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Density-dependent: Affect a population more or less as the population is bigger. Examples: [1] A bigger population may be more vulnerable to diseases and parasites. A bigger population may have more intraspecific competition, while a smaller population may have more interspecific competition.
Ecologists have been unable to successfully explain regular population cycles for many decades; delayed density dependence may hold the answer. [2] Here populations are allowed to increase above their normal capacity because there is a time lag until negative feedback mechanisms bring the population back down.
When a cell population reaches a certain density, the amount of required growth factors and nutrients available to each cell becomes insufficient to allow continued cell growth. [citation needed] This is also true for other organisms because an increased density means an increase in intraspecific competition. Greater competition means an ...
Thus r is the maximum theoretical rate of increase of a population per individual – that is, the maximum population growth rate. The concept is commonly used in insect population ecology or management to determine how environmental factors affect the rate at which pest populations increase. See also exponential population growth and logistic ...
Based on factors of dispersal, disturbance, resources limiting climate, and other species distribution, predictions of species distribution can create a bio-climate range, or bio-climate envelope. The envelope can range from a local to a global scale or from a density independence to dependence.
This is a graph of population change utilizing the logistic curve model. When the population is above the carrying capacity it decreases, and when it is below the carrying capacity it increases. When the Verhulst model is plotted into a graph, the population change over time takes the form of a sigmoid curve, reaching its highest level at K.
The most well known example of creatures which have a population cycle is the lemming. [3] The biologist Charles Sutherland Elton first identified in 1924 that the lemming had regular cycles of population growth and decline. When their population outgrows the resources of their habitat, lemmings migrate, although contrary to popular myth, they ...
In Africa, future population growth amplifies risks from sea level rise. Some 54.2 million people lived in the highly exposed low elevation coastal zones (LECZ) around 2000. This number will effectively double to around 110 million people by 2030. By 2060 it will be around 185 to 230 million people, depending on the extent of population growth.