Population dynamics has a major impact on economic growth development and on sustainable use of resources. Population dynamics comprises trends and changes in population growth, urbanization, age structures, density, and population migration. Population growth will primarily be driven by growth in developing countries due to high birth rates and a high population of young people. However, this would hamper efforts to alleviate poverty and accelerate economic growth besides outstripping investments in health and education among others. Fertility decline and increased lifespan leads to an increase in the number and proportion of people aged 60 and above in comparison to those under 14. More than half of the global population lives in urban areas and this is expected to increase to 70 percent by 2050. A third of the populace in urban areas lives in slums necessitating the need to invest more in affordable housing and other infrastructure such as transport and energy provision.
A population refers to a group of individuals, members of a single species, living in the same habitat. The population contains individuals of different ages and its density changes over time because of many factors. Population dynamics is the study of why these changes occur, when and how they occur. Population dynamics studies factors such as size, density, dispersion, and age structure. Size deals with the number of individuals while density refers to population size in a certain area at a given period. Population dispersion refers to spatial pattern in habitat while age structure refers to the proportion of individuals in each age group in a population. The change in population size is determined by births, deaths, immigrations, and emigrations. The change is arrived at by adding deaths and emigrations and subtracting the figure thereof from the total of births and immigrations.
Other factors, biotic or abiotic, impact on the population growth by influencing one or more of the variables listed above, that is births, immigration, deaths and immigration. Such factors are referred to as secondary ecological events. They affect the frequency, magnitude, extent, or duration of the primary ecological event. For instance, famine could lead to increased death due to malnutrition leading to population reduction. Improved availability of food due to technological improvements may lead to increased births from a well-fed population and reduced deaths increasing the population (Gauthier, 2007). The secondary ecological factors play the role of regulating the population growth. The secondary factors are ether density-dependent or density-independent factors.
The density-independent factors refer to conditions, often weather or climate-related, that affect all individuals in a population equally, the overall population density notwithstanding. Wildfires, excess precipitation, hurricanes, floods, heat waves, and drought belong to this category. The effect they have on a small population would not be different with a large population in terms of percentages. Density-dependent factors refer to conditions whose effects on a population depend on its size. Examples are predators, parasites and diseases. For instance, parasites and diseases would quickly spread in a densely populated area as compared to a sparsely populated area. A decline in the number of prey would lead a predator to migrate to areas with high population or to concentrate on the most available prey (Sachs, & Sachs, 2004).
When growth conditions are favorable and food is in plenty, a population has the ability to increase from one generation to the other. The populations’ intrinsic growth rate (r) measures the rate of the increase. Geometric population growth occurs when the population increase from one generation to the other is a constant percentage of the total population. Geometric growth refers to exponential growth. Population growth is dependent on population size and the higher the size, the faster the growth. The increase cannot continue indefinitely though. This is due to limitation in resources such as space and food.
As the population increases, it reaches the environmental carrying capacity where the available resources cannot support anymore increase. As the population nears this point, competition becomes more severe, mortality rate increases while birth rate slows down. As a result, the population levels out and stabilize below the environment carrying capacity or briefly go beyond the carrying capacity before crashing forming a pattern of boom and bust. (Macbeth, & Collinson, 2002). Alternatively, the population would oscillate around the carrying capacity. The carrying capacity is the maximum populace a habitat can accommodate over a given period due to environmental resistance. Environmental resistance includes factors such as decreasing oxygen supply, low food supply, diseases, predators, and limited space.
The goal of every species is to produce the maximum number of offspring possible. However, each individual in a population has limited energy to invest in life and reproduction. This results in a trade-off between long life and high reproduction rate. Natural selection has evolved two strategies for species; R-strategy and K-strategy. Organisms in r-strategy spend most of their time in exponential growth (Sachs, & Sachs, 2004).They give birth to the highest number of offspring possible to ensure as many as possible survive due to their short lifespan.
R-strategists are characterized by many small offspring, minimum parental care or none at all and early reproductive age. Most of the offspring in r-strategists die before reaching reproductive age and therefore those that survive has to give birth to the maximum offspring possible. The adults are small and adapted to unstable climatic and environmental conditions (Cohen, 2003).The population size experiences wide fluctuations above and below the carrying capacity. Species in in this category have low ability to compete. Examples include majority of the insects such as houseflies and rodents like rats among others.
In K-strategists, the population grows grow steadily until it approaches the carrying capacity, K. Henceforth, it is fairly stable around the carrying capacity. The lifespan is long, have fewer and larger offspring with high adaptability skills to climate and environmental challenges. They live in a specialized niche and have high ability to compete for resources. Examples are human beings, elephants, rhinos and Kangaroos.
The world human population doubled itself in 2010 over the 1965 population. According to the UN, it is estimated to reach 9.3 billion by 2050 and 10 billion by 2085. Much of the growth is expected to come from poor developing countries with 803 million growth in 2010 and 1.7 billion in 2050 (De Silva, 2012). This is attributable to high birth rates and a relatively high proportion of young people. The growth is also driven by increased lifespan due to improved health provision with global life expectancy rising from below 50 years in the 1950s to about 70 years currently with a projection of 80 years by the turn of the century. Between 1950s and 2010s, the global fertility rate has fallen from 5 children per woman to about 2.5 today. It stands at around 4 in the least developed countries and less than 2 in developed countries.
The growth in population leads to increased demand for food, energy, water, land and other resources straining the environment. As much of the growth is concentrated in poor countries, efforts to alleviate poverty and increase economic growth are undermined. The population growth outstrips investments in health, sanitation, education, and other services. The environment suffers from degradation due to over cultivation, deforestation, and pollution resulting in global warming and climate change.
The decline in fertility and increase in life expectancy mean the number and proportion of the aged people, that is those over 60 years, has increased over the years to 810 million worldwide as of 2014. The number is expected to reach 2 billion by 2050 when those over 60 years would be more than those under 15 years of age (Van Der Gaag, & De Beer, 2014). Developed countries account for much of the population of the aged. The number of people needing support because of age outstrips the number of those expected to assist leading to neglect for the aged. In some places migration and the HIV pandemic has wiped out a whole generation leaving the old people shouldering the burden of bringing up their grandchildren.
The young people aged 15-24 are at an all-time high figure of 1.2 billion people. They form a very important human resource due to their creativity and innovation capacity. Governments should ensure the young people get the necessary education and skills to prepare them for the job market (Van Der Gaag, & De Beer, 2014). Employment opportunities and access to reproductive health services are other services that young people needs.
Urbanization is projected to increase sharply with 70 percent of the world population living in urban areas by 2050. A third of those living in urban areas live in slums and this number is expected to rise due to internal migration and population growth. Urbanization becomes an engine for growth of national economies if it is well planned to promote sustainable cities. This calls for provision of affordable housing and other infrastructure with special emphasis on slum upgrading.
Migration increased by 40 % between 1990 and 2010 reaching an all-time high of 214 million annually as of 2010 (De Silva, 2012). Large-scale migration as is happening from Syria to Europe and from some Balkan countries to Northern Europe can lead to significant consequences to the countries of origin and destination countries alike. Migration leads to labor transfer, remittances to the countries of origin and a reduction of pressure in countries of origin with an increase of the same in host countries. Migrants however face challenges while in transit and also at the host countries.
The world population dynamics would keep changing due to the aging population in developed countries and a young population in developing countries. Developing countries would face the challenge of taking care of the aged as their number increase relative to that of the young. Increase in healthcare spending and pensions is expected. Developing countries face challenges of urban housing, employment provision for the young, reproductive health services and poverty alleviation. As the mortality rates decrease and birth rates stabilizes, the world population would continue growing primarily driven by growth in developing countries. Since natural resources are limited, the growth would exert pressure. Humanity must find innovative and sustainable ways of utilizing natural resources to avoid degradation and exhaustion as a result of overexploitation.