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The impact of population increase

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Birth rate, death rate and population increase


Human populations grow and shrink due the balance between births and deaths. The number of births per 1000 people is called the birth rate, and the number of deaths per 1000 people is the death rate.


The Population Growth Rate

Population growth rate = birth rate – death rate


It’s really not a complicated equation, you must admit. Say the birth rate of Switzerland was 23/1000 and the death rate 28/1000. The population growth rate works out as -5/1000 (23/1000 – 28/1000). As a percentage, this is -0.5% growth. This means that there is a net decrease of 5 people per thousand.


The Demographic Transition Model

This is a model used to classify different populations depending on their birth rate, death rate, overall population size, and the factors behind these numbers. There are 5 different stages:


Stage 1

Birth rate is high due to lack of contraception and low education.
Death rate is also high due to poor sanitation, high infant mortality and starvation.
Therefore, overall population size remains low.


Stage 2

In stage 2, the causes of high death rate ameliorate, but not those behind high birth rate, therefore:
Birth rate is high for all the reasons in stage 1.


Death rate decreases as more food becomes available and healthcare improves.
Overall population size increases steeply.


Stage 3

Birth rate decreases steeply due to contraception availability and family planning.
Death rate decreases more slowly.


Overall population size increases.


Stage 4

Birth rate is low due to more money being directed towards assets, and the lack of need for child labour.


Death rate is low.


Overall population size is high and stable.


Stage 5
Birth rate decreases as children are expensive to have.

Death rate is stable as many older people die, counteracting the effect of advancing healthcare.


Overall population size decreases for the first time.


Non-human populations have other factors affecting their population sizes, including competition. All individual actions between organisms form a web which impacts on all populations in an ecosystem, therefore determining their sizes.


Interspecific competition refers to competition between members of different species for the same resources (food, light, water. etc.). Often when a new species is introduced in a habitat, say the American ladybird to the UK, if the invader species is better adapted, then the host population decreases in size. This may lead to extinction in some cases of the host species.


[Can’t remember the difference between interspecific and intraspecific? Interspecific is like the internet – different things come together.]


Intraspecific competition refers to competition between members of the same species. If a population of apple trees all compete for a source of light, then each apple tree is taking up some light that has now become unavailable to a different apple tree. There are only so many apple trees which that habitat can sustain. The maximum population size sustainable indefinitely in a habitat is called the carrying capacity.


Life expectancy and Survival Rates

Life expectancy graphs refer to the numbers of people who are expected to survive to a certain age.



Here, it can be seen that for 1981 (triangles) 25% conceived survived up to 70 years. In this case, very few people reached 80 years old.


To find out any figure from the graph, just choose a percent first on the y axis, e.g. 50%, then draw a parallel line to the x axis until it meets the curve. Now draw a line from that crossing point down to the x axis (parallel to the y axis) until it crosses it, and read off the corresponding value (for 1900 it’s about 50 years).


Age-Population Pyramids

These are special graphs which represent the numbers of males and females in different age brackets. Any significant sex differences can be clearly seen at each age range, as well as the life expectancy of the population, and the proportions of younger to older people.



You can see above that, with time, the proportion of children in Japan (below 15 years old) decreased from 35.4% to 13.5%. From this data it can be projected (predicted based on past trends) that by 2050 this percentage will drop further to 8.6%.


It can also be seen that the percentage of people aged 65+ increased from 4.9% to 21.5% between 1950 – 2007.


Also, in 2007 there can be seen significant numbers of people aged 90+ appearing, of which most correspond to females.


Life expectancy also rose very significantly, with many more people surviving to an older age in 2007 than in 1950.


Impacts of rising human population

The accelerating growth of human populations has had multiple impacts on ecosystems and biodiversity, both through abiotic factors and biotic factors.


Impacts on abiotic factors include climate change, soil and water quality, while impacts on biotic factors cover changes in biodiversity.


Human industrial activity has contributed large amounts of chemicals, notably carbon dioxide (from combustion activity), to the Earth’s atmosphere that is changing the climate in many areas with varying outcomes and intensity, from an overall average increase in temperature.



Aside from CO2, methane is also a greenhouse gas – that is, it has the potential to increase the Earth’s average temperature. Greenhouse gases are responsible for the Earth being about 33 degrees Celsius warmer than it would be without them.



The issue arises when the otherwise slow, natural development of global weather patterns is significantly sped up by the burning of fossil fuels. The receding of the North Pole ice (from the yellow line):



A seemingly small increase of several degrees Celsius can have vast effects on the Earth’s crop plants, insect pests and wild plants and animals.


For example, the life cycle of many insect pests is tightly regulated by temperature. A very finely tuned heating up or cooling down triggers development and reproduction. The result of warming is a faster life cycle which means that instead of one generation arising yearly, there might be two or three generations arising yearly instead. This poses problems for the protection of crop plants.


Another example is the redistribution of wild animals. Changes in temperature cause migrations towards the poles of the Earth, and increased desertification at the equator. Pollen in North America has been shown to become increasingly allergenic:



The susceptibility of various parts of the world to be desertificated has also been projected:



In terms of soil, the industrial past has left pollutants behind, notably heavy metals and mineral oil (in Europe). Water quality has been contaminated in areas of industry presence. Decreasing soil and water health and quality pose risks to life in ecosystems, humans included.



Heavy metals, for example, become contaminants from industries as diverse as waste incineration, ammunition, thermometers, glass and agrochemicals. Rising human populations that consume the same things as before would only lead to an increase in these industries and the associated pollution.



Through the water cycle, contaminants can spread far from their origin. Even the trivial act of using road salt to deal with ice and snow in winter can potentially contaminate the environment, due to various toxic chemicals added to the salt, such as the anti-caking agent ferrocyanide, and calcium, iron, lead, etc.


Similarly massive impacts have been recorded in terms of biotic factors, notably biodiversity. Human activity has diminished many species of plants and animals, and in turn, climate change is shifting ecosystems so that some species go extinct, while others may actually increase. Species such as crop pests can therefore cause issues. These indirect effect on biodiversity are on top of the very direct effects of displacing species for trade.


CITES is the Convention on International Trade in Endangered Species of Wild Fauna and Flora, or the Washington Convention. It is decades old now, and has been signed by almost the whole world. Its purpose is to ensure that trading plants and animals does not result in their extinction from their original habitat. To this end, it confers different levels of protection to tens of thousands of species.



These are only the recorded transactions, and they approach one million. Traders must take part in a licensing system, and failure to respect the restrictions on specific species e.g. elephants for ivory, can result in various sanctions. Biodiversity is a key consideration in CITES. Since its implementation, it has succeeded in allowing some elephant populations to recover in the wild after banning the trade of ivory.

Issues of economy in certain places like Japan, where bluefin tuna constitutes a major component in it animal trade, can interfere with the restrictions that CITES votes to implement. Politicians can be sent in large delegations to argue for economic points such as wealth, or even the opposite, poverty, to influence the conservation efforts set by the CITES community. Rules are implemented on a two thirds majority basis.


Some species have had success through CITES, such as reptile, amphibian (sold as pets on the internet) and tigers, while others such as the Atlantic bluefin tuna haven’t, due to governments voting against conservation measures at CITES meetings (which take place every 3 years in different cities).


Importance of species diversity


Species diversity is the diversity of species in a community. Put simply, how many different species are there in a community? 5 or 5,000? Which has the higher diversity? Not rocket science I hope.


^That’s some rocket science, I don’t really know what it is, but I don’t wish to find out, and neither do you. Just a little motivator to not complain about biology.


Now for a little talk about deforestation and agriculture. Deforestation is the removal of trees in forests. and agriculture is the cultivation of useful plants to people which are often carefully selected for, and occupy a large area by themselves (like corn).


It’s not hard to figure out the impact both have on species diversity. Deforestation practically removes many, whole trees, and with them goes the shelter and food source of many other organisms. A great reduction in species diversity can be expected as a result.


Agriculture by humans results in a single dominant species which occupies vast land at the expense of others. Humans actively remove other species by the use of pesticides, insecticides and (indirectly) fertilisers. This, too, will lead to a great decrease in species diversity.


Biodiversity changes geographically, as well as over time.


The importance of species biodiversity is felt in multiple areas including ecology, economy and science. The state of global biodiversity has far-reaching impacts on things like aesthetics, medicine and agriculture.


Aesthetics is the experience of beauty coming from biodiversity. Humans rely on biodiversity in the natural environment for connection and enjoyment, whether it be national parks, botanical gardens, gardening, bird-watching or the role some species play as national symbols and culturally significant plants and animals.


In medicine, basic research relies on species biodiversity. Many key advances rely on the unique properties of different species, such as the green fluorescent protein isolated from jellyfish, penicillin discovered from the Penicillium fungus, studies on house flies (Drosophila melanogaster) thanks to their quick generation turnover, cloning DNA through PCR (polymerase chain reaction) at high temperature thanks to the extreme heat-resistant polymerase sourced from microorganisms, or repurposing a natural defence mechanism against viruses to edit DNA in live organisms with precision through CRISPR-Cas9.


In agriculture, biodiversity underpins the available sources of food that we have. A handful of plant species represent over half of all the food we eat. The practice of monoculture (cultivating a single species on a plot) renders that species vulnerable to changing conditions, and diminishes its genetic diversity. In turn, the vast areas used for monoculture strip away the pre-existing biodiversity of the land.


Simpson’s index of diversity

Species diversity is described as the number of species in a community. The more species, the higher the diversity. What if there are two separate communities like this:


Community #1 has 150 individuals per each of 20 different species (3000 individuals in total)
Community #2 has 10 individuals per each of 19 species, and 2990 individuals of the last species (3000 individuals in total)


It doesn’t take a complex formula to figure out that community #1 is far more diverse compared to community #2, despite them having the same number of species and individuals. The distribution of individuals to species is important in determining a community’s diversity.


The above example is easy enough, but for most purposes a formula is needed. This formula measures the index of diversity a.k.a. Simpson’s index of diversity, which is simply a measure of diversity in a community. By calculating it and obtaining a numerical value, different communities can be easily compared.


Right, here it comes…



No, don’t run away yet! Wait and see how easy it is to work out.

D = Diversity index
N = total number of all organisms
n = total number of organisms of each species
Σ = sum of


Now it’s simply a matter of replacing numbers. Look, I made it all purple so you would enjoy looking at it. Let’s work out the index of diversity for community #1 (from above).


Firstly, we need a value for N. What’s the total number of organisms? 3000. Sorted.
Next, we need a value for N – 1. No calculators! …2999, sorted.
Finally, we need a value for n and n – 1. n = 150, while n – 1 = 149.

Drawing up a table helps:
 species  n n – 1  n(n – 1)
 a 150 149  22350
 b 150 149  22350
 c 150 149  22350
 d 150 149  22350
 e 150 149  22350
 f 150 149  22350
 g 150 149  22350
 h 150 149  22350
 i 150 149  22350
 j 150 149  22350
 k 150 149 22350
 l 150 149 22350
 m 150 149 22350
 n 150 149 22350
 o 150 149 22350
 p 150 149 22350
 q 150 149 22350
 r 150 149 22350
 s 150 149 22350
 t 150 149   22350
 Total  3000  2980  447000
                3000*2999       8,997,000
So, D = —————– =  ————— = 20
                 447000            447000


20 in this case is maximum diversity (there are 20 different species). If the index was 1, then diversity would have been non-existent. An index of 10 would indicate moderate diversity.

Now work out the index of diversity for community #2 using the table above and the walk through as a guide. You should get a pretty low value. I know it’s a bit confusing that the above numbers are identical in all the columns, but if you work out community #2 then the values for 1 species should be different to the other 19.


Most of the time all species will have different values. The working of it is the same though.
Plants are difficult to count in individuals, so the percentage cover in a quadrat is usually used instead.


Food security


Increasing human population leads to concerns over food security. Food security refers to people’s ability to access food of a sufficient quality and quantity.


Food production must increase, but do so in a sustainable way that doesn’t compromise the natural resources it ultimately depends on.



The “pillars” of food security are availability, access, utilisation and stability.


Availability refers to the production, distribution and exchange of food, and includes issues of land ownership, crop selection, livestock management and harvesting.


Access refers to affordability, food preferences and food allocation. Access may be challenged by fluctuations in food prices, with those in poverty being affected the most. Those who can afford higher prices would not suffer from unexpected spikes.


Utilisation is how the metabolism of humans makes the most of the food that is available. Infection can lead to some food being used by intestinal parasites instead, while sanitation determines how much food can be eaten safely. The cultural settings of food consumption can also affect utilisation, while health can determine how well food is metabolised.


Finally, stability refers to the ability to maintain food security over time. Transient shortages caused by droughts or conflicts impact stability, and can make households more susceptible to chronic instability if transient famine occurs repeatedly.


Food system challenges include food safety, food fraud, food crime and consumer trust.


Food safety refers to the contamination status of food e.g. if it causes food poisoning. Food safety procedures must take place from the manufacturing point through to packaging, transport, storage and finally by the consumer in handling, storing and washing food appropriately to keep it safe to eat. For example, fruit and vegetables must be washed to remove any soil particles that may be contaminated with bacteria like E. coli.


Raw chicken, on the other hand, must not be washed prior to cooking due to risk of contamination with Campylobacter.


Other food safety areas include food additives, GMOs and food labelling. Allergies and intolerances are a food safety concern relevant to adequate labelling of foods. Certain food additives are banned in some countries but not others, as their safety is judged differently. For example, recombinant bovine growth hormone (rBGH) is allowed in the United States to increase milk production, but banned in Europe because it causes infections in cows, upping their antibiotic intake, as well as increasing levels of insulin-like growth factor (IGF) which is linked to breast, colon and prostate cancer.


Food fraud refers to any activity by manufacturers and distributors of food that does not abide by local regulations. Food fraud does not typically threaten food safety, and is of a financial nature. Fraud increases profits from food at the expense of sourcing, producing or presenting food and drink in a transparent fashion. For example, food may be presented differently to what it actually is.



Food fraud is also appealing because it is not a high priority for enforcement authorities. The horse meat scandal (where horse meat was found in meat sold as beef) prompted the creation of a specialised network to include food fraud specialists – the EU Food Fraud Network (FFN).


Other than misrepresenting food, food fraud can also take place in the form of overpricing. This can cost consumers money as they are not getting what they are paying for. Additionally, evasion of duties and VAT (value-added tax) result in large amounts of lost contributions.


Food crime can pose serious threats to safety, for example by substituting ingredients in food, or mis-selling food to consumers and tarnishing the reputation of a whole food sector. It can extend to methods of manufacturing food that are illegal or substandard, and selling food under certain health claims or quality standards that turn out to be false.


Instances of food crime can be reported to the Food Standards Agency in the UK.


Consumer trust refers to the attitude and expectation consumers have regarding their food. Incidents of food fraud and poor food safety break consumer trust, resulting in a drop in sales for a specific product, brand or whole food type e.g. beef or rocket.


Globally, the United Nations Food and Agriculture Organisation (FAO) is tasked with lifting the standards of food security through helping to eliminate hunger, malnutrition and insecurity; making food sources like farms and fisheries more productive and sustainable; reducing rural poverty; enabling inclusive and efficient food systems; and increasing the resilience of livelihoods to disasters and threats.


To achieve these goals, the FAO operates through its prevention arm and a response arm, together making up the Food Chain Crisis Management Network (FCC).


Prevention and early warning are accomplished via the Emergency Response System (EMPRES). For example, EMPRES has helped establish National Locust Control Units in Chad, Mali and Niger (and others in the Western Region of Africa). Locust infestations represent pests that threaten crops.



Response is accomplished via the FCC operational arm which can provide rapid-, medium- and longer-term responses. For example, FAO data is used to construct live world maps of emerging threats. These include the aforementioned locusts, diseases such as Lumpy Skin Disease in cows, and other pests like tomato leaf miner.





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