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Population dynamics is the branch of life sciences that studies the size and age composition of populations as dynamic systems, and the biological and environmental processes that drive them (such as birth and death rates, and immigration and emigration). The example scenarios are the aging of the population, the growth of the population or the decline of the population.
Population dynamics have traditionally been the dominant branch of mathematical biology, which has a history of more than 210 years, although more recently the reach of mathematical biology has greatly expanded. The first principle of population dynamics is widely regarded as the exponential law of Malthus, according to Malthus’s growth model. The initial period was dominated by demographic studies such as the work of Benjamin Gompertz and Pierre François Verhulst at the beginning of the 19th century, who refined and adjusted Malthus’s demographic model.
Over the past 30 years, population dynamics have been supplemented by evolutionary game theory, first developed by John Maynard Smith. Under these dynamics, the concepts of evolutionary biology can take a deterministic mathematical form. The dynamics of the population overlap with another active area of research in mathematical biology: mathematical epidemiology, the study of infectious diseases that affect populations. Several viral dissemination models have been proposed and analyzed, and provide important results that can be applied to health policy decisions.
Growth of the human population: a brief history.
The human population has grown rapidly due to the expansion of agriculture and industrial production and lower mortality rates due to improvements in hygiene and medicine.
In 2006, the population of developed countries grew exponentially to 0.1% per year.
Developing countries grew (15 times faster to 1.5% per year.
There are likely to be between 7.2-10.6 billion people on earth by 2050.
97% of growth in developing countries living in acute poverty.

Fig. U.N. projection of the world population based on women with an average of 2.5 (high), 2.0 (medium) or 1.5 (low) children.

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FACTORS THAT AFFECT THE SIZE OF THE HUMAN POPULATION
The population increases due to births and immigration and decreases through deaths and emigration.

Instead of using raw numbers, crude birth rates and crude death rates are used (according to the total number of births or deaths per 1,000 people in a population).

Average crude and birth rates for several groupings of countries in 2006.

Limits of population growth:
No population can increase its size indefinitely.
The intrinsic rate of increase (r) is the rate at which a population would grow if it had unlimited resources.
Loading capacity (K): the maximum population of a given species that a particular habitat can sustain indefinitely without degrading the habitat.
Exponential and logistic demographic growth: curves J and curve in S

FIG; Populations grow rapidly with ample resources, but as resources become limited, their growth rate decreases and stabilizes
Population density and population change: effects of overcrowding
Population density: the number of individuals in a population that is in a particular area or volume.
The density of a population can affect how quickly it can grow or decrease.
eg biotic factors such as disease
Some factors of population control are not affected by population density.
eg Abiotic factors such as weather.
Factors that affect birth rates and fertility rates
Importance of children in the workforce.
Urbanization
Cost of raising and educating children
Availability of private and public pensions.
Religious beliefs, traditions and cultural norms.
Educational and employment opportunities
Infant mortality rate
Average age in marriage
Availability of a reliable contraceptive method
Factors that affect mortality rates
Mortality rates have decreased due to:
Increase in food supplies, better nutrition.
Advances in medicine.
Improved sanitation and personal hygiene.
More secure water supplies.
Urbanization
Urban areas must import most of their food, water, energy, minerals and other resources.
They produce huge amounts of waste that can contaminate air, water and land.
44% of the world’s population lives in urban areas that occupy only 5% of the world’s land and consume 75% of the world’s resources.
Effect of resource abundance on population dynamics
The abundance of resources
Environmental factors such as food, water and space determine how the abundance of the population changes over time. In the presence of unlimited resources, populations grow exponentially. If you plot the number of individuals in a population that grows exponentially over time, you will find a J-shaped curve where the slope becomes steeper. This curve is described by the following equation: N t; = N 0; e rt Where N 0 is the initial number of individuals, N t is the number of individuals in the future, r is the rate of increase, t is the time e it is the base of the natural logarithm (approximately 2.718). The rate of increase (r) is determined by the difference between birth and death rates of the population. In 1999, the US Census Bureau UU He estimated that the rate of increase in population (r) for the world population was 0.0129 (or 1.29 percent) per year. Few natural populations grow at exponential rates for long periods of time because resources typically become limiting when the abundance of the population is very high. Using concepts from the basic biology of the population, biologists have distinguished two strategies for population growth. Some species have characteristics that allow them to grow rapidly when an environment with abundant resources is created (for example, a new clearing in a forest). These species are known as r -selected species and typically breed at an early age and produce many offspring. Other species, called K -selected species, have characteristics that make them suitable for life in environments where there is intense competition for limited resources. These species are often strong competitors, reproduce later in life and produce fewer offspring than the selected r species. The abundance of environmental resources determines the growth rate of the population over time. Effect of variability in environmental conditions on population dynamics A key assumption of logistics The population growth model for environments where resources are limiting is that the environmental conditions are constant. In nature, environmental conditions can vary substantially over time. In such variable environments, the abundance of individuals in a population can also fluctuate over time. Some populations cycle predictably. Populations that fluctuate widely or have low abundance are especially vulnerable to extinction, an event in which the abundance of the population decreases to zero. Extinctions can be local or global. For example, the migratory pigeon, which was once one of the most numerous birds on Earth, became globally extinct in 1914 due to overhunting and habitat loss. Effect of physical and biological factors in the regulation of population dynamics. The abundance of the population is affected by a variety of biological and physical factors. For example, the abundance of a given species (for example, snails) could be controlled by the abundance of organisms that have a negative effect on the species of interest, such as competitors, predators and diseases. Similarly, the abundance of the population could be limited by the abundance of organisms that benefit the species of interest (for example, the algae consumed by the snails). In fact, some organisms require the presence of other species called symbionts with which they live in direct contact. For example, corals use food molecules synthesized by symbiotic zooxanthellae (a type of algae), and zooxanthellae receive nutrients and protection from corals. However, not all populations are regulated by biological factors that involve interactions with other species. Physical factors such as water availability and temperature can control the abundance of the population of some species. What type of factor (biological or physical) has a stronger effect on the dynamics of the population? As one might suspect, the answer depends to a large extent on the population being studied. Some populations are regulated mainly by biological factors, others are controlled by physical factors and most populations are affected by biological and physical factors. Human aspects in natural systems We have used technology to alter much of the rest of nature in ways that threaten the survival of many other species and could reduce the quality of life of our own species. Objectives: to provide universal access to family planning services. Improve health care for infants, children and pregnant women. Promote the development of national population policies. and opportunities of the work. Increase access to education for girls. Increase the participation of men in the responsibility of raising children and family planning. Take measures to eradicate poverty. Reduce and eliminate unsustainable patterns of production and consumption.

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