Notes on Ecosystems, Energy Flow, and Nutrient Cycling
Ecosystem Definition: An ecosystem consists of all organisms in a community and the abiotic factors they interact with, encompassing energy flow and chemical cycling.
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Autotrophs and Energy Flow in Ecosystems
Role of Autotrophs: These organisms convert inorganic carbon (e.g., nitrogen, phosphorus) into organic molecules (e.g., photoautotrophs, chemoautotrophs).
Definition of Autotrophs: Also known as primary producers, they derive their necessary organic carbon and elements from their environment.
Heterotrophs' Role: Heterotrophs consume autotrophs or other heterotrophs for necessary organic compounds. This group includes decomposers, which recycle nutrients back to the system in inorganic forms.
Trophic Interactions
Trophic Structure: It describes the community's composition regarding energy flow from autotrophs to heterotrophs.
Food Chains vs. Food Webs:
Food Chains: Represent a singular pathway of energy flow showcasing trophic levels where each species resides only in one level.
Food Webs: Illustrate all possible interactions within the community across multiple trophic levels.
Trophic Levels: These refer to the position of an organism in the food web, ranging from primary producers (level 1) to apex predators (level 5).
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Food Chains and Energy Transfer
Flow of Energy: Begins with autotrophs at level 1 and transfers through primary consumers (level 2) to various predator levels (levels 3 to 5).
Apex Predators: Generally the top tier of the food chain, with quaternary consumers being the highest observed.
Energy Loss: Energy and biomass are diminished at each trophic level as it transfers up the chain, a phenomenon explained by Trophic Transfer Efficiency (TTE).
Trophic Transfer Efficiency (TTE)
Definition: TTE measures the energy efficiency of transfer between trophic levels and is often approximated using biomass as a proxy.
TTE Calculation: TTE = (Production at trophic level n) / (Production at trophic level n-1). On average, TTE is about 10%. Key factors affecting TTE include endothermy (warm-blooded organisms) and diet.
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Energy and Nutrient Flow
Energy Conversion: Primary producers convert inorganic carbon and nitrogen into organic forms through photosynthesis. Consumers then utilize these organic materials, while decomposers transmute compounds back to an inorganic state, completing the cycle.
Nutrient Cycling vs. Energy Flow: Nutrients cycled within an ecosystem, while energy follows a one-way path from producers up through consumers. Energy losses occur at each trophic level, primarily as heat.
Trophic Pyramid: Visually represents the distribution of biomass or productivity across different trophic levels, indicating that energy flow correlates closely with biomass in terrestrial ecosystems.
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Energy Transfer Efficiency Calculation
Example Calculation
Assuming:
Initial Energy at trophic level 1 (primary producers) = 1000 kg of grasses
Trophic Transfer Efficiency (TTE) = 10%
Energy at trophic level 2 (primary consumers) = 100 kg of mice
Calculation:
TTE = E{n}/{E{n-1}}
0.10 = {E{n}/{1000 kg} E{n} = 100
To produce 100 kg of mice requires 1000 kg of grasses.
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Understanding Food Webs
Food Web Characteristics: Shows comprehensive interactions among species (predator/prey) with several levels involved simultaneously, affected by TTE similarly to food chains.
Apex Predators: Represent the highest feeding level.
Predator Energy Needs: Predators require consuming multiple individuals at lower trophic levels to meet their energy needs due to less biomass availability at higher levels.
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Factors Impacting Energy in Food Webs
Water Availability: Limitations in arid environments restrict photosynthesis.
Nutrient Availability: Different ecosystems face distinct limiting nutrients (nitrogen in forests, phosphorus in oceans, iron in coastal systems).
Sunlight: Influence of solar radiation is variable across geographical areas, affecting photosynthetic rates.
Primary Productivity
Definition: The efficiency at which autotrophs convert energy into organic materials through photosynthesis.
Liebig’s Law of the Minimum: The nutrient that is least available will limit productivity—much like how a bucket can only hold water to the height of its shortest stave.
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Marine Areas and Productivity
Iron Limitation: Studies indicate that regions in the Pacific Ocean demonstrate low productivity despite sufficient nitrogen and phosphorus levels, prompting the hypothesis of iron limitations.
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Solar Hours Variability
Equatorial Regions: Consistent daylight across seasons (approximately 12 hours).
Polar Regions: Extreme variations in daylight with 24 hours during summer solstice and no light during winter solstice.
Note that southern hemisphere undergoes opposite seasonal experiences relative to the northern hemisphere.
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Solstice Variability
All areas encounter equal solar hours during equinoxes.
Seasonal changes drastically affect insolation levels, aligning with earth’s tilt and orbit.
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Summary of Energy Influences
Water availability limits photosynthesis.
Nutrient availability across specific ecosystems.
Solar energy reaches different areas in varying intensities depending on latitude.
Seasonal changes shifted by the Earth's axial tilt and elliptical orbit, magnifying variances in seasonal weather.
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Summary of Insolation Factors
Insolation: Amount of solar radiation hitting an area, varying with solar angles and seasonal relief.
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Seasonal Insolation Dynamics
Correlated with day length across locations based on Earth’s curvature affecting the penetration of solar rays.
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Atmospheric Circulation Patterns
Hadley Cells: Drive trade winds, crucial in creating tropical climates and influencing global circulation patterns.
ITCZ Dynamics: Uplift areas cause low pressure due to rising warm air creating seasonal rainfall patterns.
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World Deserts
Desert Formation: Occur due to areas of high altitude subsidence absorbing moisture.
THREE SETS OF CIRCULATION PATTERNS EXIST
Trade Winds (Hadley cells) – surface winds in tropics, driven by uplift within
ITCZ
Easterlies (Polar cells) – surface winds in polar regions, driven by subsidence
Westerlies (Ferrell cells) – surface winds driven by cells to either side of them
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Impact of Tilt and Orbit on Climate
Elliptical Orbit Impacts: Varying distances from the sun provide effects on seasonal weather patterns.
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Orbital Forcing and Climate Changes
Axial tilt plays a larger role in climate than mere elliptical orbit could, mainly influencing sunlight distribution during classical seasons.
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Primary Production Drivers
Biodiversity enhances resource utilization efficiency within ecosystems, thus enhancing primary productivity.
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Predation Impacting Ecosystem Balance
Grazing influences plant health through resource reallocation aiding ecosystem resilience.