6.3 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 is a group-living, territorial mammal in which individuals react more aggressively to members of neighboring bands than to strangers. 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? C. 6.4 The gall-forming cottonwood poplar aphids studied by Tom Whitham 108110108-110 compete for spots near the midribs of leaves. Figure 6.13 shows the reproductive consequences for asexual females that secure places near the base of a leaf versus those that form their galls farther along the midrib. Table 6.1 shows how well female aphids do on leaves of different sizes. Given these data, where do you predict the most intense or lengthiest fights for territory will occur? What is the importance of the finding that the females farther along the midrib of a medium-size leaf (which they have chosen after another female has settled on the basal portion of the leaf) do as well as females that have a small leaf all to themselves? D. 6.5 In one study of brown bears (grizzlies) 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. So here, as in Belding's ground squirrels and many other mammals, males disperse while most females remain on or near their natal territories. 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? E. 6.6 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. (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? F. 6.7 Figure 6.22 shows the heart rates and wing beat frequencies of great white pelicans flying in V-formation as opposed to flying alone. Birds traveling behind others can take advantage of updrafts created by the wing beats of their companions, which enables them to cut their energetic costs by about 10 percent. Perhaps this is why so many large birds, like Canada geese, typically fly in V-formation when migrating. But what is there about Figure 6.22 that constitutes a Darwinian puzzle? See the paper by Henri Weimerskirch et al., where they explain how they managed to get these big birds to divulge information on their heart rates and wing beat frequencies. G. 6.8 Swainson's thrush (C. ustulatus), one of the species in the genus Catharus mentioned earlier, breeds in a large region right across North America. Those birds that live in the northwestern part of North America do not all follow the same migratory route. Some birds go right down the Pacific coast and winter in Central America. But others travel all the way to the eastern part of North America before flying south to winter in South America (Figure 6.26). One hypothesis to account for the behavior of the thrushes taking the long way south is that these birds are descendants of those that expanded the species' range from the East Coast far out to the west and north after the retreat of the glaciers about 10,000 years ago. What kind of evolutionary hypothesis is this? Is the behavior maladaptive? How can you account for the persistence of the trait? H. 6.9 For some whale species that migrate from the Arctic or Antarctic Ocean to give birth in warmer water nearer the equator, food cannot provide a benefit, since the adults do not feed on the calving grounds. Therefore, other hypotheses for whale migration have been advanced, such as the idea that whale calves can gain weight more quickly in subtropical waters, where they need to invest less energy in keeping warm. Alternatively, some scientists have suggested that infant whales in these waters are less likely to be attacked by predators, especially killer whales. How would you test these hypotheses, given the practical difficulties of directly measuring the metabolic costs of thermos regulation by whale calves or of actually observing killer whale attacks in any environment? I. 6.10 Imagine that there are other places in Mexico or the southern United States where monarchs could overwinter even more safely and successfully than they do in their current Mexican wintering grounds. Imagine that the only reason the butterflies do not utilize these locations is that the mutations that are needed to change their migratory route have not occurred. In other words, the accidents of monarch history are responsible for their present migratory choices. Does this mean that the adaptation approach to monarch migration is flawed in this instance because the migratory behavior of today's monarch butterflies could be more efficient than it is? J. 6.11 Recently Sonia Altizer and her colleagues have found that the monarch butterflies that travel the longest distances have the lowest levels of infection by a protozoan parasite, whereas the prevalence of these parasites is highest in the nonmigratory populations of the butterfly. They suggest that because badly infected individuals cannot reach distant destinations, migration has the beneficial effect of culling parasite carriers, which keeps the species healthier than it would be otherwise. According to this hypothesis, who benefits from the removal of infected monarchs? From a theoretical perspective, why does this matter? K. 6.12 Some males of the white-ruffed manakin of costa Rica move temporarily to lower areas while others skip migration to stay in the higher-elevation breeding locations. Birds that stay have greater mating success than those that leave. So why do any males migrate? Use conditional strategy theory to make some predictions about the age and condition of the birds that leave the breeding area. L. 6.13 As an exercise, apply conditional strategy theory to the western fox sparrow case in the same way that we did with European blackbirds. Use your hypothesis to make predictions about what decisions individuals of different competitive abilities would make about remaining in an area year-round versus migrating various distances. For example, if your hypothesis were correct, what should happen if a bird improved its condition from one year to the next? What information presented above permits you to evaluate your predictions? Is it useful to know that in the white-crowned sparrow. resident and migrant individuals have almost identical annual survival rates, or that those sparrow species that migrate relatively long distances do not have lower survival rates than other species that travel shorter distances? M. 6.14 Conditional strategy theory is one of many evolutionary theories that we have examined thus far. Others include natural (direct) selection theory, kin (indirect) selection theory, inclusive fitness theory, group selection theory, optimality theory, game theory, ideal free distribution theory, and evolutionary stable strategy theory. Some of the theories listed above can be considered part of another theory (for example, ideal free distribution theory is derived from game theory. Produce an organizational scheme that ranks theories in terms of their relationships. How would you define a scientific theory? Why are theories so important to scientific research? N.