Hapter 18 Ecology of Organisms and Populations


Regulation of Population Growth


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Regulation of Population Growth – There are 2 major categories of limiting factors (1) Density-Dependent (2) Density-Independent.
(1) Density-Dependent – these are factors that change in intensity as a function of population density (i.e. the more individuals crammed into a finite space with finite resources, the more severe the density-Dependent Limiting Factors.

Includes Intra-specific Competition – members of the same species and same population compete for limited resources. This is a major factor in population dynamics. As you can imagine, this type of struggle for resource does in fact usually lead to survival of the fittest. Those individuals more capable of acquiring resources will usually survive better and leave more offspring.

(2) Density-Independent – these are limiting factors that are more or less random in that they don’t act as a function of population density. However, these limiting factors can have extreme effects upon population growth. These factors include: floods, drought, lighting, fires, volcanic eruptions, …………………



Human Population Growth – The graph below says it all. Yes, we have escaped (for the time being) the bounds of nature; that is, most limiting factors. With medical advancements and abundant food supplies, the worldwide human population has increased dramatically. Since the industrial revolution, the human population has become less and less dependent on the ability to acquire resources directly from nature – we have become a consumer species with many luxuries. As you will soon learn, over-population of humans is straining all of Earth’s resources.

Remember, population growth is characterized by birth rate minus death rate. So, lower birth rates doesn’t simply lead to lower population growth – if the death rates are also dropping then the population might be growing.



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