5.1 HOW POPULATIONS GROW
The three important characteristics of a population are its geographic distribution, density, and growth rate. Geographic distribution is a term that describes the area inhabited by a population. Population density is the number of individuals per unit area. This number can vary greatly depending on the species and its ecosystem. The three factors that can affect population size is the number of births, number of death, and the amount of immigrants or emigrants. If the amount of birth is more than amount of death, then the population will grow. If the amount of death rate is greater than the amount of birth rate, then the population will decrease. If both the birth rate and death rate are equal to each other, the population will stay the same. Immigration is the movement of individuals into an area, this factor can cause a population to grow. Emigration is the movement of individuals out of an area, this factor can cause a population to decrease.
If a population is protected from predators, disease, and have an abundance of resource (such as space and food), the population size will increase greatly. Exponential growth occurs when the individuals in a population reproduce at a constant rate. At first, this increase will start slowly, but over time, it will increase dramatically. Under ideal conditions with unlimited resources , a population will grow exponentially.
Populations cannot grow in size forever, soon it will gradually slow down. As resources become less available, the growth of a population slows or stops. Logistic growth occurs when a population growth slows or stop following a period of exponential growth. A population slows down when the birth rate decrease and death rate increases. It could also happen when there are more emigrants that immigrants. Carrying capacity is the number of individuals that a given environment can support.
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