3.2 Energy flow and nutrient cycling in ecosystems
4 min read•august 16, 2024
Ecosystems are all about energy flow and nutrient cycling. These processes keep life going, with plants capturing sunlight and nutrients moving through food webs. It's like a giant recycling system where everything's connected.
Understanding these cycles helps us see how ecosystems work and how we affect them. From carbon in the air to nitrogen in the soil, these cycles show how life and the environment are linked. It's crucial for grasping the bigger picture of biodiversity and ecosystem health.
Energy flow through ecosystems
Thermodynamics and energy transfer
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- Energy flow in ecosystems follows the laws of thermodynamics (energy transfers and transforms but never creates or destroys)
- Solar radiation serves as the primary energy source for most ecosystems
- Autotrophs capture solar energy through
- Autotrophs convert solar energy into chemical energy
- Energy transfer between trophic levels operates at ~10% efficiency
- Heat loss and metabolic processes account for the 90% energy loss
- Ecological pyramids visually represent decreasing energy at higher trophic levels
- Types include energy pyramids, biomass pyramids, and numbers pyramids
- Net primary productivity (NPP) quantifies available energy for transfer to higher trophic levels
- NPP accounts for energy remaining after producer
Food chains and food webs
- Food chains model simple linear energy flow in ecosystems
- Food webs illustrate complex interconnections between species in ecosystems
- Both food chains and food webs demonstrate energy transfer between organisms
- Examples of food chains:
- Grass → Grasshopper → Frog → Snake → Hawk
- Phytoplankton → Zooplankton → Small fish → Large fish → Seabird
Producers, Consumers, and Decomposers
Primary producers (Autotrophs)
- Organisms capable of synthesizing their own food from inorganic compounds
- Primarily use photosynthesis or chemosynthesis for energy production
- Examples of :
- Terrestrial plants (trees, grasses, shrubs)
- Algae and phytoplankton in
- Chemosynthetic bacteria in deep-sea hydrothermal vents
Consumers (Heterotrophs)
- Rely on other organisms for energy
- Classified based on position in :
- Primary (herbivores) eat
- Secondary consumers (carnivores) eat primary consumers
- (top predators) eat secondary consumers
- Examples of consumers:
- Primary consumers (rabbits, deer, zooplankton)
- Secondary consumers (foxes, owls, small fish)
- Tertiary consumers (wolves, sharks, eagles)
Decomposers and their ecological role
- Primarily bacteria and fungi break down dead organic matter and waste products
- Release nutrients back into ecosystem for reuse by producers
- Crucial for nutrient cycling and energy flow in ecosystems
- Examples of :
- Soil bacteria (Bacillus, Clostridium)
- Fungi (mushrooms, molds)
- Detritivores (earthworms, millipedes)
Ecosystem balance and keystone species
- Interconnected roles of producers, consumers, and decomposers form the basis of energy flow
- Nutrient cycling in ecosystems depends on the balance between these groups
- Keystone species have disproportionate impact on ecosystem structure and function
- Can be producers, consumers, or decomposers
- Examples (sea otters in kelp forests, beavers in riparian ecosystems)
- Ecosystem stability and resilience rely on maintaining balance between these groups
Nutrient cycling in ecosystems
Carbon cycle
- Describes carbon movement through atmosphere, biosphere, hydrosphere, and geosphere
- Key processes involved:
- Photosynthesis removes carbon dioxide from atmosphere
- Respiration releases carbon dioxide back into atmosphere
- Decomposition of organic matter releases carbon
- Ocean absorption and release of carbon dioxide
- Fossil fuel formation and combustion
- Human activities significantly alter the carbon cycle (deforestation, fossil fuel burning)
Nitrogen cycle
- Involves exchange of nitrogen between atmosphere, soil, and living organisms
- Key processes mediated by microorganisms:
- Nitrogen fixation converts atmospheric nitrogen to biologically available forms
- Nitrification converts ammonium to nitrate
- Denitrification returns nitrogen to the atmosphere
- Ammonification converts organic nitrogen to ammonium
- Examples of nitrogen-fixing organisms (Rhizobium bacteria, cyanobacteria)
Phosphorus and water cycles
- primarily sedimentary
- Main reservoir in rock and soil minerals
- Processes include weathering, plant uptake, and aquatic sediment deposition
- Water cycle (hydrologic cycle) crucial for nutrient distribution
- Involves evaporation, transpiration, precipitation, and runoff
- Dissolves and transports nutrients throughout ecosystems
Human impacts on ecosystems
Land use changes and agricultural practices
- Deforestation alters primary productivity and disrupts energy flow patterns
- Agricultural practices lead to nutrient imbalances and water pollution
- Fertilizer use causes eutrophication in water bodies
- Pesticides affect non-target species and disrupt food webs
- Examples of impacts:
- Amazon rainforest deforestation for agriculture and ranching
- Gulf of Mexico "dead zone" caused by agricultural runoff
Overfishing and hunting
- Cause trophic cascades, altering ecosystem structure and function
- Examples of impacts:
- Collapse of Atlantic cod fishery off Newfoundland
- Removal of wolves from Yellowstone National Park (later reintroduced)
Urbanization and climate change
- Urbanization increases energy consumption and waste production
- Alters local and global
- Climate change affects energy flow and nutrient cycling through:
- Changes in temperature and precipitation patterns
- Increased frequency of extreme weather events
- Shifts in species distributions and phenology
Conservation and mitigation efforts
- Reforestation and sustainable agriculture aim to restore ecosystem balance
- Development of renewable energy sources reduces disruption of natural cycles
- Examples (solar, wind, geothermal energy)
- Circular economy practices promote efficient resource use and waste reduction
- Conservation efforts focus on protecting keystone species and critical habitats
- Examples (marine protected areas, wildlife corridors)
Key Terms to Review (19)
10% rule: The 10% rule is an ecological principle stating that, on average, only about 10% of the energy from one trophic level is transferred to the next when organisms consume each other. This concept highlights the inefficiencies in energy transfer within ecosystems and emphasizes the importance of primary producers in supporting the entire food web.
Aquatic ecosystems: Aquatic ecosystems are ecosystems that are dominated by water and can be classified into freshwater and marine environments. These ecosystems play a crucial role in supporting biodiversity, regulating climate, and providing essential resources and services to humans. Understanding their structure and function is vital for recognizing how energy flows and nutrients cycle through these environments.
Biogeochemical cycles: Biogeochemical cycles refer to the pathways by which essential elements and compounds move through the biological, geological, and chemical components of the Earth. These cycles are crucial for understanding how nutrients flow through ecosystems, as they connect living organisms with their environment, ensuring that elements like carbon, nitrogen, and phosphorus are recycled and made available for various forms of life.
Carrying Capacity: Carrying capacity refers to the maximum number of individuals of a particular species that an environment can sustainably support over time without degrading the ecosystem. This concept is essential for understanding population dynamics, as it influences growth rates and the overall health of ecosystems. It also plays a key role in how energy flows and nutrients cycle, shaping the structure and function of ecosystems while informing sustainable development practices.
Consumers: Consumers are organisms that obtain energy and nutrients by consuming other organisms or organic matter, playing a crucial role in the flow of energy and cycling of nutrients within ecosystems. They can be classified into various categories based on their feeding habits, such as herbivores, carnivores, and omnivores, all contributing to the structure and function of ecosystems. By interacting with producers and decomposers, consumers help maintain ecological balance and support the complexity of life on Earth.
Decomposers: Decomposers are organisms, primarily bacteria and fungi, that break down dead organic matter and recycle nutrients back into the ecosystem. By decomposing this material, they play a vital role in energy flow and nutrient cycling, ensuring that essential elements like carbon, nitrogen, and phosphorus are made available to producers, such as plants. This process supports the overall structure and function of ecosystems by maintaining soil fertility and facilitating the growth of primary producers.
Food chain: A food chain is a linear sequence that shows how energy and nutrients flow through an ecosystem by connecting different organisms, starting from primary producers to various levels of consumers. Each step in the chain illustrates who eats whom, highlighting the interconnectedness of life forms and their reliance on one another for energy transfer.
Food web: A food web is a complex network of interconnected food chains that illustrates how energy and nutrients flow through an ecosystem. It highlights the relationships between different organisms, including producers, consumers, and decomposers, and demonstrates how they depend on each other for survival. Understanding food webs is essential to grasp the intricacies of energy flow and nutrient cycling within ecosystems and how these components interact to maintain ecological balance.
Limiting Factors: Limiting factors are environmental conditions that restrict the growth, abundance, or distribution of a population within an ecosystem. These factors can be biotic, like competition and predation, or abiotic, like temperature and nutrient availability. Understanding limiting factors is crucial because they directly influence energy flow and nutrient cycling in ecosystems, determining how populations thrive or struggle.
Nitrogen cycle: The nitrogen cycle is a natural process that describes the movement of nitrogen through the atmosphere, lithosphere, hydrosphere, and biosphere. It plays a crucial role in ecosystem functioning as it transforms nitrogen from its atmospheric form into compounds usable by living organisms, and then back into the atmosphere, maintaining balance within the environment.
Phosphorus cycle: The phosphorus cycle is the biogeochemical process that describes the movement of phosphorus through the lithosphere, hydrosphere, and biosphere. Unlike other nutrient cycles, phosphorus does not have a gaseous phase and primarily moves through soil, water, and living organisms. This cycle is crucial for ecosystem functioning as phosphorus is an essential nutrient for plant growth and energy transfer within living cells.
Photosynthesis: Photosynthesis is the process by which green plants, algae, and some bacteria convert light energy into chemical energy, specifically glucose, using carbon dioxide and water. This process not only fuels the growth and energy needs of these organisms but also plays a crucial role in the carbon cycle and the overall functioning of ecosystems by releasing oxygen as a byproduct.
Primary producers: Primary producers are organisms that can create their own food through the process of photosynthesis or chemosynthesis, forming the base of the food chain in ecosystems. They play a critical role in energy flow and nutrient cycling by converting sunlight or chemical energy into organic matter, which is then available for consumption by other organisms. This makes them essential for maintaining the structure and function of ecological communities.
Producers: Producers are organisms that create their own food using photosynthesis or chemosynthesis, forming the base of the food chain in ecosystems. They convert sunlight or chemical energy into organic compounds, which serve as energy sources for other organisms, known as consumers. This process is essential for energy flow and nutrient cycling, making producers crucial for maintaining ecosystem stability and function.
Respiration: Respiration is a biochemical process in which living organisms convert glucose and oxygen into energy, carbon dioxide, and water. This process is essential for maintaining cellular functions and supports the flow of energy through ecosystems by providing the energy needed for growth, reproduction, and maintenance of biological systems.
Terrestrial ecosystems: Terrestrial ecosystems are communities of living organisms, including plants, animals, and microorganisms, that exist on land and interact with their physical environment. These ecosystems are characterized by distinct climate conditions, soil types, and vegetation patterns, which influence the biodiversity and ecological processes within them. Understanding these systems involves examining how energy flows through them and how nutrients cycle, which are crucial for sustaining life and maintaining ecological balance.
Tertiary consumers: Tertiary consumers are organisms that occupy the highest level in a food chain, primarily feeding on secondary consumers. These predators play a critical role in maintaining the balance of ecosystems by regulating the populations of other species, thus contributing to the overall health and stability of their environment. Their position in the food web indicates their reliance on both energy flow and nutrient cycling, as they depend on the lower trophic levels for sustenance.
Trophic cascade: A trophic cascade is an ecological phenomenon that occurs when the removal or addition of a top predator in an ecosystem causes a series of changes in the population sizes and dynamics of other species within the food web. This disruption can impact various levels of the ecosystem, affecting everything from primary producers to herbivores and lower trophic levels, thus altering energy flow and nutrient cycling.
Trophic efficiency: Trophic efficiency refers to the percentage of energy that is transferred from one trophic level to the next in a food chain or food web. This concept is crucial for understanding how energy flows through ecosystems and how much energy is available to higher trophic levels, influencing the structure and dynamics of ecosystems. Trophic efficiency typically ranges from 5% to 20%, reflecting the loss of energy through metabolic processes, heat, and waste at each level.