Problem 2
Discuss the advantages and disadvantages of physical versus chemical defenses in plants.
Problem 4
An early view of plant-herbivore interactions was that plants and their insect herbivores are engaged in an evolutionary arms race, and for many interactions pairwise coevolution was the dominant explanation for the observed patterns of plant defense. This view is not widely held now (Stamp 2003). Discuss why the evolutionary arms race analogy might not hold for plant-herbivore interactions.
Problem 6
Sap-feeding insects do more poorly on water-stressed plants, while leaf- chewing insects on average are not affected by water-stressed plants. Discuss why this difference in response might occur. Huberty and Denno (2004) discuss these results.
Problem 8
Caughley and Lawton (1981) suggest that the growth of many plant populations will be close to logistic. Review the assumptions of the logistic equation, and discuss why this suggestion might be true or false.
Problem 9
Eucalyptus trees in Australia have high rates of insect attack on leaves, with \(10 \%-50 \%\) of the leaves eaten every year, even though these trees also contain very high concentrations of essential oils and tannins (Gras et al. 2005 ). Discuss how this situation could occur if eucalyptus oils and tannins are defensive chemicals.
Problem 10
Large herbivorous mammals are not always present in habitats dominated by spiny plants. Why might this be? Janzen (1986) reviews the vegetation of the Chihuahuan Desert of north-central Mexico and interprets the abundance of spiny cacti as reflecting the "ghost of herbivory past." Read Janzen's analysis and discuss how one might test his ideas.
