Ecosystems Overview and Energy Flow

Ecosystems Overview

• Ecosystems encompass all living organisms (community) and their interaction with non-living factors (abiotic).
• They vary in size, from small (e.g., aquarium) to large (e.g., lake or forest).
• Key processes in ecosystems are energy flow and chemical cycling.
• Energy moves through ecosystems; matter cycles within.

Physical Laws and Energy Flow

• Physical and chemical laws govern energy and matter transformations within ecosystems.
• The first law of thermodynamics—energy cannot be created or destroyed, only transformed.
• Energy enters ecosystems as solar radiation; it's conserved and lost as heat.
• The second law of thermodynamics—each energy exchange increases the universe's entropy.
• Energy conversions in ecosystems aren't perfect; some energy is inevitably lost as heat.

Conservation of Mass

• Matter cannot be created or destroyed—it only changes forms.
• Essential chemical elements cycle repeatedly in ecosystems.
• Ecosystems exchange matter with their surroundings.

Energy, Mass, and Trophic Levels

• Autotrophs produce their own organic compounds using photosynthesis or chemosynthesis.
• Heterotrophs rely on other organisms for organic compounds.
• Energy and matter flow from producers to consumers (herbivores, carnivores, tertiary consumers).
• Detritivores (decomposers) break down dead organic matter.

Energy and Nutrient Dynamics in Ecosystems

• The diagram shows a simplified representation of an ecosystem with energy flow and chemical cycling between primary producers, consumers, and decomposers.

Gross and Net Primary Production

• Gross primary production (GPP) measures the total amount of solar energy converted to chemical energy by autotrophs.
• Net primary production (NPP) is GPP minus the energy used by primary producers for respiration.
• Only NPP is available to consumers.
• Standing crop is the total biomass of photosynthetic autotrophs at a particular time.
• Tropical rainforests, estuaries, and coral reefs are among the most productive ecosystems per unit area, though marine ecosystems are large contributors to global NPP due to volume.

Primary Production in Aquatic Ecosystems

• Light and nutrients limit primary production in aquatic ecosystems.
• Light penetration depth affects the photic zone in lakes and oceans.
• Limiting nutrients (usually nitrogen and phosphorus) often restrain marine production.

Primary Production in Terrestrial Ecosystems

• Temperature and precipitation influence terrestrial primary production.
• Actual evapotranspiration reflects the balance of water loss by transpiration and evaporation from a landscape.
• Soil nutrients often set a limit for primary production.

Energy Transfer Between Trophic Levels

• Secondary production is the conversion of chemical energy in food to biomass.
• Approximately 10% of the energy at one trophic level is transferred to the next.
• Trophic efficiency takes into account energy transfer losses between trophic levels.

Biological and Geochemical Processes

• Nutrient circuits connect biotic and abiotic components and are called biogeochemical cycles.
• Elements cycle between organic and inorganic reservoirs.
• Gaseous elements (carbon, oxygen, nitrogen, sulfur) cycle globally.
• Less mobile elements cycle locally (e.g., phosphorus).

Water Cycle

• Water is essential for all life (97% in the oceans, 2% in ice caps/glaciers).
• Water cycles through evaporation, transpiration, condensation, precipitation, and movement through surface and groundwater.

Carbon Cycle

• Carbon-based organic molecules are vital for all life.
• Reservoirs include fossil fuels, soils, sediments, biomass, and the atmosphere.
• CO2 is taken up by photosynthesis and released by respiration, volcanic eruptions, and the burning of fossil fuels.

Nitrogen Cycle

• Nitrogen is crucial for amino acids, proteins, and nucleic acids.
• The main reservoir is the atmosphere (N2); nitrogen fixation converts it to usable forms.
• Conversion to ammonia (NH3) and nitrates (NO3-) supports plant growth through various biological processes.

Phosphorus Cycle

• Phosphorus is essential for nucleic acids and ATP.
• The major reservoir is sedimentary rock and marine organisms.
• The cycle involves erosion, weathering, and other factors contributing to the cycling of phosphate through terrestrial and aquatic environments.

Decomposition and Nutrient Cycling Rates

• Decomposers (detritivores) are key for chemical cycling.
• Decomposition rates depend on temperature, moisture, and nutrient availability.
• Rapid decomposition often results in lower nutrient levels in the soil.

Case Study: Nutrient Cycling in the Hubbard Brook Experimental Forest

• Vegetation strongly controls nutrient cycling.
• Research in the Hubbard Brook Experimental Forest involves long-term monitoring of nutrient cycling.
• Studies can examine how human processes or natural events influence ecosystems.

Agriculture and Nitrogen Cycling

• Soil quality depends on organic matter content.
• Agricultural practices affect ecosystem nutrient cycles.
• Replacing lost nitrogen, while common, can impact ecosystems negatively.

Contamination of Aquatic Ecosystems

• Critical load for nutrients determines the threshold before ecosystems are harmed.
• Excess nutrients (e.g., from agriculture) can cause cultural eutrophication and harm freshwater ecosystems.

Toxins in the Environment

• Humans introduce and release many harmful chemicals that persist in ecosystems.
• Toxic chemicals can accumulate in organisms at higher levels of the food chain through biological magnification.

Greenhouse Gases and Global Warming

• Increased atmospheric CO2 from human activities leads to global warming.
• Rising CO2 levels amplify the greenhouse effect.
• Geographic changes in precipitation patterns are consequences of global warming.

Depletion of Atmospheric Ozone

• Ozone in the stratosphere protects life from harmful UV radiation.
• Human-produced chemicals (e.g., CFCs) damage the ozone layer.
• Ozone depletion has environmental ramifications (e.g. DNA damage in plants and poorer phytoplankton growth).

Explore the intricate relationships within ecosystems, focusing on the interaction between living organisms and their abiotic environment. This quiz covers key concepts including energy transformation, the conservation of mass, and fundamental physical laws that govern ecosystem dynamics.