Welcome to Ecosystems and Sustainability!

Hi there! This chapter, "Ecosystems and sustainability," is incredibly important because it moves beyond just studying the physical world and looks at how all living things (the biosphere) interact with the physical environment and, crucially, how human actions are impacting these vital life-support systems.

As part of the wider "Ecosystems under stress" section, we will explore why biodiversity is declining and how we can manage the planet's resources sustainably. Don't worry if the concepts seem large; we'll break down the structure of an ecosystem, how energy moves through it, and how ecosystems change over time, using clear examples.

1. The Foundation: Ecosystems and Biodiversity (3.3.2.1)

Before diving into stress and change, we need to know what we are protecting.

1.1 What is an Ecosystem?

An ecosystem is a dynamic, functional unit of nature where living (biotic) and non-living (abiotic) components interact. It can be as small as a pond or as large as a rainforest.

1.2 The Concept of Biodiversity

Biodiversity refers to the variety of life on Earth. It is usually measured at three levels:

  • Genetic Diversity: The variety of genes within a species (e.g., all the different types of potato).
  • Species Diversity: The number of different species in an area.
  • Ecosystem Diversity: The variety of habitats, communities, and ecological processes.

1.3 Trends and Threats to Biodiversity

We are currently facing rapid, global decline in biodiversity. This decline is mainly driven by human activity.

The primary causes of declining biodiversity can be remembered using the acronym HICPO:

  1. Habitat Destruction (e.g., deforestation for farming).
  2. Invasive Species (non-native species out-competing native ones).
  3. Climate Change (changing weather patterns stress existing habitats).
  4. Pollution (water, air, and soil contamination).
  5. Over-exploitation (unsustainable fishing, hunting, or resource extraction).

1.4 The Importance of Ecosystems for Humans

Ecosystems provide essential Ecosystem Services—the benefits people obtain from ecosystems. These are vital, especially as global population and economic development continue to grow:

  • Provisioning Services: Products obtained from ecosystems (e.g., food, fresh water, wood, medicine).
  • Regulating Services: Benefits obtained from the regulation of ecosystem processes (e.g., climate regulation, flood control, disease regulation).
  • Cultural Services: Non-material benefits (e.g., recreation, spiritual enrichment, aesthetic value).

Quick Review: Ecosystems are the basic life support systems; biodiversity is their variety. We need biodiversity for essential services like clean air and water.

2. Ecosystem Structure and Function (3.3.2.2)

Understanding how an ecosystem works means looking at how energy and materials move through it.

2.1 The Systems Approach

We can model ecosystems as open systems, meaning they have:

  • Inputs: Energy (sunlight) and materials (water, carbon dioxide, nutrients).
  • Stores/Components: The places where energy or materials are held (e.g., biomass of trees, water in the soil).
  • Flows/Transfers: The movement of energy and materials (e.g., respiration, feeding, decomposition).
  • Outputs: Energy or materials leaving the system (e.g., water via evapotranspiration, heat loss).

Analogy: Think of a phone battery (Store), charging it (Input), using apps (Flows), and the heat it releases (Output).

2.2 Energy Flows: Trophic Levels, Food Chains and Webs

Energy drives the ecosystem. It usually enters via sunlight and flows through different feeding levels, known as trophic levels:

  1. Producers: Organisms that produce their own food (usually plants/algae through photosynthesis). They form the base of the chain.
  2. Primary Consumers: Herbivores (eat producers).
  3. Secondary Consumers: Carnivores/Omnivores (eat primary consumers).
  4. Tertiary Consumers: Top predators.

Energy is lost at each level (about 90%) as heat, movement, or waste. This means the total mass of living things decreases drastically as you move up the trophic pyramid.

A food chain is a simple path of energy flow (grass → rabbit → fox). A food web is a much more realistic, interconnected network of multiple food chains.

2.3 Biomass and Primary Production

  • Biomass: The total mass of living matter in a specific area.
  • Primary Production: The rate at which energy is converted by producers into organic substances.
  • Net Primary Production (NPP): This is the crucial figure. It is the total energy stored by plants after they have used some for their own respiration (Growth Rate minus Respiration Loss). NPP represents the amount of food available to consumers and is a key measure of an ecosystem's health.

2.4 Mineral Nutrient Cycling

Nutrients (like nitrogen and phosphorus) are essential materials. They move between the biotic and abiotic stores:

  1. Uptake: Plants absorb nutrients from the soil or water. (Store: Biomass)
  2. Litter/Death: Organisms die, or leaves fall, creating litter on the surface. (Store: Litter)
  3. Decomposition: Decomposers (bacteria, fungi) break down the litter.
  4. Leaching/Release: Nutrients are released back into the soil or lost through runoff. (Store: Soil)

Did you know? In hot, wet ecosystems like the Tropical Rainforest, nutrient cycling is incredibly fast, meaning the soil store is very small because nutrients are immediately recycled back into the biomass (trees).

Key Takeaway: Ecosystem function depends on energy flowing up the trophic levels and materials cycling between the biosphere and the soil/atmosphere.

3. Ecosystem Change Over Time: Succession (3.3.2.2 & 3.3.2.4)

Ecosystems are dynamic; they naturally change in a predictable sequence called ecological succession.

3.1 The Concept of Succession

Succession is the progressive, orderly change in a community of organisms over time, leading to a more stable community.

  • Seral Stages: The intermediate communities that develop sequentially (e.g., pioneer, intermediate, mature).
  • Pioneer Species: The first species to colonise a bare or new area, often hardy and simple (e.g., lichen on bare rock).

3.2 The Climatic Climax Community

If succession is allowed to proceed without disturbance, it will eventually reach a stable state known as the Climatic Climax community. This community is determined by the dominant climate of the region (e.g., deciduous forest in temperate zones, grassland in semi-arid zones).

  • Climax characteristics include maximum biomass, high diversity, and efficient energy/nutrient use.

3.3 Types of Succession (Seral Stages)

The syllabus requires you to know about succession as illustrated by one type. Let's look at Psammoseres (sand dune succession):

  1. Pioneer Stage: Bare sand is colonised by hardy plants like Marram Grass, which are tolerant of salty, mobile conditions.
  2. Building Stage: Marram grass roots bind the sand, and the plants start adding small amounts of organic matter. The dune stabilises.
  3. Fixed Dune Stage: Deeper soil forms, reducing mobility. Shrubs and small trees (scrub) colonise, and species diversity increases.
  4. Climatic Climax: If the local climate supports it, a stable community like woodland or forest develops.

3.4 Human Activity and Disruption: Plagioclimax

Human interference often prevents an ecosystem from reaching its natural climatic climax. This arrested state is called a Plagioclimax (or sub-climax).

Example: Maintaining Grassland
If a natural forest ecosystem is cleared for farming and is regularly grazed by cattle or mowed, the ecosystem is held in a grassland stage. The grazing/mowing prevents tree saplings from growing, thus preventing the succession to woodland climax. This managed grassland is a plagioclimax.

Key Takeaway: Succession is natural progress towards stability (Climax). Humans often stop this progress, creating a Plagioclimax.

4. Biomes: Ecosystems at a Global Scale (3.3.2.3)

A biome is a very large-scale ecosystem defined by its dominant vegetation type, which is strongly linked to climate.

4.1 Contrasting Biomes: Tropical Rainforest (TRF) and Savanna Grassland

Feature Tropical Rainforest (TRF) Savanna Grassland
Climate Hot (25–30°C), very wet (2,000+ mm/year), low seasonal variation. Hot, distinct wet (summer) and dry (winter) seasons. Annual rainfall (500–1500 mm).
Vegetation/Adaptations High density and diversity. Four distinct layers (Emergent, Canopy, Understorey, Shrub). Trees have buttress roots for support and drip tips to shed water. Dominated by grass and widely scattered deciduous trees/shrubs. Plants adapt to drought and fire (e.g., thick bark, deciduous leaves).
Soil/Nutrient Cycling Poor soils (Laterite). Cycling is extremely fast and mainly relies on the biomass store. Infertile soil with low organic content. Soil moisture budget is highly seasonal.

4.2 Human Impact and Development Issues

Both biomes face major sustainability challenges due to human activity:

TRF Development Issues:
  • Logging and Deforestation: Conversion to cattle ranching or mono-culture plantations (e.g., palm oil).
  • Impact: Massive loss of biodiversity, disruption of the water and carbon cycles, soil erosion, and climate change implications.
Savanna Grassland Development Issues:
  • Agricultural Extension/Intensification: Over-grazing by domesticated animals, increasing farming into fragile areas.
  • Impact: Can lead to desertification (especially in savanna margins) and reduction of native wildlife (e.g., conflict between livestock and large predators).

Quick Review: Biomes are global ecosystems. The TRF has high NPP and rapid nutrient cycling; the Savanna is seasonal and relies on adaptations to fire and drought.

5. Specialized Ecosystems Under Threat (3.3.2.5 & 3.3.2.6)

We must also look at specialized and often fragile marine and local systems.

5.1 Marine Ecosystems: Coral Reefs

Coral reefs are highly diverse marine ecosystems, often called the "rainforests of the sea." They develop under specific environmental conditions:

  • Temperature: Warm water (18°C–29°C).
  • Depth: Shallow (sunlight needed for symbiotic algae called zooxanthellae).
  • Salinity: Optimal (not too fresh, not too salty).
  • Clarity: Clear water (low sediment content).
Factors Affecting Coral Health (Natural and Human)

The health and survival of reefs are under severe pressure:

  • Natural Stressors: Increased water temperature (causing coral bleaching), increased acidity (due to absorbed CO2), and algal blooms (can suffocate coral).
  • Human Stressors:
    • Pollution: Runoff from coastal development, oil spills, and plastic waste.
    • Drainage Basin Schemes: Dams upstream reduce freshwater and sediment flow, changing coastal salinity and clarity.
    • Tourism and Fishing: Damage from boat anchors, divers, and unsustainable fishing methods (like dynamite fishing).

Future Prospects: The future is uncertain. Climate change remains the greatest long-term threat. Conservation strategies focus on creating Marine Protected Areas (MPAs) and restoring damaged reef sections, but global action on carbon emissions is necessary.

5.2 Local Ecosystems (e.g., Coastal Dunes or Managed Parkland)

Your syllabus requires you to study a distinctive local ecosystem. The focus should be on its characteristics, how flora/fauna adapt to the conditions (climate, soil), and how human activity has changed it.

Local Factors in Change:
  • Agriculture/Urban Change: Direct habitat loss (e.g., converting marshland to housing).
  • Planned Species Introduction: Introducing species for a specific benefit (e.g., using a non-native grass for stabilisation).
  • Unplanned Species Introduction: Invasive species arriving accidentally (e.g., carried on ships), which can disrupt local food webs.
Management and Conservation:

Local sustainability focuses on practical, site-specific strategies:

  • Conservation Strategies: Establishing nature reserves, controlling access (e.g., fenced dunes), and active restoration projects (e.g., planting native species).
  • Managing Impacts: Implementing pollution control measures or designing pathways to reduce human erosion (e.g., boardwalks in a dune system).

Don't worry if this seems tricky at first! When you approach a case study, always link the physical nature of the environment (e.g., wet, dry, unstable soil) directly to how the plants and animals have survived there (their adaptations).


Final Key Takeaway

The core message of "Ecosystems under stress" is the increasing conflict between human development needs and the integrity of natural systems. Sustainable management requires understanding the system's structure, recognizing human impacts (especially habitat loss and climate change), and implementing effective conservation and restoration strategies at local, regional, and global scales.