lecture 7

Overview
- Offers fun and informative events for BIO220 students.
- Complete schedule available on Quercus under Modules  Beyond BIO.

How to Find Sources
- Date: Wednesday, January 29th
- Time: 1:10 – 2:00 pm
- Format: Online via Zoom (link on Quercus)
- Description: Learn strategies for finding academic sources tailored to the Sources Assignment & Climate Change Report.
Koffler Scientific Reserve Info Session
- Date: Wednesday, February 5th
- Time: 1:10 – 2:00 pm
- Format: Online via Zoom (link on Quercus)
- Description: Information session about KSR, a large field research station owned by U of T; opportunities to get involved.

Fundamental Ecological Processes (BIO120)
- Focused on natural systems.
Current focus in BIO220:
- Effects of natural processes on humans and vice versa.
- Key theme: Total Impact = Per capita impact * # of capita.
Shift in focus:
- Requires an ecosystem perspective.
- Involves political, sociological, and ethical issues.

Topics Covered:
- Carrying capacity of the earth?
- Human impact as a function of:
  - Population
  - Consumption (affluence and technology)
- Areas of focus:
  - Population history and projections
  - Biology of food supply
  - Biogeochemical cycles
  - Climate change
  - Biological feedbacks

Example: Mexico City
- Population: 21.7 million
- Public transit daily ridership: 4.5 million

Exponential Growth Model:
- If rates are constant and (birth + immigration) > (death + emigration), the growth trajectory is density-independent and exponential.
- Mathematical Model:
  - dN/dt = rN; solved as Nt = N0e^(rt)
- Exponential growth occurs if r > 0.

Limitations of Exponential Growth:
- Cannot continue unchecked; more complex models are necessary.
Logistic Growth Model:
- Viewed as an ecological law in mid-20th century.
- Model Representation:
  - dN/dt = rN(K - N)/K
- Demonstrates sigmoid growth and asymptotic approach to carrying capacity (K).

Influential Ecology Textbook:
- Allee, Emerson, Park, Park & Schmidt (1949), "The Great APPES."
- Early human population projection showed leveling off at 2.6 billion.

Historical Data Overview
- Population Milestones:
  - 10,000 BCE: ~4 million
  - Year 0: ~190 million
  - 1800: 990 million
  - 1928: 2 billion
  - 7 billion: 2011; 8 billion: 2023; 10 billion projected for 2058.
- Global life expectancy changes from <30 years (before 1800) to 73 years (2023).
- Black Death pandemic caused significant mortality in 14th century Europe.

Limitations of Logistic Models:
- Poor predictions due to overshoot and the assumption of constant r and K.

Factors Influencing Growth (r):
- Balance of fertility rates and mortality.
- Declines in death rates due to healthcare advancements.
- Increases in carrying capacity (K) due to agriculture improvements.

UN Projections:
- Peak at 10.4 billion in 2086; fluctuations in predictions observed.
- Current growth rate of about 1.1%.
- Leveling off requires reduced birth rates or increased mortality.

Age structure implications:
- Rapidly developing populations exhibit excess young individuals leading to population momentum.
- Changes in age structure have significant impacts on future growth trajectories.

Stages:
- Stage 1: High birth and death rates; stable population.
- Stage 2: Decreasing death rates; population explosion.
- Stage 3: Declining birth rates; growth rate slows.
- Stage 4: Stable birth and death rates; equilibrium.

Motivations for parents include:
- Child survival, economic considerations, and societal security.
- Factors such as contraception availability and changing family structures.

Themes to consider:
- Understanding logistic growth, demographic transitions, and age pyramids.
- Exploring non-coercive strategies to address population growth and ensuring resource equity.