Ecology: the biology of interaction. 6.02. Demographic explosion

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6.01. The Ecological Crisis of Our Time

D. Shabanov, M. Kravchenko. Ecology: Biology of Interaction Chapter 6. Human Ecology and Conservation

6.03. Demographic transition

6.02. Demographic Explosion Did it surprise you that we named the growth of the human population as the main cause of the current ecological crisis? Firstly, we should consider how this growth occurred. Different sources provide different estimates, but the general trend of human population growth is not in doubt. When our species appeared in Africa, its population could not exceed hundreds of thousands of individuals, and at some points in time, as we have already said, it decreased to a few tens of individuals. Having spread throughout Eurasia, populations of our species reached several million, survived the crisis of the Neolithic revolution, and began to grow steadily (Table 6.2.1). This growth was significantly slowed only during the epidemics of the Black Death in medieval Europe, where a significant part of the entire human population lived at that time. As you can see, this growth was accelerating. It is this avalanche-like acceleration of human population growth that gives grounds to call it a demographic explosion. Table 6.2.1. Growth of the human population (N)

Year

N, млн.

Year

N, млн.

Year

N, млн.

Year

N, млн.

-10000

1900

1600

1973

3928

1997

5905

-5000

1927

2000

1974

4004

1998

5985

-4000

1951

2584

1975

4079

1999

6064

-3000

1952

2631

1976

4155

2000

6143

-2000

1953

2678

1977

4230

2001

6223

-1000

1954

2725

1978

4305

2002

6302

-500

100

1955

2773

1979

4381

2003

6381

-200

150

1956

2822

1980

4458

2004

6461

170

1957

2873

1981

4537

2005

6542

200

190

1958

2926

1982

4617

2006

6624

600

200

1959

2980

1983

4700

2007

6706

700

210

1960

3035

1984

4784

2008

6789

800

220

1961

3092

1985

4871

2009

6873

900

240

1962

3150

1986

4961

2010

6957

1000

275

1963

3211

1987

5053

2011

7041

1100

320

1964

3274

1988

5145

2012

7126

1200

350

1965

3340

1989

5237

2013

7211

1400

360

1966

3408

1990

5327

2014

7295

1500

450

1967

3479

1991

5414

2015

7380

1600

500

1968

3552

1992

5499

2016

7464

1700

610

1969

3626

1993

5582

2017

7548

1760

770

1970

3700

1994

5663

2018

7631

1804

1000

1971

3776

1995

5744

2019

7713

1850

1200

1972

3852

1996

5825

2020

7795

An interesting opportunity to get a glimpse of the human population size is realized on the Worldometers project webpage. Here you can see the number of figures corresponding to the human population (you can scroll the page sideways and down) and see how new figures are added to the existing ones. Each of us is one figure on this sheet. The dynamics shown in Table 6.2.1 can be easily visualized on a graph. The result is shown in Fig. 6.2.1. Fig. 6.2.1. Dynamics of human population growth The growth shown in Fig. 6.2.1 differs from exponential growth (Fig. 6.2.2)! The results of modeling human population growth show that its increase is proportional not to the number of individuals, as in the exponential model, but to its square. Doubling the human population corresponds to a fourfold increase in its growth rate! Such growth is called hyperbolic. Population growth according to the hyperbolic model is described by the equation dN/dt = N²/C, where C is a constant (compare this formula with the exponential equation!). Fig. 6.2.2. Linear (A.), exponential (B.), and hyperbolic (V.) growth The paradoxical form of hyperbolic human population growth was reported by Heinz von Foerster, one of the founders of cybernetics, who published (along with his colleagues) an article in 1960 titled "The End of the World: Friday, November 13, 2026". According to the data available to von Foerster, if the human population had continued to grow at the same rate as before, it would have reached infinity on this day! Naturally, this is impossible. Therefore, we should expect some fundamental changes that will stop the growth of the human population. It remained to understand what these changes would be. Heinz von Foerster and his colleagues managed to show that the change in human population (from year 1 AD to 1958) is described with amazing accuracy by a surprisingly simple formula: Nt = C/(t₀ – t), where Nt is the human population at time t, and C and t₀ are constants. The value of t₀ can be interpreted as the moment when the human population reaches infinity. In von Foerster's calculations, it turned out to be 2026.87, which corresponds to November 13, 2026. It turned out that this day was not just the thirteenth of the month, but also a Friday, and also von Foerster's birthday! The denominator of the fraction, the expression t₀ – t, simply means the number of years until the "end of the world." With the substitution of the corresponding coefficients, von Foerster's equation takes the form approximately Nt = 215,000/(2027 – t). After the work of von Foerster and co-authors, their conclusions were repeatedly checked and confirmed. The growth described by this equation continued until the 1970s (and then the human population began to "lag behind" – Fig. 6.2.3). The human population grew fastest in 1968 and 1969 – by 102.09% annually. Currently, the human population is growing by 101.05% per year. Fig. 6.2.3. Annual growth rate of the human population (in % of the previous year's population) As further research has shown, the hyperbolic equation began to "work" with considerable accuracy in describing the human population even several million years before our era – that is, even before the appearance of the species Homo sapiens! Naturally, we do not have exact data on the planet's population for any period of its history. Even now, in the era of comprehensive censuses, data on the Earth's population are quite approximate. For example, the Earth's population size when it was inhabited by Homo erectus has to be determined from indirect data. However, one should not demand absolute accuracy from von Foerster's equation, as from any model. However, it allows for an estimate that agrees well with the available data. The hyperbolic dependence is applicable only to the entire human population as a whole, and not to the population of individual countries. This suggests that the hyperbolic dependence is applicable to the properties of humanity as a single whole. Note the fluctuations in the human population growth curve that occurred during our era (Fig. 6.2.1). As mentioned, the strongest influence on it was the "Black Death" epidemic in Europe; smaller fluctuations were associated with less large-scale disasters: wars and natural anomalies. How did the global human population react to these disasters? To better understand the result obtained from studying historical data, let's consider it with a hypothetical example (Fig. 6.2.4). Fig. 6.2.4. Impact of disasters on hyperbolic growth of the global human population (hypothetical example corresponding to actual data) As already mentioned, hyperbolic growth became characteristic of humanity long before historical times. Long before the demographic explosion, the growth of humanity reflected a mathematical dependence that determined the time when it should be expected. Let's consider how a catastrophe like the "Black Death" (indicated by an arrow in Fig. 6.2.4) could have affected this growth. This catastrophe reduces the human population to a level that was characteristic of it some time ago. If the growth of the human population were determined by its reproductive capacity, this would lead to the demographic explosion occurring at a later time (such a hypothetical curve is shown in Fig. 6.2.4 by a gray dotted line). However, the real human population behaved differently (gray solid line in the graph). Its growth accelerated, and in a short time, it returned to the same trajectory along which it had been developing before the catastrophe. (Dear reader: if you are not surprised, then you have not understood the last thought; reread this paragraph again, realize the paradox described in it, and be surprised!). To understand the result obtained, let's consider how a population growing according to the logistic model reacts to a decrease in its numbers. As you remember (see Fig. 4.15.2), two phases can be distinguished in logistic growth: the r-phase and the K-phase. In the r-phase, the population's reproductive capacity has a greater influence on population growth, while in the K-phase, the amount of available resources is more influential. It can be seen that the population reacts differently to a decrease in numbers at the r- and K-phases (Fig. 6.2.5). Fig. 6.2.5. Impact of disasters on the population size growing according to the logistic model A decrease in population size in the r-phase seems to return the population, growing according to the logistic model, to the past (i.e., to a stage with a smaller population). The response to a decrease in population size is a slowdown in growth (since growth depends primarily on the number of potential parents, and there are fewer of them). In the K-phase, on the contrary, the response to a decrease in population size is an acceleration of growth (since growth depends primarily on the amount of available resources, and their quantity increases when the population decreases). However, even in the K-phase, a decrease in population size leads to a certain "lag" of the population from the initially expected trajectory; the K level will be reached with some delay. How does the reaction of the population shown in Fig. 6.2.5 to an impact at the K-phase differ from the reaction of the global human population shown in Fig. 6.2.4? The global human population returns to the same curve along which it had previously developed. How can this be explained? The logistic model defines the K level; having survived the impact, the population returns to it. The hyperbolic equation also defines an upper limit for the human population, but this limit turns out to be accelerating! It seems that humanity's reproductive capacity has always been in excess and was limited by mortality. However, the maximum population size allowed by mortality due to insufficient resources has been constantly increasing. Due to the lag of the human population behind this growing limit, it quickly caught up with it, i.e., returned to the initial curve of its dynamics. Thus, the hyperbolic dependence describes precisely the change in the carrying capacity of the environment! What is this related to? The fact is that humans, unlike any other animal species and living organisms in general, are capable of rapidly changing their way of life. The current nature of humanity's interaction with the environment fundamentally differs from what was characteristic of it a few centuries ago, and even more so – a few millennia or a few million years ago. This circumstance gives hope for an explanation of hyperbolic growth. Probably (although this problem cannot yet be considered definitively solved), the explanation for the described feature of human population growth is as follows. The more people live on Earth, the more intensive technological progress becomes, the wider the ecological niche of our species becomes, and the greater the available environmental carrying capacity, the faster the human population grows, the more potential inventors appear in it, and the faster technological progress proceeds... "A system of positive feedback arises, which spins up the flywheel of hyperbolic world population growth: technological growth – increase in the ceiling of Earth's carrying capacity – demographic growth – more potential inventors – acceleration of technological growth – accelerated growth of Earth's carrying capacity – even faster demographic growth – accelerated growth in the number of potential inventors – even faster technological growth – further acceleration of Earth's carrying capacity growth, etc." (A.V. Markov, A.V. Korotaev, 2011). We know that no population can grow exponentially for an unlimited time – sooner or later its growth will be replaced by either deceleration or catastrophe. The growth of humanity must also stop. "...throughout almost its entire history, humanity has been in the so-called Malthusian trap: any technological progress, as well as an increase in food production, was nullified by population growth. As soon as harvests increased, fertility immediately increased, and an excess of mouths to feed appeared. After a short period of satiety, human society again found itself on the brink of hunger and poverty. Such periodic crises were very characteristic of agrarian societies. <...> A period has come when population growth has ceased to keep pace with technological growth and has begun to lag behind it occasionally. Thus, humanity has found a way out of the Malthusian trap, although today we can speak of its complete overcoming only in relation to the most developed countries." (A.V. Markov, A.V. Korotaev, 2011). Not only the population size is growing on Earth, but also the standard of living and industry. Later studies showed that if von Foerster and his colleagues had data on the growth of global gross domestic product (GDP) for the period from 1 AD to 1973, they could also calculate the date of the economic "end of the world." However complex it may be to compare the production of dried dates in Ancient Rome and the production of aircraft in the modern world, some comparative assessment of the volumes of this production is possible. GDP is growing even faster than the population – according to a quadratic-hyperbolic dependence. According to the quadratic-hyperbolic model, humanity's GDP was supposed to become infinitely large on Saturday, July 23, 2005. Did you notice anything on that day? This means that the dependencies that determined the growth of the world economy throughout its history have ceased to operate. This happened during the lifetime of a significant portion of the current Earth's population. Note: the "turning point" affected both the economy and population growth, which are now changing with an increasing lag from the models we have described. By the way, according to the meaning of the terms "crisis," "catastrophe," and "collapse," which we discussed at the beginning of the chapter, the crisis has ALREADY turned into a catastrophe – a change in the system's character. Now our task is not to allow the catastrophe to turn into a collapse. Thus, the turning point in human population growth occurred in the 1970s of the 20th century. It was then that humanity began to lag behind the growth rates "assigned" by the hyperbolic growth equation, entering the demographic transition (see section 6.3). It can be roughly stated that until the 1970s, the population grew by 2% annually, and now it is slightly more than 1% (the peak has been overcome). Before humanity's growth began to slow down, food production grew by 2.3% annually, and now it is less than 2%. But the biosphere has to pay a very high price for this growth. With current technologies, a two-percent increase in food production is achieved by a 5% increase in energy consumption, 7% in water consumption, 7% in fertilizer production, and 10% in pesticide production. It is likely that in the 21st century, the population will grow by less than half, while the consumption of resources and energy will increase 5-6 times. However, the main problem of modern humanity is not even this. It lives thanks to the use of fossil fuels, which will inevitably run out. What will happen after the fossil fuels run out, and it becomes impossible to increase the load on ecosystems? One version of the answer to this question suggests that humanity will "come up with something," as it has done before. Unfortunately, there is still no hope that humanity will be able to maintain the necessary environmental qualities through its technologies. The largest experiment of this kind was conducted at the end of the 20th century in Arizona. There, "Biosphere-2" was created ("Biosphere-1" was considered by the organizers of the experiment to be the Earth's biosphere). On an area of 1.3 hectares, an isolated dome with various elements of ecosystems was placed, which were supposed to support the life of 8 volunteer humans. In 1991, the shell of "Biosphere-2" was sealed. After 15 months, the shell's airtightness had to be breached, and the volunteers had to be rescued, as the intensity of photosynthesis and the amount of oxygen in the artificial biosphere fell below critical levels. Of the 25 vertebrate species placed under the dome, 18 became extinct; all insect pollinators died; the "natural" purification of water and air was disrupted. The main conclusion of the experiment was the recognition that we do not know many details of the mechanism that ensures the stable existence of ecosystems. Instead of expanding the carrying capacity of the environment, characteristic of "Biosphere-1," in "Biosphere-2," the carrying capacity of the environment catastrophically decreased.

6.01. The Ecological Crisis of Our Time

D. Shabanov, M. Kravchenko. Ecology: Biology of Interaction Chapter 6. Human Ecology and Conservation

6.03. Demographic transition