Scientific Reasoning Module - Act 3 Final Assignment

Scientific Reasoning Module - Act 3 Final Assignment Background A population is a group of organisms of the same species that live in a particular geographic location. For example, people living in the city of Phoenix are considered a population of humans. Biologists estimate the number of organisms in a population (population size) to know whether a species has become too rare or too abundant. Knowing a population's size also enables biologists to manage the resources needed to sustain the population. For example, biologists have estimated how many people will live in Phoenix during the next 40 years to know whether the current water supply will support the future population. A population grows when the number of organisms born exceeds the number that die. Conversely, a population shrinks when the number of organisms that die exceeds the number born. If the population of humans in Phoenix grows from one year to the next, the number of people born must have exceeded the number of people who died. Growth rate is a measure of how a population’s size changes over time. A positive growth rate means that the population size increases over time (i.e., the population grows). A negative growth rate means that the population size decreases over time (i.e., the population shrinks). A growth rate of zero means that the population size does not change over time (i.e., the population neither grows nor shrinks, but remains stable). Population size increases from year to year if its growth rate is greater than 0. For example, if the growth rate for Phoenix for the last 10 years were 0.16, the population size would have increased by 16% (a mean of 1.6% per year). If the nearby town of Sierra Vista experienced a growth rate of -0.05 during the same period, its population size decreased by 5% over 10 years (a mea