♻️AP Environmental Science Unit 1 – The Living World: Ecosystems

Key Concepts and Definitions

• Ecosystems are communities of living organisms interacting with each other and their physical environment
• Biotic factors include all living components of an ecosystem (plants, animals, microorganisms)
• Abiotic factors encompass non-living components (temperature, light, water, soil, nutrients)
• Biodiversity refers to the variety of life forms within an ecosystem or across ecosystems
• Trophic levels organize organisms based on their position in the food chain (producers, primary consumers, secondary consumers, tertiary consumers)
• Ecological niche describes the role and position of a species within an ecosystem
  • Includes the species' habitat, food sources, and interactions with other organisms
• Carrying capacity is the maximum population size an ecosystem can sustain given available resources

Ecosystem Components and Structure

• Producers, also known as autotrophs, convert light energy or chemical energy into organic compounds through photosynthesis or chemosynthesis
  • Examples of producers include plants, algae, and some bacteria
• Consumers, or heterotrophs, obtain energy by feeding on other organisms
  • Primary consumers (herbivores) feed on producers (rabbits, zooplankton)
  • Secondary consumers (carnivores) feed on primary consumers (snakes, small fish)
  • Tertiary consumers (top predators) feed on secondary consumers (hawks, sharks)
• Decomposers break down dead organic matter, releasing nutrients back into the ecosystem (fungi, bacteria)
• Food chains represent linear pathways of energy transfer from producers to consumers
• Food webs illustrate the complex interconnections among multiple food chains within an ecosystem

Energy Flow in Ecosystems

• Energy enters ecosystems through primary producers, which convert solar energy into chemical energy via photosynthesis
• Only about 10% of energy is transferred from one trophic level to the next, known as the 10% rule
  • The remaining 90% is lost as heat or used for metabolic processes
• Gross primary productivity (GPP) is the total amount of energy captured by producers through photosynthesis
• Net primary productivity (NPP) is the energy remaining after producers use some for respiration ($NPP = GPP - Respiration$)
• Secondary productivity refers to the energy captured by consumers
• Biomass represents the total mass of living organisms in an ecosystem
  • Biomass pyramids depict the decrease in biomass at each successive trophic level

Nutrient Cycles and Biogeochemical Processes

• Nutrient cycles describe the movement and exchange of organic and inorganic matter within ecosystems
• The water cycle (hydrologic cycle) involves the continuous movement of water through evaporation, transpiration, condensation, precipitation, and runoff
• The carbon cycle encompasses the exchange of carbon among the atmosphere, oceans, and living organisms through processes like photosynthesis, respiration, and decomposition
  • Carbon dioxide ($CO_2$) is a key component of the carbon cycle
• The nitrogen cycle converts atmospheric nitrogen ($N_2$) into usable forms for living organisms through nitrogen fixation, nitrification, and denitrification
  • Bacteria play crucial roles in the nitrogen cycle
• The phosphorus cycle involves the movement of phosphorus through the environment, including weathering of rocks, uptake by organisms, and decomposition

Ecosystem Dynamics and Succession

• Succession describes the gradual changes in species composition and community structure over time
• Primary succession occurs in newly formed or bare environments (volcanic islands, glacial moraines)
  • Pioneer species colonize the area first, followed by intermediate and climax species
• Secondary succession takes place in previously inhabited areas after disturbances (abandoned agricultural fields, forests after fires)
• Climax communities represent the final, relatively stable stage of succession
• Disturbances such as fires, hurricanes, and human activities can disrupt succession and reset the process
• Resilience is the ability of an ecosystem to recover and return to its original state after a disturbance

Human Impacts on Ecosystems

• Habitat destruction, fragmentation, and degradation result from human activities like deforestation, urbanization, and agriculture
  • Loss of habitat is a major threat to biodiversity
• Overexploitation of resources through overfishing, overhunting, and overharvesting can lead to species declines and ecosystem imbalances
• Pollution, including air, water, and soil pollution, can disrupt ecosystem functions and harm organisms
  • Examples include acid rain, eutrophication, and plastic pollution
• Climate change, largely driven by human activities, affects ecosystems through rising temperatures, altered precipitation patterns, and increased frequency of extreme events
• Invasive species, often introduced by humans, can outcompete native species and disrupt ecosystem balance
  • Invasive species examples include kudzu, zebra mussels, and Burmese pythons

Conservation and Management Strategies

• Habitat conservation involves protecting and restoring critical habitats to support biodiversity
  • Establishing protected areas, wildlife reserves, and national parks
• Ecosystem management focuses on maintaining the health and integrity of entire ecosystems rather than individual species
• Sustainable resource management practices aim to balance human needs with ecological sustainability
  • Examples include sustainable forestry, fishing quotas, and renewable energy
• Restoration ecology involves actively restoring degraded or damaged ecosystems to their natural state
  • Reforestation, wetland restoration, and coral reef rehabilitation
• Invasive species management includes preventing introductions, early detection, and eradication or control efforts
• Environmental policies and regulations, such as the Endangered Species Act and the Clean Air Act, provide legal frameworks for conservation and protection

Real-World Applications and Case Studies

• Yellowstone National Park: Reintroduction of gray wolves and the subsequent trophic cascade effects on the ecosystem
• Amazon Rainforest: Deforestation, biodiversity loss, and the role of the rainforest in global carbon cycling
• Great Barrier Reef: Coral bleaching and the impacts of climate change on marine ecosystems
• Chesapeake Bay: Nutrient pollution, eutrophication, and efforts to restore the bay's ecosystem
• Invasive species case studies:
  • Zebra mussels in the Great Lakes
  • Kudzu vine in the southeastern United States
• Sustainable forestry practices in the Pacific Northwest, balancing timber production and ecosystem conservation
• Urban ecology and the integration of green spaces in cities to support biodiversity and ecosystem services