Science 1206: Sustainability of Ecosystems - Comprehensive Study Guide
Fundamental Components of Sustainable Systems
Definition of Sustainable System: A sustainable system is an ecosystem capable of withstanding external pressures and providing continuous support to a diverse range of organisms.
The Two Pillars of Sustainability: - To Support: The ability of the environment to provide necessary resources (food, habitat, water) for living things. - To Endure: The ability of the system to remain functional and stable over long periods of time.
Examples of Sustainability Issues: - Gray-cheeked Thrush: This species is highly dependent on sustainable ecosystems; disruptions in habitat or resource availability can lead to population instability. - American Eel: Population declines in this species serve as an indicator of unsustainable systems, often caused by habitat fragmentation, pollution, or overfishing that the system cannot withstand.
Biotic Components and Interactions
Definition of Biotic Factors: These are the living components of an ecosystem, including all organisms and their subsequent interactions.
Biotic Interactions and Sustainability: - Symbiosis: A close, long-term interaction between two different species. - Mutualism: Both species benefit from the interaction. - Commensalism: One species benefits while the other is neither helped nor harmed. - Parasitism: One organism (the parasite) benefits at the direct expense and harm of another (the host). - Predation: An interaction where one organism (the predator) consumes another (the prey). This is a primary driver of population control. - Competition: The struggle between organisms for limited resources (food, space, mates). - Interspecific Competition: Competition occurring between members of different species. - Intraspecific Competition: Competition occurring between members of the same species.
Abiotic Components and Environmental Impact
Definition of Abiotic Factors: These are the non-living physical and chemical parts of an ecosystem that influence living organisms and the functioning of the ecosystem.
Crucial Abiotic Characteristics: - Water: Essential for all life processes; its availability determines the types of organisms that can survive in a region. - Oxygen: Required for cellular respiration in most organisms ($O_2$). - Light: The primary energy source for producers (via photosynthesis); influences behavior and growth cycles. - Nutrients: Chemical elements required for growth and maintenance. - Soil: Provides physical support for plants and acts as a reservoir for water and nutrients.
Global Biomes and Geographical Distribution
Definition of a Biome: Large ecosystems characterized by distinct climate patterns and specific biotic communities. Distribution is primarily dictated by abiotic factors.
Key Abiotic Determinants for Biomes: - Radiant energy (sunlight). - Precipitation levels. - Nutrient availability. - Elevation.
The Fundamental Rule: Abiotic factors determine biotic factors. Because similar abiotic conditions (climate, water, geography) exist in different parts of the world, biome distribution is global.
Examples of Global Biomes: - Tropical Rainforest: Found in equatorial regions with high radiant energy and precipitation. - Grassland: Characterized by moderate rainfall and specific nutrient levels in the soil. - Boreal Forest: High-latitude forests influenced by colder temperatures and specific soil conditions.
Case Study: Deserts: All deserts have cacti or similar succulents because they share abiotic factors like low precipitation and high radiant energy.
Case Study: Aquaculture/Salmon: Salmon can be farmed in diverse locations like the south coast of Newfoundland, the North Sea (Norway, Scotland), and South America (Chile) because these areas provide similar abiotic conditions (water temperature, salinity, oxygen levels).
Biogeography Examples: - Atlantic Cod: Range is determined by specific water temperatures and depth (abiotic conditions). - Hare: Found across different continents (e.g., North America and Eurasia) within similar biomes. While the specific species differs, the type of animal is the same due to similar abiotic stressors. - Polar Bears: Inhabit Greenland, Alaska, Northern Russia, and Labrador because these regions share the specific arctic abiotic factors required for their survival.
Population Dynamics and Sustainability
Population: A group of organisms of one specific species living in the same geographic area at the same time, capable of successful reproduction.
Equilibrium: A state of balance where there is no net change in population size over time. In natural populations, this occurs when: -
Exponential Growth: Accelerating growth characterized by a "J-shaped" curve on a graph. This is usually temporary as resources are eventually limited. - Examples: Algae in a new pond, protected Elephant populations in South Africa, and mouse plagues in Australia.
Limiting Factors: Factors that restrict the growth, distribution, or size of a population. - Abiotic Examples: Temperature, light, water, nutrients, oxygen. - Biotic Examples: Competition, predation, disease, food availability.
Density-Dependent and Density-Independent Factors
Density-Dependent Factors: Impact increases as the population density increases (usually biotic). - Disease: Spreads faster in crowded conditions. - Predation: Predators may focus more on highly dense prey populations. - Competition: More individuals leads to higher competition for resources. - Parasitism: Easier transmission between hosts at high densities. - Space and Stress: Crowding can lead to increased aggression and physical stress.
Density-Independent Factors: Affect populations regardless of their size or density (usually abiotic/natural phenomena). - Climate Events: Floods, droughts, tornadoes, hurricanes, ice storms. - Natural Disasters: Forest fires, earthquakes. - Human Activities: Pollution, clear-cutting land.
Carrying Capacity
Definition: The maximum number of individuals of a specific species that an ecosystem can support and maintain indefinitely without degrading the resource base.
Sustainability Threshold: Beyond the carrying capacity, the ecosystem cannot support additional individuals. When a population is at carrying capacity, it is considered to be in equilibrium.
Biogeochemical Cycles
Nutrients: Essential chemicals (elements) for life processes. There are chemical nutrients essential to life.
Nutrient Stores: Nutrients accumulated for varying durations in the atmosphere, oceans, and land masses.
The "Big Four" Nutrients: Carbon ($C$), Hydrogen ($H$), Nitrogen ($N$), and Oxygen ($O$) make up the vast majority of living matter.
Nutrient Cycling: Nutrients move through biotic (decomposition, food chains) and abiotic (water cycle) processes.
The Carbon and Oxygen Cycles
Photosynthesis: Occurs in the chloroplasts of green plants. Converts light energy into chemical energy. - Reaction: Produces Oxygen ($O_2$) and sugar from Carbon Dioxide ($CO_2$).
Cellular Respiration: Occurs in the mitochondria of most organisms. Releases stored energy for life processes. - Reaction: Produces Carbon Dioxide ($CO_2$) and water from sugar and Oxygen ($O_2$).
Human Impact on Carbon/Oxygen Balance: - Mining and Burning Fossil Fuels: Releases long-stored carbon into the atmosphere as $CO_2$. - Burning Forests: Releases stored carbon and removes the plants that absorb $CO_2$. - Clearing Vegetation: Reduces the number of organisms performing photosynthesis. - Acid Rain: Can damage photosynthetic organisms and soil health. - Raising Cattle: Increases methane ($CH_4$) and other carbon-based byproduct emissions.
The Nitrogen Cycle
Atmospheric Composition: Nitrogen ($N_2$) makes up approximately of the air, but most organisms cannot use it in its gaseous form.
Biological Importance: Vital for synthesizing proteins and DNA.
Nitrogen Fixation (Creation of Nitrates): Plants require nitrates ($NO_3^-$) to build proteins. This occurs via: 1. Lightning: Converts atmospheric nitrogen into nitrates locally. 2. Aerobic Bacteria: Found in the soil. 3. Nitrogen-fixing Bacteria: Living in the root nodules of legumes.
Eutrophication: The outcome of nutrient buildup (especially nitrogen/phosphorus) in aquatic systems. - Natural Eutrophication: A slow process over hundreds or thousands of years where deep, cold lakes become shallow, warm, and nutrient-rich. - Human-Accelerated Eutrophication: Caused by sewage runoff and fertilizer use. - Process: Increased nutrients $\rightarrow$ Algal Bloom $\rightarrow$ Algae die $\rightarrow$ Bacteria decompose algae $\rightarrow$ Decomposition consumes oxygen $\rightarrow$ Fish and other animals die from hypoxia.
Energy Transfers and Trophic Levels
Energy Source: The SUN is the ultimate source of energy for nearly all ecosystems.
Trophic Levels: Categories of organisms based on how they acquire energy. - 1st Trophic Level (Producers): Autotrophs (e.g., spruce trees, algae). - 2nd Trophic Level (Primary Consumers): Herbivores that eat producers (e.g., deer, insects). - 3rd Trophic Level (Secondary Consumers): Carnivores that eat primary consumers (e.g., wolves). - 4th Trophic Level (Tertiary Consumers): Carnivores eating secondary consumers. - 5th Trophic Level (Top Carnivores): The apex of the food chain.
Bioaccumulation and Biomagnification
DDT and PCBs: Historically used insecticides and industrial chemicals. DDT is soluble in fat but NOT in water.
Bioaccumulation: The process where a toxin is ingested at a rate faster than it can be eliminated, causing it to build up in an individual's body over time.
Biomagnification: The increase in concentration of a toxin as it moves up the food chain. Organisms at higher trophic levels (e.g., Bald Eagles, Beluga whales) have significantly higher concentrations of toxins than those at the bottom. - Ecological Impact: High DDT levels in Bald Eagles caused soft eggshells, leading to reproductive failure.
Modern Solutions: Use of water-soluble pesticides which can be excreted via urine or sweat. However, these are easily washed away by rain (requiring frequent application) and are often not species-specific.
Soil Quality and Fertilizers
Role of Fertilizers: Replace nitrogen and phosphorus depleted by crops to increase production.
Soil Process: Soil bacteria convert nitrogen in fertilizer into usable nitrates.
Potential Problems: - Acidification: Nitrates can increase nitric acid levels in soil, dropping the pH. - Microbial Damage: Low pH can kill decomposing bacteria and other beneficial soil organisms. - Run-off: Irrigation and spring melt carry fertilizers into water bodies, triggering the aforementioned eutrophication and algal blooms.
Questions & Discussion
Q: Could exponential growth in populations occur forever? - A: No, because resources (food, space, water) are finite. Eventually, the population will reach its carrying capacity or crash due to limiting factors.
Q: What factors prevent the perch population from growing exponentially? - A: Factors include available food, presence of predators, competition from other fish, and levels of dissolved oxygen in the water.
Q: Why wouldn't the hare be found in South America or Southern Africa? - A: The abiotic factors in those regions (climate, temperature, vegetation types) do not match the physiological and survival requirements of the hare species found in the northern biomes.
Q: What can be done about eutrophication? - A: Effective strategies include treatment of sewage before discharge, careful application of fertilizers to reduce runoff, and protecting freshwater buffer zones.