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Population Dynamics J vs. S shaped growth Principles of Population Growth • What is a population? • A healthy or stable population will grow and die at a steady rate unless it runs out of food or space, or is attacked in some way by disease or predators. (it encounters a limiting factor of some type) • Scientists study growth in a variety of ways • One way involves introducing an organism into a sterile, nutrient rich environment. – This is going to be for smaller organisms such as bacteria • Another way is through field studies and radio tagging organisms – Larger organisms such as elk • Populations do not follow linear growth increase. • Instead they start out slowly but once they build up the rate increases dramatically Population Growth of Houseflies Population size 1 million 500,000 100 One year • This type of growth is called exponential growth. • Exponential growth means that as a population size increases the rate of growth also increases. • Exponential growth results in a J-shaped graph curve. • If left unchecked exponential growth would continue forever. • In reality we know that it doesn’t. At some point growth stops. • This is where limiting factors come into play. • They are going to prevent the population from exceeding an imaginary line called a carrying capacity. • A carrying capacity is the number of organisms that an environment can support indefinitely, without outside assistance. • When looking at a graph illustrating population growth with a carrying capacity the j-shaped curve becomes an s-shaped curve Population Carrying capacity 0 J curve S curve Time FOOD PREDATORS SPACE Exponential growth DISEASE Characteristics of Population Growth • Most species follow a set path of population growth – They start of with slow growth – Then there is a period of rapid growth as it enters exponential growth – Next it reaches its carrying capacity and levels off – However there are still some fluctuations in the numbers