Articles

Density dependent factors


The so-called density-dependent factors are those that prevent excessive population growth due to the large number of individuals in a given population: disputes over space, food, sexual partner eventually lead to decreased reproductive rate and increased mortality.

O predatism it's the parasitism These are two other density-dependent factors as predators and parasites find it easier to spread among individuals in a large population.

The human species and the limiting capacity

Population growth of the human species has occurred explosively in recent centuries. About 500 million people inhabited the earth in 1650. Within two centuries, the number of inhabitants reached 1 billion. Between 1850 and 1930, it was already 2 billion, and in 1975 4 billion people lived on our planet. The doubling time has decreased and today we surpass 7 billion people. Each year, 93 million people are added.

This increase in human population size has a lot to do with the cultural evolution of our species and our survival habits.

The human is no longer hunter-gatherer About 10,000 years ago, it abandoned nomadism and settled in definite locations on Earth, forming groups involved in the creation of plants and animals of food interest. The birth rate has risen, and in times of war and plague, human population growth has become a reality.
Little by little, however, the risks of excessive population growth are being assessed. Increasing pollution, global warming, ozone depletion, acid rain and other problems are evidence of the planet's weathering. At the Cairo Conference on Population and Development held in September 1994, more than 180 UN-linked countries tried to reach consensus on a policy to prevent the explosion of the human population. Differences in birth control methods have hitherto prevented the adoption of globalizing solutions, although in some countries serious measures are already underway to control the excessive population growth of our species.

Representative Epidemic and Endemic Curves

Epidemic is the situation in which there is an exaggerated increase in the number of cases of a disease in a certain population at a given time. In general, it is caused by viruses or bacteria that cause disease outbreaks in a particular region. Influenza, dengue and cholera are diseases that usually have epidemic character.

Endemic is the situation in which a disease affects a constant number of individuals in a population over time.
It is characteristic of diseases caused by worms (schistosomiasis, teniasis, ascariasis) and protozoa (Chagas diseases, malaria etc.). Depending on the disease, the affected population and the area considered, an epidemic for a particular country may be epidemic for, for example, a particular municipality in that country.

Pandemic is a situation in which an epidemic occurs simultaneously in various places on the planet. This is the case of AIDS, for example.


Example of epidemic curve