C3 Revision Questions – Ecosystems

Ecosystem Definition

An ecosystem is a dynamic system made up of living organisms known as biotic components and the non living environment known as abiotic components, interacting through transfers of energy and cycling of nutrients.

Biotic Component Concept

Biotic components are the living parts of an ecosystem including plants, animals, fungi, bacteria and all other organisms that interact within food webs and nutrient cycles.

Abiotic Component Concept

Abiotic components are the non living physical and chemical factors that influence ecosystems including temperature, sunlight, water availability, soil characteristics and atmospheric gases.

Ecosystem Inputs

Ecosystems receive inputs of energy and matter. The main energy input is solar radiation while matter enters through water, nutrients, gases and organic material.

Ecosystem Outputs

Outputs from ecosystems include heat energy released through respiration, water leaving through evaporation and transpiration, and nutrients lost through processes such as leaching.

Nutrient Cycling Principle

Nutrients are continuously transferred between biomass, litter and soil stores, allowing ecosystems to maintain productivity over time.

Biomass Store Definition

Biomass is the total mass of living organisms within an ecosystem and acts as a major nutrient store.

Litter Store Definition

Litter consists of dead plant material, dead animals and organic waste that accumulates on the ecosystem surface before decomposition.

Soil Store Definition

The soil store contains nutrients dissolved in soil water, organic matter and mineral particles available for plant uptake.

Transfer Flow Definition

A transfer is the movement of nutrients or energy from one store to another within an ecosystem.

Plant Uptake Process

Plants absorb nutrients such as nitrogen and phosphorus from the soil through their root systems and incorporate them into living tissues.

Litterfall Process

Litterfall occurs when leaves, branches, fruit, dead organisms and waste products enter the litter store from biomass.

Decomposition Process

Decomposition is the breakdown of organic material by bacteria, fungi and detritivores, releasing nutrients back into the soil.

Leaching Process

Leaching occurs when nutrients dissolve in water and are transported downward through the soil beyond the reach of plant roots.

Weathering Contribution

Weathering releases minerals from rocks into soils, providing an additional source of nutrients for ecosystem functioning.

Tropical Rainforest Nutrient Cycle

Tropical rainforests have very rapid nutrient cycling because warm temperatures and abundant moisture accelerate decomposition and plant growth.

Rainforest Biomass Dominance

In tropical rainforests most nutrients are stored in living biomass rather than soil because uptake occurs extremely rapidly.

Rainforest Soil Limitation

Despite dense vegetation, tropical rainforest soils are often relatively nutrient poor because nutrients are quickly absorbed by plants rather than remaining in soil stores.

Desert Nutrient Cycle

Desert ecosystems experience slow nutrient cycling because low moisture levels restrict decomposition and biological activity.

Desert Biomass Store

The biomass store in deserts is relatively small because harsh conditions limit plant growth and productivity.

Desert Litter Persistence

Organic matter remains in desert ecosystems for long periods because decomposition rates are extremely slow.

Energy Flow Principle

Energy moves through ecosystems in a one way direction and cannot be recycled like nutrients.

Producer Definition

Producers are organisms that create organic compounds from inorganic materials using photosynthesis and form the base of food chains.

Photosynthesis Role

Photosynthesis converts solar energy into chemical energy stored within organic compounds such as glucose.

Primary Consumer Definition

Primary consumers are herbivores that obtain energy directly from producers by feeding on plant material.

Secondary Consumer Definition

Secondary consumers feed on primary consumers and are usually carnivores or omnivores.

Tertiary Consumer Definition

Tertiary consumers feed on secondary consumers and often occupy high trophic positions within food webs.

Quaternary Consumer Definition

Quaternary consumers are apex predators occupying the highest trophic level with few or no natural predators.

Decomposer Importance

Decomposers break down dead organic matter and waste products, ensuring nutrients are returned to the ecosystem.

Detritivore Function

Detritivores physically break down dead organic matter into smaller fragments, increasing surface area for decomposition.

Trophic Level Concept

A trophic level describes an organism's feeding position within a food chain or food web.

Ten Percent Rule

Only around ten percent of available energy is typically transferred from one trophic level to the next because much energy is lost through respiration, movement and waste.

Respiratory Energy Loss

Organisms release significant amounts of energy as heat during respiration, reducing the energy available to higher trophic levels.

Net Primary Productivity Definition

Net Primary Productivity measures the rate at which producers accumulate biomass after subtracting energy used during respiration.

NPP Formula Concept

Net Primary Productivity equals Gross Primary Productivity minus Respiratory Losses, showing how much energy remains available to consumers.

Solar Radiation Influence

Higher levels of solar radiation increase photosynthesis rates and generally raise net primary productivity.

Water Availability Influence

Water is required for photosynthesis so ecosystems with greater water availability tend to have higher productivity.

Temperature Productivity Relationship

Warmer temperatures increase enzyme activity and photosynthetic rates up to an optimum level, increasing productivity.

Growing Season Effect

Long growing seasons allow photosynthesis to occur for longer periods, increasing total annual productivity.

Nutrient Availability Influence

Greater nutrient availability supports plant growth and increases biomass production.

Equatorial Productivity Advantage

Equatorial regions experience high net primary productivity because they receive intense solar radiation and maintain warm temperatures year round.

Swamp Productivity Maximum

Swamps and marshes often have exceptionally high productivity because water and nutrients are abundant.

Tropical Rainforest Productivity Maximum

Tropical rainforests are among the most productive ecosystems on Earth because warm and wet conditions persist throughout the year.

Desert Productivity Limitation

Deserts have low productivity because water scarcity severely restricts photosynthesis and plant growth.

Cold Environment Productivity Limitation

Cold ecosystems have low productivity because low temperatures and short growing seasons reduce photosynthetic activity.

Biodiversity Definition

Biodiversity refers to the variety of life within an area including species diversity, genetic diversity and ecosystem diversity.

Biodiversity Stability Relationship

Highly diverse ecosystems are generally more stable because ecological functions are shared among many species.

Biodiversity Disease Resistance

Greater biodiversity often reduces the likelihood that diseases will spread rapidly through an ecosystem.

Species Richness Definition

Species richness measures the total number of different species present within an ecosystem.

Species Evenness Definition

Species evenness measures how evenly individuals are distributed among different species within an ecosystem.

High Richness Low Evenness Example

An ecosystem may contain many species but still have low biodiversity if one species dominates most of the population.

Simpson Diversity Index Purpose

The Simpson Diversity Index combines species richness and species evenness into a single measure of biodiversity.

Simpson Diversity Interpretation

Values closer to one indicate high biodiversity whereas values closer to zero indicate low biodiversity.

Direct Human Action Definition

Direct action involves immediate human interventions that physically alter ecosystems, species or habitats.

Indirect Human Action Definition

Indirect action influences ecosystems through wider social, economic or political processes rather than direct environmental modification.

Invasive Species Definition

An invasive species is a non native organism that spreads rapidly and causes ecological or economic harm in a new environment.

Grey Squirrel Example

Grey squirrels have contributed to declines in native red squirrel populations through competition for resources and disease transmission.

Brown Tree Snake Example

Brown tree snakes introduced to Guam caused severe declines and extinctions among native bird populations.

Kudzu Vine Example

Kudzu vine spreads rapidly and smothers native vegetation, altering habitat structure and reducing biodiversity.

Chytrid Fungus Threat

Chytrid fungus has caused major declines in amphibian populations across many regions of the world.

Hybridisation Threat

Some invasive species interbreed with native species, reducing genetic uniqueness and potentially causing genetic extinction.

Emerald Ash Borer Impact

The emerald ash borer has killed millions of ash trees, demonstrating how invasive species can transform ecosystems.

Invasive Species Success Factors

Many invasive species succeed because they lack natural predators, reproduce rapidly and tolerate a wide range of environmental conditions.

Rat Eradication Success

The removal of invasive rats from South Georgia Island has allowed native wildlife populations to recover significantly.

Deforestation Definition

Deforestation is the large scale removal of forest cover, usually to make way for agriculture, infrastructure or resource extraction.

Agricultural Expansion Driver

Agriculture is one of the leading causes of deforestation through activities such as cattle ranching, soy production and palm oil cultivation.

Logging Driver

Commercial logging removes forest trees for timber, paper and construction materials, often reducing biodiversity.

Infrastructure Development Driver

Road building, mining projects and dam construction frequently require extensive forest clearance.

Climate Impact of Deforestation

Deforestation contributes to climate change because forests store large quantities of carbon that are released when vegetation is removed.

Water Cycle Disruption

Forest removal reduces evapotranspiration and can alter regional rainfall patterns.

Soil Erosion Consequence

Without tree roots to stabilise soil, deforestation increases erosion and nutrient loss.

Golden Toad Example

The golden toad is frequently cited as an example of a species driven to extinction partly through habitat loss and environmental change.

Sumatran Tiger Threat

The Sumatran tiger remains endangered due largely to habitat loss from deforestation.

Over Exploitation Definition

Over exploitation occurs when organisms are harvested faster than populations can naturally recover.

Atlantic Cod Collapse

Intensive overfishing caused a dramatic collapse of Atlantic cod stocks and demonstrated the dangers of unsustainable harvesting.

Passenger Pigeon Extinction

The passenger pigeon became extinct following extreme levels of hunting and exploitation.

Sea Otter Food Web Role

Declines in sea otter populations allowed sea urchins to increase, leading to destruction of kelp forest ecosystems.

African Elephant Genetic Threat

Poaching reduces elephant populations and can decrease genetic diversity within surviving groups.

Vaquita Crisis Example

The vaquita is one of the world's rarest mammals and has been driven close to extinction largely through bycatch in fishing operations.

Rhino Poaching Threat

Rhinos are heavily targeted for their horns, making illegal hunting a major biodiversity threat.

Pangolin Trafficking Example

Pangolins are among the most heavily trafficked mammals globally due to demand for scales and meat.

Mangrove Aquaculture Impact

Mangrove forests are often destroyed to create shrimp farms, reducing biodiversity and ecosystem services.

Climate Change Biodiversity Threat

Climate change alters habitats, species distributions and ecosystem processes, increasing extinction risk.

Range Shift Response

Many species are moving towards cooler latitudes or higher elevations as temperatures rise.

Ocean Acidification Threat

Increasing carbon dioxide absorption by oceans lowers pH levels and harms organisms that build shells or skeletons from calcium carbonate.

Coral Bleaching Mechanism

Corals under thermal stress expel their symbiotic zooxanthellae, causing bleaching and reducing survival chances.

Phenological Mismatch

Climate change can disrupt ecological timing when species that depend on one another respond differently to environmental change.

Ocean Dead Zone Formation

Warming and nutrient pollution can reduce oxygen levels in water, creating dead zones where most aquatic life cannot survive.

Amazon Tipping Point Risk

Scientists warn that extensive environmental change could eventually transform parts of the Amazon rainforest into savanna ecosystems.

Coral Reef Ecosystem Importance

Coral reefs support exceptionally high biodiversity and provide habitat for thousands of marine species.

Coral Reef Climate Threat

Rising sea temperatures, stronger storms, changing ocean circulation and acidification all threaten coral reef survival.

Zooxanthellae Relationship

Corals depend on symbiotic zooxanthellae algae for much of their energy through photosynthesis.

El Nino Bleaching Connection

Major El Nino events have triggered widespread coral bleaching by raising ocean temperatures above normal levels.

Coral Reef Decline Statistic

Approximately half of the world's coral reefs have been lost since 1950 according to the document.

Jarvis Island Recovery Example

Jarvis Island demonstrates that some coral communities can recover even after experiencing severe bleaching events.

Tropical Rainforest Biodiversity Importance

Tropical rainforests contain some of the highest concentrations of biodiversity found anywhere on Earth.

Mining Threat to Rainforests

Extraction of minerals and fossil fuels frequently requires large scale forest clearance and infrastructure development.

Ghana Mining Statistic

Deforestation linked to mining has left only about twelve percent of Ghana's original rainforest intact.

Global Extinction Risk Estimate

Some estimates suggest that a quarter or more of all species could be lost within fifty years if current trends continue.

West African Rainforest Loss

Almost ninety percent of West Africa's rainforest has already been destroyed.