What similar energy demands do all organisms have?
- Basal metabolism
- Thermoregulation
- Reproduction
- Activity
- Growth
How do organisms differ in their energy demands?
Each organism differs in the amount of energy that they spend to meet each demand.
- Ex. python doesn’t need to thermoregulate, but they need to constantly grow. A penguin spends more energy on thermoregulation and activity, not growing as an adult.
How can energy use be calculated to determine what organism uses more energy?
By dividing kcal/yr by total g of organism.
Ex. Penguin - 340 000 kcal/yr / 4000 g = 85 kcal/yr x g.
What is an endotherm?
An organism that regulates their body temperature. Ex. Penguin.
What is an ectotherm?
An organism that conforms to environmental temperature. Ex. Python.
Do ectotherms or endotherms require more energy?
Endotherms require much higher energy per gram than ectotherms.
What is true about larger organisms and energy dispersal?
Larger organisms require higher absolute (total) energy.
What is true about smaller organisms and energy dispersal?
Smaller organisms require higher energy per gram of body mass.
Why do we have to logarithmically transform data when calculating energy dispersal?
- Organisms range in mass, there are huge differences.
- By logarithmically transforming, the data turns linear making it easier to read and more dispersed.
What is a scaling relationship (allometry)?
- Describes biological characteristics changing as an organism’s body size grows or shrinks.
What is the log-transformed equation of a scaling relationship? What do the coefficients mean?
- y = mx + b
- m = line slope / allometric coefficient
- y = parameter calculated (ex. metabolic rate)
- x = body size (mass)
- b = intercept
What is the allometric coefficient (a)?
- Indicates the scaling relationship.
- Equivalent to line slope (m).
What is an isometric scaling relationship?
- When the parameter increases proportionally with increasing mass.
- a = 1
- Original graph and log-transformed graph are both linear.
What is a hypermetric scaling relationship?
- When the parameter increases to a great proportion with increasing mass.
- a > 1
- Original graph curves up as mass grows, log-transformed graph is linear.
What is a hypometric scaling relationship?
- When the parameter increases to a lesser proportion with increasing mass.
- a < 1
- Original graph goes up then plateaus, log-transformed graph is linear.
Can the allometric coefficient be negative? Why?
- Yes, the same as how a slope can be negative.
- This means a parameter is decreasing in some proportion with increasing mass.
- Ex. increasing mass = lesser offspring.
How can we describe energy scaling in all life forms?
- Hypometric growth
- a = ~0.75
When classifying endotherms, microbes, and ectotherms, what order would they be in on a log energy scale?
- Microbes, ectotherms, then endotherms.
- Huge jump in energy requirements between all three groups.
Why is there a difference between the energy scaling of microbes versus multicellular organisms?
- Multicellular organisms are more complex (organ systems, tissues, etc.) and require more energy to move nutrients into cells.
- Sexual reproduction (fertilization, development, mitosis) requires more energy than asexual reproduction (binary fission).
Why do ectotherms and endotherms differ in their energy scaling?
- Ectotherms require little energy to change their body temperature to environmental temperature. They often show intermediate growth.
- Endotherms need to maintain a body temperature despite environmental changes which requires high energy. Often show determinate growth.
What is the difference between intermediate growth and determinate growth?
Intermediate growth - growth continues throughout lifespan (ex. reptiles).
Determinate growth - growth stops when “adult” state is reached (as it requires high energy to grow).
Why is energy budgeting so important for organisms?
- Natural selection will favour organisms that can manage their energy budgets better (key to evolution).
- They must make sure they have enough energy remaining to reproduce (all) and raise offspring (some).
What is the ideal to support an organism?
- Unlimited resources to support maximum growth, lifespan, and production of offspring that have high survival.
- Most organisms do not live under these conditions, so they have to budget their energy.
What is the life-history theory?
- Natural selection has resulted in numerous energy strategies.
- Explains how natural selection shapes survival and reproduction for organisms through trade-offs and resource allocation.
