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Counting carnivores Ecologists look at data to learn about nature鈥檚 patterns. One pattern they have identified relates the size of a carnivore (body mass in kilograms) to how many of those carnivores exist in an area. A good measure of 鈥渉ow many鈥 is to count carnivores per 10,000 kg of their prey in the area. The scatterplot shows this relationship between body mass and abundance for 25 carnivore species.

The following graphs show the results of two different transformations of the data. The first graph plots the logarithm (base 10) of abundance against body mass. The second graph plots the logarithm (base 10) of abundance against the logarithm (base 10) of body mass.

a. Based on the scatterplots, would an exponential model or a power model provide a better description of the relationship between abundance and body mass? Justify your answer.

b. Here is a computer output from a linear regression analysis of log(abundance) and log(body mass). Give the equation of the least-squares regression line. Be sure to define any variables you use.

c. Use your model from part (b) to predict the abundance of black bears, which have a body mass of 92.5 kg.

d. Here is a residual plot for the linear regression in part (b). Do you expect your prediction in part (c) to be too large, too small, or about right? Justify your answer.

Short Answer

Expert verified

(a) Power model

(b)logy=1.9503-1.04811x

(c) The predicted abundance is 0.775532per 10000kgper prey

(d) The forecast of 2is nearly right.

Step by step solution

01

Part (a) Step 1: Given information

The given data is

02

Part (a) Step 2: Explanation

The scatter plot between log(abundance) and log(abundance) is seen (body mass). Because the scatter plot's two variables do not have a lot of curvatures, a linear model between them would be appropriate. As a result, a linear model between log(abundance) and log(abundance) is adequate (body mass).

Expect log(abundance) and log(abundance) using a general linear model (body mass).

log(abundance)=a+b(bodymass)

abundance=elog(abundance)=ea+b(body mass)

=eaeb(body mass)

As a result, the model is associated with abundance=eaeb(body mass). It's a powerful model that combines abundance with body bulk.

Although the linear model of abundance and log (body mass) is useful, the power model of abundance and body mass is equally useful.

03

Part (b) Step 1: Given information

The given data is

04

Part (b) Step 2: Explanation

The equation for square regression line is

y^=b0+b1x

In the row "constant" and the column "Coef" of the computer output, the calculated constant b0is mentioned.

b0=1.9503

In the row "Distance" and the column "Coef" of the computer output, the calculated slope b1is mentioned.

b1=-1.04811

On substituting the values

y^=1.9503-1.04811x

Calculating the log value

logy=1.9503-1.04811logx

Where x stands for body mass andy stands for abundance.

05

Part (c) Step 1: Given information

The given data is

06

Part (c) Explanation

From part (b)

logy=1.9503-1.04811logx

Where xstands for body mass and ystands for abundance.

Substituting the value of x

logy=1.9503-1.04811log(92.5)logy=-0.1104

Then take the exponential

y^=10logyy^=10-0.1104y^=0.775532

As a result, 0.775532is the predicted abundance per10000kgper prey.

07

Part (d) Step 1: Given information

The given data is

08

Part (d) Step 2: Explanation

It is estimated that the body mass will be 92.5kg based on portion (c).

log(92.5)=1.966142

The dots between 1.5and 2.0are both below and above the horizontal line at 0, as shown in the residual figure. Furthermore, the horizontal line 0 is in the middle of these dots, implying that the forecast of 2is nearly right.

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