Fundamentals
| Term | Definition |
|---|---|
| Species population | All individuals of a species. |
| Metapopulation | A set of spatially disjunct populations, among which there is some immigration. |
| Population | A group of conspecific individuals that is demographically, genetically, or spatially disjunct from other groups of individuals. |
| Aggregation | A spatially clustered group of individuals. |
| Deme | A group of individuals more genetically similar to each other than to other individuals, usually with some degree of spatial isolation as well. |
| Local population | A group of individuals within an investigator-delimited area smaller than the geographic range of the species and often within a population (as defined above). A local population could be a disjunct population as well. |
| Subpopulation | An arbitrary spatially delimited subset of individuals from within a population (as defined above). |
The first laws of population ecology is the Thomas Malthus' exponential law of population growth...
A population will grow (or decline) exponentially as long as the environment experienced by all individuals in the population remains constant.
This principle in population ecology provides the basis for formulating predictive theories and tests that follow.
Simplified population models usually start with four key variables including death, birth, immigration, and emigration. Mathematical models used to calculate changes in population demographics and evolution hold the assumption (or null hypothesis) of no external influence. Models can be more mathematically complex where "...several competing hypotheses are simultaneously confronted with the data." For example, in a closed system where immigration and emigration does not take place, the per capita rates of change in a population can be described as:
where N is the total number of individuals in the population, B is the number of births, D is the number of deaths, b and d are the per capita rates of birth and death respectively, and r is the per capita rate of population change. This formula can be read as the rate of change in the population (dN/dT) is equal to births minus deaths (B - D).
Using these techniques, Malthus' population principle of growth was later transformed into a mathematical model known as the logistic equation:
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). From these basic mathematical principles the discipline of population ecology expands into a field of investigation that queries the demographics of real populations and tests these results against the statistical models. The field of population ecology often uses data on life history and matrix algebra to develop projection matrices on fecundity and survivorship. This information is used for managing wildlife stocks and setting harvest quotas
Read more about this topic: Population Ecology