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This modelling problem has been called the "atto-fox problem", an atto-fox being a notional 10 −18 of a fox. A density of 10 −18 foxes per square kilometre equates to an average of approximately 5×10 −10 foxes on the surface of the earth, which in practical terms means that foxes are extinct. Hamiltonian structure of the system
where N is the biomass density, a is the maximum per-capita rate of change, and K is the carrying capacity of the population. The formula can be read as follows: the rate of change in the population (dN/dt) is equal to growth (aN) that is limited by carrying capacity (1 − N/K).
Demographic transition. In demography, demographic transition is a phenomenon and theory which refers to the historical shift from high birth rates and high death rates in societies with minimal technology, education (especially of women) and economic development, to low birth rates and low death rates in societies with advanced technology ...
This is a list of countries and dependencies ranked by population density, sorted by inhabitants per square kilometre or square mile. The list includes sovereign states and self-governing dependent territories based upon the ISO standard ISO 3166-1. The list also includes unrecognized but de facto independent countries.
Allee effects are classified by the nature of density dependence at low densities. If the population shrinks for low densities, there is a strong Allee effect. If the proliferation rate is positive and increasing then there is a weak Allee effect. The null hypothesis is that proliferation rates are positive but decreasing at low densities.
In science and engineering, the parts-per notation is a set of pseudo-units to describe small values of miscellaneous dimensionless quantities, e.g. mole fraction or mass fraction. Since these fractions are quantity-per-quantity measures, they are pure numbers with no associated units of measurement. Commonly used are parts-per-million ( ppm ...
Population growth is the increase in the number of people in a population or dispersed group. Actual global human population growth amounts to around 83 million annually, or 1.1% per year. [2] The global population has grown from 1 billion in 1800 to 7.9 billion in 2020. [3] The UN projected population to keep growing, and estimates have put ...
Salinity ( / səˈlɪnɪti /) is the saltiness or amount of salt dissolved in a body of water, called saline water (see also soil salinity ). It is usually measured in g/L or g/kg (grams of salt per liter/kilogram of water; the latter is dimensionless and equal to ‰). Salinity is an important factor in determining many aspects of the ...