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Energy, Metabolism, & Fuel
Energy Metabolism
The sum of processes by which animals
acquire energy, channel energy into useful
functions, and dissipate energy from their
bodies.
Energy
Energy = the ability to do work
The transfer of energy defines
inanimate animate
Energy
4 Main Types:
◦ Chemical Energy
◦ Electrical Energy
◦ Mechanical Energy
◦ Heat
Physiological Work
All forms of energy are not equally capable of doing physiological work in animals.
Animals CANNOT use heat to do any form of physiological work
Physiological work: any process carried out by an animal that increases order. Ex:
◦ Synthesis of macromolecules such as proteins
◦ Generates electrical or chemical gradients
◦ Contracts muscles to move materials
Two Forms of Energy
High-grade Energy-
◦ can do physiological work =
chemical, electrical, & mechanical
Low-grade Energy-
◦ cannot do physiological work = heat
To Degrade Energy = transforming energy
from a high-grade form to low-grade. (heat)
Max Kliber
Kliber coined the term: “Fire of Life”
Life is a combustion process.
Explained relationship between oxygen,
heat production, and metabolism:
If you have an active life, and are using
oxygen, you are producing heat.
“Fire of Life”
OXYGEN
HEAT
METABOLISM
Antoine Lavosier
Lavosier:
Theory of Combustion and Metabolism
Lavosier’s equation:
Animal + Oxygen CO2 + H2O
Heat
Theory of Combustion and Metabolism
OXYGEN
HEAT
METABOLISM CO2
WATER
Fundamentals You are CONSUMING oxygen:
◦ Eat 1.4 lbs food/day
◦ Consume 1.5 lbs oxygen/day
You consume oxygen and food in order to produce ENERGY
Animals use energy for 3 major functions:
◦ Biosynthesis
◦ Maintenance
◦ Generation of external work.
3 Major Energy Functions
Biosynthesis:
An animal synthesizing its body’s constituents , such as proteins and lipids
Maintenance:
All the processes that maintain the integrity of the body.
Generation of External Work:
When an animal applies a mechanical force to objects outside its body.
Metabolism
Metabolism = Sum of all of the
biochemical processes occurring within the
cells and tissues of an organism.
Metabolic Rate = rate at which an animal
converts chemical energy into heat and
external work. Defined as: Metabolism
Time
Linking Metabolism & Fuel
The amount of ENERGY and HEAT
produced depends on the substrate eaten
Biological macromolecules found in food:
◦ Lipids (fats) = 9.3 kcal/gram
◦ Protein = 4.1 kcal/gram
◦ Carbohydrates = 4.1 kcal/gram
Importance of Metabolic Rate
Determinant of how much food an animal
needs.
Provides a quantitative measure of the total
activity of all physiological processes.
And can measure the drain the animal places on
the physiologically useful energy supplies of its
ecosystem.
Measuring Metabolism
Direct Calorimetry
Indirect Calorimetry
Direct Calorimetry
Directly measuring heat production
resulting from animal’s metabolism.
Rate of heat production = rate of heat
loss to the environment
Lavoisier’s
Direct
Calorimeter
Measure how
much heat is
produced by
measuring how
much ice melts.
1g ice melted =
334 J
Direct Calorimetry
Good measure because of the basic
relationship between these parameters:
Fuel + O2 Energy & Heat
Hard to do with many animals.
Indirect Calorimetry
Respirometry: measuring an animal’s rate of respiratory gas exchange with its environment. ◦ O2 Consumption
◦ CO2 Production
Material-Balance Method: measuring the chemical energy content of the organic matter that enters or leaves the animal’s body.
Other methods…
Respirometry
Closed Respirometry
Open Flow Respirometry
Both give discrete measures of metabolism
over relatively short time periods
Closed Respirometry
Difference between starting and ending [O2]
and [CO2] after a given amount of time
The mouse will
eventually become
hypoxic.
OXYGEN
ANALYZER
COMPUTER
VO2 PER MINUTE
Open-Flow Respirometry
VCO2 PER MINUTE
Open-Flow Respirometry
Can measure different
behaviors/ activity levels …
Mountain lions on treadmills!
Diving dolphins
Resting elephants
Can measure animals in air
or in water …
Linking Metabolism & Fuel
Each “fuel” demonstrates a characteristic
relationships between the amounts of:
(1) ATP produced
(2) O2 consumed
(3) CO2 produced
Linking Metabolism & Fuel
Respiratory Quotient = VCO2 / VO2
Carbohydrates = 1
Protein = 0.8
Fatty Acids = 0.7
RQ provides insight into which fuels are
being used to support metabolism.
Material Balance
Measure the chemical energy content of
all the food an animal eats over a period
of time, as well as, the chemical content of
the feces and urine eliminated over the
same time period.
Energy Ingested – Energy
Excreted = Metabolic Rate
Assimilation Efficiency
Other Methods
Fat Loss
Migrating Whales
Migrating Birds
Humpback Whales (no, this is not a
migratory bird, but
it is on a scale…)
Other Methods
Doubly-Labeled Water Technique
Isotopes D2 (dueterium) and 18O
◦ “heavy isotopes”
Administer dose of doubly-labeled water and measure elimination rates of D2 and 18O in the subject over time:
◦ regular sampling (blood draw) of heavy isotope concentrations in the body water.
Doubly Labeled Water
Time Between Sampling:
Small animals: as short as 24 hours
Larger animals: as long as 14 days.
Breakdown of isotopes (loss) allows us to calculate a long term metabolic rate.
Average daily metabolic rate is often also called the field metabolic rate (FMR).
Time-Energy Budgets
Categorize all of animals behaviors into a few categories
Using laboratory studies, or other means, determine metabolic rate of individual while engaging in those activities.
Using field observations, determine how much time individuals spend engaging in those activities during a 24 hour period.
Time-Energy Budgets
Multiply time spend engaging in a specific
behavior by the metabolic cost of that
behavior.
Sum energetic costs of all behaviors over
a 24 hour day to obtain total daily
energetic expenditure.
Sea Otter Activity Budget
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
Pre MP MP Post MP Dept
Imm
Indp Imm ADULT
Perc
en
t o
f 24
Ho
ur
Day
Other
Swimming
Grooming
Foraging
Nursing
Resting
FMR of Southern Sea Otters
0
500
1000
1500
2000
2500
3000
3500
4000
Pre Molt
Pup
Molting
Pup
Post
Molt Pup
Dept.
Imm.
Indp.
Imm.
Adult
Daily E
nerg
eti
c E
xp
en
dit
ure
(kcal*
day-1
)
Other
Swimming
Grooming
Foraging
Nursing
Resting
Other Methods
Accelerometer Instrumentation
Records periods of rest and activity over a long period of time.
Very powerful can be used to estimate short term & long term metabolic rates.
Measures things such as limb-stroke frequency & body acceleration.
Accelerometer Instrumentation
Accelerometer Instrumentation
Allows the discrimination of behavioral
patterns while animals are out of sight.
Study showed gliding behavior improves
energetic efficiency in diving marine mammals:
◦ ie. Weddell seals realized a 9.2 to 59.6% reduction
in diving energetic costs.
Sink or Swim: Strategies for Cost-Efficient
Diving by Marine Mammals. Williams et al.
2000. Science vol. 288 p. 133-136.
Levels of Metabolism
Basal Metabolic Rate (BMR) /
Standard Metabolic Rate (SMR)
Resting Metabolic Rate (RMR)
Active Metabolic Rate VO2 Max
Levels of Metabolism
BMR is the minimum metabolic rate for an organism.
Measured under specific conditions.
Kliber Conditions =
◦ Fasted
◦ Adult
◦ Resting
◦ Thermally Neutral Environment
Thermal Neutral Zone
Environmental temperature (°C)
Meta
bolic
Rat
e
Lower critical
temperature
Upper critical
temperature
BMR
(Adapted from Eckert 2001)
Metabolic Regulation
Heat Production Active Heat
Dissipation
Tb
Levels of Metabolism
Factorial Aerobic Scope=
VO2 Max
BMR or SMR
Tells us something about the range of athletic capabilities an animal has.
◦ Average Mammal = 8-10
◦ Terrier Dog = 25
◦ MMs, Monitor Lizards, Lions = 5-7
Levels of Metabolism
BMR used for endotherms
SMR used for ectotherms b/c there is no thermally neutral zone for these animals
RMR is non-active, pre-exercise.
◦ Can be double BMR
Active metabolic rate is highly variable
◦ Can be10-25x BMR
Levels of Metabolism
Average daily metabolic rate
FMR = Field Metabolic Rate
◦ How much energy an animal is expending
over a 24 hour period
Or we may want to know how much
energy animals are expending in the wild
over an even greater period of time…
Energetic Budgets Energy in = Energy out
Energetic Demand =
◦ Activity Costs
◦ Maintenance Costs
◦ Thermoregulatory Costs
◦ SDA (cost of digestion)
Important to Remember: Metabolism varies with temperature, activity level, diet, lactation, pregnancy, time of day, age, gender, EVERYTHING.
Thermal Neutral Zone
Environmental temperature (°C)
Meta
bolic
Rat
e
Lower critical
temperature
Upper critical
temperature
BMR
(Adapted from Eckert 2001)
Metabolic Regulation
Heat Production Active Heat
Dissipation
Tb
4
9
14
19
24
0 5 10 15 20 25 30 35
Water temperature (oC)
Ox
yg
en
co
ns
um
pti
on
(m
LO
2k
g-1
min
-1)
(Williams et al., 2001)
4
9
14
19
24
0 5 10 15 20 25 30 35
Water temperature (oC)
Ox
yg
en
co
ns
um
pti
on
(m
LO
2k
g-1
min
-1)
(Adapted from Morrison et al., 1974; Costa and Kooyman 1984)
Surface Area to Volume Ratio
Specific Dynamic Action
Energetic Budgets
All of these things get factored into the
energetic budgets of these animals
However, we need to also think about
energetic budgets at different scales
Energetic Budgets
Species manage their energetic budgets
on very different time and spatial scales.
DAILY
SEASONALLY
Energetic Budgets
Individuals: Ein = Eout
Population: Ein > Eout
