APES Unit 1

1.1: Introduction to Ecosystems

Ecosystem: A particular location of Earth with interacting biotic and abiotic components (living and nonliving).

Biosphere: Combination of all ecosystems on Earth

Community Ecology: Organisms in an ecosystem must both rely on and compete with surrounding species, and there are few ways in which these relationships can form.

• Predator-prey relationships: One animal will kill and consume another animal.

• Ways prey avoid being eaten:

  • Behavioral (Hide)

  • Morphological (Camouflage or attack)

  • Chemical (Poisons)

Symbiosis: The close interaction between species where at least one of the species benefits from the relationship.

• Mutualism: Benefits both (Bees and flowers)

• Commensalistic: One benefits, one unharmed (Orchids growing on branches)

• Parasitic: One benefits, one harmed (Parasites)

  • Parasitoids: lays eggs inside a host organism, eggs hatch and larvae eat host for energy

Competition: Occurs when organisms must share a limited resource. Ex: Two competitors species prey on one species

• Resource Partition: Species who share a common resource but divide equally needed resources according to survival needs. Ex: Two species eat different parts of the same plant.

• Temporal Partition: Species using resources at different times of the day

• Spatial Partition: Using different areas of a shared habitat

• Morphological Partitioning: Using different resources based on different evolved body features

Keystone Species: Species that plays a large role in its ecosystem despite being quite low in the population. The removal of the keystone species can have cascading effects on the ecosystem. Ex: Sea otters feed on sea urchins which destroy kelp beds which are homes to many different species.

• Ecosystem engineers: Special types of keystone species that create or maintain habitats for other species. Ex: Elephants prevent wildfires and create watering holes for smaller animals just by taking giant steps. 

1.2: Terrestrial Biomes

Biome: An area that shares a combination of avg, yearly temp and precipitation (climate). Characterized by temperature and precipitation.

Tropical Rainforest

• Average annual temperature of 20 degrees Celsius and frequent precipitation with little seasonal variation.

• Between 20 degrees North and 20 degrees South of the equator

• Few nutrients in the soil due to fast growing vegetation taking nutrients rapidly

• More biodiversity than any other terrestrial biome.

Tropical Seasonal Forest/ Savanna

• Warm temperatures and distinct wet and dry seasons

• Relatively open landscapes dominated by grasses and scattered deciduous trees. 

• Few nutrients in the soil due to low precipitation 

Subtropical Desert

• Hot day temperatures, cool nights and extremely dry conditions, little vegetation

• Located around 30 degrees north and south 

• Leaves in plants of this biome are modified to be small or spines. Outer layer is thick too prevent water loss (cacti)

Temperate Deciduous Forest

• Warm summers and cold winters

• Dominated by broadleaf deciduous trees such as maple and oak

• Warm summer temperatures favor rapid decomposition, creating soils with high nutrient and long fertility times, used as one of the first biomes to be used for agriculture.

Temperate Grassland/ Cold Desert

• Cold harsh winters and dry summers

• Combination of relatively long growing seasons and rapid decomposition adds large amounts of nutrients to the soil, making it one of the most productive biomes in the world. 

Woodlands/ Shrubland/ Chaparral

• Hot dry summers result in frequent wildfires, causing many plants to be well adapted to fire (plants sprout quickly after a fire)

• Rainy winters allow plant biomass growth, which can act as fuel for summer wildfires the following summer.

Taiga

• Coniferous evergreen trees that can tolerate cold winters and short growing seasons such as birch trees, fir trees and aspen.

• Plant growth is constrained by temperature rather than by precipitation.

Tundra

• Cold and treeless biome, with low growing vegetation

• Soil completely freezes during winter

• Contains permafrost, an impermeable, permanently frozen layer of subsoil that prevents water from draining and roots from penetrating. Permafrost prevents deep-rooted plants such as trees from living in the tundra.

• Due to low temperatures, dead plants and animals decompose slowly.

1.3 Aquatic Biomes

• Characterized by physical characteristics: Salinity, depth, water flow

Streams

• Flowing freshwater that can originate from underground springs or runoff of rains or snow.

• Typically narrow while rivers are typically wider and carry large amounts of water.

• Fast moving streams and rivers have stretches of turbulent water called rapids, where water and air are mixed together and results in atmospheric oxygen dissolving into the water. This high oxygen environment can support fish species such as trout and salmon.

Lakes/ Ponds

• Mostly still freshwater, sometimes too deep to support vegetation growth

• Divided into zones:

  • Littoral zone: Shallow area near the shore, most photosynthesis occurs

  • Limnetic zone: No rooted plant, only phytoplankton

  • Profundal zone: No sunlight, no producers, very low dissolved oxygen

  • Benthic zone: Bottom of the lake or pond 

Freshwater Wetlands

• Characterized by submersion by water for at least part of each year, but shallow enough to support vegetation.

• Organisms that live in wetlands are specialized to survive in submerged soils

• Swamps(cyprus tree), marshes(reeds Dan cattails) and bogs (spruce and sphagnum moss) 

• Benefits: 

  • One of the most productive terrestrial biomes, also provides habitats for many species.

  • Wetlands can intake large amounts of rainwater and release it slowly into groundwater, reducing the severity of floods and droughts.

  • Wetlands can filter pollutants and recharge groundwater with clean water. 

Coral Reef

• Found in warm, shallow waters beyond the shoreline

• Corals are tiny animals that secrete a layer of calcium carbonate (limestone) to form an external skeleton

• The animal living inside the hard exoskeleton (polyp) is essentially a hollow tube with tentacles that draw in plankton and detritus

• When coral die and decompose, their skeletons remain creating coral reefs

• Environmental issues:

  • Pollutants and sediments make it difficult for corals to survive

  • Coral bleaching: Corals die, turning the reefs white. Reasons for death is a combination of diseases and environmental changes

Intertidal Zone

• Narrow band of coastline between high and low tide

• Organisms must be adapted to survive crashing waves and direct sunlight/heat during low tide

• Shells and touch outer skin can prevent drying out during low tides

Open Ocean

• Largest biome on Earth

• Majority of oxygen in the atmosphere is produced by the oceans

• Zones:

  • Intertidal Zone: Coastline that exists between high tide and low tide. Relatively stable environment conditions when submerged in high tide, relatively harsh conditions during low tide.

  • Photic Zone: Upper layer of the ocean that can support photosynthesis 

  • Aphotic Zone: Deeper layer of water without sufficient light for photosynthesis

  • Benthic Zone: The bottom of the ocean where water and land meet

1.4 The Carbon Cycle

Cycle: 

1. Carbon Dioxide in the Atmosphere

Carbon exists in the atmosphere as carbon dioxide (CO₂). It is a key part of the Earth's climate system.

2. Photosynthesis

Plants, algae, and some bacteria absorb CO₂ from the atmosphere and use sunlight to convert it into glucose (sugar) during photosynthesis. This process stores carbon in plants.

3. Consumption by Animals

Animals eat plants (or other animals) and consume the carbon stored in the plants. This carbon becomes part of their bodies.

4. Respiration

Plants and animals release CO₂ back into the atmosphere through cellular respiration as they break down glucose for energy.

5. Decomposition

When plants, animals, and other organisms die, decomposers (bacteria and fungi) break them down, releasing carbon back into the soil or the atmosphere as CO₂ or methane (CH₄).

6. Carbon Storage in Fossil Fuels

Over millions of years, some dead organisms become buried and compressed, forming fossil fuels like coal, oil, and natural gas, which store carbon underground.

7. Combustion

When humans burn fossil fuels for energy, stored carbon is released back into the atmosphere as CO₂.

8. Ocean Absorption

Oceans absorb CO₂ from the atmosphere. Some of it stays dissolved in the water, while other parts form carbonate compounds, which can become part of marine life and sediments.

9. Rock Formation and Weathering

Over time, carbon can become part of rocks like limestone. These rocks can eventually weather, releasing carbon back into the atmosphere or oceans.

This cycle ensures that carbon moves through the biosphere, atmosphere, hydrosphere, and lithosphere, maintaining a balance essential for life on Earth.

Human Impact + Solutions: 

1. Burning Fossil Fuels

• Impact: Humans burn coal, oil, and natural gas for energy, releasing large amounts of carbon dioxide (CO₂) into the atmosphere.

• Result: This adds more CO₂ than the natural processes (e.g., photosynthesis) can absorb, contributing to the greenhouse effect and climate change.

2. Deforestation

• Impact: Cutting down forests reduces the number of trees available to absorb CO₂ through photosynthesis.

• Result: This leads to higher atmospheric CO₂ levels and disrupts carbon storage in ecosystems.

3. Agriculture

• Impact: Certain farming practices, like rice cultivation and livestock farming, release methane (CH₄), a potent greenhouse gas.

• Result: Methane intensifies the greenhouse effect, contributing to global warming.

4. Industrial Activities

• Impact: Cement production and other industrial processes release CO₂ by breaking down limestone (calcium carbonate).

• Result: These emissions further increase atmospheric carbon levels.

5. Land Use Changes

• Impact: Urbanization, mining, and soil degradation disturb the natural carbon storage in soils and vegetation.

• Result: Carbon that was locked in the soil is released into the atmosphere.

6. Pollution and Ocean Acidification

• Impact: CO₂ absorbed by the ocean forms carbonic acid, lowering the pH of seawater.

• Result: This harms marine ecosystems, especially organisms like corals and shellfish, which rely on carbonate ions for their shells.

7. Climate Feedback Loops

• Impact: Human activities amplify natural processes, such as melting permafrost, which releases stored methane and CO₂.

• Result: This creates a feedback loop that accelerates global warming.

Ways to Reduce Impact

• Transition to renewable energy sources.

• Reforestation and afforestation.

• Sustainable farming practices.

• Carbon capture and storage technologies.

• Reducing energy consumption and promoting energy efficiency.

1.5 The Nitrogen Cycle

1. Nitrogen Fixation

• Process: Atmospheric nitrogen (N₂) is converted into ammonia (NH₃) or nitrate (NO₃⁻), which plants can absorb.

• Methods:

  • Biological fixation: Performed by nitrogen-fixing bacteria (e.g., Rhizobium in legume root nodules) and cyanobacteria.

  • Atmospheric fixation: Lightning converts N₂ into nitrates.

  • Industrial fixation: Human-made processes (e.g., Haber-Bosch) produce fertilizers containing ammonia.

2. Assimilation

• Process: Plants absorb nitrogen (as nitrate or ammonium) from the soil and incorporate it into organic compounds like amino acids and proteins.

• Importance: Allows nitrogen to enter the food web, as animals consume plants and utilize nitrogen for growth and metabolism.

3. Ammonification

• Process: Decomposition of organic nitrogen (from dead organisms and waste products) into ammonium (NH₄⁺).

• Agents: Decomposers like bacteria and fungi break down proteins and nucleic acids.

4. Nitrification

• Process: Conversion of ammonium (NH₄⁺) into nitrate (NO₃⁻) through two steps:

  1. Nitrosomonas bacteria convert NH₄⁺ into nitrite (NO₂⁻).

  2. Nitrobacter bacteria convert NO₂⁻ into NO₃⁻.

• Importance: Produces nitrate, the form most accessible to plants.

5. Denitrification

• Process: Conversion of nitrate (NO₃⁻) back into nitrogen gas (N₂) or nitrous oxide (N₂O), releasing it into the atmosphere.

• Agents: Anaerobic bacteria (e.g., Pseudomonas) in oxygen-poor environments like wetlands or deep soil.

6. Leaching (Optional Step)

• Process: Excess nitrates can be washed away from the soil into water bodies, causing eutrophication.

• Importance: Highlights the impact of human activity, such as over-fertilization, on the nitrogen cycle.

1.6 The Phosphorus Cycle

Steps of the Phosphorus Cycle

1. Weathering of Rocks

• Process: Phosphorus is stored in rocks as phosphate minerals. Over time, weathering releases phosphate ions (PO₄³⁻) into the soil and water.

2. Absorption by Plants

• Process: Plants absorb phosphate ions from the soil through their roots. Phosphorus is vital for energy transfer (ATP) and DNA in plants.

3. Consumption by Animals

• Process: Animals obtain phosphorus by eating plants or other animals. Phosphorus becomes part of their bodies, especially in bones and teeth.

4. Decomposition

• Process: When plants, animals, and other organisms die, decomposers (like bacteria and fungi) break them down. This releases phosphorus back into the soil or water.

5. Sedimentation in Water

• Process: Some phosphorus from soil runoff ends up in rivers, lakes, and oceans. Over time, it settles as sediment and forms new phosphate rocks.

6. Geological Uplift

• Process: Over millions of years, tectonic forces push phosphate-rich sedimentary rocks back to the surface, completing the cycle.

Human Impacts on the Phosphorus Cycle.

1. Overuse of Fertilizers

• Impact: Synthetic fertilizers rich in phosphorus are used in agriculture. Excess phosphorus often runs off into water bodies.

• Result: This causes eutrophication, leading to harmful algal blooms, oxygen depletion, and the death of aquatic life.

2. Mining of Phosphate Rocks

• Impact: Humans mine phosphate rocks to produce fertilizers and detergents, depleting natural reserves.

• Result: This disrupts the natural geological processes that slowly replenish phosphate levels.

3. Wastewater and Detergents

• Impact: Detergents and untreated sewage release phosphorus into waterways.

• Result: This increases nutrient levels in water bodies, intensifying eutrophication.

4. Soil Erosion

• Impact: Agricultural practices and deforestation lead to soil erosion, causing phosphorus in the soil to wash away into water systems.

• Result: This reduces soil fertility and increases water pollution.

5. Livestock Farming

• Impact: Animal waste from intensive farming contains high levels of phosphorus.

• Result: Runoff from farms contributes to water pollution and algal blooms.

Ways to Mitigate Human Impacts

• Reduce reliance on synthetic fertilizers by using organic alternatives.

• Implement sustainable farming practices like crop rotation and buffer strips.

• Treat wastewater before release.

• Reduce phosphate use in household products.

• Support the development of technologies to recover and recycle phosphorus from waste.

1.7 The Water Cycle

Steps of the Water Cycle

The water cycle, also known as the hydrologic cycle, describes how water moves through the Earth's atmosphere, surface, and subsurface in a continuous loop. Here are the key steps:

1. Evaporation

• Process: Heat from the sun causes water from oceans, rivers, lakes, and other water bodies to turn into water vapor.

• Importance: This moves water into the atmosphere.

2. Transpiration

• Process: Plants release water vapor from their leaves into the atmosphere through transpiration.

• Importance: This is part of the water moving from the biosphere to the atmosphere.

3. Condensation

• Process: Water vapor cools as it rises in the atmosphere and condenses to form clouds.

• Importance: This transforms water vapor back into liquid or ice.

4. Precipitation

• Process: Water falls back to Earth as rain, snow, sleet, or hail when clouds become saturated.

• Importance: This returns water to the surface and replenishes water bodies and soil.

5. Runoff

• Process: Water flows over the surface of the land into rivers, lakes, and oceans.

• Importance: This transports water across the landscape and replenishes larger bodies of water.

6. Infiltration and Percolation

• Process: Water seeps into the ground (infiltration) and moves deeper into soil and rock layers (percolation).

• Importance: This replenishes underground aquifers.

7. Groundwater Flow

• Process: Water stored in underground aquifers slowly moves through rock layers and eventually flows into rivers, lakes, or oceans.

• Importance: This ensures a steady supply of water in ecosystems.

8. Ocean Storage

• Process: Most of Earth’s water is stored in the oceans, which serve as the starting and ending point for much of the cycle.

• Importance: Oceans act as a major reservoir in the cycle.

Human Impacts on the Water Cycle

Human activities significantly alter the water cycle, affecting its natural flow and balance.

1. Urbanization

• Impact: Paved surfaces reduce infiltration and increase runoff.

• Result: This leads to flooding, decreased groundwater recharge, and polluted waterways.

2. Deforestation

• Impact: Removing trees reduces transpiration and increases runoff.

• Result: This disrupts local rainfall patterns and leads to soil erosion.

3. Overuse of Water Resources

• Impact: Excessive groundwater pumping and surface water extraction for agriculture and industry deplete water reserves.

• Result: Aquifers dry up, rivers shrink, and ecosystems suffer.

4. Pollution

• Impact: Human activities release pollutants like chemicals, plastics, and waste into water bodies.

• Result: This affects water quality and harms aquatic life.

5. Climate Change

• Impact: Global warming accelerates evaporation and disrupts precipitation patterns.

• Result: This leads to extreme weather events, droughts, and flooding.

6. Dam Construction

• Impact: Dams alter the natural flow of rivers and reduce downstream water availability.

• Result: This impacts ecosystems and sediment transport.

Ways to Reduce Human Impacts

• Adopt sustainable water management practices.

• Protect forests and wetlands to maintain natural water storage and flow.

• Reduce pollution by treating wastewater and minimizing chemical use.

• Limit groundwater extraction and use water-efficient technologies.

• Mitigate climate change by reducing greenhouse gas emissions.

1.8 Primary Productivity

Primary productivity refers to the rate at which energy is converted by autotrophs (producers) into chemical energy through photosynthesis or chemosynthesis.

1. Types of Primary Productivity
a. Gross Primary Productivity (GPP)

• The total amount of solar energy that producers in an ecosystem capture and convert into chemical energy through photosynthesis over a given time.

• Example: The energy plants capture from sunlight before any is used for respiration.

b. Net Primary Productivity (NPP)

• The energy remaining after producers use some for their own cellular respiration. This energy is available to consumers in the ecosystem.

• Formula: NPP = GPP - Respiration

• Importance: Represents the energy available for the food web.

2. Factors Influencing Primary Productivity
a. Light Availability: More sunlight increases productivity, especially in tropical regions.
b. Water Availability: Essential for photosynthesis; drought reduces productivity.
c. Nutrient Availability: Nutrients like nitrogen and phosphorus are critical for plant growth. Example: Fertile soils have higher productivity.
d. Temperature: Warmer temperatures enhance enzyme activity, increasing productivity in optimal ranges.
e. Carbon Dioxide Levels: More CO₂ supports photosynthesis, up to a point.
f. Ecosystem Type: High NPP in rainforests, estuaries, wetlands; low NPP in deserts, tundra, open ocean.

3. Ecosystem Comparison of NPP

• Terrestrial: Highest in tropical rainforests due to abundant sunlight, water, and nutrients.

• Aquatic: Highest in estuaries and coastal zones where nutrient levels are high.

4. Importance of Primary Productivity

• Foundation of food webs: Provides energy for all trophic levels.

• Carbon cycle: Producers absorb CO₂, reducing greenhouse gases.

• Ecosystem services: Contributes to oxygen production and nutrient cycling.

5. Human Impacts on Primary Productivity
a. Deforestation: Reduces GPP and NPP by destroying producer habitats.
b. Pollution: Eutrophication from nutrient pollution can cause algal blooms, disrupting aquatic ecosystems.
c. Climate Change: Alters temperature, water availability, and CO₂ levels, impacting productivity.
d. Agriculture: Monoculture farming can reduce soil fertility and long-term productivity.

Key Metrics to Remember

• GPP measures total energy captured.

• NPP measures energy available to consumers.

• NPP varies across biomes due to environmental conditions.

1.9 Trophic Levels

Trophic levels describe the hierarchical stages in a food chain, representing the flow of energy and nutrients through an ecosystem. Each level consists of organisms that share the same function in the food chain and obtain energy from similar sources.

1. Levels of the Food Chain
a. Primary Producers (Trophic Level 1)

• Autotrophs, such as plants, algae, and some bacteria, convert solar or chemical energy into organic compounds via photosynthesis or chemosynthesis.

• Foundation of the food web, providing energy for all other trophic levels.

b. Primary Consumers (Trophic Level 2)

• Herbivores that feed on producers.

• Example: Deer, rabbits, zooplankton.

c. Secondary Consumers (Trophic Level 3)

• Carnivores or omnivores that eat primary consumers.

• Example: Frogs, small fish, spiders.

d. Tertiary Consumers (Trophic Level 4)

• Carnivores or omnivores that consume secondary consumers.

• Example: Snakes, large fish, birds of prey.

e. Quaternary Consumers (Trophic Level 5)

• Apex predators at the top of the food chain with no natural predators.

• Example: Lions, orcas, hawks.

f. Decomposers and Detritivores

• Organisms like fungi, bacteria, and earthworms break down dead organisms and recycle nutrients back to the ecosystem.

• Essential for nutrient cycling but not assigned a specific trophic level.

2. Energy Transfer in Trophic Levels
a. 10% Rule

• Only about 10% of the energy at one trophic level is passed to the next level.

• The remaining 90% is lost as heat, used in metabolism, or left in uneaten parts.

b. Energy Pyramid

• Shows the energy available at each trophic level, with producers at the base and apex predators at the top.

3. Importance of Trophic Levels

• Maintain ecosystem balance by controlling population sizes.

• Facilitate energy flow and nutrient cycling.

• Highlight ecosystem dynamics, such as the impact of removing or introducing species.

4. Human Impacts on Trophic Levels
a. Overfishing: Reduces populations of tertiary and quaternary consumers, disrupting food webs.
b. Deforestation: Eliminates primary producers, affecting all higher trophic levels.
c. Pollution: Toxins like pesticides and heavy metals accumulate in higher trophic levels (biomagnification), harming apex predators.
d. Climate Change: Alters habitats and availability of resources, affecting species at all trophic levels.

5. Key Terms to Remember

• Autotrophs: Organisms that produce their own food.

• Heterotrophs: Organisms that consume others for energy.

• Biomagnification: The increase in toxin concentration as you move up trophic levels.

• Food Chain vs. Food Web: Food chains are linear representations of energy flow, while food webs show interconnected relationships.

1.10 Energy Flow and the 10% Rule

Energy flow in ecosystems refers to how energy moves through trophic levels, starting from the sun and moving through producers and consumers. 

1. Energy Flow in an Ecosystem

a. Source of Energy

• The primary energy source for most ecosystems is the sun.

• Producers (e.g., plants, algae) capture sunlight through photosynthesis and convert it into chemical energy.

b. Energy Transfer

• Energy flows from producers to consumers through feeding interactions.

• Energy decreases as it moves up trophic levels due to inefficiencies in transfer.

c. Energy Loss

• Most energy is lost as heat during metabolic processes (e.g., respiration, movement).

• Some energy remains in undigested or uneaten parts of organisms.

2. The 10% Rule

a. Definition

• On average, only 10% of the energy available at one trophic level is transferred to the next level.

b. Implications

• Producers store the most energy, supporting fewer consumers as you move up the food chain.

• Higher trophic levels (e.g., apex predators) receive less energy, limiting their population sizes.

c. Energy Pyramid

• The pyramid shows the energy available at each trophic level.

• Energy diminishes as you go up, forming a triangular shape.

3. Examples of Energy Transfer

• Producers: Capture 100% of solar energy they receive.

• Primary Consumers: Receive 10% of the producer's energy.

• Secondary Consumers: Receive 10% of the primary consumer's energy (1% of the original).

• Tertiary Consumers: Receive 10% of the secondary consumer's energy (0.1% of the original).

4. Importance of Energy Flow

a. Ecosystem Function

• Drives all biological processes and supports life.

• Ensures nutrient and energy cycling within ecosystems.

b. Population Size

• Lower energy availability at higher trophic levels restricts population sizes of secondary and tertiary consumers.

5. Human Impacts on Energy Flow

a. Deforestation: Reduces producers, limiting energy input into the ecosystem.
b. Overharvesting: Disrupts food chains by removing key species.
c. Pollution: Affects energy transfer by harming organisms at various trophic levels.
d. Agriculture: Monocultures reduce ecosystem diversity, impacting energy flow stability.

Key Concepts to Remember

• Energy flow is one-way, not recycled like matter.

• The 10% rule explains why food chains rarely exceed 4-5 trophic levels.

• Energy pyramids illustrate diminishing energy as it moves up trophic levels.

1.11 Food Chains and Food Webs

1. Food Chain

a. Definition

• A linear sequence that shows how energy flows through an ecosystem from one organism to another.

• Each step in the chain represents a trophic level (e.g., producer, consumer, decomposer).

b. Structure

• Producers: The base, using energy from the sun (e.g., grass).

• Primary Consumers: Herbivores that eat producers (e.g., grasshoppers).

• Secondary Consumers: Carnivores or omnivores that eat herbivores (e.g., frogs).

• Tertiary Consumers: Carnivores that eat secondary consumers (e.g., snakes).

• Decomposers: Break down dead organisms, recycling nutrients (e.g., fungi, bacteria).

c. Example of a Food Chain
Grass → Grasshopper → Frog → Snake → Hawk

2. Food Web

a. Definition

• A complex network of interconnected food chains within an ecosystem.

• Represents the multiple feeding relationships between organisms.

b. Structure

• Includes producers, consumers, and decomposers.

• Organisms can occupy multiple trophic levels depending on their diet.

• Example: A hawk might be a tertiary consumer in one chain and a secondary consumer in another.

c. Importance

• Reflects the complexity and stability of ecosystems.

• Highlights interdependence among organisms.

3. Differences Between Food Chains and Food Webs

4. Importance of Food Chains and Food Webs

a. Energy Transfer

• Show how energy moves through ecosystems.

• Help understand energy loss at each trophic level.

b. Ecosystem Stability

• Food webs demonstrate the resilience of ecosystems when one species is lost.

c. Nutrient Cycling

• Decomposers in both systems recycle nutrients back to the environment.

5. Human Impacts on Food Chains and Food Webs

a. Habitat Destruction

• Reduces biodiversity, breaking links in food chains and destabilizing food webs.

b. Overfishing and Hunting

• Removes key predators or prey, disrupting energy flow.

c. Pollution

• Biomagnification of toxins affects higher trophic levels in food chains and food webs.

d. Climate Change

• Alters species distribution and availability of resources, breaking feeding relationships.

Key Terms to Remember

• Trophic Level: A step in a food chain or web.

• Biomagnification: Accumulation of toxins in higher trophic levels.

• Producers and Consumers: Producers create energy; consumers use it.

• Keystone Species: Species critical to maintaining ecosystem balance.