Primary Productivity, Trophic Levels, and Food Webs

APES Unit 1.8: Primary Productivity - Learning Objective ENG-1.A: Explain how solar energy is acquired and transferred by living organisms. - Suggested Skill 1.A: Concept Explanation - Describe environmental concepts and processes. - Essential Knowledge ENG-1.A.1: Primary productivity is defined as the rate at which solar energy (sunlight) is converted into organic compounds via photosynthesis over a unit of time. - Essential Knowledge ENG-1.A.2: Gross primary productivity (GPP) is the total rate of photosynthesis in a given area. - Essential Knowledge ENG-1.A.3: Net primary productivity (NPP) is the rate of energy storage by photosynthesizers in a given area, after subtracting the energy lost to respiration. - Essential Knowledge ENG-1.A.4: Productivity is measured in units of energy per unit area per unit time, specifically expressed as $kcal/m^2/yr$. - Essential Knowledge ENG-1.A.5: Light penetration in aquatic ecosystems affects photosynthesis. Most red light is absorbed in the upper $1\,m$ of water. Blue light penetrates deeper, reaching depths greater than $100\,m$ in the clearest water. Aquatic photosynthesizers have adapted mechanisms to address this lack of visible light. - Primary Productivity Basics: - It is the rate of photosynthesis for all producers in an area over a given period. - It can be viewed as the amount of plant growth in an area over time. - High PP correlates with high plant growth, which provides abundant food and shelter. - Ecosystems with high PP are generally more biodiverse (higher diversity of species) than those with low PP. - Calculating Primary Productivity: - Formula: $NPP = GPP - RL$. - Respiration Loss (RL): Plants use a portion of the energy they generate via photosynthesis for cellular respiration (e.g., movement, internal transportation). This can be thought of as a tax the plant must pay. - Gross Primary Productivity (GPP): The total amount of sun energy captured and converted into glucose. Think of this as the total paycheck. - Net Primary Productivity (NPP): The energy or biomass leftover for consumers after plants satisfy their own respiration needs. Think of this as the actual take-home pay. - Ecological Efficiency: - This refers to the portion of incoming solar energy captured by plants and converted into biomass (food for consumers). - Only approximately $1\%$ of all incoming sunlight is captured and converted into GPP. - Approximately $99\%$ of solar energy arrives in wavelengths plants cannot use, so it is reflected or passes through them. - Of the initial $1\%$ captured, an average of $40\%$ (or $0.4\%$ of the total incoming solar energy) is converted into NPP (biomass/growth). - Trends in Productivity: - Higher productivity biomes support a wider diversity of animal life. - High NPP factors include water availability, higher temperature, and nutrient availability. - Shortage of these factors decreases NPP. - High NPP Biomes: Tropical Rain Forest, Swamps. - Low NPP Biomes: Deserts (low water/nutrients), Tundra (low temperature/liquid water), Open Ocean (low nutrients; photosynthesis limited to the photic zone). # APES Units 1.9 & 1.10: Trophic Levels and The 10% Rule - Learning Objective ENG-1.B: Explain how energy flows and matter cycles through trophic levels. - Learning Objective ENG-1.C: Determine how the energy decreases as it flows through ecosystems. - Suggested Skill 1.B: Explain environmental concepts and processes. - Suggested Skill 6.C: Mathematical Routines - Calculate an accurate numeric answer with appropriate units. - Conservation of Matter and Energy: - Matter and energy are never created or destroyed; they only change forms. - Example of Matter: A tree dies and its Carbon ($C$), Nitrogen ($N$), Water ($H_2O$), and Phosphorus ($P$) return to the soil and atmosphere. - Example of Energy: Sun rays hitting leaves are converted from light energy into glucose (chemical energy). - First Law of Thermodynamics: Energy is never created or destroyed. - Biogeochemical cycles (C, N, H2O, P) demonstrate the conservation of matter. - Food webs demonstrate the conservation of energy (e.g., a rabbit eating a leaf transfers energy to its own tissues as fat or muscle). - Second Law of Thermodynamics: Each time energy is transferred, some is lost as heat ($90\%$ loss). - The amount of usable energy decreases as you move up the food chain because organisms use it for movement and development. - The 10% Rule (ENG-1.C.1): Only about $10\%$ of energy from one trophic level is passed to the next. - Trophic Pyramids: Used to model energy movement. - Trophic levels: Producers (convert light to chemical energy), Primary Consumers (herbivores), Secondary Consumers (carnivores/omnivores), Tertiary Consumers (apex predators). - Biomass and Energy Transfers: - The $10\%$ rule also applies to biomass (the mass of all living things at a level). - To calculate biomass or energy at the next level up, divide by $10$ or move the decimal one spot to the left. - Biomass Example: Producers ($8,000\,kg$) -> Primary Consumers ($800\,kg$) -> Secondary Consumers ($80\,kg$) -> Tertiary Consumers ($8\,kg$). # APES Unit 1.11: Food Chains and Food Webs - Learning Objective ENG-1.D: Describe food chains and food webs, and their constituent members by trophic level. - Suggested Skill 2.A: Visual Representations - Describe characteristics of an environmental concept, process, or model represented visually. - Essential Knowledge ENG-1.D.1: A food web is a model of interlocking food chains depicting the flow of energy and nutrients. - Essential Knowledge ENG-1.D.2: Feedback loops (positive and negative) play a role in food webs. Removing or adding a species affects the entire web. - Flow of Energy: Arrows in a food web indicate the direction of energy flow, pointing toward the organism taking in the energy. - Food Chain vs. Food Web: - Food chains show one linear path. - Food webs contain interconnected chains and show organisms can exist at multiple trophic levels. - Example: A grasshopper eating grass is a primary consumer; an owl eating a robin that ate the grasshopper is a tertiary consumer. - Trophic Cascades: The addition or removal of a top predator ripples through lower levels. - Example: Decline in wolves leads to an increase in deer, causing overgrazing and a decline in trees. # Questions & Discussion - Practice FRQ 1.8: Describe the process of NPP and its relationship to biodiversity. Response: $GPP - Respiration = NPP$. Large NPP leads to greater biodiversity because plants are the energy foundation. - Practice FRQ 1.9 & 1.10: Why can a large forest only support small numbers of wolves? Response: Due to the $10\%$ rule, energy is lost at each level; as apex predators, wolves have significantly less energy available to them. - Practice FRQ 1.9 & 1.10 Calculation: If plants produce $100,000\,J$ of energy (after respiration), how much is available to a tertiary consumer? Response: $100,000\,J$ (Producers) -> $10,000\,J$ (Primary) -> $1,000\,J$ (Secondary) -> $100\,J$ (Tertiary). - Practice FRQ 1.11: Describe a direct effect of a decline in the frog population. Response: It would lead to a decrease in its predators (e.g., pythons) and an increase in its prey (e.g., grasshoppers). - Practice FRQ 1.11 Organism Identification: Identifying an organism that acts as both a secondary and tertiary consumer depends on tracing multiple paths from the producers through different food chains in the web.