Population Dynamics III
A density dependent factor is a factor that influences population regulation, having a greater impact as population density increases or decreases. A density dependent factor is a factor which can impact populations, yet have greater effects if the density of the population increases or decreases.
There are density-dependent factors of which many populations encounter today. Some density dependent factors include “competition predation, disease, and other biological phenomenon, such as the Allee Effect.”(Di Giuseppe, 2003)
Charles Darwin recognized that the struggle for available resources within a growing population would inherently limit population size, which also relates to his theory of Evolution. He discovered that the growth of a population is dependent on the amount of resources the environment has to offer. 2.
Intraspecific competition is an ecological interaction in which individuals of the same species or population compete for resources within their habitat. Interspecific competition occurs between different types of species, when competing for resources, mostly food. Intraspecific competition is when two individuals of the same species compete for a vital resource, because they compete between one another. In contrast, interspecific competition could be competition between two different species within one ecosystem. For example, plants of the same species can be competing for amounts of sunlight, water, and temperature ranges, (intraspecific competition) whereas a tiger and deer can compete for food resources. This is an example of interspecific competition.
As the population density increases, individuals encounter hardships competing for vital necessities. When population density increases, there is more competition among individuals for resources; therefore the growth rate gradually slows. As competition for food increases, the amount of food per individual decreases. This can have a profound effect on reproductive success of individuals. 3.
Predation is an ecological interaction in which a predator catches, kills, and consumes prey, usually carnivores. Predation is an example of interspecific interaction that occurs when the population density of one species (predators) increases while the population density of another species (prey) decreases.
Some predators prefer one type of prey over another, because the population of the prey is larger, and easier to catch. For example, sharks can hunt several species for food, however faster prey are the ones who are able to hide from sharks, therefore may survive longer. Slower fish that do not have places to hide might be the shark’s food of choice, because it is more efficient and convenient.
Disease acts as a density dependent factor, which limits population size. In overcrowded population, “disease is able to pass from host to host easier because there are more hosts available in close proximity to one another”(Di Giuseppe,2003). The population decreases in size as a result of increased mortality.
The Allee effect is a density-dependent phenomenon that occurs when a population cannot survive or fails to reproduce enough to offset mortality, once the population density is too low. (Drake & Kramer) Some species have a high fecundity, yet have very high death rates. These species may not be able to produce adequate numbers of offspring, which is not enough to counteract death rate, therefore the species could face extinction.
The extinction of the passenger pigeon is a demonstration of the Allee effect, because human interference has caused a declination in their population size. Humans hunted the pigeons for ‘cheap meat’. The population could not regenerate to balance the death rates, because the passenger pigeons only laid one egg per nest and would breed only in large colonies, which made it cease to exist.
The minimum viable population...
Bibliography: PDF Files:
* Unit 3: Population Dynamics - Grade12BiologyCALC - MyBookezz.org. (n.d.). Free eBooks online - MyBookezz.org. Retrieved June 21, 2013, from http://www.mybookezz.org/ebook.php?u=aHR0cHM6Ly9ncmFkZTEyYmlvbG9neWNhbG
* Drake, J., & Kramer, A. (n.d.). Retrieved from http://www.nature.com/scitable/knowledge/library/allee-effects-19699394
* Biomagnification Definition Page. (n.d.).USGS Toxic Substances Hydrology Program. Retrieved June 21, 2013, from
* Giuseppe, M. (2003). Nelson biology 12. Toronto: Nelson Thomson Learning.
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