Chapter 4TemperatureRelations.docx

1、Chapter 4 Temperature RelationsChapter 4 Temperature RelationsPeter Kevan had come to Ellesmere Island, which lies at about 82 N latitude in the Northwest Territories of Canada, to study sun-tracking behavior by arctic flowers. It was summer, there was little wind, and the sun stayed above the horiz

2、on 24 hours each day. As the suns position in the arctic sky changed, one of the common tundra flowers, Dryas integrifolia (fig. 4.1 ), like the sunflowers of lower latitudes, followed.Kevan found that the sun-tracking behavior of Dryas increased the temperature of its flowers. Though the air temper

3、ature hovered around 15, the temperature of the Dryas flowers was nearly 25. Kevan discovered that the flowers act like small solar reflectors; their parabolic shape reflects and concentrates solar energy on the reproductive structures. He also observed that many species of small insects, attracted

4、by their warmth, basked in the sun-tracking Dryas flowers, elevating their body temperatures as a consequence (fig. 4.1). Dryas depends on these insects to pollinate its flowers.FIGURE 4.1 Sun-tracking behavior of Dryas integrifolia.How does Dryas and its insect visitors benefit from their basking b

5、ehaviors? How does cloud cover affect the temperature and sun-tracking behavior of Dryas flowers? These are the kinds of questions addressed by Kevan (1975) and other ecologists who study the ecology of temperature relations, one of the most fundamental aspects of ecology. In their quest for answers

6、 to questions like these, ecologists learn how the world works.The thermometer was one of the first quantitative instruments to appear in the scientific tool kit, and we have been measuring and reporting temperatures ever since. Human concern for temperature shows itself everywhere. Local television

7、 reviews the high and low temperatures of the preceding day and forecasts temperatures for the coming day. Daily newspapers report temperatures from nearly every corner of the globe. If two people from different regions meet, the first questions they ask concern the weather: Are the summers very hot

8、? Are the winters cold? We wear our endurance of extreme temperatures like badges of heroism; yet today we listen apprehensively to the forecast of a small temperature change-the prospect of global warming.Why is Homo sapiens so concerned with temperature? For us and all other species, the impact of

9、 extreme temperatures can range from discomfort, at a minimum, to extinction. Long-term changes in temperature have set entire floras and faunas marching across continents, some species thriving, some holding on in small refuges, and others becoming extinct. Areas now supporting temperate species we

10、re at times tropical and at other times the frigid homes of reindeer and woolly mammoths.We defined ecology as the study of the relationships between organisms and their environments. In chapter 4. we examine the relationship between individual organisms and temperature, one of the most important en

11、vironmental factors in the lives of organisms.CONCEPTS Macroclimate interacts with the local landscape to produce microclimates. Most species perform best in a fairly narrow range of temperatures. Many organisms have evolved ways to compensate for variations in environmental temperature by regulatin

12、g body temperature. Many organisms survive extreme temperatures by entering a resting stage.CASE HISTORIES: microclimatesMacroclimate interacts with the local landscape to produce microclimates.What do we mean by macroclimate and microclimate? Microclimate is what weather stations report and what we

13、 represented with climate diagrams in chapter 2. Microclimate is climatic variation on a scale of a few kilometers, meters, or even centimeters, usually measured over short periods of time, You acknowledge microclimate when you choose to stand in the shade on a summers day or in the sun on a winters

14、 day. Macroclimate and microclimate are usually substantially different. Because many organisms live out their lives in very small areas during periods of time ranging from days to a few months, macroclimate may be less important than microclimate. Microclimate is influenced by landscape features su

15、ch as altitude, aspect, vegetation, color of the ground, and presence of boulders and burrows. The physical nature of water reduces temperature variation in aquatic environments.AltitudeAs we saw in chapter 2 (see fig. 2.38), temperatures are generally lower at high elevations. These lower average t

16、emperatures are a consequence of several factors. First, because atmospheric pressure decreases with elevation, air rising up the side of a mountain expands. The energy of motion (kinetic energy) required to sustain the greater movement of air molecules in the expanding air mass is drawn from the su

17、rroundings, which cool as a result. A second reason that temperatures are generally lower at higher elevations is that there is less atmosphere to trap and radiate heat back to the ground.AspectTopographic features such as hills, mountains, and valleys create microclimates that would not occur in a

18、flat landscape. Mountains and hillsides create these microclimates by shading parts of the land. In the Northern Hemisphere, the shaded areas are on the north-facing sides, or northern aspects, of hills, mountains, and valleys, which face away from the equator. In the Southern Hemisphere, the southe

19、rn aspect faces away from the equator.You can see the effect of aspect, in miniature, around buildings. If you want to warm yourself on a sunny winters day in the Northern Hemisphere, you go to the south side of a building, to its southern aspect, which faces the equator. In the Southern Hemisphere,

20、 you would generally find the warmest spot on the north side of a building. Similarly, the northern and southern aspects of mountains and valleys offer organisms contrasting microclimates. The microclimates of north- and south-facing aspects of hillsides may support very different types of vegetatio

21、n (fig. 4.2).FIGURE 4.2 Vegetation on north- and south-facing slopes.VegetationBecause they also shade the landscape, plants create microclimates. For instance, trees, shrubs, and plant litter (fallen leaves, twigs, and branches) produce ecologically important microclimates in deserts. The desert la

22、ndscape, which often consists of a mosaic of vegetation and bare ground, is also a patchwork of sharply contrasting thermal environments. Such a patchwork is apparent near Kemmerer, Wyoming, a cold desert much like the Gobi in Mongolia (see fig. 2.19). Like the Gobi, Kemmerer can be bitterly cold in

23、 winter and blistering in summer. One summers day Robert Parmenter and his colleagues (1989) measured the temperatures in various parts of the Kemmerer landscape. Parmenter found that while the temperature on bare soil soared to 48, a few meters away in plant litter under a tall shrub the temperatur

24、e was a moderate 21 (fig. 4.3). Meanwhile, temperatures under low shrubs with less leaf area were a bit warmer but still not as hot as soil in the open. A small organism in this landscape could choose microclimates differing in temperature by 27.FIGURE 4.3 Desert shrubs and microclimate (data from P

25、armenter, Parameter, and Cheney 1989).Color of the GroundAnother factor that can significantly affect temperatures is the color of the ground. This statement may sound a bit odd if you are from a moist climate, either temperate or tropical, where vegetation usually covers the ground. But, as we have

26、 just seen, much of the arid or semiarid landscape is bare ground, which can vary widely in color. Colors have been used to name deserts around the world, such as the central Asian deserts called Kara Kum, which means black sand in Turkish. and Kyzyl Kum, or red sand, and White Sands, New Mexico (fi

27、g. 4.4).FIGURE 4.4 White and black sands.Bare ground is the dominant environment offered by beaches. Neil Hadley and his colleagues (1992) studied the beaches of New Zealand, which range in color from white to black and offer a wide range of microclimates to beach organisms. These beaches heat up un

28、der the summer sun, but black beaches heat up faster and to higher temperatures. The black beaches heat up more because they absorb more visible light than do the white beaches (fig. 4.5). When air temperatures at both beaches hovered around 30, Hadley and his colleagues found that the temperature o

29、f the sand on the white beach averaged around 45. In contrast, they measured sand temperatures on the black beach as high as 65. Though these white and black beaches are exposed to nearly identical macroclimates, they have radically different microclimates.FIGURE 4.5 Color of the ground and temperat

30、ure (data from Hadley, Savill. and Schultz 1992).Presence of Boulders and BurrowsMany children soon discover that the undersides of stones harbor a host of organisms seldom seen in the open. This is partly because the stones create distinctive microclimates. E. B. Edneys studies (1953) of the seasho

31、re isopod Ligia oceanica documented the effect of stones on microclimate. Edney found that over the space of a few centimeters, Ligia could choose air temperatures ranging from 20 in the open to 30 in the air spaces under stones, which heated to between 34and 38. This small-scale variation in temper

32、ature is summarized in figure 4.6.FIGURE 4.6 Microclimates under stones (data from Edney 1953).Animal burrows also have their own microclimates, in which temperatures are usually more moderate than at the soil surface. For example, while daily temperatures under a shrub in the Chihuahuan Desert ranged from 17.5to 32, temperatures in a nearby mammal burrow ranged from 26 to 28. This burrow was cooler than the surface during the day and warmer at night. What do these data suggest about the microclimates experienced by plant roots, soil bacteria, and burro