Topic 7 - Energy Budgets

Energy Budgets

Organisms must balance their energy intake with their use of energy for metabolism, reproduction, parental care, and energy storage.

Energy is often a major limiting factor in determining an organism’s survival.

Energy budget factors

Size matters

• Larger animals require higher total energy, but less energy per gram

• Faster growing plants consume more energy to support rapid growth (canola)

Environment matters

• The environment in which you live will affect energy needs (polar bear in arctic needs more)

Thermoregulation matters

• Ectotherms require less energy than endotherms

Body Size Influences Energy Demand

Organism range in mass across 20 orders of magnitude. Size effects the energy expenditure of organisms:

• Impacts the way organism move, how often they eat and what they eat

• How size affects anatomy or bio processes is called scaling

Surface Area and Volume

More surface area = more membrane/skin for exchanges

More volume = more mass

• Small animals have a large surface area to volume ratio

• Large animals have a small surface area to volume ratio (developed intestines to increase surface area, in order to exchange matter and energy with environment)

Implication of body size scaling

Organisms need to obtain resources and excrete waste to support their mass (volume)

Organisms exchange matter and generate across their membranes (surface area)

Disadvantages of SA:V for large organisms

Reduced efficiency

• lots of biomass that needs to exchange gases, nutrients and waste - but has little surface area to do it with

Diffusion Distance

• For big organisms, things need to flow a long way from the inside to the outside

Specialized Systems

• Big organism need to divert energy to building and maintaining systems to increase SA (circulatory, respiratory and digestive system)

Advantages of SA:V for large organisms

Heat retention

• heat is produced by the entire volume, but has less SA to lose it through

Other

• water conservation

• Structural strength

Allometry

Many biological phenomena do not vary linearly with body size (not straight line)

Y = aX^b

• a = the constant (y per unit mass)

• b = scaling exponent

  • b = 1 - isometry (linear)

  • b = 0 - bio variable is independent of mass

  • b = anything else - allometry (not linear)

• X = mass (g)

When log is applied : log Y = b log x + log a

B = slope and log a is the intercept

Hyperallometry

Positive allometry

• one dimension increases, and the other increases at a faster rate

• Ex. Crabs - claw grows at a faster rate than the rest of body

Hypoalllometry

Negative allometry

• as one dimension increases - the other increases at a slower rate (line still goes up)

• Ex. Human brain grows at a slower rate than the rest of the body

Daily Energy Budgets

Energy in = Energy out

Energy in = Energy assimilation (what gets used by organism) + Energy excretion

Energy assimilation = Energy rmr (resting metabolic rate) + Energy activity (reproduction, thermoregulation) + Energy production (stored by organism)

Energy assimilation = Energy in - Energy excretion

Body size affects Energy in

Larger animals need more food and have greater energy in per unit time

Larger animals can eat more food (eat less relative to body size)

Larger animals take in more air with each breath and pump more blood with each heartbeat (slower rate)

Smaller animals have a higher metabolic rate

Strategies to minimize Energy excretion

Organism excrete in many ways

• heat, urine, feces, sweat

Organisms have many ways to assimilate more energy from food, and excrete less of the energy

• chewing, palatable foods, length of gut, food retention time

Metabolic Rate (Energy rmr)

It is the rate of energy consumption

• rate at which organism convert chemical energy to heat and external work

Why this matters

• helps determine how much food an animal needs

• Measurement of total energy use

• Helps determine the preside on energy supplies in the ecosystem

Different measure of metabolic rate

Resting (RMR)

• energy expenditure at rest, cut routine activities/day

Basal (BMR)

• metabolism at complete rest - lowest psossible

Standard (SMR)

• metabolic rate measured at a specified temperature (ectotherms)

Field (FMR)

• metabolic rate measured in wild animals

Measuring metabolic rate

Used for endotherms

• BMR - metabolic rate wile its in thermoneutral zone

Used for ectotherms

• SMR - metabolic rate while fasting and resting - but it is specific to the prevailing body temperature

Ways to measure

• direct calorimetry - measures rate that heat leaves animal’s body (expensive and difficult)

• Indirect calorimetry - measures rate of respiratory gas exchange with environment and chemical energy content of the matter that enters and leaves the body

Growth and Reproduction uses Energy

Energy production = both growth and reproduction

• if an organism has a balanced energy budget value will = 0 (not common)

• If more than enough energy is consumed the value is positive and mass will increase

• If not enough energy is consumed the value is negative and the mass will decrease