Table of Contents
Humans as a Biological Factor
Humans are part of the biosphere, but unlike most other species, we alter it on a global scale. Our influence is now so extensive that many scientists describe the current geological epoch as the “Anthropocene” – the age dominated by human impact.
In this chapter the focus is on humans as ecological actors:
- How our numbers have changed.
- How we use land and seas.
- How we extract and consume resources.
- How these activities connect to the structure and functioning of the biosphere.
Details on specific problems (climate change, pollution, biodiversity loss, laws) are covered in later chapters of this section.
1. Humans as Ecosystem Engineers
Many species modify their environment (beavers build dams, corals build reefs), but humans:
- Operate at planetary scale.
- Change environments very rapidly (decades instead of millennia).
- Use technology and culture to amplify their effects.
Typical human “engineering” activities:
- Land transformation: Clearing forests, draining wetlands, irrigating deserts, building cities.
- Hydrological changes: Dams, canals, groundwater pumping.
- Biogeochemical alterations: Changing the carbon, nitrogen, phosphorus, and water cycles by burning fossil fuels, fertilizing fields, and diverting water.
- Biological reshuffling: Moving species around the globe (crops, livestock, pets, pests, invasive species).
Many of these actions are driven by:
- Growing population.
- Rising per-capita consumption.
- Economic and technological development.
These drivers and their history are explored more in the following sections.
2. Growth of the Human Population
The development of the world population is covered in the next chapter in detail. Here the emphasis is on why population growth is ecologically important.
Key ideas:
- For ecological impact, a simple but useful relationship is:
$$ \text{Impact} \approx \text{Population} \times \text{Affluence} \times \text{Technology} $$
(Often called the IPAT formula.) - Population (P): Number of people.
- Affluence (A): Average resource use and waste per person.
- Technology (T): The methods used to provide goods and services, which can increase or decrease environmental damage.
Thus, ecological impact increases when:
- There are more people.
- Each person uses more energy, food, and materials.
- Technologies used are inefficient or polluting.
2.1 Unequal Contributions to Impact
Not all humans contribute equally to environmental change:
- High-income countries:
- Slower or no population growth.
- Very high per-person energy and material use.
- Disproportionate contribution to greenhouse gases, resource extraction, and waste.
- Low-income countries:
- Often still rapidly growing populations.
- Lower per-person resource use, but:
- Reliance on local natural resources (firewood, wild foods).
- Vulnerability to environmental degradation and climate change.
Ecologically, it is crucial to consider both number of people and lifestyle when assessing human impact on the biosphere.
3. Patterns of Human Resource Use
Humans use three main categories of resources:
- Renewable resources: Can regenerate (e.g., forests, fish stocks, groundwater, fertile soils, solar and wind energy).
- Non-renewable resources: Form extremely slowly on geological timescales (e.g., fossil fuels, metal ores, phosphate rock).
- Ecosystem services: Benefits provided by ecosystems (e.g., pollination, water purification, climate regulation, soil formation, coastal protection).
3.1 Sustainable vs. Unsustainable Use
From an ecological viewpoint:
- Use is sustainable if:
- The rate of resource use does not exceed the rate at which it can regenerate or be safely absorbed by the environment.
- Use is unsustainable if:
- Stocks are depleted (overfishing of oceans, deforestation).
- Regenerative capacity or ecosystem structure is damaged (soil erosion, coral reef destruction).
- Waste and pollutants accumulate faster than ecosystems can process or store them safely (greenhouse gases, persistent chemicals).
Many human activities currently exceed ecological limits. This is often described by:
- Ecological footprint: The biologically productive area needed to produce consumed resources and absorb wastes.
- Earth Overshoot Day: The date each year when humanity’s total resource use exceeds what Earth can regenerate in that year.
4. Transformation of Land and Seas
Human use of land and seas has direct consequences for ecosystems and biodiversity, and indirect consequences for climate and biogeochemical cycles.
4.1 Land-Use Change
Main types:
- Agriculture:
- Conversion of natural ecosystems to cropland and pasture.
- Simplified ecosystems: Often large monocultures with few species.
- Heavy use of fertilizers and pesticides.
- Forestry:
- Logging (selective or clear-cut).
- Plantations with few tree species.
- Urbanization and infrastructure:
- Cities, roads, industry, mines.
- Seals soil surfaces, alters water flow, fragments habitats.
Ecological consequences:
- Habitat loss and fragmentation.
- Changes in local climate and hydrology.
- Altered fire regimes.
- Reduced connectivity between populations of wild species.
These topics will be further linked to biodiversity decline and climate change in later chapters.
4.2 Use of the Seas
Humans use marine environments for:
- Fishing and aquaculture:
- Targeted removal of particular species.
- Bycatch of non-target species.
- Habitat damage (e.g., bottom trawling).
- Pollution from fish farms (nutrients, chemicals).
- Transport and infrastructure:
- Shipping lanes, harbors, offshore platforms, submarine cables.
- Resource extraction:
- Oil, gas, and minerals.
- Coastal development:
- Ports, tourism areas, land reclamation.
Ecological effects include:
- Overexploitation of marine species.
- Disturbance of food webs.
- Pollution (oil spills, ship noise, plastic waste).
- Destruction of coastal habitats (mangroves, seagrass, coral reefs).
The next chapter on “Resources and Management of Land and Seas” will discuss options for more sustainable use.
5. Humans and Biogeochemical Cycles
Human activity has become a major force in global element cycles (carbon, nitrogen, phosphorus, sulfur). The previous ecology chapter introduced these cycles; here we focus on the human role.
5.1 Carbon Cycle and Energy Use
Key human influences:
- Burning of fossil fuels (coal, oil, natural gas) for energy and transport.
- Deforestation and land-use change (less carbon stored in vegetation and soils, more CO₂ in the atmosphere).
- Production of cement (releases CO₂).
Ecological consequences:
- Increased atmospheric CO₂ and other greenhouse gases.
- Enhanced greenhouse effect and global climate change.
- Ocean acidification due to CO₂ uptake by seawater.
Climate change and its detailed ecological impacts are treated in the chapter on climate change.
5.2 Nitrogen and Phosphorus
Humans have strongly altered the nitrogen and phosphorus cycles:
- Nitrogen:
- Industrial fixation of nitrogen for fertilizers.
- Combustion of fossil fuels (NOₓ emissions).
- Phosphorus:
- Mining of phosphate rock for fertilizers and detergents.
Ecological impacts:
- Nutrient enrichment of soils and waters.
- Eutrophication of lakes, rivers, and coastal seas.
- Changes in species composition (nitrate-tolerant versus nitrate-sensitive species).
- Dead zones in coastal waters due to oxygen depletion.
These changes illustrate how local agricultural practices can have far-reaching ecosystem effects, including in distant marine environments.
6. Human-Induced Global Change
Many human impacts overlap and reinforce each other. Ecologists therefore often speak of global change rather than isolating single problems.
Important components of global change driven by humans include:
- Climate change: Resulting mainly from greenhouse gas emissions.
- Land-use change: Including deforestation, urbanization, and agricultural expansion and intensification.
- Biodiversity loss: Extinctions, population declines, and simplification of ecosystems.
- Biological invasions: Spread of species to new regions via trade, transport, and deliberate introductions.
- Pollution: Chemical contamination (pesticides, heavy metals, plastics, pharmaceuticals), air and water pollution.
- Alteration of disturbance regimes: Changes in the frequency and intensity of fires, floods, and storms through land management and climate effects.
These drivers often interact:
- Deforestation adds CO₂ to the atmosphere, contributing to climate change.
- Climate change can make ecosystems more vulnerable to invasive species.
- Pollution and climate stress can weaken organisms and ecosystems, making them less resilient to disturbances.
Later chapters in this section will explore several of these aspects in more depth.
7. Socio-Ecological Systems and Feedbacks
Humans depend on the biosphere, but our actions also change it. This forms a feedback loop:
- Humans use ecosystems for food, water, materials, and climate regulation.
- Human activities alter ecosystems and cycles.
- Changed ecosystems can:
- Continue to support human societies.
- Or become degraded, reducing their capacity to provide services.
Examples:
- Overuse of groundwater can lead to falling water tables and land subsidence, making agriculture and settlement more difficult.
- Overfishing reduces fish populations, harming the livelihoods of fishing communities.
- Coastal wetland destruction removes natural flood protection, increasing damage from storms.
Recognizing these feedbacks is a key step towards managing human interactions with the biosphere more sustainably.
8. Cultural and Technological Dimensions
Unlike other species, humans can change their behavior, technologies, and institutions relatively quickly through learning and cultural evolution.
This creates both:
- Risks:
- Rapid spread of environmentally harmful practices.
- Short-term economic interests outweigh long-term ecological considerations.
- Opportunities:
- Development of cleaner technologies.
- International agreements and laws.
- Education and changes in values and consumption patterns.
Examples of cultural-technical developments relevant to the biosphere:
- Transition from hunting-gathering to agriculture and later to industrial agriculture.
- Urbanization and the growth of megacities.
- Fossil-fuel-based energy systems and the emerging transition toward low-carbon energy.
- Conservation movements and protected area networks.
The chapters on “Laws and Measures” and “Nature and Environmental Protection” will examine how societies attempt to steer these developments.
9. The Challenge: Living Within Planetary Boundaries
To understand the scale of human influence, some scientists propose the concept of planetary boundaries – thresholds in Earth-system processes beyond which the risk of abrupt or irreversible environmental change increases sharply.
Processes considered include:
- Climate system.
- Biodiversity and biosphere integrity.
- Land-system change.
- Biogeochemical flows (nitrogen, phosphorus).
- Freshwater use.
- Ocean acidification.
- Atmospheric aerosol loading and chemical pollution.
Key idea:
- Human societies must meet their needs and support well-being while keeping human pressures within safe limits for the functioning of the biosphere.
The following chapters on world population, resource use, pollution, waste, and environmental protection will discuss in more concrete terms:
- Where and how humans are approaching or exceeding these limits.
- Which strategies are used or proposed to reduce pressure on the biosphere.
- How ecological knowledge can guide decision-making for a more sustainable future.