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# Population Dynamics

Population dynamics is an important concept in ecology and refers to the ways in which a population’s composition changes over time, both in the short-term and the long-term. Understanding the composition of a population is imperative to understanding growth trends and thus, a population’s demography.

Population dynamics is not a novel term in ecology. In fact, studying population size goes far back in scientific research. Early research can be dated back to the 1600s. It was in 1662 that John Graunt was fascinated by mortality rates in Britain and made a treatise for the population of Britain to analyse what influenced the age of death.

Furthermore, population dynamics is a rather mathematical branch of ecology because it uses equations to model how a population may evolve over time. There is a simple equation which can be used to model how populations change over time. This equation considers BIDE dynamics:

Nt+1 = Nt + B + I – D – E

Variables:

Nt+1 = population size at some future point

Nt = size of population at an earlier time (t)

B = number of individuals born at time (t)

I = number of individuals who immigrated at time (t)

D = number of individuals who died at time (t)

E = number of individuals who emigrated at time (t)

The above equation is a basic model which can represent an open or closed system. For a closed system, the variables I and E are removed. As well, the variables B, I, D, and E can be expressed as per capita rates. This is done by dividing the rate of one of the ecological processes (say birth rates) by the total number of individuals in the population. It is critical to understand that the variables B, I, D and E do not equal their per capita rates.

Population models become much more complex as you specify the generation type of the population of interest or analyze resource availability in a population. For example, there are geometric growth models, exponential growth models and the logistic growth curve. Evidently, population dynamics is a fundamental and intricate concept in ecology which is critical to learning how to manage and regulate populations.

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