F1.1 · Analyse population growth and consumption in ecological footprints

Ontario Grade 12 Biology

Population Dynamics

How the number of people and average resource demand shape an estimate of human pressure on ecosystems

What you will learn

• Explain how population size and per-person consumption affect an estimated ecological footprint.
• Distinguish a per-person footprint from a total footprint.
• Use a simple model to calculate and compare footprint estimates.
• Identify what footprint comparisons can and cannot show.

1. SBI3U bridge: populations and resource use

• Population size affects how many people are included in an estimate.
• Average consumption affects the estimated demand per person.
• Total demand depends on both.

2. What an ecological footprint estimates

• A footprint expresses selected resource demand and some waste absorption as an area estimate.
• Per-person and total footprints are different measures.
• A footprint is an estimate based on a method and its data.

3. A simple model for population and consumption

• Multiply population by the average footprint per person to estimate a total.
• When both factors change, use both updated values.
• The model describes a relationship; it does not identify every cause of a footprint.

4. Evidence, comparison, and limits

• Check units, time periods, and whether a value is per person or a total.
• Group averages do not describe every individual.
• A footprint captures selected demands, not every environmental effect.

Two influences on an estimated total footprint

Worked example

Population growth with steady per-person demand

1. Identify the quantities
   The estimate needs the number of residents and the average footprint per resident. Since the average stays constant, only the population changes between the two estimates.
   $$F_{\text{total}}=P\times f$$
2. Calculate each total
   Multiply each population by 3.5 global hectares per person. The person unit cancels, leaving a total in global hectares.
   $$2{,}400\times3.5=8{,}400\ \mathrm{gha};\quad2{,}700\times3.5=9{,}450\ \mathrm{gha}$$
3. Compare the change
   The estimated total increases by 1,050 global hectares. Because the per-person value stayed constant, the percentage increase in the total matches the percentage increase in population.
   $$\frac{9{,}450-8{,}400}{8{,}400}\times100=12.5\%$$

Worked example

Population and per-person demand both rise

1. Calculate the initial total
   Multiply the initial population by the initial per-person value. The result is in million global hectares because the population is given in millions.
   $$1.0\times4.0=4.0\ \text{million gha}$$
2. Calculate the later total
   Use the later population and later average. Both values are higher, so both contribute to the increased total.
   $$1.1\times4.4=4.84\ \text{million gha}$$
3. Find the percentage increase
   Compare the increase with the initial total. The result is 21%, greater than the 10% increase in population alone because the average per-person footprint also rose.
   $$\frac{4.84-4.0}{4.0}\times100=21\%$$

Worked example

Per-person and total comparisons

1. Compare per-person values
   The question about average demand per person is answered directly by comparing the two per-person estimates. Population A’s value is higher.
   $$6>4\ \mathrm{gha/person}$$
2. Calculate total estimates
   Multiply each population by its own per-person value. The results are total global hectares for each population.
   $$500{,}000\times6=3{,}000{,}000\ \mathrm{gha};\quad800{,}000\times4=3{,}200{,}000\ \mathrm{gha}$$
3. Interpret both results
   Population A has the larger per-person estimate, but Population B has the larger total estimate. Its larger population more than offsets its lower per-person value.
   $$3{,}200{,}000>3{,}000{,}000\ \mathrm{gha}$$

Common mistakes and how to avoid them

Lesson summary

• Population growth changes the number of people whose resource demands are counted.
• Consumption affects estimated average demand per person.
• Estimate total footprint by multiplying population by average footprint per person.
• When both population and per-person demand change, use both new values.
• Footprints support comparisons, but they are estimates with limits.

Check your understanding

Key terms

Population

A group of individuals of the same species living in a particular area.

Consumption

The use of resources and services.

Ecological footprint

An estimate of the biologically productive area needed to provide resources used and absorb some wastes.

Biologically productive area

Land or water able to support the growth of biological resources.

Global hectare

An area unit adjusted to represent a common level of biological productivity.

Continue through SBI4U

View the complete SBI4U Ontario Grade 12 Biology curriculum and lessons

• E3.2 · Explain reproductive hormones in feedback mechanisms
• F1.2 · Evaluate Canadian technologies for feeding growing populations
• F2.1 · Use terminology for population size, growth, and carrying capacity
• F2.2 · Calculate population growth with conceptual and mathematical models
• F2.3 · Compare growth patterns of two populations
• F3.1 · Explain competition, predation, symbiosis, and other interactions

About this lesson and its review

Published by DoAssignment. This reviewed lesson follows Ontario Grade 12 Biology (SBI4U), expectation F1.1. It is a study resource, not an official curriculum publication.

Before publication, content is checked for structure, mathematical or chemical notation, calculations, course boundaries, and readability. Errors can still occur, so corrections are welcomed.

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