10_Population_Ecology (3)

# 10_Population_Ecology (3) - BI SC 002 LECTURE 9POPULATION...

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BI SC 002 LECTURE 9—POPULATION ECOLOGY Draft: December 1, 2010 Today we begin the third major topic of our course, ecology. Ecology is the study of how organisms interact with each other and their environment. Organisms can interact as populations —groups of organisms of the same species living in the same place at the same time. They can interact as communities —all of the organisms of every species living in the same place at the same time. We can also study the ecology of an ecosystem —all of the organisms plus those non-living physical factors that have an effect on the environment. In this lecture we will focus on population ecology. Two of the most important factors playing into how a population interacts are population size and population density . Population size is the number of individuals in a population, while density is the number of individuals per unit area. Also, the population dispersion , or scatter of the individuals plays into interaction of a population. Individuals may be dispersed in clumps, where several organisms are centered in one area while other areas have no organisms. This may be due to an uneven distribution of resources (more individuals will live in areas with more resources) or social aspects of the population (think prides of lions). Individuals may be dispersed uniformly, where there is even space between each member of the population. This may be due to competition for resources driving an individual to a specific area. Or, organisms may be dispersed completely randomly . . . but, this is extremely rare in nature. Probably the biggest characteristic we look at when studying populations is the ability for the population to grow. Population growth is defined as the capability for a population to increase in number. On the most basic level, a population may grow exponentially . We define the actual rate of population growth by this equation: r = (b – d) + (i – e) where r is the rate of growth, b is the birth rate, d is the death rate, i is the immigration rate (number of individuals entering the population), and e is the emigration rate (number of individuals leaving the population). Even if this rate remains constant, the increase in number of individuals accelerates rapidly as the population grows. This is because the growth rate of the population is defined by this differential

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