JQ

Ecosystems and Biogeochemical Cycles Review

Ecosystem Basics

  • Individual: One organism (e.g., elk).

  • Population (Pop.): A group of individuals of the same species (e.g., elk herd).

  • Community: All living organisms in a specific area.

  • Ecosystem: All living (biotic) and nonliving (abiotic) things in an area (e.g., plants, animals, rocks, soil, water, air).

  • Biome: The characteristic plants and animals found in a given region, primarily determined by climate (temperature and precipitation). (e.g., tropical rainforest).

Organism Interactions (Ecosystem Dynamics - ERT-1.A)

  • The availability of resources significantly influences how species interact.

Types of Interactions:

1. Predation ($\mathbf{+/-}$ Relationship)

  • Definition: One organism (predator) consumes another organism (prey) as an energy source.

  • Types of Predators and Examples:

    • True predators (Carnivores): Kill and eat prey for energy. (e.g., leopard eats giraffe).

    • Herbivores (Plant eaters): Consume plants for energy. (e.g., giraffe eats tree).

    • Parasites: Use a host organism for energy without typically killing it, often living inside the host. (e.g., mosquitoes, tapeworms, sea lamprey).

    • Parasitoids: Lay eggs inside a host organism; the eggs hatch, and the larvae consume the host for energy, eventually killing it. (e.g., parasitic wasps, bot fly).

2. Symbiosis (Close and Long-Term Interactions - ERT-1.A.2)

  • Etymology: "sym" = together, "bio" = living, "osis" = condition. Defines any close and long-term interaction between two organisms of different species.

  • Types of Symbiotic Relationships:

    • Mutualism ($\mathbf{+/+}$): A relationship that benefits both organisms.

      • Examples:

        • Coral Reefs: Coral (animals) provide structural habitat and carbon dioxide (CO2) for algae, while algae provide sugars (energy) to the coral through photosynthesis.

        • Lichen: A composite organism of fungi living with algae. Algae provide sugars (energy) to the fungi, and fungi provide nutrients and a protected environment for the algae.

    • Commensalism ($\mathbf{+/0}$): A relationship that benefits one organism without significantly impacting the other (neither harming nor benefiting).

      • Example: Birds building nests in trees.

    • Parasitism ($\mathbf{+/-}$): A relationship that benefits one organism (the parasite) at the expense of the other (the host). This is a form of predation, specifically by parasites.

      • Examples: Mosquitos, tapeworms (as mentioned under parasites).

3. Competition

  • Definition: Organisms fight over limited resources such as food, water, shelter, light, or mates.

  • Impact: Competition limits population size as fewer resources are available, meaning fewer organisms can survive.

  • Occurrence: Can occur within the same species (intraspecific) or between different species (interspecific).

Resource Partitioning (Reducing Competition - ERT-1.A.3)

  • Definition: Different species use the same limited resource in different ways, at different places, or at different times to reduce the negative impacts of competition on survival.

  • Types of Resource Partitioning:

    • Temporal partitioning: Using a resource at different times.

      • Example: Wolves hunting at night while coyotes hunt during the day.

    • Spatial partitioning: Using different areas or parts of a shared habitat.

      • Example: Different plant species in a forest developing roots of different lengths to access water and nutrients at varying soil depths.

    • Morphological partitioning: Evolving different body features to use different resources.

      • Example: Different bird species developing beaks suited for different types of seeds or insects.

Terrestrial Biomes (ERT-1.B)

  • Definition: Biomes are characterized by specific communities of plants and animals that are adapted to the region's climate, primarily determined by yearly temperature and precipitation averages.

  • Adaptations: Organisms develop unique traits to survive in their specific biomes. (e.g., camels and cacti have water-preserving traits for deserts; shrubs and wildflowers in grasslands store energy in roots to recover quickly from fire).

  • Global Distribution: Biomes are found in predictable patterns on Earth based on:

    • Latitude: Distance from the equator, which determines temperature and precipitation.

      • Higher latitudes (e.g., \text{60}^{\circ}\text{+}): Tundra and Boreal forests.

      • Mid-latitudes (e.g., \text{30}^{\circ}\text{ - 60}^{\circ}): Temperate biomes.

      • Closer to the equator: Tropical biomes.

    • Altitude: Height above sea level.

    • Climate: Temperature and precipitation patterns.

    • Geography: Landforms.

    • Nutrient Availability: The amount of essential nutrients in the soil.

    • Soil Type: The composition and characteristics of the soil.

Major Terrestrial Biomes:

  • Taiga (Boreal forest)

  • Temperate rainforests

  • Temperate seasonal forests

  • Tropical rainforests

  • Shrubland (Chaparral)

  • Temperate grassland

  • Savanna

  • Desert

  • Tundra

Nutrient Availability in Biomes:

  • Tropical Rainforests: Nutrient-poor soil due to high competition from diverse plant species and rapid decomposition/uptake.

  • Boreal Forests: Nutrient-poor soil due to low temperatures, which slow down the decomposition rate of dead organic matter.

  • Temperate Forests: Nutrient-rich soil due to abundant dead organic matter (leaves) and warm temperatures/moisture fostering decomposition.

  • Tundra: Frozen soils (permafrost) prevent decomposers from breaking down dead organic matter, leading to low soil nutrients and low water availability for plants.

Shifting Biomes (Dynamic Distribution - ERT-1.B.4)

  • The global distribution of biomes is dynamic and has changed historically and will continue to shift due to global climate changes.

  • Example: A warming climate could cause boreal forests to shift further north as tundra permafrost melts, and lower latitudes become too warm for current boreal species like aspen and spruce.

Aquatic Biomes (ERT-1.C)

  • Definition: Defined by physical characteristics such as salinity, depth, turbidity (clarity), nutrient availability, temperature, and water flow.

Characteristics Influencing Aquatic Biomes (Nonmineral Resource Distribution - ERT-1.C.3):

  • Depth: Influences sunlight penetration for photosynthesis. This affects the types of plants that can grow and, consequently, the entire food web.

  • Temperature: Warmer water holds less dissolved oxygen (\text{O}_2), which limits the aquatic organisms it can support.

  • Salinity: The amount of salt in water determines which species can survive and the water's usability for drinking.

  • Flow: Determines which plants and organisms can survive (e.g., rooted plants vs. free-floating algae) and how much \text{O}2 dissolves into the water (more flow = more \text{O}2).

Types of Aquatic Biomes:

1. Freshwater Biomes (Vital Drinking Water Source - ERT-1.C.1)

  • Rivers:

    • High \text{O}_2 levels due to water flow mixing with air.

    • Carry nutrient-rich sediments, forming fertile deltas and floodplains.

  • Lakes:

    • Standing bodies of freshwater; a key source of drinking water.

    • Zones:

      • Littoral Zone: Shallow water close to shore with emergent plants (rooted plants that extend above the water's surface).

      • Limnetic Zone: Open, sunlit surface water where light can reach for photosynthesis; no rooted plants, only phytoplankton.

      • Profundal Zone: Deepest part, too deep for sunlight penetration, thus no photosynthesis.

      • Benthic Zone: Murky bottom where invertebrates (bugs) live; nutrient-rich sediments accumulate here.

  • Wetlands:

    • Definition: Areas where soil is submerged or saturated in water for at least part of the year, but shallow enough for emergent plants.

    • Plant Adaptations: Plants must be adapted to living with roots submerged in standing water (e.g., cattails, lily pads, reeds, cypress trees).

    • Types:

      • Swamp: Characterized by trees (e.g., cypress tree).

      • Marsh: Characterized by reeds and cattails.

      • Bog: Characterized by spruce trees and sphagnum moss; often acidic with low nutrient availability.

    • Ecological Benefits:

      • Flood Control: Stores excess water during storms, reducing flooding.

      • Groundwater Recharge: Absorbs rainfall into the soil, replenishing groundwater.

      • Water Filtration: Roots of wetland plants filter pollutants from draining water.

      • High Productivity: Abundant plant growth due to plenty of water and nutrients in sediments.

2. Marine Biomes (Algae Supply Earth's Oxygen & Absorb \text{CO}_2 - ERT-1.C.2)

  • Oceans: Largest marine biome.

  • Estuaries: Areas where rivers empty into the ocean, resulting in a mix of fresh and saltwater.

    • Adaptations: Species must adapt to fluctuating salinity (e.g., mangrove trees).

    • High Productivity: Due to nutrient-rich sediments deposited by rivers.

    • Examples:

      • Salt Marsh: Estuarine habitat along temperate coasts; serves as a crucial breeding ground for many fish and shellfish species.

      • Mangrove Swamps: Estuarine habitat along tropical coasts; mangrove trees with long, stilt roots stabilize shorelines and provide diverse habitats for fish and shellfish.

  • Coral Reefs:

    • Location: Warm, shallow waters beyond the shoreline.

    • Biodiversity: Most diverse marine biome on Earth.

    • Mutualistic Relationship: Between coral (animals) and algae (zooxanthellae).

      • Coral takes \text{CO}2 out of the ocean to create its calcium carbonate exoskeleton (the reef structure) and provides \text{CO}2 to the algae.

      • Algae live within the coral tissue and provide sugars (energy) to the coral through photosynthesis.

      • This symbiotic relationship is essential for both: coral cannot survive without the algae's energy, and algae need the reef home and \text{CO}_2 from the coral.

  • Intertidal Zones:

    • Location: Narrow band of coastline between high and low tide marks.

    • Challenges: Organisms must be adapted to survive crashing waves and exposure to direct sunlight/heat (desiccation) during low tide.

    • Adaptations: Barnacles, sea stars, and crabs attach to rocks; shells and tough outer skin prevent drying out. Different organisms adapt to different sub-zones within the intertidal area (e.g., spiral wrack seaweed curls up and secretes mucus to retain water).

  • Open Ocean:

    • Productivity: Generally low productivity per unit area, as only algae and phytoplankton can survive in most regions.

    • Overall Impact: Despite low per-area productivity, the vast size of the ocean means its algae and phytoplankton produce a significant portion of Earth's \text{O}2 and absorb large amounts of atmospheric \text{CO}2.

    • Zones:

      • Photic Zone: The upper layer where sunlight can penetrate, allowing for photosynthesis.

      • Aphotic Zone (Abyssal Zone): The area too deep for sunlight, where photosynthesis cannot occur.

The Carbon Cycle (ERT-1.D)

  • Definition: The movement of atoms and molecules containing carbon (e.g., \text{CO}2, glucose, \text{CH}4) between sources and sinks.

  • Reservoirs: Carbon compounds are held in reservoirs for varying periods:

    • Long-term: Sedimentary rock, fossil fuels (millions of years).

    • Short-term: Atmosphere, plants, soil, ocean (decades to centuries).

  • Atmosphere: A key carbon reservoir; increasing atmospheric carbon levels lead to global warming.

  • Carbon Sink: A reservoir that takes in more carbon than it releases. (e.g., ocean - algae & deep sediments, plants, soil).

  • Carbon Source: A reservoir that releases more carbon than it takes in. (e.g., fossil fuel combustion, animal agriculture (methane from burps/farts), deforestation).

Key Processes:

1. Photosynthesis & Cellular Respiration

  • Photosynthesis (Carbon Sink):

    • Removes \text{CO}_2 from the atmosphere and converts it into glucose (a biological form of carbon and stored chemical energy).

    • Performed by plants, algae, and phytoplankton.

    • A very quick process.

  • Cellular Respiration (Carbon Source):

    • Breaks down glucose using \text{O}_2 to release stored energy.

    • Releases \text{CO}_2 into the atmosphere.

    • Performed by plants and animals.

    • A very quick process.

  • Balance: These two processes cycle carbon between the biosphere and atmosphere in a largely balanced amount naturally, without a net increase in atmospheric carbon.

2. Ocean & Atmosphere Interactions

  • Direct Exchange: \text{CO}_2 moves directly between the atmosphere and the ocean by dissolving into and out of ocean water at the surface.

    • This is a quick process and naturally balances \text{CO}_2 levels between the two.

    • Implication: Increasing atmospheric \text{CO}2 also increases ocean \text{CO}2, leading to ocean acidification.

  • Biological Processes:

    • Algae & Phytoplankton: Take \text{CO}_2 from both the ocean and atmosphere through photosynthesis.

    • Marine Organisms: Coral reefs and organisms with shells extract \text{CO}_2 (as carbonates) from the ocean to form calcium carbonate exoskeletons and shells.

  • Sedimentation: Calcium carbonate precipitates out of the water as sediment and settles on the ocean floor.

  • Burial: Over long periods, the pressure of water compresses carbon-containing sediments on the ocean floor into sedimentary rock (e.g., limestone, sandstone), forming long-term carbon reservoirs.

3. Burial, Extraction, & Combustion

  • Burial (Very Slow Process):

    • A slow, geological process storing carbon in underground sinks like sedimentary rock or fossil fuels.

    • Sediments (bits of rock, soil, organic matter) are compressed over millions of years into sedimentary rock or fossil fuels by immense pressure.

  • Fossil Fuels (FFs):

    • Coal, oil, and natural gas are formed from the fossilized remains of organic matter. (e.g., dead ferns form coal; marine algae and plankton form oil).

  • Extraction & Combustion (Very Quick Processes):

    • Digging up or mining fossil fuels and burning them as an energy source.

    • This rapidly releases large amounts of stored \text{CO}_2 into the atmosphere.

  • Imbalance: The rate of fossil fuel formation (burial) is vastly slower than the rate of extraction and combustion, leading to a rapid increase in atmospheric \text{CO}_2 concentrations over the past 250 years.

The Nitrogen Cycle (ERT-1.E)

  • Overview: The movement of nitrogen-containing molecules between sources and sinks/reservoirs.

  • Importance: Nitrogen (N) is a critical plant and animal nutrient, essential for DNA and amino acids (to make proteins).

  • Main Reservoir: The atmosphere, where nitrogen exists primarily as unuseable \text{N}_2 gas.

  • Reservoir Duration: Nitrogen reservoirs generally hold N for relatively short periods compared to the carbon cycle (e.g., plants, soil, atmosphere).

Key Steps:

1. Nitrogen Fixation

  • Definition: The process of converting unuseable atmospheric \text{N}2 gas into biologically available forms like ammonia (\text{NH}3) or nitrate (\text{NO}_3^{\text{-}}).

  • Methods:

    • Bacterial Fixation: Certain soil bacteria, or bacteria in symbiotic relationships with plant root nodules (e.g., rhizobacteria in legume roots), convert \text{N}2 into \text{NH}3.

      • Rhizobacteria fix N for legumes in return for amino acids from the plant.

    • Synthetic Fixation: High-energy industrial processes (like the Haber-Bosch process) or fossil fuel combustion convert \text{N}_2 gas into ammonia.

      • Synthetic \text{NH}_3 is added to synthetic fertilizers and applied to agricultural soils.

2. Nitrification

  • Definition: Conversion of ammonium (\text{NH}4^{\text{+}}) into nitrite (\text{NO}2^{\text{-}}) and then into nitrate (\text{NO}_3^{\text{-}}) by soil bacteria.

    • Nitrate is the form most readily useable by plants.

3. Assimilation

  • Definition: Plants and animals taking in nitrogen and incorporating it into their body tissues.

    • Plants: Absorb \text{NO}3^{\text{-}} or \text{NH}3 from the soil through their roots.

    • Animals: Assimilate nitrogen by eating plants or other animals.

4. Ammonification

  • Definition: Soil bacteria, microbes, and decomposers convert waste products (e.g., urine, feces) and dead biomass back into \text{NH}_3 and return it to the soil.

5. Denitrification

  • Definition: Conversion of soil nitrogen (primarily \text{NO}3^{\text{-}}) back into nitrous oxide (\text{N}2\text{O}) gas or \text{N}_2 gas, which then returns to the atmosphere.

    • Occurs under anaerobic conditions by denitrifying bacteria.

Human Impacts on the Nitrogen Cycle:

  • Leaching & Eutrophication: Excessive synthetic fertilizer use leads to nitrates (\text{NO}_3^{\text{-}}) being carried out of the soil by water (leaching). This runoff into local water bodies causes algae blooms (eutrophication).

    • Eutrophication Impacts: Algae blooms block sunlight, killing underlying aquatic plants. When algae die, bacteria decompose them, consuming large amounts of dissolved oxygen (\text{O}_2) in the water (decomposition is an aerobic process, known as hypoxia or anoxia). This leads to fish kills and further deoxygenation.

  • Ammonia Volatilization: Excess fertilizer use can lead to \text{NH}_3 gas entering the atmosphere.

    • Impact: \text{NH}_3 gas in the atmosphere causes respiratory irritation in humans and animals and can contribute to fine particulate matter pollution.

  • Climate Change: \text{N}_2\text{O} (nitrous oxide) is a potent greenhouse gas, warming Earth's climate.

    • Source: Primarily produced by denitrification of nitrate in agricultural soils, especially when waterlogged or over-watered.

The Phosphorus Cycle (ERT-1.F)

  • Overview: The movement of phosphorus (P) atoms and molecules between sources and sinks/reservoirs.

  • Rate: The P cycle is significantly slower than the C, \text{H}_2\text{O}, and N cycles.

  • Major Reservoirs: Rocks and sediments containing phosphorus-bearing minerals. It takes a very long time for P minerals to be weathered out of rocks and carried into soil or water.

  • No Atmospheric Component: Phosphorus does not have a gas phase; it does not directly enter the atmosphere.

  • Limiting Nutrient: Because it cycles so slowly, phosphorus is often a limiting nutrient in both aquatic and many terrestrial ecosystems, meaning plant growth is frequently limited by P availability in soil/water.

  • Importance: P is essential for all organisms for DNA, ATP (energy currency), bone, and tooth enamel in some animals.

Key Steps and Sources:

  • Major Natural Source: Weathering of rocks containing P minerals.

    • Wind and rain break down rocks, releasing phosphate (\text{PO}_4^{\text{-3}}), which dissolves into water.

    • Rainwater carries phosphate into nearby soils and bodies of water.

  • Synthetic (Human) Sources: Mining phosphate minerals and adding them to agricultural products and consumer goods.

    • Synthetic Fertilizers: Phosphates are added to fertilizers for lawns and agricultural fields; runoff carries P into nearby water bodies.

    • Detergents/Cleaners: Phosphates from these products enter bodies of water via wastewater.

  • Assimilation & Excretion/Decomposition: A mini-loop within the P cycle.

    • Assimilation: Plants absorb phosphate from soil (or water); animals assimilate P by consuming plants or other animals.

    • Excretion/Decomposition: Animal waste, dead plant matter, and other biomass are broken down by bacteria and soil decomposers, returning phosphate to the soil (ammonification-like process).

  • Sedimentation & Geological Uplift:

    • Sedimentation: Phosphate doesn't dissolve well in water; much of it forms solid bits that fall to the bottom as sediment.

    • Over long periods, these P sediments can be compressed into sedimentary rock by the pressure of overlying water.

    • Geological Uplift: Tectonic plate collisions can force up rock layers, forming mountains. This exposes buried P-rich rocks to weathering, allowing the P cycle to restart.

Eutrophication (Excess Nutrients - N & P)

  • Cause: Since N and P are limiting nutrients in aquatic ecosystems, excessive input (from fertilizer runoff, human/animal waste contamination) leads to eutrophication.

  • Process:

    1. Nutrient Load Up: Excessive nutrients (N & P) from fertilizers are flushed into rivers or lakes by rainwater.

    2. Plants Flourish/Algae Bloom: These pollutants cause rapid growth of aquatic plants like algae and duckweed, leading to an algae bloom that covers the water surface.

    3. Sunlight Blocked & Oxygen Depleted: The algae bloom prevents sunlight from reaching other submerged plants below, killing them. This also starts to deplete oxygen (\text{O}_2) as algae respire and eventually die.

    4. Decomposition Further Depletes Oxygen: Dead plants and algae are broken down by bacteria (decomposers) in an aerobic process, using up even more dissolved \text{O}_2 in the water.

    5. Death of the Ecosystem: \text{O}2 levels (dissolved oxygen) in the water fall to a point where aquatic life, especially fish, cannot survive. This creates a positive feedback loop: less \text{O}2 leads to more dead organisms, which leads to more bacterial decomposition, further reducing \text{O}_2.

The Hydrologic (Water) Cycle (ERT-1.G)

  • Overview: The movement of water in its various phases (solid, liquid, gas) between sources and sinks.

  • Energy Driver: Powered by energy from the sun.

  • Key Aspects: Understanding the state of matter and the location where water is moving is crucial.

  • Primary Reservoir: Oceans are the largest water reservoir on Earth's surface.

  • Smaller Reservoirs: Ice caps and groundwater are smaller but vital reservoirs, containing fresh and useable water for humans.

Key Processes:

1. Evaporation & Evapotranspiration

  • Evaporation: The process where liquid water on Earth's surface (e.g., from oceans, lakes) gains energy (from the sun) and changes into water vapor (gas), entering the atmosphere. Sometimes called "vaporization."

  • Transpiration: The process by which plants draw groundwater from their roots up to their leaves. Leaf openings (stomata) open, allowing water to evaporate (transpire) into the atmosphere from the leaf surface. This movement creates low water potential in the leaf, pulling water up from the roots.

  • Evapotranspiration: The combined amount of water that enters the atmosphere from both transpiration and evaporation.

    • Both processes are driven by solar energy.

2. Condensation & Precipitation

  • Condensation: As water vapor rises in the atmosphere, it cools and changes back into liquid water droplets or ice crystals, forming clouds.

  • Precipitation: Water (in liquid or solid form) released from clouds and falling to Earth's surface (e.g., rain, snow, sleet, hail).

    • Example: atmospheric water (gas) moves to land or surface water (liquid).

3. Runoff & Infiltration

  • Precipitation Fate: After precipitation, water either:

    • Runoff: Flows over Earth's surface into a body of water (e.g., rivers, lakes, oceans).

    • Infiltration: Trickles through the soil down into groundwater aquifers.

  • Freshwater Reservoirs: Groundwater (aquifers) and surface waters (lakes/rivers) are important freshwater sources for humans and animals.

    • Recharge: Precipitation recharges groundwater through infiltration, but only if the ground is permeable.

    • Pollution: Runoff recharges surface waters but can also carry pollutants into water sources.

Primary Productivity (ENG-1.A)

  • Definition: The rate at which solar energy (sunlight) is converted into organic compounds (glucose) via photosynthesis over a unit of time. Also understood as the amount of plant growth (biomass) in an area over a given period.

  • Units: Measured in units of energy per unit area per unit time (e.g., \text{kcal/m}^2\text{/yr}).

  • Significance: High primary productivity (PP) indicates high plant growth, which provides abundant food and shelter for animals. Ecosystems with high PP are generally more biodiverse.

Calculating Primary Productivity:

  • Gross Primary Productivity (GPP):

    • Definition: The total amount of sun energy that plants capture and convert into chemical energy (glucose) through photosynthesis.

    • Analogous to a plant's total paycheck before taxes.

  • Net Primary Productivity (NPP):

    • Formula: \text{NPP} = \text{GPP} - \text{RL}

    • Definition: The rate of energy storage by photosynthesizers in a given area, after subtracting the energy lost to respiration.

    • Respiration Loss (RL): The energy plants use up for their own metabolic processes (movement, internal transportation, cellular respiration). Analogous to taxes a plant "pays" from its paycheck.

    • NPP represents the biomass leftover and available for consumers.

Ecological Efficiency

  • Definition: The portion of incoming solar energy captured by plants and converted into biomass (NPP) or food available for consumers.

  • Typical Efficiency:

    • Generally, only \text{1%} of all incoming sunlight is captured and converted into GPP via photosynthesis.

    • Of that \text{1%}, only about \text{40%} (or \text{0.4%} of total incoming solar energy) is converted into NPP (biomass/plant growth).

  • Some ecosystems are more efficient (have higher NPP) than others.

Factors Affecting Productivity & Trends

  • High NPP Factors: Water availability, higher temperature, and nutrient availability.

  • Low NPP Factors: Shortage of any of the above factors.

  • Relationship with Biodiversity: The more productive a biome is, the wider the diversity of animal life it can support (higher biodiversity).

  • Examples of Low Productivity Biomes:

    • Terrestrial: Deserts (low water & nutrients), Tundra (low temperature & liquid water).

    • Aquatic: Open ocean (low nutrients).

Light Penetration in Aquatic Ecosystems

  • Color Absorption: Most red light is absorbed within the upper 1 meter of water. Blue light penetrates deeper, sometimes beyond 100 meters in the clearest water.

  • Impact on Photosynthesis: This differential light absorption limits photosynthesis in deeper aquatic ecosystems, leading to adaptations in photosynthesizers to address the lack of visible light (e.g., using different pigments).

Trophic Levels & The 10% Rule (ENG-1.B, ENG-1.C)

Conservation of Matter & Energy (First Law of Thermodynamics - ENG-1.B.2)

  • Principle: Matter and energy are never created or destroyed; they only change forms.

    • Example (Matter): When a tree dies, its carbon, nitrogen, water, and phosphorus are returned to the soil and atmosphere through decomposition.

    • Example (Energy): Sun rays (light energy) hitting leaves are converted into glucose (chemical energy) via photosynthesis. When a rabbit eats a leaf, the energy from the glucose is transferred to the rabbit and stored as body tissue (fat/muscle).

  • Demonstrations:

    • Biogeochemical Cycles: Demonstrate the conservation of matter for elements like C, N, \text{H}_2\text{O}, P.

    • Food Webs: Demonstrate the conservation of energy and its flow through ecosystems.

The Second Law of Thermodynamics & The 10% Rule (ENG-1.C.1, ENG-1.C.2)

  • Principle: Each time energy is transferred, some of it is lost as heat (entropy increases).

  • Application to Food Webs: The amount of useable energy decreases as one moves up the food chain because organisms use most of the energy for their own metabolic processes (movement, development, maintaining body temperature).

  • The 10% Rule: Approximates that only about \text{10%} of the energy from one trophic level is transferred to the next trophic level.

    • The remaining \text{90%} of energy is used by the organism for life processes and lost as heat.

Trophic Pyramids (Energy and Biomass Flow)

  • Definition: A model illustrating how energy and biomass decrease at successive trophic levels.

  • Trophic Levels:

    • Producers (Autotrophs): The lowest trophic level. Plants, algae, and phytoplankton convert the sun's light energy into chemical energy (glucose).

      • Base of the pyramid (e.g., \text{100,000 J} or \text{8,000 kg} biomass).

    • Primary Consumers (Herbivores): Organisms that eat producers (plants).

      • Second level (e.g., \text{10,000 J} or \text{800 kg} biomass).

      • Only \text{10%} of energy from producers is available.

    • Secondary Consumers (Carnivores & Omnivores): Organisms that eat primary consumers.

      • Third level (e.g., \text{1,000 J} or \text{80 kg} biomass).

      • Only \text{10%} of energy from primary consumers is available.

    • Tertiary Consumers (Top/Apex Predators): Organisms that eat secondary consumers.

      • Fourth level (e.g., \text{100 J} or \text{8 kg} biomass).

      • Only \text{10%} of energy from secondary consumers is available.

  • Biomass Application: The 10% rule also applies to biomass (the total mass of living things at each trophic level). Since energy is needed for growth, only \text{10%} of the biomass can be sustained at each successive level.

Calculating Biomass & Energy Transfer

  • To calculate the energy or biomass available at the next trophic level up, divide the current level's value by 10 (or move the decimal place one spot to the left).

    • Example: If producers have \text{95,000.00 J}, primary consumers get \text{9,500.00 J}, secondary consumers get \text{950.00 J}, and tertiary consumers get \text{95.00 J}.

  • Example Calculation: If plants have \text{100,000 J} of energy (after respiration):

    • Primary Consumers: \text{100,000 J} \times 0.10 = \text{10,000 J}

    • Secondary Consumers: \text{10,000 J} \times 0.10 = \text{1,000 J}

    • Tertiary Consumers: \text{1,000 J} \times 0.10 = \text{100 J}

Food Chains and Food Webs (ENG-1.D)

Food Web Basics (Model of Energy & Nutrient Flow - ENG-1.D.1)

  • Definition: A model representing the interlocking pattern of multiple food chains, depicting how matter (C, N, \text{H}_2\text{O}, P) and energy (glucose, muscle tissue) flow through an ecosystem between organisms.

  • Direction of Flow: Arrows in food webs point from the organism being eaten to the organism that eats it, indicating the direction of energy transfer.

Food Web vs. Food Chain

  • Food Chain: Shows a single, linear pathway of energy and matter flow. (e.g., grass \rightarrow hare \rightarrow owl).

  • Food Web: Consists of at least two different, interconnected food chains. They illustrate that organisms can occupy multiple trophic levels and consume various types of prey.

    • Example: Grass \rightarrow hare \rightarrow owl (owl is a secondary consumer), AND grass \rightarrow grasshopper \rightarrow robin \rightarrow owl (owl is a tertiary consumer).

Interactions & Trophic Cascade (ENG-1.D.2)

  • Interconnectedness: Food webs demonstrate how increases or decreases in the population size of one species can have widespread impacts throughout the rest of the food web.

    • Example: An increase in python population can lead to:

      • Decrease in frog and rat populations (pythons eat them).

      • Increase in grasshopper population (fewer frogs to eat them).

      • Decrease in corn (more grasshoppers eating corn).

  • Trophic Cascade: The removal or addition of a top predator (or a significant change at any trophic level) can have a ripple effect (often profound and indirect) down through lower trophic levels.

    • Example: A decline in the wolf population leads to an increase in the deer population, which then results in overgrazing and a decline in tree populations.

Positive and Negative Feedback Loops

  • Food webs can exhibit both positive and negative feedback loops, stabilizing or destabilizing populations based on these interactions. The removal or addition of a species often triggers such loops across the web.

    • Example of Negative Feedback: Predator population increases \rightarrow prey population decreases \rightarrow predator population decreases due to lack of food \rightarrow prey population recovers.

    • Example of Positive Feedback: (As seen in a trophic cascade) Decline in wolves \rightarrow increase in deer \rightarrow decline in vegetation \rightarrow further habitat degradation for other species.