Line	In the Sonoran Desert of northwestern Mexico and
	southern Arizona, the flowers of several species of
	columnar cacti—cardon, saguaro, and organ
	pipe—were once exclusively pollinated at night by
(5)	nectar-feeding bats, as their close relatives in arid
	tropical regions of southern Mexico still are. In these
	tropical regions, diurnal (daytime) visitors to columnar
	cactus flowers are ineffective pollinators because,
	by sunrise, the flowers’ stigmas become unreceptive
(10)	or the flowers close. Yet the flowers of the Sonoran
	Desert cacti have evolved to remain open after sunrise,
	allowing pollination by such diurnal visitors as bees and
	birds. Why have these cacti expanded their range of
	pollinators by remaining open and receptive in daylight?
(15)	This development at the northernmost range of
	columnar cacti may be due to a yearly variation in the
	abundance—and hence the reliability—of migratory
	nectar-feeding bats. Pollinators can be unreliable
	for several reasons. They can be dietary generalists
(20)	whose fidelity to a particular species depends on
	the availability of alternative food sources. Or, they
	can be dietary specialists, but their abundance may
	vary widely from year to year, resulting in variable
	pollination of their preferred food species. Finally, they
(25)	may be dietary specialists, but their abundance may
	be chronically low relative to the availability of flowers.
	Recent data reveals that during spring in the
	Sonoran Desert, the nectar-feeding bats are
	specialists feeding on cardon, saguaro, and
(30)	organpipe flowers. However, whereas cactus-flower
	abundance tends to be high during spring, bat
	population densities tend to be low except near
	maternity roosts. Moreover, in spring, diurnal cactus-
	pollinating birds are significantly more abundant in
(35)	this region than are the nocturnal bats. Thus, with bats
	being unreliable cactus-flower pollinators, and daytime
	pollinators more abundant and therefore more reliable,
	selection favors the cactus flowers with traits that
	increase their range of pollinators. While data suggest
(40)	that population densities of nectar-feeding bats are
	also low in tropical areas of southern Mexico, where
	bats are the exclusive pollinators of many species
	of columnar cacti, cactus-flower density and bat
	population density appear to be much more evenly
(45)	balanced there: compared with the Sonoran Desert’s
	cardon and saguaro, columnar cacti in southern Mexico
	produce far fewer flowers per night. Accordingly,
	despite their low population density, bats are able to
	pollinate nearly 100 percent of the available flowers.

    In 1975 Chinese survey teams remeasured Mount Everest, the highest of the Himalayan mountains. Like the British in 1852, they used the age-old technique of "carrying in" sea level: surveyors marched inland from the coast for thousands of miles, stopping at increments of as little as a few feet to measure their elevation, and marking each increment with two poles. To measure the difference in elevation between poles, surveyors used an optical level—a telescope on a level base—placed halfway between the poles. They sighted each pole, reading off measurements that were then used to calculate the change in eleva tion over each increment. In sight of the peaks the used theodolites—telescopes for measuring vertical and horizontal angles—to determine the elevation of the summit.

    The Chinese, however, made efforts to correct for the errors that had plagued the British. One source of error is refraction, the bending of light beams as they pass through air layers of different temperature and pressure. Because light traveling. down from a summit passes through many such layers, a surveyor could sight a mirage rather than the peak itself. To reduce refraction errors, the Chinese team carried in sea level to within five to twelve miles of Everest's summit, decreasing the amount of air that light passed through on its way to their theodolites. The Chinese also launched weather balloons near their theodolites to measure atmospheric temperature and pressure changes to better estimate refraction errors. Another hurdle is the peak's shape. When surveyors sight the summit. there is a risk they might not all measure the same point. In 1975 the Chinese installed the first survey beacon on Everest, a red reflector visible through a theodolite for ten miles, as a reference point. One more source of error is the unevenness of sea level. The British assumed that carrying in sea level would extend an imaginary line from the shore along Earth's curve to a point beneath the Himalaya. In reality, sea level varies according to the irregular interior of the planet. The Chinese used a gravity meter to correct for local deviations in sea level.

    In recent years, Western business managers have been heeding the exhortations of business journalists and academics to move their companies toward long-term, collaborative "strategic partnerships" with their external business partners (e.g., suppliers). The experts' advice comes as a natural reaction to numerous studies conducted during the past decade that compared Japanese production and supply practices with those of the rest of the world. The link between the success of a certain well-known Japanese automaker and its effective management of its suppliers, for example, has led to an unquestioning belief within Western management circles in the value of strategic partnerships. Indeed, in the automobile sector all three United States manufacturers and most of their European competitors have launched programs to reduce their total number of suppliers and move toward having strategic partnerships with a few.

    However, new research concerning supplier relationships in various industries demonstrates that the widespread assumption of Western managers and business consultants that Japanese firms manage their suppliers primarily through strategic partnerships is unjustified. Not only do Japanese firms appear to conduct a far smaller proportion of their business through strategic partnerships than is commonly believed, but they also make extensive use of "market-exchange" relationships, in which either party can turn to the marketplace and shift to different business partners at will, a practice usually associated with Western manufacturers.