Environmental Science Summative Study Guide: Sustainability, Ecological Footprints, and Experimental Design

Environmental scientists determine if a country is living sustainably by evaluating the relationship between its ecological footprint and its biocapacity.
Sustainability is fundamentally a matter of resource management. A country is categorized as "more sustainable" if it maintains a lower ecological footprint in conjunction with a higher biocapacity.
This determination is made because sustainability requires that resource use, land use, and waste production remain below the Earth's threshold for absorbing those wastes and producing new resources.

Global trends reveal a distinct correlation between a country's development status (measured by GDP per capita) and its ecological footprint.
Developed Countries (Higher GDP per capita):
- These nations typically exhibit higher ecological footprints because individuals have more personal wealth available for consumption.
- High-income individuals frequently purchase luxury goods, such as automobiles, cell phones, and airplane travel.
- The production of these goods requires extensive mining to extract metals.
- The operation of luxury transport, specifically airplanes, produces significant amounts of $CO_2$ via the combustion of fossil fuels in engines.
- Wealthier populations can afford to consume more meat; meat production is resource-intensive, requiring more land than grain or corn cultivation and contributing higher levels of $CO_2$ to the atmosphere.
Developing Countries (Lower GDP per capita):
- These nations generally have lower ecological footprints, reflecting lower individual income and reduced access to luxury goods and meatndensity diets.
Population Influence on Total Footprint:
- A country's total ecological footprint is calculated by multiplying the per capita footprint by the entire population size.
- Consequently, a country with a very high population size can have a larger total ecological footprint than another nation, even if its per capita (per person) footprint is significantly smaller.

Open Access and Resource Depletion:
- Open access refers to a scenario where everyone has equal and unrestricted access to a resource.
- Without the implementation and enforcement of specific regulations and rules, open access typically leads to the resource being entirely used up.
The Tragedy of the Commons Solution:
- To solve the tragedy of the commons, a proposed solution must clearly identify how it facilitates resource recovery.
- Simple terms like "regulation" are considered too vague. Effective solutions must specify mechanisms, such as providing fish with enough time to reproduce or allowing grass enough time to regrow after grazing.
Classification of Resources:
- Renewable Resources: Resources that naturally replenish over time.
- Nonrenewable Resources: Resources that exist in a finite amount and will eventually run out.
- Potentially Renewable Resources: These are resources that can be considered renewable if they are managed sustainably. This requires giving the resource enough time to replenish between harvests or uses. However, if they are harvested too quickly to replenish, they convert to nonrenewable status because the supply becomes finite.

Scenario Overview:
- A biopsychologist is investigating how anabolic steroids affect aggressive behavior in female rats.
- The study uses 48 female rats: 24 receive daily injections of a steroid, and 24 receive daily injections of a placebo (a fake drug).
- Interaction is monitored via round-the-clock videotapes of communal cages to count and time aggressive encounters.
Testable Hypothesis:
- If female rats are administered steroids, then they will exhibit increased aggression because steroids are chemicals that impact the brain circuits responsible for decision-making.
Variable Identification:
- Independent Variable: The amount of steroid injected.
- Dependent Variable: The number or amount of aggressive encounters. Note that the dependent variable must always be measurable.
- Control Group: The group of rats that receive no steroid injection (the placebo group).
- Control Variables (Constants): To ensure a fair test, the following must remain identical for all subjects:
  - Type of food.
  - Amount of food.
  - Amount of water.
  - Temperature of the cages.
  - Amount of space available in the cages.
Data Interpretation:
- The results support the hypothesis if the rats injected with steroids engage in more fights than the rats in the control group. This would demonstrate that steroids increase aggressive fighting behavior.

Background on Tree Rings:
- The thickness of annual tree rings reflects the environmental conditions during the year of development.
- Thin Rings: Indicate rough periods, such as forest fires, insect infestations, or a lack of water.
- Thick Rings: Indicate prosperous periods of development.
Comparative Data Table (Forest A vs. Forest B):

Variable Identification in Tree Studies:
- Independent Variable: Age of tree (years), Time (years), or the Type of forest.
- Dependent Variable: Thickness of rings measured in $mm$ .
- Control Variables: Factors that must be held constant include the number of trees in the forest, the age of the forest, the types of animals present in the forest, and the specific tool used to measure the rings.
Specific Data Findings:
- The average thickness for a 40-year-old tree in Forest A is exactly $34\,mm$ . (Note: Numerical values without units, such as "34" alone, are considered incorrect in a scientific context).
Conclusions and Relationships:
- Health Comparison: Forest A is less healthy than Forest B because the average ring thickness is consistently lower in Forest A.
- Relationship Type: There is a direct relationship between the age of the trees and the average thickness of the tree rings, meaning as age increases, thickness also increases.