Class Discussion 3: Chapters 6 and 7
Topics : (Chapter Five) Avoiding Predators and Finding Food; and (Chapter 6) The Evolution of Habitat Selection, Territoriality, and Migration

Answer all questions:

Chapter 6 Questions:

1. Some people might say that the fact that most noctuid moths have ultrasound-sensitive ears is “simply” a reflection of their shared ancestry, a holdover from the past, and therefore that ultrasound sensitivity is not an adaptation in these species (Brooks and McLennan 1991). Others disagree, arguing that it makes no sense to define adaptations in a way that limits them to just those traits that have diverged from the ancestral pattern (Reeve and Sherman 1993). Who is right?

2. Assassin bugs are honey bee killers that sometimes prey on bees as they are settling down for the night. Devise at least three alternative hypotheses on the possible anti-assassin bug value of these sleeping clusters, and list the predictions that follow from each hypothesis.

3. When Scott Creel and colleagues studied elk (Cervus canadensis) behavior in Montana, they found that elk tended to form larger groups when foraging in the open far away from forest cover (Creel et al. 2005, Creel and Christianson 2008). Why might this result lead us to interpret large group formation by elk as an antipredatorresponse? Creel and company noted that the elk aggregated only on days when wolves (Canis lupus) were absent. In the presence of wolves, elk remained in smaller herds. What is the significance of these observations for the antipredator hypothesis about the tendency of elk to group together under some conditions? In scientific terms, which label should be given to these observations: hypothesis, prediction, test data, or scientific conclusion? What is the significance of this work for studies of puddling by butterflies?

4. Why might game theory be useful in analyzing decision making by Adélie penguins (Pygoscelis adeliae) as they wait to enter the water by the edge of their breeding colonies? The penguins gather in groups before diving into the ocean where a huge predator, a leopard seal (Hydrurga leptonyx), may be lurking. How might one individual’s decision to dive in be dependent on what other penguins are doing?

Chapter 7 Questions:

1. The dear enemy effect has been explained in terms of familiarity (individuals learn who their neighbors are, and as they become familiar with these others, they become less aggressive toward them). An alternative explanation can be labeled the threat level hypothesis, which states that the dear enemy effect results from the reduced threat to the fitness of a territory holder offered by neighbors that no longer challenge the territory owner next door. Could both of these hypotheses be right? The banded mongoose (Mungos mungo) is a group-living, territorial mammal in which individuals react more aggressively to members of neighboring bands than to strangers (Müller and Manser 2007). If the threat level hypothesis is right, what prediction can you make about the nature of interactions between two neighboring bands versus the band and an intruding stranger?

2. In one study of brown bears (Ursus arctos) in Sweden, 15 of 16 males left their mothers and natal territories behind while only 13 of 32 females dispersed. Older and heavier females were less likely to be part of the dispersing cohort (Zedrosser et al. 2007).So here, as in Belding’s ground squirrels and many other mammals, males disperse while most females remain on or near their natal territories (see Box 7.2). Given the information above, do the explanations given for the pattern of ground squirrel dispersal also apply to brown bears? What other information would be useful in order to evaluate these hypotheses?

3. Data on the travel routes of migrating birds today largely come from extremely lightweight radios, geolocators, and satellite tags, which can be safely attached to individual birds.The use of geolocator backpacks has revealed that migrant wood thrushes and purple martins take much longer to travel from Pennsylvania to the Amazon basin in the fall than they do when going in the opposite direction in the spring (Stutchbury et al. 2009). For example, one martin completed its spring migration in about 2 weeks, which required an average trip of 600 kilometers each day. Why the difference in speed of travel between the fall and spring migrations?

Just answer these questions.