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Ecology Notes

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Western University
Biology 2483A
Hugh Henry

Ecology Notes Sept. 20/12 - Two frog species, wood frogs and boreal chorus frogs, live in the arctic tundra biome and are able to survive extended periods of subfreezing air temperatures in shallow burrows in a semi-frozen state, with no heartbeat, no blood circulation, and no breathing. - Two options for coping with environmental change (such as seasonal temperatures) are tolerance and avoidance. - The potential geographic ranges of species are determined by the physical and biological environments. The physical environment influences an organisms ecological success (its survival and reproduction) in two ways: 1. It affects the availability of energy and resources, impacting growth and reproduction. 2. Extreme conditions can exceed tolerance limits and impact survival. Energy supply can influence an organisms ability to tolerate environmental extremes. The actual geographic distribution of a species is also related to other factors, such as disturbance and competition. The abundance of organisms is at a maximum at an optimal value across an environmental gradient (temperature, precipitation, salinity). So the abundance of organisms would be highest when temperature is at some optimal value (not too high, not too low). The abundance decreases at extreme values that constrain the potential geographic distribution of the organism. The actual distribution of organisms will probably be lower than the potential distribution because of factors like competition and disturbance, which constrain the geographic range. - Because plants dont move, they are good indicators of the physical environment. Example Aspen tree distribution can be predicted based on climate. Low temperatures and drought affect reproduction and survival. The effects of low temperatures on survival and reproduction limit aspens northern range. The effects of drought on survival and reproduction limit aspens southwestern range. The aspens actual distribution covers a smaller area than its predicted distribution. A species climate envelope is the range of conditions under which it occurs and it is a useful tool for predicting a species response to climate change. - Physiological ecology is the study of interactions between organisms and the physical environments that influence their survival and persistence. - Physiological processes have optimal environmental conditions for functioning. Deviations from the optimum reduce the rate of the process. Stress is the condition in which an environmental change results in decreased rates of physiological processes, lowering the potential for survival, growth, or reproduction. - Acclimatization is when organisms adjust their physiology, morphology, or behaviour to lessen the effect of an environmental change and minimize the associated stress. It is usually a short-term, reversible process. Acclimatization is a response under field conditions, acclimation is a response under controlled laboratory conditions. Acclimatization to high elevations involves higher breathing rates, greater production of red blood cells, and higher pulmonary blood pressure. The acclimatization reverses when you return to lower elevations. - 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. Adaptation is similar to acclimatization in that both processes involve a change that minimizes stress, but adaptation is different because it is a long-term genetic response of a population to environmental stress that increases its ecological success under the stressful conditions. - Organismal responses to stress: The rate of a physiological process decreases very quickly when an organism is exposed to a stressful situation. Over time, the organism may respond to the stress through acclimatization, compensating for the effect of the stress. Over several generations, apopulation may undergo adaptation to the stress, and the physiological process may return to its pre- stress rate. - Acclimatization and adaptation require investments of energy and resources, representing possible trade-offs with functions that can also affect survival and reproduction. Acclimatization and adaptation must therefore increase the survival and reproductive success of the organisms in order to be favoured over other patterns of energy and resource investment. - Ecotypes are populations with adaptations to unique environments. Ecotypes may represent responses to both abiotic and biotic environmental factors. Ecotypes can eventually become separate species as populations diverge and become reproductively isolated. - Temperature: Environmental temperatures vary greatly throughout the biosphere. The survival and functioning of organisms is strongly tied to their internal temperature. Some archaea and bacteria in hot springs can function at 90C. The lower limits for organismal function are determined by the temperature at which water freezes in cells (-2 to -5C). Some organisms can survive periods of extreme heat or cold by entering a state of dormancy, in which little or no metabolic activity occurs. The internal body temperature ranges for life on earth for different organisms vary. The extreme upper limit is about 50C. - Metabolic reactions are catalyzed by enzymes, which have narrow temperature ranges for optimal function. High temperature destroys enzyme function (they become denatured). Enzymes in bacteria in hot springs remain stable to 100C. Antarctic fish and crustaceans their enzymes function at -2C. Soil microbes are active at temperatures as low as -5C. 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 solidify, embedded proteins cant function, and the cells leak metabolites. Plants that thrive at low temperatures hav
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