Chapter 5 Temperature Relations 1 Chapter 5 Temperature Relations Introduction Temperature is a measure of the average kinetic energy or energy of motion of the molecules in a mass of a substance The kinetic energy in a mass of a substance is generally referred to as heat energy or simply as heat Kevan discovered that the flowers act like small solar reflectors their parabolic shape reflects and concentrates solar energy on the reproductive structures The fundamental importance of temperature to organisms including humans is a consequence of temperature s influences on rates of chemical reactions including those reactions that control life s essential processes photosynthesis and respiration The impact of extreme temperatures can range from discomfort at a minimum to extinction Many studies indicate rapid adaptation to the warming climate through natural selection 5 1 Microclimates Macroclimate interacts with the local landscape to produce microclimatic variation in temperature Microclimate is a fundamental aspect of environmental variation Macroclimate is what weather stations report and what we represented with climate diagrams Microclimate is climatic variation on a scale of a few kilometers meters or event centimeters usually measured over short periods of time Microclimate is influenced by landscape features such as altitude aspect vegetation color of the ground and presence of boulders The physical nature of water and soil reduces temperature variation in aquatic environments and in animal burrows Altitude Aspect Temperatures are generally lower at high elevations for two reasons 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 drawing from the surrounding which cool as a result There is less atmosphere to trap and radiate heat back to the ground 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 North facing slopes remain moist approximately 2 5 times longer than south facing slopes following rainfall probably as a result of lower evaporation rates In the Southern Hemisphere the southern aspect faces away from the equator Vegetation Color of the Ground Because they shade the landscape plants create microclimate Much of an arid or semiarid landscape is bare ground which can vary widely in color Bare ground is also the dominant environment offered by beaches Though black and white beaches are exposed to nearly identical macroclimates they have radically different microclimates Presence of Boulders and Burrows Aquatic Temperatures Animal burrows also have their own microclimates in which temperatures are usually more moderate than that of soil surface Temperature generally fluctuates more than water temperatures for a couple reasons It takes approximately 1 calorie of energy to heat 1 cm3 of water 1 C The thermal stability of the aquatic environment derives partly from the high capacity of water to absorb heat energy without changing temperature specific heat A second cause of the thermal stability of aquatic environments is the large amount of heat absorbed by water as it evaporates latent heat of vaporization A third cause of the greater thermal stability of aquatic environments is the heat energy that water gives up to its environment as it freezes latent heat of fusion The aquatic environments with greatest thermal stability are generally large ones such as the open sea These are environments that store large quantities of heat energy and where daily fluctuations are often less than 1 C Other factors besides the physics of water can affects the temperatures of aquatic environments 5 2 Evolutionary Trade Offs Chapter 5 Temperature Relations 2 Riparian vegetation that is vegetation that grows along rivers and streams influences that temperature in streams in the same way that vegetation modifies the temperature of desert soils by providing shade Adapting to one set of environmental conditions generally reduces a population s fitness in other environments All known organisms are adapted to a limited range of environmental conditions at least partially as a consequence of energy limitation The Principle of Allocation All organisms have access to limited energy supplies One of those consequences is that energy allocated to one of life s functions such as reproduction defense again disease or growth will reduce the amount of energy available for other functions Richard Levins was the first to use a mathematical approach to analyze the evolutionary consequences of such trade offs which he referred to as the principle of allocation Levins concluded that as a population adapts to a particular set of environmental conditions its fitness in other environments is reduced Testing the Principle of Allocation The central question of their work was whether adaptation to a low temperature would be accompanied by a loss of fitness at a high temperature Bennett and Lenski hypothesized that they would observe just such a tradeoff in fitness a prediction that follows directly from Levin s principle of allocation This principle in turn offers an explanation for the observation that most organisms perform best under a limited range of environmental conditions including thermal conditions Most species perform best in a fairly narrow range of temperatures Whether in response to variations in temperature moisture light or nutrient availability most species do not perform equally well across the full range of environmental conditions to which they are exposed most perform best under a narrower range of conditions Enzymes usually work best in some intermediate range of temperatures There is usually some optimal range of temperatures for most enzymes If this concentration is low the enzyme is performing well at low concentrations of the substrate The affinity of an enzyme for its substrate is one measure of its performance Extreme Temperatures and Photosynthesis Photosynthesis the conversion of light energy to the chemical energy of organic molecules is the basis for the life of plants their growth and reproduction and is the ultimate source of energy for most heterotrophic organisms Light interacts with chlorophyll carbon dioxide and water combine to produce sugar and oxygen Extreme temperatures generally reduce