Some species seem to thrive in captivity, whereas others are prone to health and behavior difficulties when caged. Maternal care problems in some captive species, for example, lead to high infant mortality. Can these differences be predicted? The following data are measurements of the infant mortality (percentage of births) of 20 carnivore species in captivity along with the log (base-10) of the minimal home-range sizes (in km2 ) of the same species in the wild (Clubb and Mason 2003). The size of the home range is the area that an individual moves through during its daily life.

a. Draw a scatter plot of these data, with the log of home-range size as the explanatory variable.

Describe the relationship between the two variables in words.

b. Estimate the slope and intercept of the least squares regression line, with the log of home-range size as the explanatory variable. Add this line to your plot.

c. Does home-range size in the wild predict the mortality of captive carnivores? Carry out a formal test. Assume that the species data are independent.

d. Outliers should be investigated because they might have a substantial effect on the estimates of the slope and intercept. Recalculate the slope and intercept of the regression line from part (c) after excluding the outlier at large home-range size (which corresponds to the polar bear). Add the new line to your plot. By how much did it change the slope?