🐇Honors Biology Unit 19 – Ecosystem Dynamics & Biogeochemical Cycles

Key Concepts

• Ecosystems are complex systems composed of living organisms (biotic factors) and non-living components (abiotic factors) that interact with each other
• Energy flows through ecosystems in a unidirectional manner, starting with primary producers (autotrophs) and moving to consumers (heterotrophs) and decomposers
• Nutrients cycle through ecosystems, being used and reused by different organisms in various forms
  • Major biogeochemical cycles include the carbon cycle, nitrogen cycle, phosphorus cycle, and water cycle
• Population dynamics describe how populations change over time, influenced by factors such as birth rates, death rates, immigration, and emigration
• Communities are composed of multiple interacting populations, with interactions such as competition, predation, and symbiosis shaping their structure and function
• Human activities, such as habitat destruction, pollution, and climate change, can have significant impacts on ecosystems, altering their structure, function, and biodiversity
• Understanding ecosystem dynamics and biogeochemical cycles is crucial for addressing environmental issues and developing sustainable management practices (conservation, restoration)

Ecosystem Structure and Function

• Ecosystems are composed of biotic factors (living organisms) and abiotic factors (non-living components) that interact with each other
  • Biotic factors include producers, consumers, and decomposers
  • Abiotic factors include temperature, light, water, soil, and nutrients
• Trophic levels describe the feeding relationships within an ecosystem, with producers at the bottom, followed by primary consumers, secondary consumers, and tertiary consumers
• Food chains and food webs illustrate the transfer of energy and matter through ecosystems
  • Food chains show a linear sequence of energy transfer from one trophic level to the next
  • Food webs show the complex interactions and multiple pathways of energy transfer between organisms
• Ecological pyramids (pyramids of numbers, biomass, and energy) visually represent the relative abundance, biomass, or energy at each trophic level
• Ecosystem services are the benefits that humans derive from ecosystems, such as clean air and water, pollination, and nutrient cycling
• Biodiversity, the variety of life within an ecosystem, plays a crucial role in maintaining ecosystem stability and resilience

Energy Flow in Ecosystems

• Energy enters ecosystems through primary producers (autotrophs) that convert sunlight into chemical energy through photosynthesis
• Only a small fraction (typically 10%) of the energy is transferred from one trophic level to the next, with the rest being lost as heat or used for metabolic processes
• Gross primary productivity (GPP) is the total amount of energy captured by primary producers through photosynthesis
• Net primary productivity (NPP) is the energy remaining after primary producers use some for their own metabolic needs (respiration)
• Secondary productivity refers to the energy captured by consumers (heterotrophs) from lower trophic levels
• Decomposers (bacteria and fungi) break down dead organic matter, releasing nutrients back into the ecosystem and making them available for primary producers
• Energy flow through ecosystems is governed by the laws of thermodynamics, with energy being conserved but transformed and some being lost as heat at each trophic level

Nutrient Cycles

• Nutrients cycle through ecosystems, being used and reused by different organisms in various forms
• The carbon cycle involves the exchange of carbon between the atmosphere, biosphere, hydrosphere, and geosphere
  • Photosynthesis, respiration, decomposition, and combustion are key processes in the carbon cycle
• The nitrogen cycle involves the transformation of nitrogen between various forms (nitrogen fixation, nitrification, denitrification, ammonification)
  • Nitrogen-fixing bacteria convert atmospheric nitrogen (N2) into usable forms for plants
• The phosphorus cycle involves the movement of phosphorus between the biosphere, hydrosphere, and geosphere
  • Weathering of rocks releases phosphorus, which is taken up by plants and moves through food webs
• The water cycle (hydrologic cycle) describes the continuous movement of water on, above, and below the Earth's surface (evaporation, transpiration, precipitation, infiltration, runoff)
• Human activities, such as fossil fuel combustion, deforestation, and agricultural practices, can disrupt natural nutrient cycles, leading to environmental problems (eutrophication, climate change)

Population Dynamics

• Populations are groups of individuals of the same species living in a particular area
• Population size is determined by factors such as birth rates, death rates, immigration, and emigration
• Exponential growth occurs when a population grows at a constant rate, resulting in a J-shaped curve
• Logistic growth occurs when a population's growth slows down as it approaches the carrying capacity (K), resulting in an S-shaped curve
  • Carrying capacity is the maximum population size that an environment can sustain given the available resources
• Density-dependent factors (competition, predation, disease) have a greater impact on population size as the population density increases
• Density-independent factors (natural disasters, climate change) affect population size regardless of population density
• Age structure diagrams (pyramids) show the distribution of individuals in different age groups within a population, providing insights into its growth potential and future trends

Community Interactions

• Communities are composed of multiple interacting populations of different species
• Competition occurs when two or more species compete for the same limited resources (food, water, space)
  • Intraspecific competition occurs between individuals of the same species
  • Interspecific competition occurs between individuals of different species
• Predation is an interaction where one species (the predator) feeds on another species (the prey)
  • Predator-prey relationships can lead to population oscillations and help maintain ecosystem balance
• Symbiosis is a close and long-term interaction between two different species
  • Mutualism is a symbiotic relationship in which both species benefit (pollination, nitrogen fixation)
  • Commensalism is a symbiotic relationship in which one species benefits while the other is unaffected (barnacles on whales)
  • Parasitism is a symbiotic relationship in which one species (the parasite) benefits at the expense of the other (the host)
• Keystone species are species that have a disproportionately large impact on the structure and function of their ecosystem relative to their abundance (sea otters, wolves)

Human Impact on Ecosystems

• Habitat destruction, fragmentation, and degradation are major threats to ecosystems and biodiversity
  • Deforestation, urbanization, and agricultural expansion are common causes of habitat loss
• Pollution (air, water, soil) can disrupt ecosystem processes, harm organisms, and alter nutrient cycles
  • Eutrophication is the excessive growth of algae and aquatic plants due to nutrient pollution (nitrogen, phosphorus)
• Overexploitation of natural resources (overfishing, overhunting) can lead to population declines and ecosystem imbalances
• Invasive species, introduced intentionally or accidentally by humans, can outcompete native species and alter ecosystem dynamics
• Climate change, largely driven by human activities (fossil fuel combustion, deforestation), can affect species distributions, phenology, and ecosystem functioning
• Conservation efforts, such as protected areas, habitat restoration, and sustainable resource management, aim to mitigate human impacts and preserve ecosystems

Real-World Applications

• Understanding ecosystem dynamics and biogeochemical cycles is essential for developing sustainable agriculture, forestry, and fisheries practices
• Ecological knowledge informs conservation efforts, such as designing protected areas, managing invasive species, and restoring degraded habitats
• Ecosystem services (carbon sequestration, water purification, pollination) highlight the economic and social value of preserving healthy ecosystems
• Bioremediation uses living organisms (bacteria, plants) to clean up contaminated environments (oil spills, heavy metal pollution)
• Agroecology applies ecological principles to design sustainable and resilient agricultural systems that minimize environmental impacts
• Urban ecology studies the interactions between organisms and their environment in urban settings, informing sustainable city planning and green infrastructure development
• Ecological models and simulations help predict the impacts of human activities and environmental changes on ecosystems, guiding management decisions and policy-making