Lecture3 - 1 Biol 585 R. D. Howard Fall 11 Physiological...

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1 Biol 585 Fall 11 R. D. Howard Physiological Ecology II Temperature and geographic distribution . One of the goals of ecology is to understand reasons that underlie the geographical distribution of species. Temperature is a critical feature in this regard. Perhaps, the greatest influence of temperature on the geographic range of a species is the optimal temperature range required for reproduction. Within a taxon of endothermic homeotherms, evolved responses between surface area to volume relationships and local temperature regimes have been noted which form the basis of some biogeographical "laws". One such law was proposed in 1847 and is referred to as Bergmann's Rule . This rule states that, in widely distributed bird and mammal taxa, the forms inhabiting more northerly areas should be larger in size than closely related forms that inhabit more southerly areas. A related rule is Allen's Rule, which states that endothermic homeotherms from colder areas should have shorter extremities (ears and limbs) than related forms that inhabit warmer areas. Allen's law appears to be more generally true than Bergmann's. This may be the case because numerous other selective forces influence overall body size besides thermal adaptation. Bergmann’s rule has also been applied to ectotherms recently; however, there appears to be even more exceptions here, and its generality is under dispute. Plant Adaptations Obviously, plants also possess numerous physiological adaptations. In terms of temperature tolerances, plants can far exceed animals. The stem of a cactus can survive temperatures of 60 o C for long periods; whereas, mammals and birds can't survive temperatures in excess of 40 o C for very long. The thermal environment of an individual plant can vary immensely throughout its body. Roots are typically buffered from temperature extremes by the soil; above ground structures experience widely varying temperatures, even at the same time if some are shaded and others are in the full sun. Plants regulate their body temperature by losing part of the energy they absorb. They maintain their heat balance by re-radiation, convection, and transpiration. Re- radiation accounts for 1/2 of the energy they absorb. Convection across boundary layers transfers heat from the leaf to the cooler air. Transpiration accounts for additional heat loss and is also the major way that plants lose water. Water loss results because transpiration during photosynthesis involves the uptake of CO 2 from the air through stomates, and CO 2 is a larger molecule than H 2 O, therefore membranes can't allow CO 2 to enter without losing water. Furthermore, the concentration of O 2 in the atmosphere is about 20% and the concentration of CO 2 is only 0.03%. As a result, photosynthesis involves more water loss than does respiration. Thus, plant adaptations to desert conditions must involve water collection and retention. As with animals, plants have minimum and maximum temperatures for survival
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This note was uploaded on 08/28/2011 for the course ESE 585 taught by Professor Richardhoward during the Fall '11 term at Purdue University-West Lafayette.

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Lecture3 - 1 Biol 585 R. D. Howard Fall 11 Physiological...

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