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This 4 page Class Notes was uploaded by Michaela Humby on Tuesday February 2, 2016. The Class Notes belongs to Bio 260 at University of Tennessee - Knoxville taught by Charles Price in Spring 2016. Since its upload, it has received 13 views. For similar materials see Ecology in Biology at University of Tennessee - Knoxville.
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Date Created: 02/02/16
Physiological ecology: adaptation of an organism's physiology to environmental conditions. Organisms have two options for coping with environmental variation: tolerance and avoidance. Example: Spruce trees in the boreal forest must be able to tolerate temperatures from –50°C to 30°C. Each species has a range of environmental tolerances that determines its potential geographic distribution. The physical environment influences an organism’s ecological success (survival and reproduction) in two ways: • Availability of energy and resources—impacts growth and reproduction. • Extreme conditions can exceed tolerance limits and impact survival. • The actual geographic distribution of a species is also related to other factors, such as dispersal ability, disturbances, and competition. • Because plants do not move, they are good indicators of the physical environment. • Limiting factors include low temperatures and drought, which affect reproduction and survival. • A species’ climate envelope is the range of conditions over which it occurs. • It is a useful tool for predicting the species’ response to climate change. • Physiological processes have optimal conditions for functioning. • Deviations from the optimum reduce the rate of the process. Stress—environmental change results in decreased rates of physiological processes, lowering the potential for survival, growth, or reproduction Acclimatization: Adjusting to stress through behavior or physiology. It is a short-term, reversible process, (e.g. acclimatization to high elevations involves higher breathing rates, greater production of red blood cells, and higher pulmonary blood pressure). Over time, natural selection can result in adaptation of a population to environmental stress. Individuals with traits that enable them to cope with stress are favored. Over time, these genetic traits become more frequent in the population. Ecotypes: Populations with adaptations to unique environments. The temperature of an organism is determined by exchanges of energy with the external environment. Some organisms can survive periods of extreme heat or cold by entering a state of dormancy, in which little or no metabolic activity occurs. Organisms must either tolerate temperature change or modify it by physiological, morphological, or behavioral means. For terrestrial plants, energy inputs include sunlight and infrared radiation from surrounding objects, as well as from conduction and convection if the ground or air is warmer than the plant. Losses of energy include emission of infrared radiation, conduction and convection, and evapotranspiration. Transpiration rates can be controlled by specialized guard cells surrounding leaf openings called stomates. Variation in degree of opening and number of stomates controls the rate of transpiration and thus leaf temperature. Other mechanisms include pubescence—hairs on leaf surfaces that reflect solar energy. But hairs also reduce conductive heat loss. Ectotherms: Regulate body temperature through energy exchange with the external environment. Endotherms: Rely primarily on internal heat generation—mostly birds and mammals. Ectotherms generally have a greater tolerance for variation in body temperature than endotherms. Tolerance to freezing involves minimizing damage associated with ice formation in cells. Some insects have high concentrations of glycerol, a chemical that lowers the freezing point of body fluids. Ectotherms in temperate and polar regions must avoid or tolerate freezing. Avoidance behavior includes seasonal migration to lower latitudes or to microhabitats that are above freezing (e.g., burrows in soil). The water balance of an organism is determined by exchanges of water and solutes with the external environment. Marine organisms live in an isoosmotic environment, so water balance is not a problem. Freshwater organisms lose solutes to and gain water from their hypoosmotic environment. Terrestrial organisms lose water to the dry atmosphere. Aquatic environments may be: • Hyperosmotic—more saline than an organism’s cells • Isoosmotic—same salinity • Hypoosmotic—less saline • Water flows along energy gradients. • Gravity: Water flows downhill. The associated energy is gravitational potential (experienced in tall trees). • Osmotic potential: Water flows from a region of high concentration (low solute concentration) to a region of low concentration (high solute concentration). • Matric potential: Energy associated with attractive forces on surfaces of large molecules inside cells or on surfaces of soil particles. • Pressure: From an area of higher pressure to lower. The associated energy is pressure (turgor) potential. • Water potential (units of pressure, usually megapascals) is the sum of all these energy components: • Resistance: A force that impedes water movement (or other substances). • Barriers include skin, and waxy cuticles of insects and plants. • Cell walls allow development of turgor pressure—when water moves into a cell, the expanding cell presses against the cell wall. Can plants exhibit avoidance of temperature extremes? Yes because they can adjust to stress through behavior or physiology. It is a short-term, reversible process; example in cold places, they just freeze; in hot places, they close stomas during the day they avoid evaporation and at night they open it; Some organisms can survive periods of extreme heat or cold by entering a state of dormancy, in which little or no metabolic activity occurs; behavioral adaptations; seasons where certain plants grow so that they avoid growing during the extremes; Ecology3e-Fig-04-08-0R.jpg describe energy gains and losses from a leaf
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