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Biology 2483A
Mark Moscicki

Ecology Sept 24 2013 Coping with Environmental Change  Tolerance: Trees must tolerate extreme temperatures because they are immobile  Avoidance: Animals can migrate when conditions get rough Ecological Success  Ecological success is its survival and reproduction  Geographical range of an organism is determine by its physical environment which influences an organisms ecological success in two ways. These are not mutually exclusive as one can affect the other (energy supply influences an organisms ability to tolerate environmental extremes. 1. Physical environment affects the ability of an organism to obtain energy and resources-impacts growth and reproduction (rates of photosynthesis and prey abundance are determined by climatic factors) 2. Extreme conditions can exceed tolerance limits and impact survival (temp, water supply, chemicals, etc)  Actual geographic distribution of a species is also related to other factors, such as disturbance and competition Organism Abundance Abundance Across Environmental Gradients  Organismal abundance reaches a theoretical max at some optimal value across an environmental gradient and drops off at either end at values that constrain the potential geographic distribution of the organism. (highest abundance at species ideal physiological conditions) Actual differs from potential due to interactions with other organisms (competition) Aspen Distribution  Plants don't move, so they are good indicators of the physical environment  Aspen distribution can be predicted by climate. The predicted distribution (left) is based on climatic factors that affect their reproduction and survival. The actual distribution (right) is limited by low temps (flowers can't easily survive frost) and drought. Climate and Aspen Distribution Climate and Aspen Distribution 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 such as growth or photosynthesis 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 (Ex: Climbing to high elevations/areas of low oxygen results in a decrease in the amount of oxygen going to our tissues-hypoxia)  Acclimatization: Adjusting to stress through behaviour or physiology. It is usually a short term, reversible process. Acclimatization to high elevations involves higher breathing rates, greater RBC production, and higher pulmonary blood pressure. This will lead to the delivery of more oxygen to the tissues. This process reverses when the stress ends. Acclimatization is a type of adaption.  Adaptation: This is how we respond to environmental variation. Over time, natural selection results in adaptation of a population to environmental stress. Individuals with traits that enable them to cope with stress are favoured. Over time, these genetic traits become more frequent in the population. This is a long term genetic response of a population to minimize stress. Adaptations can vary among populations. There are multiple ways populations can adapt/respond to the same stressor  Acclimatization and adaption are similar in that they both involve a change to minimize stress. Both require investments of energy and resources, representing possible trade-offs with other functions that can also affect survival and reproduction Environmental Control of Physiological Processes Organismal Responses to Stress response to stress by the individual adaptation by the acclimatization population by the individual Ecotypes  Populations with adaptations to unique environments. These adaptations may be a response to biotic or abiotic factors. It is a population of a species that differs genetically from other populations of the same species because local conditions have favoured certain characteristics  Ecotypes can eventually become a separate species as populations diverge and become reproductively isolated Temperature  Environmental temperatures vary greatly throughout the biosphere Temperature Ranges  Survival and functioning of for Life on Earth (internal body temperature) organisms is strongly tied to their internal temperature  Extreme upper limit for multicellular plants/animals is about 50 degrees C. (when enzymes denature) Some archaea and bacteria in hot springs can function at 90 degrees C.  Lower limits are determined by temperature at which water freezes in cells (-2 to -5 degrees C)  Metabolic reactions are catalyzed by enzymes, which have narrow temperature ranges for optimal function. High temperature destroys enzyme function (denature). The upper lethal temperature for most organisms is lower than the temperature at which their enzymes denature because metabolic coordination is lost.  Most enzymes become denatured at 40-70 degrees C. However, enzymes in some bacteria (bacteria in hot springs) are stable to 100 degrees C. Enzymes in Antarctic fish and Crustaceans function at -2 degrees C because the salt concentration of the sea in which they live lowers its freezing point. Enzymes in soil microbes are active at temperatures as low as -5 degrees C.  Some species produce different forms of enzymes (isoenzymes) with different temperature optima that allow acclimatization to changing conditions (responding to seasonal changes in temperature)  Temperature also affects the properties of cell membranes, which are composed of two layers of lipid molecules. At low temperatures, these membranes 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.  Internal temp of an organism is determined by a balance between the energy it gains from and the energy it loses to the external environment. Organisms must either learn to tolerate these internal temperature changes or modify their internal temperature by some physiological, morphological or behaviour means. Ectotherm/Endotherm  Ectotherm: Regulate body temperature through energy exchange with the external environment  Greater tolerance for variation in body temperature because they are less able to adjust their body temperatures than endotherms  Exchange of heat is dependent on amount of surface area relative to the volume of the animal. A larger surface area relative to volume allows for greater heat exchange, but makes it harder to maintain a constant internal temperature in the face of variable external temperatures. A smaller surface area relative to volume decreases the animals ability to gain or lose heat. Generally, surface area to volume decreases as body size increases, and the animals ability to exchange heat with the environment decreases as well.  Small aquatic ectotherms remain the same temperature as the water. Some large ectotherms can maintain higher body temperatures than the surrounding water. An example is skipjack tuna. Heat generated in the muscles warms blood flowing through them, which is carried toward the body surface in veins. Those veins run parallel to arteries carrying cool blood from the gills, warming that blood before it reaches the swimming muscles. It can have a body temperature 14 degrees C warmer than the surrounding sea water.  Many terrestrial ectotherms can move around to adjust temperatures. Many insects and reptiles bask in the sun to warm up after a cold night, but this increases predation risk, increasing benefits of camoflauge.  Ectotherms in temperate and polar regions must avoid or tolerate freezing. Avoidance behaviour includes seasonal migration to lower latitudes or to microsites that are above freezing (Ex: 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 freezing temperatures due to their larger size and physiological complexity.  Endotherm: Rely primarily on internal heat generation-mostly birds and mammals **Can maintain internal temperatures near optimum for metabolic functions. Can extend geographic range  Some other organisms that generate heat internally include bees (defense), some fish (tuna) and even some plants  Skunk cabbage warms its flowers using metabolically generated heat in early spring  Tolerate a narrower range of body temperatures (30-45 degrees & 86-113 degrees)  Endotherms can remain active at sub freezing temperatures  The cost of being endothermic is a high demand for energy (food) to support metabolic heat production.  M
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