🔬General Biology I Unit 46 – Ecosystems

Key Concepts and Definitions

• Ecosystem consists of a community 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)
• Habitat refers to the natural environment where an organism lives and grows
• Niche describes an organism's role within an ecosystem, including its interactions with other species and its use of resources
• Biodiversity measures the variety of life within an ecosystem, including genetic diversity, species diversity, and ecosystem diversity
• Trophic levels organize organisms based on their position in the food chain (producers, primary consumers, secondary consumers, tertiary consumers)
• Ecological succession describes the gradual process of change in an ecosystem's species composition over time, from pioneer species to a climax community

Ecosystem Components and Structure

• Producers (autotrophs) form the foundation of ecosystems by converting light energy into chemical energy through photosynthesis
  • Examples of producers include plants, algae, and cyanobacteria
• Consumers (heterotrophs) obtain energy by feeding on other organisms
  • Primary consumers (herbivores) feed directly on producers (rabbits, caterpillars, zooplankton)
  • Secondary consumers (carnivores) feed on primary consumers (birds, spiders, small fish)
  • Tertiary consumers (top predators) feed on secondary consumers (hawks, wolves, sharks)
• Decomposers break down dead organic matter, releasing nutrients back into the ecosystem (bacteria, fungi)
• Food chains represent linear pathways of energy transfer from producers to consumers
• Food webs illustrate the complex network of feeding relationships within an ecosystem, connecting multiple food chains

Energy Flow in Ecosystems

• Energy enters ecosystems through primary producers, which convert sunlight into chemical energy via photosynthesis
• Only a small fraction (typically 10%) of energy is transferred from one trophic level to the next, with the remaining energy lost as heat or used for metabolic processes
• Ecological pyramids visually represent the flow of energy, biomass, or numbers of organisms at each trophic level
  • Pyramid of energy shows the decrease in available energy at each successive trophic level
  • Pyramid of biomass illustrates the total mass of living organisms at each trophic level
  • Pyramid of numbers depicts the number of individuals at each trophic level
• Primary productivity measures the rate at which primary producers convert light energy into chemical energy
  • Gross primary productivity (GPP) represents the total energy captured by producers
  • Net primary productivity (NPP) accounts for the energy used by producers for respiration

Nutrient Cycling

• Biogeochemical cycles describe the movement of essential nutrients (carbon, nitrogen, phosphorus, water) through ecosystems
• Carbon cycle involves the exchange of carbon between the atmosphere, living organisms, and Earth's crust
  • Photosynthesis removes carbon dioxide from the atmosphere and incorporates it into organic compounds
  • Respiration and decomposition release carbon dioxide back into the atmosphere
• Nitrogen cycle encompasses the processes of nitrogen fixation, nitrification, and denitrification
  • Nitrogen-fixing bacteria convert atmospheric nitrogen (N2) into ammonia (NH3), which plants can use
  • Nitrifying bacteria convert ammonia into nitrites (NO2-) and nitrates (NO3-)
  • Denitrifying bacteria convert nitrates back into atmospheric nitrogen
• Phosphorus cycle involves the weathering of rocks, uptake by organisms, and return to sediments
• Water cycle (hydrologic cycle) describes the continuous movement of water through evaporation, transpiration, precipitation, and runoff

Ecosystem Interactions and Relationships

• Competition occurs when two or more species vie for the same limited resources (food, water, space)
  • Intraspecific competition happens between individuals of the same species
  • Interspecific competition takes place between individuals of different species
• Predation is an interaction where one organism (predator) hunts and consumes another organism (prey)
  • Predator-prey relationships can lead to population fluctuations and adaptations in both species
• Symbiosis describes close and long-term interactions between two different species
  • Mutualism benefits both species involved (clownfish and sea anemones, pollinators and flowers)
  • Commensalism benefits one species while the other is unaffected (barnacles on whales, epiphytes on trees)
  • Parasitism benefits one species (parasite) at the expense of the other (host)
• Keystone species have a disproportionately large impact on their ecosystem relative to their abundance (sea otters, wolves, beavers)

Ecosystem Types and Diversity

• Terrestrial ecosystems are land-based and include biomes such as forests, grasslands, deserts, and tundra
  • Forests are characterized by a dense canopy of trees (tropical rainforests, temperate forests, boreal forests)
  • Grasslands have grasses as the dominant vegetation (prairies, savannas, steppes)
  • Deserts are dry ecosystems with sparse vegetation adapted to low water availability (cacti, succulents)
  • Tundra occurs in cold regions with low-growing plants adapted to harsh conditions (mosses, lichens, sedges)
• Aquatic ecosystems are water-based and include marine and freshwater environments
  • Marine ecosystems cover the majority of Earth's surface (oceans, coral reefs, estuaries)
  • Freshwater ecosystems include rivers, lakes, wetlands, and streams
• Ecotones are transitional areas between two adjacent ecosystems, often displaying high biodiversity (forest edges, coastal zones)

Human Impact on Ecosystems

• Habitat destruction and fragmentation result from human activities such as deforestation, urbanization, and agriculture
  • Loss of habitat is a major threat to biodiversity and can lead to species extinctions
• Pollution affects ecosystems by introducing harmful substances into the environment (air pollution, water pollution, soil contamination)
  • Pollutants can accumulate in food chains through biomagnification, affecting organisms at higher trophic levels
• Overexploitation occurs when humans harvest resources (fish, timber, wildlife) at unsustainable rates
  • Overfishing has led to the collapse of many fish populations and disrupted marine ecosystems
• Climate change, driven by human activities that increase greenhouse gas emissions, alters ecosystems worldwide
  • Rising temperatures, changing precipitation patterns, and more frequent extreme weather events affect species distributions and ecosystem functioning
• Invasive species, often introduced by human activities, can disrupt ecosystems by outcompeting native species and altering ecosystem dynamics
  • Examples include kudzu in the southeastern United States, zebra mussels in the Great Lakes, and cane toads in Australia

Applications and Case Studies

• Ecosystem services are the benefits that humans derive from ecosystems (food production, water purification, carbon sequestration, recreation)
  • Valuing ecosystem services can help inform conservation and management decisions
• Ecological restoration aims to repair and restore degraded ecosystems to their natural state
  • Examples include reforestation projects, wetland restoration, and coral reef rehabilitation
• Bioremediation uses living organisms (bacteria, fungi, plants) to clean up contaminated environments
  • Microorganisms can break down pollutants such as oil spills, pesticides, and heavy metals
• Agroecology applies ecological principles to agricultural systems to promote sustainability and biodiversity
  • Practices include crop rotation, intercropping, and integrated pest management
• Ecosystem-based management considers the entire ecosystem, including humans, when making decisions about resource use and conservation
  • Marine protected areas (MPAs) are an example of ecosystem-based management in ocean conservation
• Citizen science involves public participation in scientific research, often focused on ecological monitoring and data collection
  • Examples include bird counts, water quality monitoring, and invasive species tracking