Ecosystems: Cycling of Matter and Flow of Energy

• Ecosystems are dynamic systems that depend on the cycling of matter and the flow of energy.
• Matter, such as nutrients and water, cycles within an ecosystem, constantly being reused.
• Energy flows through an ecosystem in a one-way direction, typically from the sun to producers to consumers.

Biogeochemical Cycles

• Biogeochemical cycles involve the movement of elements or molecules through the biotic (living) and abiotic (non-living) parts of an ecosystem.
• These cycles are crucial for the availability of essential elements for life processes.
• Key biogeochemical cycles include the water, carbon, nitrogen, and phosphorus cycles.

The Water Cycle

• The water cycle, also called the hydrologic cycle, involves the continuous movement of water on, above, and below the surface of the Earth.
• Key processes include evaporation (liquid to gas), transpiration (water release from plants), condensation (gas to liquid), precipitation (water falling back to Earth), and runoff (water flowing over the surface).
• Evaporation is the process where the sun heats water and changes it into vapor or steam.
• Transpiration is the evaporation of water from plant leaves.
• Condensation occurs when water vapor in the air cools and changes back into liquid form, forming clouds.
• Precipitation happens when water droplets in clouds get too heavy and fall back to Earth as rain, snow, sleet, or hail.
• Runoff is the process where water flows over the land surface and into streams, rivers, lakes, and oceans.

The Carbon Cycle

• The carbon cycle involves the movement of carbon through the atmosphere, oceans, land, and living organisms.
• Photosynthesis, respiration, decomposition, and combustion are key processes.
• Photosynthesis removes carbon dioxide from the atmosphere and converts it into organic compounds.
• Respiration releases carbon dioxide back into the atmosphere as organisms break down organic compounds.
• Decomposition releases carbon into the soil and atmosphere as decomposers break down dead organisms.
• Combustion, such as burning fossil fuels, releases carbon dioxide into the atmosphere.
• Carbon is stored in various reservoirs including the atmosphere (as carbon dioxide), oceans (dissolved carbon), land (in soil and organic matter), and fossil fuels (coal, oil, natural gas).
• Human activities such as deforestation and burning fossil fuels have increased the concentration of carbon dioxide in the atmosphere, contributing to climate change.

The Nitrogen Cycle

• The nitrogen cycle involves the conversion of nitrogen into various forms that can be used by organisms.
• Nitrogen fixation, nitrification, denitrification, and assimilation are key processes.
• Nitrogen fixation converts atmospheric nitrogen (N2) into ammonia (NH3), which can be used by plants. This process is mainly carried out by bacteria.
• Nitrification converts ammonia into nitrites (NO2-) and then into nitrates (NO3-), which are more easily absorbed by plants.
• Denitrification converts nitrates back into atmospheric nitrogen, reducing the amount of usable nitrogen in the ecosystem.
• Assimilation is the process by which plants absorb ammonia, ammonium ions, and nitrate ions through their roots.
• Nitrogen is a component of amino acids and nucleic acids, essential molecules for life.
• Farmers often use fertilizers containing nitrogen compounds to enhance crop growth.

The Phosphorus Cycle

• The phosphorus cycle involves the movement of phosphorus through rocks, water, soil, and living organisms.
• Weathering, absorption by plants, and decomposition are key processes.
• Phosphorus is essential for DNA, RNA, and ATP production.
• Weathering of rocks releases phosphate into the soil.
• Plants absorb phosphate from the soil through their roots.
• Animals obtain phosphorus by eating plants or other animals.
• Decomposition returns phosphorus to the soil.
• Unlike the carbon and nitrogen cycles, the phosphorus cycle does not have a significant atmospheric component.
• Phosphorus is often a limiting nutrient in ecosystems, meaning its availability limits the growth of organisms.
• Phosphate runoff from fertilizers and sewage can lead to eutrophication in aquatic ecosystems.

Energy Flow in Ecosystems

• Energy flow in an ecosystem is unidirectional, starting with the sun.
• Producers (autotrophs) capture solar energy through photosynthesis and convert it into chemical energy.
• Consumers (heterotrophs) obtain energy by feeding on producers or other consumers.
• Decomposers break down dead organic matter and release nutrients back into the ecosystem.
• Trophic levels represent the different feeding positions in a food chain or food web.
• Energy is lost at each trophic level, primarily as heat, due to metabolic processes.

Food Chains and Food Webs

• A food chain is a linear sequence of organisms through which nutrients and energy pass as one organism eats another.
• A food web is a complex network of interconnected food chains representing the feeding relationships within an ecosystem.
• Food webs provide a more accurate representation of energy flow in an ecosystem than simple food chains.
• Decomposers play a crucial role in food webs by breaking down dead organic matter and recycling nutrients.

Ecological Pyramids

• Ecological pyramids are graphical representations of energy, biomass, or number of organisms at each trophic level in an ecosystem.
• Pyramids of energy always decrease as you move up trophic levels because energy is lost as heat during metabolic processes.
• Pyramids of biomass represent the total mass of organisms at each trophic level.
• Pyramids of numbers represent the number of individual organisms at each trophic level.
• These pyramids illustrate the energy flow and trophic structure of an ecosystem.

Productivity of Ecosystems

• Primary productivity is the rate at which producers convert solar energy into chemical energy.
• Gross primary productivity (GPP) is the total rate of photosynthesis, while net primary productivity (NPP) is the rate of energy storage as biomass after accounting for respiration.
• Ecosystems with high primary productivity, such as tropical rainforests and coral reefs, support a greater diversity and abundance of life.
• Factors affecting primary productivity include sunlight availability, temperature, water availability, and nutrient availability.

Interactions Among Organisms

• Symbiosis is a close and long-term interaction between different species in a community.
• Mutualism is a symbiotic relationship in which both species benefit.
• Commensalism is a symbiotic relationship in which one species benefits and the other is neither harmed nor helped.
• Parasitism is a symbiotic relationship in which one species (the parasite) benefits and the other (the host) is harmed.
• Competition occurs when two or more species require the same limited resource, resulting in negative effects on both species.
• Predation occurs when one organism (the predator) kills and consumes another organism (the prey).

Ecosystem Stability and Resilience

• Ecosystem stability refers to the ability of an ecosystem to maintain a relatively constant state over time.
• Ecosystem resilience refers to the ability of an ecosystem to recover from disturbances, such as fires, floods, or pollution.
• High biodiversity can enhance ecosystem stability and resilience.
• Keystone species play a critical role in maintaining the structure and function of an ecosystem.
• The loss of a keystone species can have cascading effects throughout the ecosystem.

Human Impact on Ecosystems

• Human activities can significantly disrupt the cycling of matter and the flow of energy in ecosystems.
• Pollution, deforestation, overexploitation of resources, and climate change are major threats to ecosystems.
• Pollution can contaminate water, soil, and air, harming organisms and disrupting ecological processes.
• Deforestation reduces habitat, increases erosion, and alters biogeochemical cycles.
• Overexploitation of resources can lead to the depletion of populations and the collapse of ecosystems.
• Climate change can alter temperature and precipitation patterns, leading to shifts in species distributions and ecosystem function.
• Conservation efforts are essential for protecting and restoring ecosystems.