Lecture2 - 1 Biol 585 R D Howard Fall 11 Physiological...

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1 Biol 585 Fall 11 R. D. Howard Physiological Ecology I Adaptation to needed resources differs from adaptation to environmental conditions. Resources include such things as food, nesting sites, waterholes etc. Conditions include such things as temperature, pH, humidity etc. This distinction is made because other organisms can use up resources but not conditions. That is, organisms can compete for resources but not for conditions. A “law” that applies more to resources is Leibeg’s “law of the minimum” which postulates that various measures of performance are often regulated (or limited) by some requisite that is in short supply. A “law” that applies more to conditions is Shelford’s “law of tolerance” , which postulates that various extreme values of conditions can be detrimental to an organism. This can be illustrated by an idealized curve showing that extreme levels of any condition could have lethal effects on the individual and intermediate conditions can allow for survival with or without reproduction. Thus, for an individual of any species there is a range of conditions at which reproduction is maximal, therefore continued existence is possible. It should be noted that the distinction between resources and conditions can get sort of hazy. Some of the things that organisms can compete for include particular regions of their habitat where the physical conditions are more suited to maximal reproduction. The types of adaptation that I will discuss, however, would occur if biotic interactions were absent. So, we will first consider adaptation to the physical environment as one of the types of interactions that determine a species distribution and abundance.
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2 The main physiological adaptation that I will discuss is temperature adaptation . The temperatures experienced by most organisms in nature result directly or indirectly from solar radiation. However, as you know, environmental temperatures vary, and they vary on several timescales (e.g., daily, seasonally, yearly, and longer cycles). For example, in West Virginia, the mean annual temperature is ~12 o C, but during the year, temperatures can vary from -37 o C to 44 o C. Daytime temperatures are often 17 o C higher than nighttime temperatures (note: in some deserts, this range can be as great as 40 o C!). In addition, temperatures taken at exactly the same time can differ by 30 o C or more depending on whether they are measured in the shade or the sun. The ability of animals to withstand temperature extremes varies among species. The maximum temperature that any animal or protozoan can survive is 52 o C; although some bacteria can survive and grow at temperatures greater than 90 o C. However, the upper lethal temperature is much lower than 52 o C for most animals. Organisms gain heat from
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Lecture2 - 1 Biol 585 R D Howard Fall 11 Physiological...

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