AP Environmental Science: Ecosystems Lecture Notes

Ecosystems 1.1

Introduction

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Warm Up (1/7/2026)

  • Task: Identify a local commons (e.g., parks, shared Wi-Fi, dorm social rooms) and explain how the tragedy plays out.

Objectives/EKs/Skills

Learning Objectives

  • ERT-1.A: Explain how the availability of resources influences species interactions.

  • Suggested Skill 1.A: Concept Explanation - Describe environmental concepts and processes.

Essential Knowledge

  • ERT-1.A.1: In a predator-prey relationship, the predator is an organism that eats another organism (the prey).

  • ERT-1.A.2: Symbiosis is a close and long-term interaction between two species in an ecosystem. Types of symbiosis include:

    • Mutualism: both species benefit.

    • Commensalism: one species benefits, and the other is neither helped nor harmed.

    • Parasitism: one species benefits at the expense of the other.

  • ERT-1.A.3: Competition can occur within or between species in an ecosystem where there are limited resources. Resource partitioning—using the resources in different ways, places, or at different times—can reduce the negative impact of competition on survival.

Ecosystem Basics

  • Individual = one organism (e.g., elk)

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

  • Community = all living organisms in an area

  • Ecosystem = all living and nonliving things in an area (e.g., plants, animals, rocks, soil, water, air)

  • Biome = the plants and animals found in a given region (determined by climate)

    • Example: tropical rainforest

Organism Interactions

  • Mutualism: relationship that benefits both organisms (e.g., coral reef).

  • Competition: organisms fighting over a resource like food or shelter; limits population size.

  • Predation: one organism uses another as an energy source (includes hunters, parasites, and herbivores).

  • Commensalism: relationship that benefits one organism without impacting the other (e.g., birds nesting in trees).

Predation

  • Predation interactions are described in the context of benefits/costs:

    • True predators (carnivores) kill and eat prey for energy (e.g., leopards and giraffes).

    • Herbivores (plant eaters) consume plants for energy (e.g., giraffes and trees).

    • Parasites: use a host organism for energy, often without killing the host (e.g., mosquitoes, tapeworms, sea lampreys).

    • Parasitoids: lay eggs inside a host organism; larvae consume the host for energy (e.g., parasitic wasps, bot flies).

Symbiosis

  • Definition: sym (together) + bio (living) + osis (condition)

  • Types of Symbiotic Relationships:

    • Mutualism (+/+): both organisms benefit.

      • Example: Coral provides structure and CO2 for algae; algae provide sugars for coral as energy.

    • Commensalism (+/0): benefits one organism, and the other is neither helped nor harmed.

    • Parasitism (+/-): one organism benefits at another's expense.

  • Example of lichen:

    • Composite organism of fungi and algae; algae provide sugars (energy), and fungi provide nutrients.

Competition

  • Resource Partitioning: different species utilizing the same resource in diverse ways to reduce competition:

    • Temporal Partitioning: using a resource at different times (e.g., wolves and coyotes hunting at different times: night vs. day).

    • Spatial Partitioning: utilizing different areas of a shared habitat (e.g., different root lengths of plants).

    • Morphological Partitioning: using resources based on different evolved body features.

Practice Question

  • FRQ 1.1: Identify two organisms that compete for a shared food resource. Describe how resource partitioning could reduce the competition between the two organisms you identified.

Terrestrial Biomes

Learning Objective

  • ERT-1.B: Describe the global distribution and principal environmental aspects of terrestrial biomes.

Suggested Skill

  • 1.B: Concept Explanation: Explain environmental concepts and processes.

Essential Knowledge

  • ERT-1.B.1: A biome contains characteristic communities of plants and animals that are adapted to its climate.

  • ERT-1.B.2: Major terrestrial biomes include:

    • Taiga

    • Temperate rainforests

    • Temperate seasonal forests

    • Tropical rainforests

    • Shrubland

    • Temperate grassland

    • Savanna

    • Desert

    • Tundra

  • ERT-1.B.3: The global distribution of non-mineral terrestrial natural resources, such as water and trees for lumber, varies due to climate, geography, latitude, altitude, nutrient availability, and soil conditions.

  • ERT-1.B.4: The worldwide distribution of biomes is dynamic; it has changed in the past and may shift due to global climate changes.

Community Adaptations

  • Biome communities of plants and animals are uniquely adapted to their environment:

    • Example: Camels and cacti possess traits for water preservation in deserts.

    • Example: Shrubs and wildflowers store energy in roots to recover quickly from fires in grasslands.

Biome Characteristics

  • Biomes are defined by average annual temperature and precipitation.

  • Biome Chart: predicts the geographical locations of various biomes.

    • Tundra & Boreal biomes are found at higher latitudes (60° +).

    • Temperate biomes are located in mid-latitudes (30° - 60°).

    • Tropical biomes are closer to the equator.

  • Latitude influences temperature and precipitation patterns, explaining the predictable distribution of biomes on Earth.

Nutrient Availability

  • Tropical Rainforests: have nutrient-poor soil due to high competition among diverse plant species.

  • Boreal Forests: also have nutrient-poor soil characterized by low temperatures and low decomposition rates of organic matter.

  • Temperate Forests: exhibit nutrient-rich soil due to abundant dead organic matter and favorable temperature/moisture for decomposition.

  • Nutrient availability is crucial for plant survival; for example, frozen tundra soils hinder the breakdown of organic matter, impacting nutrient access and plant survival.

Shifting Biomes

  • Climate Change: results in shifts of biomes; for example, a warming climate may move boreal forests northward as tundra permafrost melts, while lower latitudes become too hot for certain species such as aspen and spruce.

Practice Question

  • FRQ 1.2: Identify one characteristic of a biome and explain how that characteristic determines the community of organisms in the biome.

Aquatic Biomes

Learning Objective

  • ERT-1.C: Describe the global distribution and principal environmental aspects of aquatic biomes.

Suggested Skill

  • 1.B: Concept Explanation: Explain environmental concepts and processes.

Essential Knowledge

  • ERT-1.C.1: Freshwater biomes include streams, rivers, ponds, and lakes; these are vital resources for drinking water.

  • ERT-1.C.2: Marine biomes encompass oceans, coral reefs, marshland, and estuaries; algae in these biomes produce substantial oxygen and absorb carbon dioxide from the atmosphere.

  • ERT-1.C.3: The global distribution of non-mineral marine natural resources (e.g., fish) varies due to salinity, depth, turbidity, nutrient availability, and temperature.

Characteristics of Aquatic Biomes

  • Depth: influences sunlight penetration and photosynthesis.

  • Temperature: warmer waters generally hold less dissolved oxygen, limiting organism survival.

  • Salinity: affects species survival and water usability (freshwater vs. estuary vs. ocean).

  • Flow: affects the survival of plants and organisms and the amount of oxygen that can dissolve into water.

Freshwater Biomes: Rivers & Lakes

  • Rivers: exhibit high oxygen levels due to flow mixing water and air and carry nutrient-rich sediments.

  • Lakes: are standing bodies of freshwater and are classified into distinct zones.

    • Littoral Zone: shallow water with emergent plants.

    • Limnetic Zone: where light penetrates, allowing photosynthesis but no rooted plants, only phytoplankton.

    • Profundal Zone: too deep for sunlight, thus no photosynthesis occurs.

    • Benthic Zone: murky bottom where invertebrates live in nutrient-rich sediments.

Freshwater Biomes: Wetlands

  • Wetland: area with soil that is submerged or saturated with water for part of the year and shallow enough for emergent plants.

    • Plants adapted include cattails, lily pads, and reeds.

    • Benefits of Wetlands:

    • Store excess stormwater, reducing floods.

    • Recharge groundwater through water absorption.

    • Filter pollutants from drainage.

    • Facilitate high plant growth due to abundant water and nutrients in sediments.

Freshwater Types: Swamps, Marshes, and Bogs

  • Swamp: characterized by cypress trees and high biodiversity.

  • Marsh: dominated by reeds and cattails.

  • Bog: contains spruce and sphagnum moss.

Estuaries

  • Defined as areas where rivers flow into oceans, characterized by a mixture of fresh and saltwater; species adapt to such environments (e.g., mangrove trees).

  • High productivity due to nutrients deposited by rivers.

    • Salt Marsh: Temperate coastal estuary habitat; serves as breeding ground for many fish and shellfish species.

    • Mangrove Swamps: Tropical coastal habitats with mangrove trees providing shoreline stabilization and homes for diverse aquatic species.

Coral Reefs

  • Coral Reef: found in warm shallow waters beyond shorelines; most diverse marine biome.

    • Coral (animals) and algae (plants) engage in mutualistic relationships.

    • Coral extracts CO2 from the ocean for reef building and provides CO2 to algae.

  • Both organisms are dependent on each other for survival (coral relies on algae for energy; algae need coral's CO2 and habitat).

Intertidal Zones

  • Intertidal Zone: narrow coastal band between high and low tides where organisms must adapt to crashing waves and direct sunlight/heat.

    • Examples include barnacles, sea stars, and crabs.

  • Adaptations for survival may include shells to prevent desiccation during low tides.

Open Ocean

  • Characterized by low productivity as only algae and phytoplankton can thrive in most ocean areas.

    • Photic Zone: area where sunlight reaches and photosynthesis occurs.

    • Aphotic Zone (Abyssal): too deep for sunlight.

  • Despite low productivity per area, the vastness of the ocean means algae and phytoplankton significantly contribute to Earth's oxygen and carbon dioxide absorption.

Practice Question

  • FRQ 1.3: Identify an organism found in an aquatic biome and explain how that organism is uniquely adapted to live in that biome.

Carbon Cycle (1.4)

Learning Objective

  • ERT-1.D: Explain the steps and reservoir interactions in the carbon cycle.

Suggested Skill

  • 2.B: Visual Representations

Essential Knowledge

  • ERT-1.D.1: The carbon cycle is the movement of atoms and molecules containing carbon between sources and sinks.

  • ERT-1.D.2: Some reservoirs in the carbon cycle hold carbon compounds long-term, while others do so for shorter periods.

  • ERT-1.D.3: Carbon moves between photosynthesis and cellular respiration in living organisms.

  • ERT-1.D.4: Decomposition of plants and animals contributes to long-term carbon storage, and burning fossil fuels accelerates carbon release into the atmosphere in the form of carbon dioxide.

Carbon Cycle Overview

  • Movement of carbon-containing molecules (e.g., CO2, glucose, CH4) between sources and sinks.

  • Some steps are rapid (e.g., fossil fuel combustion), while others are slow (e.g., sedimentation and burial).

  • Imbalances may arise, leading to increased atmospheric carbon levels and global warming.

  • Carbon Sink: reservoir that takes in more carbon than it releases.

    • Examples include oceans (from algae and sediments), plants, and soil.

  • Carbon Source: reservoir that releases more carbon than it takes in.

    • Examples include combustion of fossil fuels (coal, oil, natural gas), animal agriculture (methane emissions), and deforestation.

Photosynthesis and Cellular Respiration

  • Photosynthesis: process by which organisms remove CO_2 from the atmosphere and convert it to glucose.

  • Plants, algae, and phytoplankton capture solar energy and store it in glucose; they utilize O2 for respiration and release CO2 back into the atmosphere.

  • Both processes cycle carbon between biosphere and atmosphere in a balanced manner, preventing net carbon increases.

Ocean and Atmosphere Interactions

  • Direct Exchange: Carbon dioxide moves between the ocean and atmosphere through dissolution at the ocean's surface, balancing carbon levels; elevated atmospheric CO2 increases ocean CO2, which leads to ocean acidification.

  • Photosynthesis by algae and phytoplankton contributes to carbon uptake from both ocean and atmosphere.

  • Coral reefs also draw down CO_2 to form calcium carbonate exoskeletons.

  • Sedimentation: calcium carbonate from dead marine organisms precipitates as sediment on the ocean floor.

  • Burial: over geological time, pressure compresses carbon-containing sediments into sedimentary rock.

Burial, Extraction & Combustion

  • Burial: slow geological process that stores carbon in underground sinks like sedimentary rock or fossil fuels.

  • Fossil fuels form from the remains of organic matter (e.g., dead ferns = coal; marine algae/plankton = oil).

  • Extraction & Combustion: the process of retrieving fossil fuels and burning them releases CO_2 into the atmosphere, substantially increasing atmospheric carbon concentrations.

Practice Question

  • FRQ 1.4: Identify one process in the diagram that happens quickly and one that happens slowly. Explain how the rate of fossil fuel transfer into the atmosphere has altered the carbon cycle over the last 250 years.

Nitrogen Cycle (1.5)

Learning Objective

  • ERT-1.E: Explain the steps and reservoir interactions in the nitrogen cycle.

Suggested Skill

  • 2.B: Visual Representations

Essential Knowledge

  • ERT-1.E.1: The nitrogen cycle involves the movement of atoms and molecules containing nitrogen between sources and sinks.

  • ERT-1.E.2: Most nitrogen reservoirs hold compounds for relatively short periods.

  • ERT-1.E.3: Nitrogen fixation converts atmospheric nitrogen into ammonia (NH3), available for plant uptake and assimilation.

  • ERT-1.E.4: The atmosphere is the primary reservoir of nitrogen.

Nitrogen Cycle Overview

  • Nitrogen is a crucial nutrient for plants and animals.

  • The atmosphere consists mainly of inert N_2 gas, not usable by living organisms.

  • Nitrogen is essential for DNA and amino acids (for protein synthesis).

Nitrogen Fixation

  • Synthetic Fixation: Burning of fossil fuels converts N_2 gas to ammonia (NH3).

  • Bacterial Fixation: Certain bacteria (free-living or symbiotic with plants - legumes) convert N_2 into ammonia, which plants can absorb.

  • NH3 is often added to synthetic fertilizers and is subsequently converted to nitrate (NO3-) for plant uptake.

Other Steps in Nitrogen Cycle

  • Nitrification: conversion of ammonium (NH4+) to nitrite (NO2-) and then to nitrate (NO3-) by soil bacteria.

  • Ammonification: bacteria and microbes convert waste and dead biomass back into ammonia, returning it to the soil.

  • Assimilation: process where plants and animals incorporate nitrogen into their bodies from the soil or consumed organisms.

  • Denitrification: conversion of soil nitrogen (NO3-) back to nitrogen gas (N2) which returns to the atmosphere.

Human Impacts on Nitrogen Cycle

  • Leaching & Eutrophication: Excessive use of synthetic fertilizers leads to nitrogen compounds (nitrates) being leached into water bodies.

  • Ammonia Volatilization: Overuse of fertilizers can lead to ammonia gas entering the atmosphere, causing respiratory issues.

  • Greenhouse Impact: Nitrous oxide (N2O) produced during denitrification acts as a greenhouse gas.

Practice Question

  • FRQ 1.5: Describe one chemical transformation in the nitrogen cycle and explain its ecological importance.

Phosphorus Cycle (1.6)

Learning Objective

  • ERT-1.F: Explain the steps and reservoir interactions in the phosphorus cycle.

Suggested Skill

  • 2.B: Visual Representations

Essential Knowledge

  • ERT-1.F.1: The phosphorus cycle involves the movement of phosphorus atoms between sources and sinks.

  • ERT-1.F.2: Major phosphorus reservoirs include rocks and sediments that contain phosphorus minerals.

  • ERT-1.F.3: There is no atmospheric component in the phosphorus cycle, limiting the return of phosphorus from oceans to land and making it scarce in many ecosystems.

Phosphorus Cycle Basics

  • P cycle operates slowly compared to other cycles.

  • Movement of P atoms b/w sources and sinks is essential for ecosystems.

  • Weathering of rocks containing phosphorus minerals (e.g., phosphate PO_4^{3-}) releases P into soils and water bodies.

  • The cycle's lack of gas phase means phosphorus is often a limiting nutrient for plant growth.

Phosphorus Sources

  • Natural sources of P: Weathering of rocks releasing phosphorus minerals.

  • Synthetic sources: Mining of phosphate minerals for fertilizers and detergents.

  • Runoff from fertilizers and wastewater contaminates water bodies.

Assimilation & Decomposition

  • Phosphorus is assimilated by plant roots and thus incorporated into their tissues.

  • Animals obtain phosphorus by consuming plants or other animals.

  • Decomposition processes return phosphorus back to the soil as organic matter breaks down.

  • Sedimentation may occur, with solid phosphorus particles settling in water.

Eutrophication (N & P)

  • Eutrophication results from the over-application of nitrogen and phosphorus fertilizers leading to excessive nutrient input into bodies of water.

  • This excess fuels algae growth, resulting in algal blooms that block sunlight, killing aquatic plants.

  • Following decomposition of dead algae, the resultant oxygen depletion can lead to widespread aquatic life mortality, creating a positive feedback loop of further depletion.

Practice Question

  • FRQ 1.6: Choose two reservoirs depicted in the diagram above and describe the phosphorus movement between them.

Hydrologic Cycle (1.7)

Learning Objective

  • ERT-1.G: Explain the steps and reservoir interactions in the hydrologic cycle.

Suggested Skill

  • 2.B: Visual Representations

Essential Knowledge

  • ERT-1.G.1: The hydrologic cycle, powered by the sun, describes water movement in various phases between sources and sinks.

  • ERT-1.G.2: Oceans represent the primary water reservoir, with ice caps and groundwater being much smaller reservoirs.

Water Cycle Overview

  • The movement of water (H_2O) in various states (solid, liquid, gas) between sources and sinks is primarily driven by solar energy.

  • Precipitation leads to movement from the atmosphere into land or surface water.

Evaporation & Evapotranspiration

  • Transpiration: process where plants draw groundwater from roots to leaves, releasing water vapor into the atmosphere.

  • The combined process of transpiration and evaporation is termed evapotranspiration. Both processes are energized by sunlight.

Runoff & Infiltration

  • Precipitation either runs off over the earth's surface into bodies of water or infiltrates through the soil into groundwater aquifers.

  • Runoff and infiltration contribute to recharge of important freshwater reservoirs but can also carry pollutants into water bodies.

Practice Question

  • FRQ 1.7: Choose a process from the diagram. Identify the process and describe the movement of water from one reservoir to another.

Primary Productivity (1.8)

Learning Objective

  • ENG-1.A: Explain how solar energy is acquired and transferred by living organisms.

Suggested Skill

  • 1.A: Concept Explanation

Essential Knowledge

  • ENG-1.A.1: Primary productivity measures the rate of conversion of solar energy into organic compounds via photosynthesis over a specified time frame.

  • ENG-1.A.2: Gross Primary Productivity (GPP): total rate of photosynthesis, while Net Primary Productivity (NPP) is the rate remaining post-respiration losses.

  • ENG-1.A.3: Productivity is quantified in energy per area per time (e.g., kcal/m^2/year).

  • ENG-1.A.4: Light penetration affects photosynthesis; red light is absorbed within the upper meter of water while blue light penetrates deeper than 100 meters.

Primary Productivity Basics

  • Primary Productivity: rate at which solar energy converts into organic compounds via photosynthesis.

    • High productivity correlates with biodiversity—a productive ecosystem provides ample food and shelter.

Measuring NPP and GPP

  • NPP = GPP - RL, where RL signifies respiration loss

    • RL acts as an energy cost deducted from GPP, akin to taxation on income.

Ecological Efficiency

  • The portion of solar energy captured and converted into biomass (NPP). Roughly 1% of incoming sunlight is captured; around 40% of that amount ends up in biomass for plant growth.

  • The efficiency varies across ecosystems, influencing biodiversity.

Trends in Productivity

  • Water availability, temperature, and nutrients are pivotal to high NPP levels.

  • Ecosystems lacking these elements typically show decreased productivity, leading to predictions about high/low productivity biomes (e.g., deserts and open oceans).

Practice Question

  • FRQ 1.8: Describe NPP and its relation to biodiversity.

Trophic Levels & The 10% Rule (1.9 & 1.10)

Learning Objective

  • ENG-1.B: Explain the flow of energy and cycling of matter through trophic levels.

  • ENG-1.C: Determine how energy decreases through ecosystems.

Essential Knowledge

  • ENG-1.B.1: Ecosystems depend oncontinued high-quality energy for structure and function through biogeochemical cycles.

  • ENG-1.C.1: The 10% energy transfer rule states roughly 10% of energy is passed from one trophic level to the next.

Conservation of Matter & Energy

  • Matter and energy transform but do not cease; decomposing matter returns nutrients back to ecosystems for reuse.

  • The 1st Law of Thermodynamics states energy cannot be created or destroyed.

2nd Law of Thermodynamics

  • Energy transfers result in energy loss as heat; the 10% Rule reflects decreasing usable energy with each trophic progression, as fundamentally illustrated through trophic pyramids.

  • Trophic Pyramid: visualizes energy flow and biomass achievability through ecosystems.

Trophic Levels & 10% Biomass

  • Overview of trophic levels:

    • Producers: organisms converting sunlight into chemical energy (e.g., plants).

    • Primary Consumers: herbivores consuming plants.

    • Secondary Consumers: carnivores that eat primary consumers.

    • Tertiary Consumers: top predators that consume secondary consumers.

  • Energy degradation ensures only about a tenth of calories or biomass transfer from one level to the next.

Calculating Biomass & Energy Availability

  • To derive available energy or biomass at the successive level, shift the decimal left or divide by 10.

Practice Questions

  • FRQ 1.9: Explain why a large forest can only support a small number of wolves.

  • FRQ1.10: Calculate energy available to tertiary consumers from 100,000 J produced by plants.

Food Chains and Food Webs (1.11)

Learning Objective

  • ENG-1.D: Describe food chains and food webs, detailing members by trophic level.

Essential Knowledge

  • A food web encapsulates multiple interconnected food chains representing energy flow.

  • Positive and negative feedback loops influence species in food webs when species are added or removed.

Food Web Basics

  • Demonstrates energy and matter flow in ecosystems: energy passes from prey to the predator.

  • Arrows in diagrams indicate energy flow direction (pointing to the energy-receiving organism).

Food Chains vs. Food Webs

  • Food Chains provide a linear energy flow pattern, while Food Webs illustrate broader interconnections between multiple food chains.

Interactions & Trophic Cascade

  • Food webs show that population changes amongst species affect interrelated populations, showing effects of trophic cascades when top predators change in abundance.

Practice Questions

  • FRQ 1.11: Explain a direct consequence of declining frog populations in food webs. Identify an organism acting as both a secondary and tertiary consumer.