BIO2129 topic 10
why is the earth a closed system
because it has limited space and resources
humans are 1000x more abundant than expected for a mammal with similar body size what does this mean
we have more individuals than natures balance allows, human population doesn't follow the usual ecological patterns seen in other mammals
food supply has grown and there is no globa l shortage but
it is unevenly distributed worldwide
why has human population growth been so fast
because death rates declined rapidly due to medical and technological advances, while birth rates remained high. this causes an imbalance where more people are being born than dying (exponential growth)
even if human growth is mortality can still spike
Example: COVID-19 increased global death rates. population growth is not guaranteed
what is the demographic transition model
a model that explains how population size and growth rate change as a country develops economically and socially. describes the change in birth/death rates in 4 stages
what are the four stages of the demographic transition model
Pre-industrial, transitional, industrial and post-industrial
what is Stage 1: Pre-Industrial Stage
Birth rates: Very high
Death rates: Very high
Population growth: Very slow or stable.
Example: Pre-1800s societies before the Industrial Revolution.
what is Stage 2: Transitional Stage
Death rates drop rapidly due to improvements in food supply, sanitation, and medicine (Industrial Revolution effects).
Birth rates remain high, so population grows explosively.
what is Stage 3: Industrial Stage
Birth rates start to decline as societies become more urbanized and economically developed.
Reasons for decline:
Increased education (especially for women).
Access to contraception and family planning.
Shift from agricultural to industrial economy — children become an economic cost instead of an asset.
Improved child survival = fewer births needed to maintain family size.
Death rates remain low → population growth slows down.
Stage 4: Post-Industrial Stage
Both birth and death rates are low → population stabilizes or even declines.Families choose to have fewer or no children due to career priorities and higher living costs.
in the demographic transition model, what causes mortality rates to decline
1. improved hygiene and sanitation (less disease transmission) 2. Better nutrition/agriculture (more stable food supply) 3. Access to modern medication (vaccines, antibiotics) 4. Civil infrastructure imporvements
Natality (birth rates) decrease because
1. economic development (higher living costs and urbanization make larger families impractical) 2. Education (educated women tend to have fewer children). 3. employment (more women in the workforce reduce family size) 4. access to contraception 5. social/cultrual shifts (children are seen as dependants and not as economic labor)
what is per capita GDP
the total value of goods and services a country produces divided by its population.
→ It measures economic prosperity per person.
As GDP increases, birth rates decrease
Wealthier nations tend to have lower fertility rates because:
Education and career priorities increase.
Access to contraception and healthcare improves.
Living costs and housing prices rise, making large families expensive
Cultural, religious, and social values affect
birth rates
what is The Ecological Footprint and IPAT Model
Human impact on the environment can be summarized by the IPAT equation:
I = P × A × T
I: Environmental impact
P: Population size
A: Affluence (consumption per person)
T: Technology (resources & energy used to produce goods or manage waste)
As population (P) or affluence (A) increase,
impact (I) usually increases.
Technology (T) can either
worsen (more pollution, resource use) or improve (clean energy, recycling) environmental impact.
Environmental scarcity arises in three ways
#1 Demand-induced scarcity: Caused by population growth = higher demand for food, water, and energy. #2 Supply-induced scarcity: from degradation of resources (pollution, soil erosion, climate change). #3 Structural scarcity: resources are unequally distributed among people (rich vs. poor). Leads to inequality and conflict
Human population growth is
hyper-exponential (faster than exponential because of technology and consumption).
Human impact is the root cause
global ecological pressure.
Ecological footprint defintion
area of productive land required to supply resources (food, water, energy, materials) and absorb waste (e.g., CO₂ emissions).
Ecological Footprint is measured in
hectares per person.
Includes land used for:
Food production
Transportation and manufacturing
Energy generation
Waste absorption
humans' resource use
exceeds Earth's biocapacity
humanity lives beyond Earth's limits
rich countries drive the overshoot through overconsumption
what are the consequences of Overshoot
83% of wilderness is modified by humans.
98% of potential farmland is already in use.
Little space remains to expand without destroying ecosystems
Monitored wildlife populations
have declined drastically since 1970.
what are ALL the Consequences of Overshoot
Land & Wilderness Loss, Wildlife Decline, Exceeding Carrying Capacity → Extinction(decline in freshwater species populations -80%)., Terrestrial Species Decline (Land species also declining globally)
climate change is mainly driven by
Industrialization, machinery, hydrocarbon burning, and aerosol emissions have greatly increased greenhouse gas concentrations.
what are the consequences of human-influenced climate change
Habitat loss and population instability as species can’t adapt fast enough to temperature shifts.
Forests are vulnerable ecosystems, deforestation releases stored carbon and reduces CO₂ absorption.
Less snow and smaller ice cover = lower albedo (reflectivity) → more heat absorbed → positive feedback that accelerates warming.
Past records show slow, natural temperature changes, but since the Industrial Revolution,
temperatures have skyrocketed due to human greenhouse gas emissions.
Explain what is happening to Arctic sea ice and why it matters
Arctic sea ice has been declining in thickness and volume and is being replaced with thin seasonal ice that melts each summer. This causes a reduction in the Earth's albedo (reflectivity), which causes more solar energy to be absorbed by the ocean. This warms up the planet, causing a feedback loop. Melting permafrost also releases methane; these effects cause global climate change by increasing warming and changing weather patterns.
climate change is caused by
human activities (burning fossil fuels, industrialization, deforestation) and is happening at a faster rate due to feedback loops like ice melting and methane release and land use change
What are some common denial patterns of climate change
1.“It’s not real.”
2.“It’s real but not caused by people.”
3.“It’s real and human-caused, but it’ll be fine or even good.”
4.“It’s a global conspiracy.”
How is climate change reshaping where and how species live?
It’s causing range shifts, changes in timing (phenology), and new ecological interactions, which causes ecosystems to reorganization.
What is a range expansion?
When species move into new areas, usually northward or poleward, due to reduced climate barriers and warmer conditions.
What is a range loss?
When species lose habitat at the southern or lower-altitude edges of their ranges due to rising temperatures.
What does the term phenological shift mean?
the changes in the timing of biological events like migration, reproduction, and flowering due to climate change.
Are phenological events happening earlier or later because of global warming?
they’re happening earlier in the year
What happens when species can’t adapt or move fast enough to track suitable climates?
They may face extinction or competition from new species that invade their habitats.
How does climate change disrupt ecological relationships?
It causes ecosystem reorganization
What are isotherms, and how do they relate to species range shifts?
Isotherms are lines of equal temperature; as the planet warms, they move northward, forcing species to follow their preferred temperature zones.
Why might lowland or polar species be especially vulnerable to climate change?
they can’t move higher or farther north, so their entire habitats disapear (e.g., alpine and polar ecosystems).
Why are the current biological impacts of climate change considered unprecedented?
Because the speed and scale of range shifts, extinctions, and ecological disruptions have no precedent in human history.
what are the worst-case scenarios for global warming
sea levels rise, uninhabitable regions, methane & carbon sink, biodiversity loss, food insecurity, loss of ecosystem services, extreme weather casualties, governance failure and conflict of resources
what are the best case senarios
sea level control, population stabilization, education & equity,, sustainable prosperity and land use integration
what are the bright spots
Growth in protected areas and conservation zones worldwide.
Some endangered species recovering; wildlife stabilization in a few regions.
Carbon emissions may be stabilizing; renewable energy use is increasing fast.
Population growth slowing globally, especially in developed regions.
Humanity has shown it can respond effectively to global threats (e.g., ozone treaties).
Rising awareness of harmful land use (like pesticides) → stronger global efforts to reduce environmental risks.