Population biology plays an important role in determining how ecosystems work and how we can sustainably harvest wild species like cod or deer.
Given optimum conditions, populations of many organisms can grow exponentially; that is, they can expand at a constant rate per unit of time.
We describe the rapidly rising curve of exponential growth as a J curve.
Without some external limits, exponential growth will cause a population to overshoot the carrying capacity of its environment and then crash catastrophically. "Weedy" organisms, or those at the lower trophic levels of a food web often exhibit extrinsically regulated growth.
Top predators, such as tigers or lions, generally have intrinsic factors that allow them to grow to a stable population size at or near the carrying capacity of their ecosystem.
The most important components of population dynamics are natality, fertility, fecundity, life span, longevity, survivorship, immigration, and emigration.
The most important biological factors in population dynamics generally are competition, predation, and disease, all of which are usually density dependent. The most important abiotic factors in population dynamics generally are weather and climate, both of which are usually density independent.
Island biogeography proposes that small islands or habitat fragments that are far from a colonization source will have little biodiversity, while larger islands or habitats closer to a colonization source will generally have more biodiversity.
Small, isolated populations often are subject to genetic drift, that is, a gradual change in gene frequencies and composition.
A population arising from only a few founder individuals can undergo a demographic bottleneck in which genetic diversity is reduced and reproductive or developmental problems can arise.
A metapopulation is a network of populations having regular or intermittent gene flow between geographically separate units. Source habitats provide surplus individuals to replenish populations in sink habitats where mortality exceeds natality.
