Population patterns may be described in two ways: in terms of its distribution (the area inhabited) and its abundance (the number of individuals in an area).
We can assess and measure distribution and abundance in a variety of ways, using standard survey and sampling methods such as transects and capture and release.
The law of mortality describes mathematically how populations change over time, while telling us very little about the various fates of the individuals.
Reduced mortality increases the population growth rate and changes population age structures, threatening economic problems if there are too many old people.
There are upper and lower limits to a viable and sustainable population density for any organism. Too low, they do not find mates, too high, they starve,
Human populations are dangerously high, or soon will be, mainly because infant mortality levels influence national birth rates more than other numbers.
There are many ways of controlling human population growth, but education of girls is one of the most effective ways of lowering future birth rates.
Population patterns and trends vary in different parts of the world where conditions and assumptions about child mortality and care of the elderly vary.
In 1662 John Graunt published his Observations on the Bills of Mortality of the City of London, establishing the art of the actuary and setting standards.
In 1679, the carrying capacity of Earth was estimated by Anton van Leeuwenhoek to be 13.385 billion people, based on what he knew of Dutch population densities.
In 1771, Richard Price created a life expectancy table based on the people on the parish register of All Souls Church, Northampton, the first such.
The poem The Deserted Village by Oliver Goldsmith was published in 1770, and pointed to the population movements of rural people to industrial towns.
In 1798, Thomas Malthus published his An Essay on the Principle of Population, arguing that in the end, population growth would outstrip resource growth.
In 1801, the first British census provided hard data to show that there were massive population shifts going on, as people flocked to the industrial cities.
In 1824, John Stuart Mill was arrested for distributing birth control literature to poor people in London. Birth control was seen then as a need for the poor.
In any predator-prey relationships involving mammals, there will be a long-term balance in the numbers, even as there are significant swings from year to year.
In predator-prey relationships involving mammals, the long-term population swings are usually generated by external effects involving resources or climate.
Evolution operates on populations when the gene frequencies change in an isolated population because the individuals with those genes have more offspring.
Only populations are able to evolve, and they can only do so when they are isolated in some way from breeding with the population that they came from.
Populations can be in the same place and still be isolated from one another by behaviours such as different mating seasons, mating displays or calls.
Populations can be isolated by geographical barriers caused by rising sea levels, glaciers, new lakes or deserts, or by one population being on an island.
When a cline exists, anything that causes a break in the flow of genes back and forth along the cline isolates the populations at both ends of the cline.