Environmental Systems and Societies SL - Comprehensive Study Notes

SYSTEMS AND MODELS

A systems approach simplifies complex interactions into models for a more holistic overview.

1.1 Components of systems

Storages: Stores of matter or energy (e.g., boxes representing size).
Flows: Transfers or transformations between storages (arrows indicating direction and size).
Inputs: Flows coming into a system.
Outputs: Flows going out of a system.
Boundaries: Dividing line between systems.

1.2 Types of systems

Open system: Energy and matter flow in and out (most systems).
Closed system: Only energy flows in and out (e.g., the entire planet).
Isolated system: Nothing flows in or out (hypothetical, e.g., the entire universe).

1.3 Energy within systems

Laws of Thermodynamics Govern Energy Flows
- 1st Law (Conservation of Energy): Energy can be transformed but not created or destroyed.
- 2nd Law (Entropy): Disorder in a system increases over time; energy dissipates to lower levels (decreasing available energy along a food chain).
Equilibrium: Systems tend to return to a stable equilibrium after disturbance.
- Steady-State Equilibrium: Open system with no long-term changes but possible short-term oscillations.
Feedback Loops
- Negative Feedback Loop: Stabilizes the system by counteracting change.
- Positive Feedback Loop: Amplifies change, destabilizing the system until a new equilibrium or tipping point is reached.
Tipping Point: Minimum change destabilizing a system, leading to a new equilibrium.
Resilient System: Maintains stability, often with larger, diverse storages.
Humans can reduce stability by reducing storage size and diversity.
Time delays in feedback loops make identifying changes and predicting tipping points difficult.

SYSTEMS IN THE NATURAL WORLD

Earth can be modeled as a system of systems, divided into biomes containing ecosystems, which contain communities of interacting species.

2.1 Flows of energy and matter

2.1.1 Solar (energy)

The sun provides Earth with an average of $1400$ watts per square meter.
Energy enters as short-wave radiation and is re-radiated as long-wave radiation trapped in the atmosphere (greenhouse effect).
Much solar energy is unavailable to ecosystems, being absorbed by inorganic matter or reflected.
Pathways of Radiation:
- Involve losses through reflection and absorption.
- Examples of energy distribution (values in W/m2):
  - Incoming solar energy: $342$
  - Reflected solar energy: $107$
  - Absorbed by atmosphere: $67$
  - Absorbed by surface: $168$
  - Energy emitted by the surface: $390$
  - Back radiation $350$
Plants convert only $0.06\%$ of solar energy into usable chemical energy via photosynthesis.
Energy is lost as heat (re-radiated) at each trophic level.
Ecological Efficiency: (energy used for new biomass / energy supplied), averages $10\%$ . All energy eventually becomes heat.
Solar energy distribution is uneven due to varying angles towards the sun at different latitudes.
Excess energy at the equator moves towards lower energy areas (north and south) via air and water vapor, causing global winds and weather.
Tricellular Model: Represents main air movement (Hadley, Ferrel, and Polar cells); actual movement is complex due to jet streams and the Coriolis effect.

2.1.2 Carbon cycle (matter)

Flows: Consumption (feeding), death, decomposition, $CO_2$ dissolving in water.
Transfers: Photosynthesis (carbon fixation), respiration, combustion, fossilization.
Storages:
- Organic: Organisms, forests.
- Inorganic: Atmosphere, soil, fossil fuels, oceans.

2.1.3 Nitrogen cycle (matter)

Flows: Absorption, consumption (feeding), death, decomposition.
Transfers: Nitrogen fixation (bacteria, lightning), denitrification (bacteria in water-logged soils), assimilation.
Storages:
- Organic: Organisms.
- Inorganic: Atmosphere, soil, fossil fuels, water bodies.
Human activities impact these cycles through burning fossil fuels, deforestation, urbanization, and agriculture.

2.2 Biomes

Biomes are defined by climatic conditions: insolation, precipitation, and temperature.
Five major classes: Forest, grassland, tundra, desert, and aquatic, with subclasses.
Arranged in bands across the Earth due to solar energy and atmospheric circulation, complicated by altitude, ocean currents, and winds.
Examples Include:
- Tropical Forest
- Temperate Deciduous Forest
- Coniferous Forest (Boreal)
- Savanna (Tropical Grassland)
- Temperate Grassland
- Chaparral (Mediterranean)
- Tundra (arctic, alpine)
- Desert (hot, cold)
- Aquatic: freshwater (swamps, lakes, ponds, streams, rivers, bogs), marine (rock shore, mud flats, coral reef, mangrove swamp, continental shelf, deep ocean).

Comparison of biomes

Biome	Area (10^6 km^2)	Solar radiation (W/m^2 year)	Annual precipitation (mm)	Net Primary Productivity (g/m^2 year)	Total plant biomass (million tonnes)	Total animal biomass (million tonnes)	Mean biomass (kg/m^2)	Location and climate	Structure
Tropical rainforests	17	175	2000–5000	2200 (40% of terrestrial ecosystems)	765000	330	45	Within 25° north and south of the equator. Warm and wet with little seasonal variation.	Large species diversity in many niches. Tall emergent trees, canopy, understory of smaller trees, shrub layer. Nutrients are predominantly in the top-soil.
Temperate forests	12	125 (greater seasonal variation)	600–2500	1200	385000	160	32.5	Between 40°–60° north and south of the equator. Mild climate.	Deciduous forests, often dominated by one species of tree. Below the trees is either a shrub layer or forest floor. Rich soils fed by the rapid breaking down of leaf litter.
Boreal forests (Taiga)	17	200-750	300–500	800	240000	57	20
Tropical grasslands	15	225	500–1300	900	60000	220	4	Mostly located in Africa (below Sahara), Brazil and northern Australia. Warm with seasonal rainfall and fires.	Ample vegetation supports the largest terrestrial mammals (elephants, giraffes) and large herds of migrating herbivores (wildebeest, zebra). These intern support large predators (lions, cheetahs).
Temperate grasslands	9	150	250–1000	600	14000	60	1.6	In centers of continents, between 40°–60°	Large range of grasses supporting large numbers of herbivore and so carnivores. Food webs and ecosystems are simple.
Arctic tundra	8	90 (high variation)	<250	140	5000	3.5	0.6	Just south of the arctic ice cap. Alpine on high mountain tops. Cold with high winds.	Permafrost prevents the growth of vegetation in the winter. In summer Low growing grasses, shrubs and mosses support a variety of small hibernating mammals.
Desert	24	up to 300	<250	90	500	0.02	0.02	30° north and south of the equator.	Supports a small number of well adapted plant and animal (mainly reptile) species. Water storage and collection are prime features.
Deep oceans	352	None below 1000 m	n/a	20–300	1000000+	800–2000	Very low	65% of Earth’s surface. Averaging 3.5 miles deep	0 m–200 m: phytoplankton, cyanobacteria and algae photosynthesis the available sunlight, supporting a range of zooplankton, fish and invertebrates. 200 m–1000 m: Larger generally carnivorous fish adapted to lower levels of light and higher pressures. 1000–bottom: Animals adapted to zero light and high pressure. Bottom: Slow moving scavengers, survive on dead organic matter from above. Hydrothermal vents: volcanic heat and sulphur support a wide range of organisms.
Coral reefs	0.28	ideal water temperature $26 °C–27 °C$	n/a	2000	0.3			Shallow, warm equatorial waters	“Rainforests of the ocean” – complex structure with high species number and diversity. Polyps create the skeleton of the reef. This provides a good holding for many sea plants.

2.3 Ecosystems

Ecosystem: A community and its physical environment, linked by energy and matter flows.
Community: A group of populations interacting in a common habitat.
Ecosystem Types:
- Marine: Sea, estuaries, salt marshes, mangroves (high salt concentration).
- Freshwater: Rivers, lakes, wetlands.
- Terrestrial: Land-based ecosystems.

2.3.1 Zonation

Zonation: Clear change in ecosystems along an environmental gradient.
Differences in temperature, precipitation, solar insolation, and soil. *Examples:
- Latitudinal
- Vertical
- Intertidal

2.3.2 Succession

Succession: Change of an ecosystem over time.
- Primary Succession: New rock (lithosere), dry soils (xerosere), or drying river deltas (hydrosere).
- Secondary Succession: Community destroyed by fire, flood, or human activity.
Sub-climax Community: Succession arrested by limiting factors.
Plagioclimax: Succession stopped deliberately by humans (e.g., harvesting crops, deforestation, grazing, burning).

r- and K- strategist species

r-strategists:
- Examples: rabbits, weeds, bacteria
- Short lifespan with high mortality in early life
- Rapid growth and early maturity
- Many small offspring
- Little parental care or protection
- Highly adaptable
- Can colonize new habitats quickly and make use of short-lived resources
K- strategist
- Examples: elephants, people, whales
- Long lifespan with mortality in later stages
- Slow growth and late maturity
- Fewer large offspring
- High parental care or protection
- Specialists
- Enables them to survive in long-term climax communities
- Time Percentage of organisms surviving
  - Type I (humans)
  - Type II (songbirds)
  - Type III (frogs)

2.4 Species

2.4.1 Definitions

Species: Organisms sharing characteristics and interbreeding to produce fertile offspring.
Habitat: Environment where a species normally lives.
Population: Group of the same species in the same area at the same time, capable of interbreeding.
Community: Group of populations in the same area at the same time.
Abiotic Factors: Non-living, physical factors influencing organisms (e.g., temperature, sunlight).
Biotic Factors: Interactions between organisms (e.g., predation, herbivory).
Niche: Abiotic and biotic conditions and resources to which an organism responds.
Fundamental Niche: Full range of conditions and resources where a species could survive.
Realized Niche: Actual conditions and resources where a species exists due to biotic interactions.
- Predation
- Herbivory
- Parasitism
- Mutualism
- Disease
- Competition

2.4.2 Changes in species population

Interactions should be understood in terms of the influences each species has on the population dynamics of others, and upon the carrying capacity of the others’ environment.
S and J population curves describe a generalized response of populations to a particular set of conditions (abiotic and biotic factors). Any system has a carrying capacity for a given species. Limiting factors will slow population growth as it approaches the carrying capacity of the system.

S curve

*S-curves start with exponential growth. No limiting factors affect the growth at first. However, above a certain population size, the growth rate slows down gradually, finally resulting in a population of constant size.
* Lag phase – population numbers are low and so birth rates are low.
* Exponential growth phase – population grows at an increasingly rapid rate unrestricted by limiting factors.
* Transitional phase – population growth slows down considerably as limiting factors are reached.
* Stationary phase – population growth stabilizes and then population fluctuates around a level that represents the carrying capacity.

J-curve

*J-curves show exponential growth in a population past the carrying capacity. These are followed by sudden population collapses known as diebacks.
* Exponential growth – population grows at an increasingly rapid rate unrestricted by limiting factors.
* Overshoot – population grows past its carrying capacity.
* Dieback – population suddenly collapses usually due to a lack of food. The population declines below its original carrying capacity as the limiting factor is depleted.
* Renewed growth – growth starts again once the depleted factor has recovered.

2.4.3 Trophic levels

The position that an organism occupies in a food chain
- Primary producers.
- Primary consumers.
- Secondary consumers.
- Tertiary consumers.
Decomposers.
*Detritivores.
The relationships between these species can been shown in food chains and food webs, where arrows indicate the flow of energy (or more bluntly who eats who). As mentioned in the previous chapter energy is passed up the food chain with a large proportion lost as heat, due to entropy. Other things are also passed up the food chain.
Bioaccumulation: Persistent pollutants build up in an organism.
Biomagnification: Pollutant concentration increases up the food chain.
DDT Case Study:
- Insecticide used in agriculture and malaria eradication.
- Led to aquatic environment contamination and food chain impacts.
- Caused thinning of eggshells in some bird species.

*Photosynthesis

carbon dioxide + water + energy (from the sun) = glucose + oxygen
Respiration

*glucose + oxygen = carbon dioxide + water + energy

2.5 Biodiversity within systems

Biodiversity: Variability in a community, ecosystem, or biome.
*
It can be defined as the combination of:
Habitat Diversity.
Species Diversity.
Genetic Diversity.
Greater genetic diversity improves resilience.
*
Natural changes in biodiversity

Natural Selection

Four points:
- Variation - genetic diversity within a population.
- Fitness - some individuals are fitter than others.
- Reproduction - fitter individuals are more successful at reproduction.
- Inheritance - offspring of fitter individuals inherit the genes that give that advantage, and so these genes will remain in the gene pool.

Speciation

The formation of new species when populations of a species become isolated and evolve differently from other populations

INVESTIGATING ECOSYSTEMS (EXPERIMENTAL METHODS)

3.1 General data collection rules

Ecosystem must be named and located.
Sampling and extrapolation must be carried out, due to their large and complex nature.
Measurements should be repeated to increase reliability of data. With almost all the following techniques, there are limitations. A key skill when planning experiments is to understand the limitations of your experiment and account for it.

3.2 Measuring abiotic factors

Experimental tools are used to quantify the non living factors in a ecosystem, measuring at numerous points/times to show:
- Change along an environmental gradient
- Change over time through succession
- Change before and after a human impact

3.3 Measuring biotic factors

Diversity and species abundance are common measurements taken within an ecosystem. Because it is unfeasible to measure an entire ecosystem, we take samples and extrapolate results. Two common sampling methods are point (quadrat) and line/belt transects.
*Sampling can be:
- Continuous – where everything is measured: the entire line transect of the entire area.
- Interrupted (transect) – points at regular intervals are measured.
- Random – points are determined by random. A good practice is to draw a grid (at the size of your quadrat) over an area, giving a number to each square. A list of random numbers can then be generated by a computer or using a table. These should then be sampled.
- Stratified random – where an area has two or more distinct areas, each area should be treated separately using the random method above.
- Systematic – points/transects are placed at a set distant. Often the first is place randomly and then the rest by a systematic method.

3.4 Collecting organisms

Non motile organisms (non or slow moving), should be counted using quadrats. The size of the quadrat should be determined by the size of the organisms being sampled. We can chose to count actual numbers, percentage cover ( $\%$ of the quadrat in which the organism—usually a plant—occurs), or percentage frequency ( $\%$ of squares in a quadrant in which the organism occurs)
Traps should be set for motile animals.
- Traps include:
  - pitfall traps
  - nets sweep, butterfly, seine, and purse
  - flight interception traps
  - small mammal traps
  - light traps
  - Tullgren funnels
  - Pooters
  - Kick sampling (water)

3.5 Identifying organisms

Methods to do this include:
- Keys.
- Comparison to herbarium or specimen collections in museums.
- Technologies such as DNA profiling.

3.6 Species abundance (Lincoln index)

Species abundance refers to the number of organisms in a species relative to its environment. We can count the number of organisms of each species in a sample and then compare their number. For plants, it is often easier to measure the percentage cover. These numbers can then be used to grade a species on the DAFOR/ACFOR scale
- Often direct counts are too great an undertaking, we therefore use an indirect method such as the Lincoln index. This method requires the use of capture-mark-release-recapture with the application of the Lincoln index.
$Lincoln index = \frac{n1 \times n2}{nm}$
$n1$ = the number caught in the first sample
$n2$ = the number caught in the second sample
$nm$ = the number caught in the second sample that were previously marked

3.7 Species diversity (Simpson index)

A function of the number of species and their relative abundance can be compared using the Simpson index. This indication of diversity is only useful when comparing two similar habitats or the same habitat over time.
$D = \frac{N(N − 1)}{Σn(n − 1)}$
Where:
- D = the Simpson diversity index
- N = the total number of organisms of all species found
- n = the number of individuals of a particular species.
The sigma notation, Σ, means the denominator is the sum of n(n − 1) for all the species that make up N. Using this formula, the higher the result, the greater the species diversity. Species richness is the number of species in a community and is a useful comparative measure.

3.8 Productivity and biomass

3.8.1 Definitions

Gross Primary Productivity (GPP): the amount of energy/biomass converted by producers per unit area per unit time. (g/m2 year)
Net Primary Productivity (NPP): the gain (after respiration) by producers in energy/biomass per unit area per unit time. (g/m2 year)
$NPP = GPP − R$
Gross Secondary Productivity (GSP): the total energy/biomass assimilated by consumers through feeding and absorption per unit area per unit time. (g/m2 year)
$GSP = food eaten − fecal loss$
Net Secondary Productivity (NSP): the gain (after respiration) by consumers in energy/biomass per unit area per unit time. (g/m2 year)
$NSP = GSP − R$
Maximum sustainable yields are those that are less than or equivalent to the net primary or net secondary productivity of a system. It is sustainable as the rate implies that the resource will not have a biomass smaller than it original had when harvested.

3.8.2 Pyramids

Pyramids are graphical models of the amount of living material stored at each trophic level of a food chain by either numbers, biomass or productivity for a given area and time. Quantitative data for each trophic level are drawn to scale as horizontal bars arranged symmetrically around a central axis. Generally, due to the loss of energy up the food chain, pyramids have a wide base and become narrower towards the apex. One common issue with pyramids is the difficulty in assigning some species (particularly omnivores) a trophic level.
- Pyramid of numbers record the number of individuals at each trophic level. They are a simple, easy method of giving an overview and are good at comparing changes in population numbers with time or season. However they do not account for size, so a tree is counted the same as an ant. This means pyramids of some ecosystems are inverted.
- Pyramid of biomass represents the biological mass of the standing stock at each trophic level at a particular point in time measured in units such as grams of biomass per square metre (g m−2). Biomass may also be measured in units of energy, such as J m−2. However as organisms must be killed to measure dry mass, samples are made and extrapolated. Therefore results are not exact. Furthermore the measure is susceptible to seasonal differences in fast growing species (e.g., algae)
- Pyramid of productivity Two organisms with the same mass do not have to have the same energy content. Pyramid of productivity shows the flow of energy (starting from solar radiation – optional) through each trophic level of a food chain over a period of time. Productivity is measured in units of flow (g m−2 yr−1 or J m−2 yr−1). Unlike the first two, this type of pyramid allows for comparison between ecosystems but is limited in comparing seasonal differences. It is impossible for these pyramids to be inverted. However, they are also the most complicated to collect data for.

3.9 Estimating biomass and productivity

*To find biomass, it is necessary to capture and kill part of a population and then extrapolate results. The organism should be heated at around $80 °C$ so that only the dry mass is measure. After weighing the dry mass, it can by combusted under controlled conditions to find the amount of energy. Data from these methods can be used to construct ecological pyramids.

To find primary productivity on land, we require 3 similar patches of the vegetation in question. One is harvested and measured as above (Sample 1); another is covered with black plastic to prevent photosynthesis (Sample 2); and the third is left as it is (Sample 3). After a set time period, the other two are harvested and measured. From these three we can determine the GPP, NPP and amount of respiration.
$GPP = \frac{Sample 3 − Sample 1}{time period}$
$Respiration = \frac{Sample 2 − Sample 1}{time period}$
$NPP = \frac{(Sample 3 − Sample 1) − (Sample 2 − Sample 1)}{time period}$
To find primary productivity in water, a light (open to light) and dark (covered from light) bottle technique can be used. The oxygen concentration of the water should be measured. The water should then be split between two bottles with no air present. An equal amount of the aquatic species should be placed in both. The oxygen concentration should be measured after several hours.
$Respiration = \frac{Initial DO{O2} - Dark DO{O2}}{100}$
$Gross\ productivity = \frac{Light DO{O2} - Dark DO{O2}}{100}$
$Net\ productivity = \frac{Light DO{O2} - Initial DO{O2}}{100}$
Secondary productivity can be found by monitoring the weight of an animal, its food and its feces over a set period of time.
$GSP = \frac{Weight\ of\ food − weight\ of\ feces}{time\ period}$
$NSP = \frac{Weight\ of\ animal\ before −Weight\ of\ animal\ after}{time\ period}$
Respiration = GSP−NSP

SYSTEMS IN THE HUMAN WORLD

4.1 Human population dynamics

Demographic tools for quantifying human population include
- Crude Birth Rate (CBR)
- Total Fertility Rate
- Crude Death Rate (CDR)
Natural Increase (NIR)
$Natural\ Increase = Crude\ Birth\ Rate − Crude\ Death\ Rate$
Doubling time (DT)
= 70/NIR (%)
*Global human population has followed a rapid growth curve but there is uncertainty as to how this may be changing. As the human population grows, increased stress is placed on all of Earth’s systems.

4.1.1 Demographic Transition Model

*The Demographic Transition Model tries to combine patterns in birth and death rates to explain and predict current demographics.

Stage 1 High and variable:

birth rates and death rates are high and variable
population growth fluctuates, only some indigenous (primitive) tribes still at this stage
UK at this stage until about 1750

Stage 2 Early expanding:

birth rate remains high but the death rate comes down rapidly
population growth is rapid
Afghanistan and Sudan are at this stage
UK passed through this stage by 1850

Stage 3 Late expanding:

birth rate drops and the death rate remains low
population growth continues but at a slower rate
Brazil and Argentina are at this stage
UK passed through this stage in about 1950

Stage 4 Low and variable:

birth rates and death rates are low and variable
population growth fluctuates
UK and most developed countries are at this stage

Stage 5 Slow declining:

the birth rate is lower than death rate
the population declines
Japan and Sweden are in this stage

4.1.2 Population pyramids

Population pyramids display information about the age and sex structure of a population.

*Concave slopes characterize a high death rate

A wide base indicates a high birth rate
*Bulges in the slope suggest baby booms or high rates of immigration or in- migration (e.g., excess males aged 20–35 years will be economic migrants looking for work; excess elderly, usually female, will inundate retirement resorts)
Narrowing base suggests falling birth rate
*‘Slices’ in the slope indicate emigration or out-migration or age-specific or sex specific deaths (epidemics, war)
Straight or near vertical sides indicate a low death rate

4.1.3 Factors that affect fertility

The general pattern for fertility is that it is lower in MEDCs and higher in LEDCs
- Status of women
- Level of Education
- Wealth
- Urban vs Rural – Relates to factors above. Also children are more of an asset in rural areas.
- Religion – Many religions are pro-natalist, however other factors tend to be stronger. For example Italy has one of the lowest birth rates in Europe despite being strongly catholic.
- Health
  *The cost of children
National and international development policies may also have an impact on human population dynamics.
Governments often attempt to control the population structure in order to avoid some of the disadvantages above. These policies are either pro-natalist (wish to increase birth rate) or anti-natalist (wish to decrease birth rate).

4.1.4 Factors that affect mortality

*There is no clear global pattern for CDR, however in general MEDCs have higher life expectancies, while LEDCs have higher rates of child and infant mortality. Infant deaths are often preventable and can therefore indicate poor water supply, sanitation, healthcare and nutrition.
* Age structure
* Social class and occupation
* Disease and war

4.2 Human resource use

Natural capital is a term used for natural resources that can produce a sustainable natural income of goods or services
Renewable natural capital can be generated and/or replaced as fast as it is being used.
Non-renewable natural capital is either irreplaceable or only replaceable over geological timescales (e.g., fossil fuels, soil, and minerals). The rate at which these resource can be replaced is know as their natural income.
If natural capital is used beyond its natural income, this use becomes unsustainable.

4.3 Pollution

Pollution is the addition of a substance or an agent to an environment by human activity, at a rate greater than that at which it can be rendered harmless by the environment, and which has an appreciable effect on the organisms within it.

*Pollution may be:
*

non-point (coming from many places) or point source
*persistent (pollutant can not be naturally broken down) or biodegradable
*acute (effect is seen shortly after pollutant is present) or chronic (pollutant has an effect over a long time).
*primary (active on emission) or secondary (arising from primary pollutants undergoing physical or chemical change).

The management strategy for combating pollution can be generalised into 3 steps, which should be attempted in descending order.
*Alter human activity to replace the pollutant

Regulate to minimise the release of pollutant
*Recover the pollutant and restore the natural environment

4.3.1 Solid Domestic Waste (SDW)

The most visually emotive type of pollution is the discarded items from our own homes, official termed Solid domestic waste. Although only $5\%$ of all waste it is something we can all control. In the EU we produce 1.4 kg of SDW per person per day.
*Below is a list or waste disposal options from best to worse for the environment

Non-disposal – dispose of less through the following
- Reduce – minimise waste through consuming less/ choosing options with less packaging;
- Reuse – repair items, or give to others so they can be used again in their current form
- Recycle – the raw materials of the item can be used to make new ones.
Composting – Naturally breaking down organic waste with microorganism This can be done in your back garden are in large scale anaerobic biodigesters. These can collect methane to be used as a fuel and the remaining solids make good fertiliser.
Incineration – burning waste. It is possible to generate energy and the ash can be used in road building. However incineration does realise carbon dioxide and sometimes worse chemicals from the burning of plastics and electronics. The extra filtering required makes incineration plants expensive to build.
Landfill – about 40% of our waste goes to big holes in the ground, where unsorted waste is disposed of. They are strategically located so as not to effect human population or leak out into the environment, but are becoming harder to find. Increasingly landfill is being placed in LEDCs where the environmental protection is less strict and so pollute the areas around them. Methane gas can be recovered and used as a power source. It is also possible to eventually build on top of.
Dumping in the sea.

HUMANS AND THEIR EFFECT ON THE BIOTIC WORLD

*Through our increasing numbers, increasing land use and increasing pollution, we are outcompeting the animal world. While global biodiversity is difficult to quantify, it is decreasing rapidly due to human activity.

The human activities that cause species extinctions include:
- Habitat destruction
- Introduction of invasive species
- Pollution
- Over-harvesting and hunting

5.1 The value of biodiversity

*Biodiversity is a resource with natural capital that only becomes clear when we imagine a world without it. The various impacts