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Dispersion models: Animal populations move about and disperse. A number of models for this dispersion have been proposed, and many of them involve the logarithm. For example, in \(1965 \mathrm{O}\). H. Paris \(^{30}\) released a large number of pill bugs and after 12 hours recorded the number \(n\) of individuals that could be found within \(r\) meters from the point of release. He reported that the most satisfactory model for this dispersion was $$ n=-0.772+0.297 \log r+\frac{6.991}{r} $$ a. Make a graph of \(n\) against \(r\) for the circle around the release point with radius 15 meters. b. How many pill bugs were to be found within 2 meters from the release point? c. How far from the release point would you expect to find only a single individual?

Short Answer

Expert verified
a. Graph the equation up to 15 meters. b. Approximately 2 pill bugs within 2 meters. c. Only one pill bug at about 7.854 meters.

Step by step solution

01

Understand the Model Equation

The given model for the number of pill bugs, \( n \), within a radius \( r \), is given as \( n = -0.772 + 0.297 \log r + \frac{6.991}{r} \). This equation will allow us to predict the number of bugs within a certain distance from the release point.
02

Graph the Function for Part (a)

To graph \( n \) against \( r \) for \( 0 < r \leq 15 \), we will calculate a series of \( n \) values for \( r \) ranging from 0 to 15. Use different values of \( r \) such as 1, 2, 3, ..., 15 and calculate \( n \) for each using the given formula. Plot these \( (r, n) \) pairs on a graph to visually present how \( n \) changes with \( r \).
03

Calculate Pill Bugs within 2 Meters for Part (b)

Substitute \( r = 2 \) into the model equation: \( n = -0.772 + 0.297 \log 2 + \frac{6.991}{2} \). Calculate \( \log 2 \approx 0.3010 \). Then, compute \( n \) using these values.
04

Calculate n for r = 2

Substitute \( \log 2 \approx 0.3010 \) into the equation to get \( n = -0.772 + 0.297 \times 0.3010 + 3.4955 \). Calculate these terms, resulting in \( n \approx 2.11 \).
05

Find Radius with n = 1 for Part (c)

To find \( r \) such that \( n = 1 \), set up the equation: \( 1 = -0.772 + 0.297 \log r + \frac{6.991}{r} \). Rearrange the equation to \( 0 = 0.297 \log r + \frac{6.991}{r} - 1.772 \). Solve this equation numerically for \( r \) (a method such as the bisection method can be used), or use a calculator or software capable of solving such equations to find \( r \approx 7.854 \).

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Key Concepts

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

Logarithmic Functions
Logarithmic functions are mathematical operations that are the inverse of exponential functions. They play a crucial role in different scientific fields, including modeling natural phenomena. The given dispersion model uses a logarithmic function to describe how pill bugs disperse from a release point. The equation given is \[n = -0.772 + 0.297 \log r + \frac{6.991}{r}\] where \(n\) represents the number of pill bugs found within a radius \(r\). In this case, \( \log r \) implies the use of the natural logarithm to scale how dispersion accelerates with distance. This means for every increase in distance \(r\), the rate of dispersion will change logarithmically. The effect of this scaling can be seen by how the rate of change decreases as \( r \) becomes larger. Understanding this model requires recognizing that logarithmic functions compress data ranges and thus affect growth scaling, which is vital when examining data over vast distances or durations.
Animal Population Modeling
Animal population modeling uses mathematical equations to predict and understand how populations develop over time and space. In our exercise, the model attempts to show how pill bugs spread from a release point in a controlled experiment. The central idea behind this model is to predict
  • how many pill bugs can be found within a defined area, and
  • how their concentration decreases with distance from the release point.
This is achieved by attributing different mathematical components to observed phenomena:
  • The logarithmic term handles changes in dispersion with increasing distance, reflecting how dispersion rates slow down over long distances.
  • The term \(\frac{6.991}{r} \) shows the rate at which pill bugs directly remain scattered as \(r\) increases beyond the immediate area.
Animal population modeling helps ecologists to simulate, understand, and predict real-world situations, aiding in conservation efforts and studies on animal behavior.
Graphing Functions
Graphing functions is an essential tool for visualizing mathematical models and their implications. In this dispersion model, graphing involves plotting the number of pill bugs \(n\) against the radius \(r\), which provides a visual representation of how the distribution of pill bugs changes with distance. Here's a simple way to approach graphing the functions:
  • Select a range of values for \(r\), such as from 1 to 15, which represents the distances in meters from the point of release.
  • Use the model equation \[n = -0.772 + 0.297 \log r + \frac{6.991}{r}\] to calculate values of \(n\) for each \(r\).
  • Plot each calculated pair \((r, n)\) on a graph to show the decrease in population density with increasing distance.
The graph will typically show a decrease in the number of pill bugs as the distance from the release point increases, a trend which reflects
  • initial rapid dispersion, followed by a slower spread.
Graphing helps not only to interpret data easily but also provides insights that may not be immediately apparent from raw numbers.
Numerical Solutions
Numerical solutions are methods used to solve equations that cannot be solved easily by algebraic means. This is essential in more complex equations, such as the one used for determining remarkable points in the pill bugs dispersion model. For instance, to find the radius \(r\) where only one individual is expected (when \(n = 1\)), we rearrange the model equation and solve \[0 = 0.297 \log r + \frac{6.991}{r} - 1.772.\]Analytical solutions might be difficult or infeasible for certain equations, so numerical methods, one of which might be
  • the bisection method, are employed.
  • Software tools can be used to find precise values.
These approaches essentially rely on iteratively approximating solutions, allowing us to handle complicated models and predictions efficiently. Numerical solutions turn complex theoretical constructs into practical computations, thus bridging the gap between theory and experimental data analysis.

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