Biosphere to Ecosystems

Table of Contents
1. Overview
2. The biosphere
3. Biomes - aquatic and terrestrial
4. Ecosystems
5. Living organisms (biotic factors)
6. Abiotic factors
7. Atmospheric gases in ecosystems
8. Winds and ecosystems
9. Energy flow through ecosystems
10. Nutrient cycles in ecosystems
11. Responsible ecotourism
12. Current environmental issues
13. Careers in environmental studies
14. Summary
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Overview

Organisms interact with other organisms and with the non-living parts of their environments so that they can survive and produce offspring. This chapter introduces the main terms and concepts used to describe these interactions and explains how people affect natural environments. Topics include the biosphere, biomes, ecosystems, energy flow, food chains and food webs, trophic pyramids, nutrient cycles, common environmental problems and principles of responsible ecotourism.

The biosphere

The biosphere is the part of Earth where life exists. It includes the air, water and land that support living organisms.

Components of the biosphere

The atmosphere

• The atmosphere is the layer of gases that surrounds Earth and helps keep environmental conditions suitable for life.
• Major components include nitrogen (about 78%), oxygen (about 21%), and smaller amounts of carbon dioxide, water vapour and trace gases (for example argon, ozone and methane).
• The atmosphere is involved in breathing and cellular respiration, in photosynthesis by plants, and in protecting the surface from harmful ultraviolet radiation.

The hydrosphere

• The hydrosphere comprises all the water on or near Earth's surface: oceans, seas, rivers, lakes, wetlands and groundwater.
• It includes saltwater (marine) and fresh water (rivers, lakes, ponds) and is the habitat for many aquatic organisms such as fish, algae and aquatic plants.

The lithosphere

• The lithosphere is Earth's outer crust and the weathered rock and soil layers at the surface.
• It provides minerals and mineral ions required by living organisms and supplies the substrates in which plants grow and animals burrow.

Studying the biosphere: key terms

• Biome - a large area with a characteristic climate and a particular assemblage of plants and animals; a biome contains many ecosystems.
• Ecosystem - the community of living organisms (plants, animals, microorganisms) together with the non-living environment (soil, water, climate) interacting as a system in a given area.
• Community - all the populations of different species living and interacting in the same place.
• Population - a group of individuals of the same species living in a defined area at the same time.
• Species - organisms of the same kind that can interbreed and produce fertile offspring.
• Niche - the role and position a species has in its environment, including how it obtains resources and interacts with other organisms.
• Habitat - the place where an organism lives.
• Organism - a single living individual.

Biomes - aquatic and terrestrial

The biosphere is divided into many biomes. Biomes may be classified as aquatic (water) or terrestrial (land). Aquatic biomes are further divided into marine (saltwater) and freshwater types. Each biome contains characteristic kinds of plant and animal life that are adapted to local conditions and is made up of several ecosystems.

Marine biomes (coastal features and regional currents)

Coastal and oceanic conditions, such as tides, currents, temperature and salinity, strongly affect which plant and animal communities occur along a coastline. In South Africa, for example, the warm Agulhas Current flows along the east coast and influences temperature and species composition, while the cold Benguela Current flows along the west coast and brings nutrient-rich waters. Where water masses mix (southern coasts), conditions and species composition change accordingly.

Thick marine forests of kelp provide food and shelter to many animals, and warm coastal waters (such as in the north-east) generally support greater species diversity than cooler south-western waters. Major marine habitat types include sandy beaches, rocky shores, coral reefs, benthic beds (the ocean floor) and the pelagic (open sea) zone.

Sandy beaches

• Have a moving layer of sand with strong wave and current action.
• Include an intertidal zone that is alternately submerged and exposed, producing cyclical wet and dry conditions to which organisms are adapted.

Rocky shores

• Provide firm surfaces for attachment and shelter.
• Support diverse communities of algae, molluscs, crustaceans and other invertebrates that are adapted to exposure and tidal changes.

Coral reefs

• Occur in warm, clear, shallow subtropical and tropical waters and support very high biodiversity.
• Are important habitats for many fish and invertebrate species.

Open sea (pelagic zone)

• Is the deep water area with no firm base; primary producers are microscopic phytoplankton.
• Zooplankton (tiny animal-like organisms) feed on phytoplankton; larger fish, whales and dolphins occupy higher trophic levels.

Estuaries

• Are transition zones where rivers meet the sea and fresh water mixes with salt water.
• Contain a mix of marine and freshwater features, and many organisms are specially adapted to varying salinity.
• Fresh water brings nutrients from land, making estuaries productive nurseries for many marine species.

Freshwater biomes

Freshwater biomes include rivers, streams, ponds, lakes and wetlands. They are influenced by climate and weather and support distinct plant and animal communities.

Wetlands

• Are areas with permanently or seasonally waterlogged soils, or shallow standing water.
• Act as natural flood controllers by slowing and storing flood water.
• Improve water quality by trapping sediments and some pollutants; they store nutrients such as nitrogen and phosphorus and provide important wildlife habitat.

Terrestrial biomes of South Africa

Major terrestrial biomes include:

• Forest
• Fynbos
• Grassland
• Nama Karoo
• Succulent Karoo
• Savanna
• Thicket

The Savanna biome

• Vegetation is a mix of grasses and scattered trees.
• Covers a large proportion of South Africa (about 46%).
• Soils are often porous and infertile; water drains quickly.
• Climate: summer rainfall, hot summers and cool, dry winters.
• Typical fauna: antelope, lion, buffalo, leopard, cheetah, hippopotamus, giraffe, zebra and elephant; many birds and grazing livestock are also common.
• Typical trees: baobab, marula, mopane and acacia.

The Grassland biome

• Dominated by grasses; woody plants are scarce.
• Covers about 24% of South Africa.
• Climate: relatively high rainfall with summer thunderstorms; frost common in winter.
• Soils are deep and fertile in many areas; used extensively for agriculture (maize, grazing, dairy).
• Wildlife includes many antelope species and predators such as lions; numerous bird species occur.
• A major threat is conversion to commercial forestry and agricultural monocultures.

The Nama Karoo biome

• Transitional semi-desert region between Cape flora and tropical savanna.
• Climate: warm, dry, semi-desert; soils sandy and low in nutrients.
• Vegetation: drought-tolerant shrubs and grasses; farming mainly sheep grazing.
• Fauna: rodents, foxes, jackals, ostrich and reptiles; several regionally endemic bird species.

The Succulent Karoo biome

• Occurs in western South Africa along the west coast; winter-rainfall region with very hot, dry summers.
• Vegetation dominated by succulents (plants with fleshy leaves or stems that store water) and other drought-adapted species.
• Many annual plants germinate and flower in the moist winter and spring, producing spectacular seasonal displays.
• Threats include overgrazing by sheep, over-collection of endemic plants and poorly managed tourism.

The Fynbos biome

• Found principally in the south-western Cape; vegetation dominated by low shrubs with fine leaves (the 'fynbos').
• Very high plant diversity and endemism; many species are found nowhere else.
• Climate: cool, wet winters and hot, dry summers; fires are a regular ecological feature and many species are fire-adapted.
• Vegetation: ericas, proteas, restios and other evergreen plants; trees are scarce.
• Uses: grazing, wild-flower harvesting, rooibos and buchu production, viticulture and horticulture.
• Threats: habitat conversion, invasive alien trees, uncontrolled fires, wetland drainage and over-harvesting of wild plants.

The Forest biome

• Indigenous evergreen and semi-deciduous forests occur in coastal lowlands and escarpment slopes; forest patches are often small.
• High rainfall supports multi-layered vegetation with reduced light under the canopy and abundant shade-tolerant species such as tree ferns and lianas.
• Fauna includes forest antelope, pigs and many bird species.
• Threats include felling for timber, collection of fuel wood and extraction of plants for traditional medicine.

The Thicket biome

• Occurs mainly in river valleys and areas with deeper, richer soils.
• Vegetation ranges from dense shrubs to small evergreen trees and succulents; many species have spines or thorns to deter grazers.
• Fauna includes small arboreal mammals and large browsers such as kudu, elephant and black rhino in some areas.

Ecosystems

An ecosystem is the interacting assemblage of living organisms and their non-living environment in a particular place. Ecosystems can be large (a mountain, a lake) or small (a pond, a tree). Artificial systems such as terraria and aquaria are also ecosystems.

Components of an ecosystem

An ecosystem consists of:

• Biotic factors - living components such as plants, animals and microorganisms.
• Abiotic factors - non-living physical and chemical components such as soil, water, temperature and sunlight.

Biotic and abiotic factors interact continuously, and these interactions determine the flow of energy and the cycling of nutrients within the ecosystem.

Interactions among organisms

Symbiosis denotes living together or long-term interactions between different species. Important types are:

• Mutualism - both organisms benefit (example: a flowering plant and its pollinating bee).
• Commensalism - one organism benefits, the other is not significantly affected (example: an epiphytic orchid growing on a tree).
• Parasitism - the parasite benefits while the host is harmed (examples: a tapeworm inside a human, mosquitoes as ectoparasites).

Living organisms (biotic factors)

Organisms in ecosystems can be grouped by how they obtain food: producers, consumers and decomposers.

Producers (autotrophs)

• Producers make organic food from inorganic substances using external energy sources; most producers are photosynthetic plants and algae.
• They use sunlight, carbon dioxide (CO₂) and water (H₂O) to produce glucose and oxygen by photosynthesis.
• Examples of plant growth-forms based on water dependence:
  • Hydrophytes - plants that grow in water (e.g. Elodea, water lily).
  • Mesophytes - plants that require moderate water and typical conditions (e.g. marula, fig, mango).
  • Xerophytes - plants adapted to dry conditions (e.g. cacti, aloes).

Consumers (heterotrophs)

• Primary consumers (herbivores) - eat producers (examples: antelope, zebra, buffalo, sheep).
• Secondary consumers (carnivores) - eat primary consumers (examples: dogs, leopards, snakes).
• Tertiary consumers - predators that feed on secondary consumers (examples: lions, hawks, eagles).
• Omnivores - consume both plants and animals (examples: humans, pigs, baboons).
• Predators - catch and kill prey for food (examples: lions, snakes).
• Scavengers - feed on dead organisms and leftovers (examples: vultures, hyenas, some crustaceans).

Decomposers

• Decomposers (saprophytes or saprovores) such as fungi and bacteria break down dead plant and animal matter and wastes.
• They release nutrients back into the soil, making them available for uptake by plants; decomposers are essential for nutrient cycling.

Abiotic factors

Abiotic factors are non-living physical and chemical features that influence ecosystems. They may be classified as physiographic, edaphic (soil-related) and physical factors.

Physiographic factors

• Slope - how steep or flat an area is. Steep slopes cause rapid run-off, increased erosion and typically have shallow, less fertile soils.
• Aspect - the direction a slope faces. North-facing slopes (in the southern hemisphere) receive more solar radiation and tend to be warmer and drier; south-facing slopes tend to be cooler and moister, favouring shade-tolerant plants.
• Altitude - height above sea level affects temperature, precipitation and wind. Higher altitudes are generally colder, windier and receive different rainfall patterns; species richness typically decreases with altitude.

Edaphic (soil) factors

• Soil pH - describes acidity or alkalinity: pH < 7 is acidic, pH = 7 neutral, pH > 7 alkaline. Soil pH affects nutrient availability.
• Humus content - humus is decayed plant and animal material; it improves fertility, retains water, supplies nutrients and increases soil aeration.
• Soil texture - proportions of sand, silt and clay determine water retention and aeration:
  • Sand - large particles, low water retention, large air spaces.
  • Clay - very small particles, high water retention but poor aeration.
  • Loam - balanced mixture with good water retention and aeration; usually fertile.
• Soil air - air in pore spaces supplies oxygen for root respiration and soil organisms; well-structured soils (with humus) have better aeration.

Physical factors

• Sunlight - the primary energy source for ecosystems; intensity and photoperiod (day length) influence plant growth and flowering, and control activity patterns (diurnal vs nocturnal) in animals.
• Temperature - affects metabolic rates and behaviour. Cold-blooded (ectothermic) animals cannot internally regulate body temperature and are inactive at extreme temperatures (examples: fish, amphibians, reptiles). Warm-blooded (endothermic) animals regulate body temperature and maintain activity across a range of external temperatures (examples: birds and mammals).
• Seasonal behaviours include migration (seasonal movement), hibernation (winter dormancy), aestivation (summer dormancy) and plant dormancy (for example seeds or underground storage organs).
• Water availability - a limiting factor in terrestrial ecosystems. Amount and seasonality of rainfall determine which plants and animals can survive in a biome. Animals obtain water by drinking and from food; plants absorb water through roots and lose water by transpiration.

Plant adaptations to conserve water

• Xerophytes - adaptations include thick waxy cuticles, reduced leaf area (spines), deep or widespread shallow roots to capture water, and specialised water-storage tissues (succulents).
• Hydrophytes - adaptations for aquatic life include large flat floating leaves, stomata on upper leaf surfaces, reduced or absent cuticle, reduced vascular tissue (xylem) and large air spaces to aid buoyancy.

Animal adaptations to conserve water

• Examples of adaptations include thick, scaly skin to reduce evaporation, efficient water reabsorption in kidneys (concentrated urine), burrowing behaviour to avoid heat, and nocturnal activity to reduce water loss.

Atmospheric gases in ecosystems

Winds and ecosystems

• Wind is moving air that influences local climate, evaporation and transpiration rates and therefore affects plant and animal communities.
• Winds disperse pollen and seeds, aiding plant reproduction and colonisation of new areas.

Energy flow through ecosystems

Energy in ecosystems originates from the sun and flows in one direction: sunlight → producers → consumers → decomposers. Energy is transformed and used at each trophic level, and a substantial proportion is lost as heat through respiration and metabolic processes.

Food chains

A food chain shows the transfer of energy from one organism to the next through feeding relationships. Example (terrestrial):

seeds from plants → mouse → snake → hawk

These successive links are called trophic levels: producers (trophic level 1), primary consumers (trophic level 2), secondary consumers (trophic level 3) and tertiary consumers (trophic level 4).

Food webs

A food web is a network of interlinked food chains that better represents the multiple feeding relationships in an ecosystem. Food webs show how energy and nutrients can move along several paths through an ecosystem.

Food pyramids (trophic pyramids)

Pyramids represent quantities at successive trophic levels and come in three types:

• Pyramid of energy - shows the flow of energy through trophic levels. Typically about 90% of energy is lost as heat at each transfer, so only about 10% is passed to the next level.
• Pyramid of biomass - represents the total mass (biomass) of organisms at each trophic level.
• Pyramid of numbers - shows the number of individual organisms at each trophic level; many small organisms may support a few large predators.

Nutrient cycles in ecosystems

Unlike energy, which flows through ecosystems, chemical elements (nutrients) are recycled. The major cycles that support life include the water, carbon, nitrogen and oxygen cycles.

The water cycle

• Evaporation - liquid water changes to water vapour by solar heating.
• Transpiration - water vapour is released by plants.
• Condensation - water vapour cools and forms droplets, producing clouds.
• Precipitation - water falls as rain, hail or snow.
• Run-off - water flows over the land into rivers, lakes and oceans, completing the cycle.

The carbon cycle

• Carbon dioxide (CO₂) is present in the atmosphere (about 0.035% in historical reference values).
• Plants take up CO₂ during photosynthesis and convert carbon into carbohydrates, proteins and fats, releasing O₂ as a by-product.
• Animals obtain carbon by consuming plants or other animals and release CO₂ by respiration.
• Decomposition returns carbon to the soil and atmosphere.
• Long-term storage (fossilisation) traps carbon in coal, oil and natural gas, while weathering and mineral processes also move carbon between reservoirs.

The nitrogen cycle

• Atmospheric nitrogen (N₂, roughly 78%) must be converted into reactive forms (nitrates, ammonia) before most plants can use it.
• Nitrogen-fixing bacteria in soil and in root nodules of leguminous plants (peas, beans, clover) convert N₂ to nitrates and ammonium that plants can use to build proteins.
• Lightning produces high temperatures that enable some nitrogen to combine with oxygen to form nitrogen oxides; these dissolve in rain and form nitrates in soil.
• Proteins and nitrogenous compounds move through food chains. When organisms die or excrete wastes, decomposers convert organic nitrogen back into ammonium and then nitrifying bacteria convert it into nitrates.
• Denitrifying bacteria convert some nitrates back to N₂, returning nitrogen to the atmosphere.

The oxygen cycle

• Oxygen (O₂) in the atmosphere (about 21%) is produced mainly by photosynthetic organisms.
• Plants and animals consume O₂ during cellular respiration and release CO₂.
• Oxygen is also involved in geological processes and in the formation of ozone (O₃) which helps shield the biosphere from harmful ultraviolet radiation.

Responsible ecotourism

Ecotourism involves visiting natural areas while acting responsibly to conserve the environment and to support the well-being of local people. Responsible ecotourism minimises negative impacts while maximising benefits for conservation and local communities.

Economic benefits

• Ecotourism provides income and job opportunities for local communities without necessarily damaging natural or cultural resources.
• It can contribute to national income and support funding for protected areas and conservation projects.

Ethics and participation

• Ethical ecotourism involves fair participation by local people in decision-making and benefits-sharing within conservation areas.
• Visitors should behave respectfully, follow rules, and avoid activities that damage habitats or cultural sites.

Opportunities created by ecotourism

• Educational opportunities for local communities and visitors.
• Employment and enterprise development (guiding, accommodation, craft sales).
• Improved infrastructure that can benefit local people (roads, water supply, health and education services), provided development is well planned and managed.

Current environmental issues

Human activities increasingly affect ecosystems at local and global scales. Key issues include air pollution, global warming, acid rain, monoculture and overpopulation.

The greenhouse effect

• Greenhouse gases (for example water vapour, carbon dioxide, methane and ozone) absorb outgoing infrared radiation and slow the escape of heat from Earth's atmosphere.
• This natural greenhouse effect keeps Earth warm enough for life, but increasing concentrations of greenhouse gases are enhancing the effect and causing additional warming.

Global warming

• Burning fossil fuels (coal, oil, natural gas), deforestation and some agricultural practices have increased concentrations of greenhouse gases in the atmosphere.
• Carbon dioxide is a major contributor to the enhanced greenhouse effect; rising CO₂ concentrations lead to a gradual increase in global temperatures (global warming).
• Consequences include altered weather patterns, increased drought in some regions, melting polar ice, sea-level rise and impacts on biodiversity and human communities, especially in coastal areas.

Acid rain

• Emissions of sulphur dioxide (SO₂) and nitrogen oxides (NO_x) from industry and vehicles dissolve in atmospheric moisture to form acids (for example sulphuric and nitric acids).
• Acid deposition (acid rain) damages vegetation, corrodes buildings and statues, increases soil acidity, harms aquatic life and affects human and animal health.

Monoculture

• Monoculture is the cultivation of a single crop species over a large area for many years. It can deplete soil nutrients and reduce biodiversity.
• Monocultures often require large inputs of chemical fertilisers and pesticides; these may run off in rain and pollute waterways, harming other organisms.

Overpopulation

• Carrying capacity is the maximum number of individuals of a species that an environment's resources can sustainably support.
• When population numbers exceed carrying capacity, resource depletion, waste accumulation and environmental degradation typically follow.
• Human overpopulation contributes to shortages of food, clean water and living space, and increases production of waste (including non-biodegradable waste).

Careers in environmental studies

Career opportunities span social, management and scientific fields. Two broad paths are recognised:

• Socio-environmental careers - examples: ecotourism specialist, environmental journalist, environmental lawyer, cultural resource specialist. These roles combine people-centred skills with conservation awareness.
• Environmental science careers - examples: nature conservation officer, marine biologist, ecologist, landscape architect, environmental impact assessor. These roles require scientific training and focus on habitat, species and resource management.
• Good environmental management integrates social participation with scientific assessment and planning.

Summary

The biosphere comprises atmosphere, hydrosphere and lithosphere and contains many biomes and ecosystems. Ecosystems are dynamic systems in which living organisms and their physical environment interact through energy flow and nutrient cycles. Understanding producers, consumers and decomposers, and the abiotic controls on life, helps explain the structure and functioning of ecosystems. Human activities both depend on and affect ecosystems; responsible approaches such as ecotourism, sustainable land use and pollution control are essential to conserve biodiversity and maintain ecosystem services for future generations.