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Lecture 4

Lecture 4 - Coping with Environmental Variation - Temperature and Water

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Western University
Biology 2483A
Hugh Henry

LECTURE 4: COPING WITH ENVIRONMENTAL VARIATION: TEMPERATURE AND WATER  The physical environment influences an organism’s ecological success in two ways: o Availability of energy and resources—impacts growth and reproduction. o Extreme conditions can exceed tolerance limits and impact survival.  Energy supply can influence an organism’s ability to tolerate environmental extremes.  The actual geographic distribution of a species is also related to other factors, such as disturbance and competition. Abundance across Environmental Gradients  Based on physiological tolerance of an organism, potential distribution tends to be highest at a moderate level  The actual distribution, however, is more constrained because of factors such as competition, environmental disturbances, or other biological factors Aspen Distribution  Because plants don’t move, they are good indicators of the physical environment  Aspen distribution can be predicted based on climate. Low temperatures and drought affect reproduction and survival  Predicted distribution based on known physiological knowledge  Actual distribution corresponds well with predicted distribution in the Northern range limit, but other factors play a role in the Southern range limit and these factors may explain the difference between predicted and actual distributions  A species’ climate envelope is the range of conditions over which it occurs Physiological Ecology  Physiological ecology is the study of interactions between organisms and the physical environments that influence their survival and persistence  Physiological processes have optimal conditions for functioning  Deviations from optimum reduce 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 usually a short-term, reversible process  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  Acclimatization and adaptation require investments of energy and resources, representing possible trade-offs with other functions that can also affect survival and reproduction  Ecotypes – populations with adaptations to unique environments o Ecotypes can eventually become separate species as populations diverge and become reproductively isolated Temperature  Environmental temperatures vary greatly throughout the biosphere.  Survival and functioning of organisms is strongly tied to their internal temperature.  Some archaea and bacteria in hot springs can function at 90°C  Lower limits are determined by temperature at which water freezes in cells (–2 to –5°C)  40 – 50°C – optimum range for most organisms  Metabolic reactions are catalyzed by enzymes, which have narrow temperature ranges for optimal function. High temperature destroys enzymes function (denatured)  Bacteria in hot springs - enzymes stable to 100°C; Antarctic fish and crustaceans - enzymes function at –2°C; soil microbes - active at temperatures as low as –5°C.  Some species produce different forms of enzymes – isozymes – with different temperature optima that allow acclimatization to changing conditions  Temperature also affects the properties of cell membranes, which are composed of two layers of lipid molecules.  At low temperatures, these lipids can solidify, embedded proteins can’t function, and the cells leak metabolites.  Plants that thrive at low temperatures have higher proportions of unsaturated lipids (with double bonds) in their cell membranes o Double bonds create kinks which results in a very fluid-like membrane  Ectotherms – regulate body temperature through energy exchange with the external environment  Endotherms – rely primarily on internal heat generation – mostly birds and mammals o Can maintain internal temperatures near optimum for metabolic functions, can extend geographic range  Some other organisms that generate heat internally include bees, some fish, such as tuna, and even some plants  Skunk cabbage warms its flowers using metabolically generated heat in early spring  Ectotherm surface area-to-volume ratio of the body is an important factor in exchanging energy with the environment  Larger surface area allows greater heat exchange, but makes it harder to maintain internal temperature  Small aquatic ectotherms remain the same temperature as the water  Some large ectotherms can maintain higher body temperature: o Skipjack tuna use muscle activity and heat exchange between blood vessels to maintain a body temperature 14°C warmer than the surrounding seawater  Many terrestrial ectotherms can move around to adjust temperature  Many insects and reptiles bask in the sun to warm up after a cold night, but this increases predation risk, increasing benefits of camouflage  Ectotherms in temperate and polar regions must avoid or tolerate freezing. Avoidance behavior includes seasonal migration to lower latitudes or to microsites that are above freezing (e.g., burrows in soil)  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  Vertebrates generally do not tolerate free
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