Graphing Changesin PopulationChanges in a popula-tion’s size can be displayedon a line graph. Figure 7 shows agraph of the changes in a rabbit population. The vertical axisshows the numbers of rabbits in the population, while the hori-zontal axis shows time. The graph shows the size of the popula-tion over a ten-year period.If birth ratedeath rate, population size increases.If death ratebirth rate, population size decreases.InequalitiesThe population statement is an example of an inequality. An inequality is a mathemati-cal statement that compares two expressions. Two signs that represent inequalities are< (is less than)> (is greater than)For example, an inequality comparing the fraction to the decimal 0.75 would be writtenPractice Problems Write an inequality comparing each pair of expressions below.1.5 ■62.0.4 ■3.2(8)■7 1.512--0.7535--
Differentiated InstructionCalculating Growth RateMaterialsnoneTime5 minutesFocusReview with students the definitions of birth rateand death rate.TeachAsk: Suppose 1,600 snow geese died in the same year that 1,400 were born. What would the growth rate be for that year?(Tell students that birth rate – death rate = growth rate: b – d = g.1,400 −1,600 = growth rate of −200 geese for that year) What does a negative growth rate mean?(The population is declining.)ApplyAsk: What might account for a death rate that is higher than the birth rate? (Possible answers: Disease; not enough food; being eaten by other animals; unfavorable environmental conditions)learning modality: logical/mathematicalChangesin a Rabbit PopulationFor: Changes in Population ActivityVisit: PHSchool.comWeb Code: cep-5012Students investigate the factors influencing changes in population size.Gifted and TalentedCalculating Growth RateTell students that ecologists use the birth and death rates to calculate a population’s growth rate, the rate at which the population is changing. The birth rate (b)minus the death rate (d)L3equals the growth rate (g): b − d = g.Have students use this formula to calculate the growth rate of rabbits discussed in the text. (600 births − 400 deaths = a growth rate of 200 rabbits per year)learning modality: logical/mathematicalMonitor ProgressL2WritingHave each student write a paragraph explaining how birth rate and death rate affect the size of a population. Students can save their paragraphs in their portfolios.AnswerFigure 7Fourth year of the study; about 850L2Year of StudyNumber of Rabbits(thousands)012345678910900800700600500400300200100From Year 4 to Year 8, more rabbits left the population than joined it, so the population decreased.FIGURE7This line graph shows how the size of a rabbit population changed over a ten-year period.