate
C3 cycle (Calvin cycle)
One major drawback of C3
pathway:
Rubisco can catalyze both
carbonxylation
CO2  RuBP  2 3  PGA
And RuBP oxygenation
O2  RuBP  CO2
Reduce the efficiency of
photosynthesis.
C3 plant: trees, forbs,
some grasses
Photosynthesis
6CO2  6H 2O  C6 H12O6  6O2
Cellular respiration
C6 H12O6  6O2  6CO2  6H 2O  ATP
Net photosynthesis = (Gross) Photosynthesis - Respiration
BIOL 4120: Principles of Ecology
Lecture 3: Adaptation to
Physical Environment: Light,
Energy and Heat
Dafeng Hui
Office: Harned Hall 320
Phone: 963-5777
Email: dhui@tnstate.edu
Recap
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Water and salt balance by plants and
animals
Solar radiation is the energy source
for life, PAR, water absorption
Photosynthesis
C3 photosynthetic pathway
3.3 Other photosynthesis
pathways: adaptation to
water and temperature
conditions
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To increase water use
efficiency in a warm dry
environment, plants have
modified process of
photosynthesis
C3
• Normal in mesophyll
with rubisco
C4
• Warm dry environment
• Additional step in
fixation of CO2
• Phosphoenolpyruvate
synthase (PEP) does
initial fixation into
Malate and aspartate
• Malate and aspartate
are transported to
bundle sheath as an
intermediate molecule
• Rubisco and CO2
convert there to
sucrose
C4 pathway
Advantages over C3 pathway
1.
PEP does not interact with O2
(RuBP react with O2 and reduce the
photosynthesis efficiency)
2.
Conversion of malic and aspartic
acids into CO2 within bundle sheath
cell acts to concentrate CO2, create
a much higher CO2 concentration.
C4 plants have a much higher
photosynthetic rate and greater
water-use efficiency.
C4 plants are mostly grasses native to
tropical and subtropical regions and
some shrubs of arid and saline
environments (Crop: corn, sorghum,
sugar cane).
CAM pathway
CAM (Crassulacean acid
metabolism) pathway
Hot desert area
Mostly succulents in the
family of Cactaceae
(cacti), Euphorbiaceae
and Crassulaceae)
Similar to C4 pathway
Different times:
Night: open stomata,
convert CO2 to malic
acid using PEP
Day:close stomata, reconvert malic acid to
CO2, C3 cycle.
Comparison of three
photosynthetic
pathways
C3: Dovefoot geranium,
C4: sorghum,
CAM: Sierra sedium
3.4 Plant adaptation to control water loss
In addition to photosynthetic pathway
differences, heat and drought-adapted plants
have anatomic and physiological modifications
that reduce transpiration, heat load and enable
plants to tolerate high temperature.
3.5 Photosynthesis of aquatic plants
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Unique features
• Lack of stomata
• Direct diffusion of CO2 across cell membrane
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Slow in water than in air (10^4 times slower)
• Some plants: CO2 reacts with H2O first to
produce biocarbonate, and Convert
biocarbonate to CO2
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Transport HCO3- into leaf then convert to CO2
Excretion of the enzyme into adjacent waters and
subsequent uptake of converted CO2 across the
membrane.
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CO2 could be a constraint in dense sea-grass beds
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Oxygen concentration in aquatic
environment
High O2 in the
surface due to
diffusion
O2 is
dissolved in
water
O2
concentration
in water is
determined
by solubility
and diffusion.
Anaerobic
conditions in
the deep
water
3.6 Carbon gained in photosynthesis is allocated to
production of plant tissues
Carbon allocation is an
important issue and has not
been well studied.
Difficult to measure, especially
below ground.
Allocation to different parts has
major influences on survival,
growth, and reproduction.
Leaf: photosynthesis
Stem: support
Root: uptake of nutrient and
water
Flower and seed: reproduction.
In dry grassland ecosystems,
plants have long roots
Allocation and environmental factors (such
as temperature and precipitation)
Hui & Jackson 2006
Constraints Imposed by the Physical
Environment Have Resulted in a Wide
Array of Plant Adaptations
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Plants must maintain a positive carbon
balance to survive, grow, and reproduce
Essential plant resources and conditions are
interdependent
• Light (PAR)
• CO2
• H2O and Minerals
• Temperature
3.7 Species of Plants are adapted
to light conditions
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Plants adapted to a shady
environment
• Lower levels of rubisco
• Higher levels of
chlorophyll (increase
ability to capture light, as
light is limiting)
• low light compensation
and saturation lights
Light intensity
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Red oak
leaves at
top and
bottom of
canopy
Plants adapted to a full sun
environment
• Higher levels of rubisco
• Lower levels of chlorophyll
• High compensation and
saturation lights
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Changes in leaf structure
evolve
Light affects photosynthesis and respiration
Stuart Davies of Harvard University studied the
photosynthesis and respiration of seedlings of nine
tree species under different light
Light also affects whether a plant allocates to
leaves or to roots
Change of allocation to leaf of
broadleaved peppermint (Reich et
al.).
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Shade tolerant (shadeadapted) species
• Plant species adapted to
low-light environments
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Shade intolerant (sunadapted) species
• Plant species adapted to
high-light environments
Shade tolerance and intolerance
Shade tolerance
Seedling
survival and
growth of
two tree
species
over a year
Augspurger
(1982)
Shade intolerance
BIOL 4120: Principles of Ecology
Lecture 3: Adaptation to
Physical Environment: Light,
Energy and Heat
Dafeng Hui
Office: Harned Hall 320
Phone: 963-5777
Email: dhui@tnstate.edu
Recap
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C4 and CAM pathways
Aquatic plants
Photosynthesis and environmental
factors
• Light, response curve, adaptation
3.9 Temperatures influence photosynthesis and
respiration
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Different responses of
photosynthesis and
respiration to temperature;
Three basic Temperature
points
• Min T, max T and optimal T
Plants need to make serious evolutionary
adaptations to temperature
C4
C4
C3
Neuropogon: Arctic lichen (C3)
Ambrosia: cool coastal dune plant (C3)
Tidestromia: summer-active desert C4 perennial
Photosyn. rate and Topt
Atriplx: everygreen desert C4 plant
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Topt: C3: <30oC; C4: 30oC to 40oC; CAM, >40oC
Plants Vary in Their Response to
Environmental Temperatures
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Temperature responses are not fixed
When individuals of the same species are
grown under different thermal conditions, a
divergence in temperature response of net
photosynthesis is often observed
• The Topt shifts in the direction of the
thermal conditions under which the plant
is grown
A similar pattern is seen in individual plants
in response to seasonal shifts in
temperature (acclimation)
Big saltbush, C4
Affinity is a good measure of enzyme function.
Produce different forms of enzyme.
3.12 Plants exhibit adaptations to
variations in nutrient availability
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Plants need nutrient for
metabolic processes and
synthesize new tissues
According to amount of
nutrient required:
• Macronutrients: needed in
large amount
N, P, K, Ca, Mg, S
• Micronutrients: needed in
lesser quantities
Zn, B, Cu, Ni, Fe
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Some nutrients can be
inhibitory
Plants exhibit adaptations to variations
in nutrient availability
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Uptake of a
nutrient through
the roots depends
on its
concentration
However there is a
maximum uptake
rate
Effect of nutrient
availability can also
reach a maximum
Photosynthesis and nutrient
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Nitrogen can limit
photosynthesis
N in enzyme
rubisco and
pigment
chlorophyll.
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Plants respond
differently to extra
nitrogen depending
on their natural
environment’s level
of nitrogen or
other nutrient
Two grass species, carpet bent
grass (A. stolonifera) in high N
and velent bent grass (A.
canina) in low N conditions.
Other factors: Impact of CO2 on
photosynthesis
Illustration of
tradeoffs of
C4, C3 plants
with CO2
concentration
Increase in
CO2 will
influence the
competition
of C3 and
C4
3.13 Regulation of internal conditions
involves homeostasis and feedback
Homeostasis: The maintenance of a
relatively constant internal environment in
a varying external environment.
Homeostasis depends on negative feedback
Negative feedback: when a system
deviates from the normal or desired state,
mechanisms function to restore the
system back to that state.
Example: room temperature setting
Homeostasis
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To stay alive, animals
need to keep their body
within certain limits
• Temperature
• Water balance
• pH
• Salt balance
Feedback systems to
help to keep within
specific limits
Outside limits –
• Dehydration
• Heat shock
• Salt imbalance
• Death
Negative feedback (thermoregulation)
Animals exchange energy with their surrounding
environment
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Body structure influences
the T exchange
Temperature (Tb, Ts, Ta)
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Tb<->Ts conduction
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• Core temperature Tb
• Surface temperature Ts
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Ts<->Ta: convection,
radiation, evaporation
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Ears
Fingers
Toes
Boundary layer (a thin layer of air
surround the body)
Insulation (air, body
covering) influences energy
exchanges
3.14 Animals have different methods of
maintaining their body temperatures
Three groups of animals
 Endothermy resulting in homeothermy
• Use of internal heat source (metabolically)
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Mammals and birds
Maintain a fairly constant temperature (warm-blooded)
Ectothermy resulting in poikilothermy
• Use of external heat sources
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Reptiles, amphibians, fish, insects and invertebrates
Results in a variable body temperature (cold-blooded)
Heterothermy
• Uses both endothermy and ectothermy
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Bats, bees and hummingbirds
Poikilotherms depend on
environmental temperatures
• As the temperature
increases, so does the
metabolic rate
• Therefore these animals
are more active during the
day
• Every 10oC doubles
metabolic rate (Q10)
• Natural condition: low
metabolic rate and high
conductivity
• Activities also controlled by
temperature
• Upper and lower limits vary
Lizards and snakes have a
5oC
o
 Amphibians have a 10 C
Operative T range: range of body T at which poikilotherms can carry
out their daily activities.
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During the day, the snake
can maintain a fairly
constant temperature by
adjusting it’s environment
(bask in sun to raise T,
seek shade to cool,
submerge in water etc)
During the night, it has
few options
• Temperature drops 1015 degrees
• Become torpid (slow
moving)
• Restricted by
environment
• Maximum size due to
need for surface area
to gather heat
• No minimum size
3.15 Homeotherms escape the thermal
restraints of the environment
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Homeotherms can escape the thermal restraints of
the environments, thus can exploit a wide range
of thermal environments
But needs energy to maintain relative constant T
Therefore homeotherms use large amounts of
glucose etc to maintain temperature (aerobic
respiration)
O2 is consumed during respiration
Rate of O2 consumption is used to measure
metabolic rate
Basal metabolic rate is considered as proportional
to their body mass (body mass 0.75) (debate? See
Hui & Jackson 2007 and others)
Metabolic rate and body mass
Resting metabolic rate and ambient
temperature
Thermoneutral zone:
a range of
environmental
temperatures within
which the metabolic
rates are minimal.
Critical T: lower and
upper critical T
BIOL 4120: Principles of Ecology
Lecture 3: Adaptation to
Physical Environment: Light,
Energy and Heat
Dafeng Hui
Office: Harned Hall 320
Phone: 963-5777
Email: dhui@tnstate.edu
Recap

Photosynthesis and environmental
factors
• (Light) Temperature
• Nutrients (and Water)
• CO2
Homeostasis and negative feedback
Endothermy and ecotothermy
Homeotherms can escape the thermal
constraints of the environments
Ways to keep body warm:
1. Insulation to reduce the convection: fur, feather, or body
fat
Mammals: fur, change fur in the winter
Fur can keep body heat in and the heat out
Birds: feather
Insects: a dense fur-like coat (moths, bees)
2. When insulation fails: shivering (a form of involuntary
muscular activity that increase heat production.
3. Small mammals: burn brown fat (bats) without shivering.
Ways to keep body Cool:
1. birds and mammals: evaporation of moisture from skin
2. mammals: sweat glands (horse, human), panting
3. birds: gular fluttering
3.16 Endothermy and Ectothermy involve
trade-offs
Endotherms can survive in large range of T,
why not all animals are endotherms?
Trade-offs:
Endothermy
Activity: under all environments
Energy: high
Food:
most for respiration, less
to growth
Limits on size:
limit on minimum size
Ectotherms
limited to environmental T
low
less for respiration
more to growth
limit on maximum size
Limited in size
Warm-blooded animals: body
mass (volume) produce
heat, lost through surface
area, the ratio of surface to
volume is key factor too.
• Small animals have
larger ratio and greater
relative heat loss to
environment, require
higher mass-specific
metabolic rate to
maintain and consume
more food energy per
unit body weight.
• Too small
 Need too much
energy to keep
temperature stable
Cold-blooded animals absorb heat through
 2 gm limit
surface, thus the surface area to volume is
 Shrew (Solex spp)
key factor. Large animals limited to warm
eats own body
weight in food every
areas.
day to maintain
temperature
S/V=6*1/L
3.17 Torpor and hibernation help
some animals conserve energy
Torpor
Small homeothemic
animals become
heterothermic
Body temperature
drops to ambient at
night
Inactive
Bats, Some mice,
kangaroos
Torpor and hibernation help some
animals conserve energy
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Hibernation
• Many poikilotherms and some mammals have winter
torpor to save energy
• Selective advantage when resources are few
• Mammals
 Heart rate, respiration fall
 Temperature drops to ambient
 Groundhogs, chipmonks
 Not all bears
• No temperature change
• Just long sleep with no eating, drinking, defecating
or urinating
• Females give birth and feed young in this period
• Can wake up easily
• Do not visit a bear cave in winter!
3.18 Some animals use unique physiological
means for thermal balance
Storing body heat:
Camel, oryx and some gazelles
Body T change from 34oc to 41oC for camel
Reduce need for evaporative cooling and save water and energy
Supercooling:
many ectothermic animals of temperate and Arctic regions
When the body T below freezing points without actually freezing
The presence of certain solute (glycerol) in the body lower the
freezing points
Wood frog, grey tree frog, spring peeper
Countercurrent heat exchange:
to conserve heat in a cold environment and to cool vital part of
body during heat stress.
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Countcurrent heat exchange happens in
homeotherms (porpoise, whale) as well as in certain
poikilotherms (tuna, mackerel shark)
To preserve heat in cold water, and get ride of heat in warm water
To cool brain, reduce T by 2-3 oC
The END