Human Biology: Human Interactions with the Biosphere
Human Population Growth Statistics and Dynamics
Current Global Population State: There are presently over billion people on the planet.
Annual Increase: More than million people are added to the global population each year.
Definition of Growth Rate: The growth rate is defined as the change in human population per year. This value is determined by: * Birth Rate (Natality): The number of births each year. * Death Rate (Mortality): The number of deaths each year.
Growth Trends: The human population is currently growing exponentially.
MDC vs. LDC Growth Rates: Growth rates (measured in percentages) differ significantly between More-Developed Countries (MDCs) and Less-Developed Countries (LDCs). * MDCs: These countries have low population growth, averaging approximately . For example, the United States growth rate is approximately . * LDCs: The growth rate in LDCs peaked at between and . While the collective growth rate has declined since then, many countries (particularly in Africa) continue to increase their populations at much higher rates.
Ecological Growth Concepts: * Biotic Potential: This is the maximum growth rate possible under ideal conditions. It is usually not attainable due to limiting environmental factors. * Carrying Capacity: This refers to the human population size that can be sustained by the environment indefinitely. Achieving this requires the growth rate to level off to near-zero.
Scientific Debates on Capacity: * Some scientists argue that humans have already exceeded the Earth's carrying capacity. * Others suggest the Earth can support between billion and billion people.
Population Momentum: Even though the worldwide growth rate has slowed, the total population will continue to increase because more women are entering their reproductive years than are leaving them.
Age Structure and Demographic Distribution
Definition of Age Structure: This refers to the relative distribution of individuals within a population among different age categories.
Standard Categories: * Prereproductive: Individuals too young to reproduce. * Reproductive: Individuals currently of childbearing age. * Postreproductive: Individuals past the age of childbearing.
Comparison of Structures: * MDCs: Often show a more stable, column-like distribution across age groups. * LDCs: Typically exhibit a pyramid-shaped distribution with a very large base of prereproductive individuals, indicating high future growth potential.
Classification of Planetary Resources and Pollution
Nonrenewable Resources: Resources that are limited in supply and cannot be replenished on a human timescale. Examples include: * Usable land. * Fossil fuels. * Minerals. * Nuclear energy sources.
Renewable Resources: Resources that are naturally replenished at a rate meaningful to human use. Examples include: * Water. * Plants. * Animals.
Impact of Technology and Population: The combination of rapid population growth and advanced technology has dramatically changed global resource availability. It has led to increased extraction and utilization while decreasing natural regeneration rates.
Pollution: This is a side effect of resource consumption. Pollution levels increase proportionally as the human population increases.
Land Use, Erosion, and Deforestation
Coastal Impacts: * Approximately of the world’s population lives within of a coastline. * Coastal development leads to beach erosion and habitat loss. * Wetlands: The loss of wetlands is noted as a "special problem" because they act as buffers for coastal storms and serve as vital spawning areas for many marine organisms.
Semiarid Lands and Desertification: * Desertification: The conversion of semiarid lands to desert-like conditions. * Primary Causes: Overgrazing, removal of natural vegetation, and depletion of available water sources.
Tropical Rainforests and Deforestation: * Deforestation leads to infertile land for agriculture or grazing and a significant loss of biodiversity due to erosion and pollution. * Current Crisis: Rates of deforestation have reached crisis levels, exceeding million hectares per year. * The Trillion Tree Campaign: An environmental initiative designed to combat deforestation and global warming. Currently, billion trees have been planted.
Freshwater Consumption and Management
Usage Trends: Globally, usage follows the hierarchy: Agricultural Use $>$ Industrial Use $>$ Domestic Use. * Agriculture: Uses the most freshwater, with of freshwater used worldwide dedicated to irrigation. * MDC Household Use: In More-Developed Countries, more water is used for bathing, flushing toilets, and watering lawns than for essential drinking and cooking.
Water Sourcing Issues: * Dams: Change river flow, result in significant water loss through evaporation/leakage, and can eventually fill with sediment. * Aquifers: Massive underground water stores are being drained. Excessive withdrawal leads to sinkholes and saltwater intrusion into freshwater supplies.
Ecological Disruption: Disruption of the natural water cycle leads to erosion, drought, desertification, increased fire risk, and the decline of species dependent on regular clean water supplies.
Conservation Measures: * Natural landscaping (Xeriscaping). * Strict irrigation and water recycling practices. * Limiting non-essential water use. * Improved industrial efficiency. * Public awareness campaigns for household efficiency.
Food Production and Environmental Impact
Sources: Human food is derived from growing crops, raising livestock, and fishing.
Harmful Farming Methods: * Planting only a few genetic varieties (monoculture). * Heavy application of chemical fertilizers and pesticides. * Excessive fuel consumption and irrigation. * Consequences: These intensive methods lead to soil loss, land degradation, and salinization (salt buildup).
Livestock Production: * Raising livestock is extremely energy-intensive and water-intensive. * Biomass Pyramid: Based on trophic levels, it takes of grain to produce of meat. Therefore, the high meat consumption in MDCs is considered wasteful. * Solution: Shifting toward plant-based diets makes more food available while reducing energy and water consumption.
Environmentally Conscious Farming: * Polyculture: Planting multiple crops together. * Contour Farming: Plowing and planting across a slope following its elevation contour lines to reduce erosion. * Crop Rotation: Changing the type of crop grown in a field each season. * No-till farming: Minimizing soil disturbance. * Integrated/Biological Pest Control: Using natural predators (e.g., ladybugs) or methods rather than chemicals.
Energy and Mineral Resources
Fossil Fuels: Currently provide of the world’s energy supply (oil, natural gas, coal). They are nonrenewable and contribute to acid rain and greenhouse gas accumulation (global warming).
Renewable Energy Sources: Naturally replenished at viable rates: Hydropower, geothermal, wind, and solar energy. Solar and hydrogen fuels are projected to eventually replace fossil fuels.
Mineral Extraction: Raw materials mined from the Earth's crust, including metallic (copper, iron) and nonmetallic (sand, phosphate) materials. * Extraction is enormously disruptive and polluting. * Targeting hard-to-get resources: As easy-to-reach minerals are exhausted, targeting deeper or lower-grade resources generates even more pollution.
Chemical Pollution: * CFCs (Chlorofluorocarbons): Damaging the ozone layer. * Biomagnification: The process where wastes (like DDT) increase in concentration as they move up the food chain. * Quantitative Example (DDT): * Water: * Zooplankton: * Small Fish: * Large Fish: * Predatory Birds:
Mining Incidents: Examples include the Gold King Mine wastewater spill (Colorado) and Pennsylvania acid mine drainage.
Biodiversity: Value and Threats
Definition: Biodiversity is the variety of life on the planet.
Primary Threats: 1. Habitat Loss: The most significant threat; loss of coral reefs and rainforests is of highest concern due to their extreme species diversity. 2. Alien Species: Exotic or invasive species that outcompete native species. 3. Pollution: Leads to acid deposition, global warming, ozone depletion, and endocrine-disrupting synthetic organic compounds. 4. Overexploitation: Humans extracting too many individuals from the wild (e.g., exotic pets, overfishing, hunting). 5. Disease: Human encroachment on wildlife habitats increases transmission and spread.
Direct Value of Biodiversity: * Medicinal Value: Drugs derived from organisms (e.g., anti-cancer chemicals from the Rosy Periwinkle; antibiotics from bacteria; medical research using the nine-banded armadillo). * Agricultural Value: Wild pollinators (e.g., the lesser long-nosed bat, Leptonycteris curasoo), biological pest control (e.g., ladybugs, Coccinella), and wild genes for crops. * Consumptive Value: Wild-caught food (fish, fruits, honey), fibers, and wood from trees (e.g., rubber trees, Hevea).
Indirect Value of Biodiversity: * Waste Disposal: Decomposers break down organic waste into inorganic nutrients. * Sponge Effect: Forests and ecosystems hold freshwater, regulating supply and reducing run-off/erosion. * Biogeochemical Cycles: Biodiversity contributes to nutrient cycling (Carbon, Nitrogen, etc.). * Climate Regulation: Forests take up . * Ecotourism: Aesthetic and recreational value.
Working Toward a Sustainable Society
Current Unsustainable Society Characteristics: * High growth in LDCs and high consumption in MDCs. * Pollution-heavy agriculture (half of U.S. yield feeds farm animals). * Reliance on nonrenewable energy leading to smog and global warming. * Urban sprawl and habitat loss.
Rural Sustainability Goals: * Plant a variety of crops and trees (polyculture). * Use integrated pest management. * Preserve and restore wetlands. * Use renewable energy (wind, biofuel). * Buy local and use recycling/composting.
Urban Sustainability Goals: * Design energy-efficient mass transit. * Utilize "green roofs" and "greenbelts." * Plant native grasses to attract pollinators (bees and butterflies). * Recycle business equipment.
Assessing Quality of Life: * Gross National Product (GNP): A measure of net money flow that fails to account for environmental or social harm. * Better Indices: The Index of Sustainable Economic Welfare (ISEW) and the Genuine Progress Indicator (GPI). These include noneconomic indicators like unpaid work and deduct the costs of pollution, mineral/energy depletion, and damage.