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Population: A scientist who is studying population data makes a plot of the logarithm of the population values as a function of time. If the population is growing exponentially, what should the plot look like?

Short Answer

Expert verified
The plot should be a straight line with a slope equal to the growth rate \( r \).

Step by step solution

01

Understanding Exponential Growth

If a population is growing exponentially, its size over time is modeled by the equation \( P(t) = P_0 e^{rt} \), where \( P_0 \) is the initial population, \( r \) is the growth rate, and \( t \) is time.
02

Using Logarithms

To analyze the growth on a logarithmic scale, we take the natural logarithm of the exponential growth equation: \( \, \ln(P(t)) = \ln(P_0 e^{rt}) \). This simplifies to \( \, \ln(P(t)) = \ln(P_0) + rt \).
03

Interpreting the Transformation

The equation \( \, \ln(P(t)) = \ln(P_0) + rt \) is in the form of a linear equation \( y = mx + c \), where \( y = \, \ln(P(t)) \), \( m = r \), and \( c = \ln(P_0) \). In this case, it represents a straight line with slope \( r \).
04

Relating to the Graph

Given the transformation, the plot of \( \, \ln(P(t)) \) as a function of \( t \) should produce a straight line. The slope of this line is equal to the exponential growth rate \( r \), and the y-intercept is \( \ln(P_0) \).

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Logarithmic Transformation
A logarithmic transformation is a mathematical technique used to simplify the exploration of exponential data by transforming it to a linear form. When working with data that grows exponentially, like populations, the raw numbers can become very large, making trends and comparisons difficult. By applying a logarithmic transformation, we convert the exponential equation into a linear form.

In the context of population modeling, the natural log of the population size, through formula manipulation, reduces the problem of understanding exponential growth to understanding straight lines. This is crucial because linear relationships are much easier to interpret and analyze. The transformation formula usually looks something like this:
  • The original exponential equation: \( P(t) = P_0 e^{rt} \)
  • The logarithmic transformation: \( \ln(P(t)) = \ln(P_0) + rt \)
This leads to a linear form, which is instrumental in analyzing exponential growth patterns by observing the plot of \( \ln(P(t)) \) versus time \( t \).
Linear Equation
A linear equation is one of the simplest forms of mathematical expressions, often displayed as \( y = mx + c \). In population modeling, once we apply a logarithmic transformation to an exponential growth model, the equation resembles this linear form.

This transformation elucidates how the parameters of the exponential model relate to a straightforward linear equation:
  • \( m \) (the slope) represents the growth rate, \( r \).
  • \( c \) (the y-intercept) equals the natural log of the initial population, \( \ln(P_0) \).
This linearity allows us to engage in linear regression analysis or easily visualize population trends over time. When plotted against time, the linear equation's graph provides a clear visual representation of how the population is changing.
Population Modeling
Population modeling with mathematical equations helps to understand and predict how a population expands over time. By using models, scientists and researchers can make educated predictions about future population sizes and growth dynamics.

For populations that grow exponentially, the mathematical model used is usually in the form \( P(t) = P_0 e^{rt} \). Here:
  • \( P(t) \) is the population at time \( t \).
  • \( P_0 \) is the initial size of the population.
  • \( r \) is the constant growth rate.
Population modeling often requires transforming data using logarithms to handle large numbers and better analyze growth rates. By focusing on the transformed, linear model, researchers can grasp how quickly or slowly a population grows and when it might face survival challenges or hit environmental limits.
Growth Rate Analysis
Growth rate analysis is an essential component of understanding population dynamics. It involves calculating how quickly a population increases over a set period. The growth rate \( r \) is a pivotal parameter in the exponential growth equation, revealing the rate at which the population size compounds.

When analyzing a population graph that has undergone logarithmic transformation, the slope of the resulting line equals the growth rate \( r \). Here’s why this is crucial:
  • The slope indicates whether the population is growing rapidly or slowly.
  • It is used to compare growth rates across different populations or time periods.
A linear graph resulting from exponential growth suggests consistent growth over time. Fluctuations in the slope could signal changes in environmental conditions or resources affecting growth rates.

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Most popular questions from this chapter

Aphid growth on broccoli: This problem and the following one are based on the results of a study by R. Root and A. Olson of population growth for aphids on various host plants.44 The value of r = 0.243 per day is valid for aphids reared on broccoli plants outdoors. The table on the next page describes the growth of an aphid population reared on broccoli plants indoors (in a controlled environment). Time t is measured in days. $$ \begin{array}{|l|c|c|c|c|c|} \hline \text { Time } t & 0 & 1 & 2 & 3 & 4 \\ \hline \text { Population } & 25 & 30 & 37 & 44 & 54 \\ \hline \end{array} $$ Calculate r for this table. Did the aphids fare better indoors or outdoors?

The pH scale: Acidity of a solution is determined by the concentration \(H\) of hydrogen ions in the solution (measured in moles per liter of solution). Chemists use the negative of the logarithm of the concentration of hydrogen ions to define the \(\mathrm{pH}\) scale: $$ \mathrm{pH}=-\log H . $$ Lower pH values indicate a more acidic solution. a. Normal rain has a pH value of 5.6. Rain in the eastern United States often has a pH level of \(3.8\). How much more acidic is this than normal rain? b. If the \(\mathrm{pH}\) of water in a lake falls below a value of 5 , fish often fail to reproduce. How much more acidic is this than normal water with a \(\mathrm{pH}\) of \(5.6 ?\)

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Grains of wheat on a chess board: A children's fairy tale tells of a clever elf who extracted from a king the promise to give him one grain of wheat on a chess board square today, two grains on an adjacent square tomorrow, four grains on an adjacent square the next day, and so on, doubling the number of grains each day until all 64 squares of the chess board were used. How many grains of wheat did the hapless king contract to place on the 64th square? There are about \(1.1\) million grains of wheat in a bushel. Assume that a bushel of wheat sells for \(\$ 4.25\). What was the value of the wheat on the 64th square?

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