According to Louw , the most critical parameter affecting an organism's thermoregulation is the ratio of the organism's surface area to body mass. Thus, a smaller organism has relatively more surface area through which to radiate heat with respect to its volume than a larger organism.
In , J. Allen expanded on Bergmann's concept, demonstrating that endotherms in cold climates tend to have shorter appendages legs, ears, etc. The principle of Allen's rule is similar to Bergmann's in that endotherms like the Arctic hare Lepus arcticus adapted to cold climates have smaller ears, shorter limbs, and rounder bodies, effectively presenting less surface area through which to lose heat in relation to the body volume.
The antelope jackrabbit L. My goal was to use commonly available, low-cost materials while maintaining biological validity. Plastic drink bottles 2 L, 1 L, and 0. I used three sizes of plastic soft drink or water bottles 2 L, 1 L, and 0. Of course, the water in the bottles will cool in still air, but using the fan provides for additional convective cooling, which will speed up the temperature changes to give better results in a shorter amount of time.
Discarded drink bottles can be used to simulate endotherms of different sizes, providing a simple and economical model system to explore Bergmann's rule. In order to minimize cost, I used only one instant-read thermometer and moved it between bottles. Obviously, separate thermometers for each bottle would simplify measurements, but it would also introduce an issue of calibration variance that could bias results.
Since the probe takes a few seconds to stabilize between readings, I measured the temperatures in the same order at each interval so that the measurement interval remained roughly equivalent for each volume across the course of the activity.
As always, replication averages-out individual variances. Pooling class data to obtain overall means for each size of model will allow for this. In this example, I used two replicates of each bottle size to calculate run means and repeated the exercise three times. I rearranged the positions of the 0. As long as the smaller bottles were not blocked by the larger 2 L bottles, their positions had no effect. Although they are not perfect cylinders, I used the standard formula for the surface area of a cylinder to approximate the surface area of each bottle.
I measured the height h from the bottom of the bottle to the level of fill. If we consider absolute amounts of heat lost, the larger the volume the more heat is lost. However, the rate of heat loss is more important in this exercise.
Students could also use a bar graph to compare temperatures at each recording time. Comparing these types of figures can open discussions on the value of different types of graphs and allows students to make a judgment as to which is more useful for a given set of data.
For time-course measurements like the ones made here, the line graph is more informative. Comparison of temperature change of simulated organisms of three different volumes over a minute time course. Finally, I calculated the rate of heat loss for each model by subtracting the temperature at time 20 from the temperature at time zero and dividing by 20 minutes i. Comparison of the rate of temperature change for three different-sized models. Make sure that the holes drilled in the caps are large enough to allow the thermometer probe to be inserted easily.
If the hole is too small and the probe must be forced, you run the risk of breakage or injury. The only safety concern would be that the probe on some thermometers may have a sharp point, although no sharper than a pencil or pen. Students should be reminded to exercise caution when moving the thermometer from bottle to bottle. Thought questions might include the following:.
How would the metabolic rate for a smaller endotherm compare to the metabolic rate for a larger endotherm in a cold climate?
Based on your observations of heat loss in models of different sizes, how would thermal regulation differ between a newborn mammal and an adult mammal? Despite higher metabolic rates, they may be incapable of maintaining constant body temperatures and must rely on external heat sources to help with thermoregulation.
Siberian tigers are larger than Sumatran tigers. Polar bears are larger than Tennessee black bears or Asian sun bears.
Which of these best demonstrates Bergmann's rule? Both the tigers and the bears can be used as examples of Bergmann's rule. However, since Siberian tigers and Sumatran tigers are members of the same species, they provide a more focused example. Depending on the specific calculations assigned, this exercise can be scaled for upper elementary or middle school through introductory-level college laboratories.
Students can prepare graphs by hand to introduce younger students to data visualization concepts, or they could use easily accessible spreadsheet software like Microsoft Excel or LibreOffice Calc. I recommend using a spreadsheet for graph preparation for more advanced students. She observed that the trophy white-tailed bucks she saw down south were tiny compared to the bucks up north.
I assured her that the southern deer were not inferior to northern deer; they were just following Bergmann's rule. Bergmann's rule is one of those common-sense principles that practicing biologists often take for granted.
Students, and especially those with less of an interest in science, may not see those principles quite so easily. Using readily available materials, students can investigate why body size matters in terms of thermal regulation in endotherms. Being able to see the principle in action should provide a better practical framework on which to build other physiological concepts. Documents: Advanced Search Include Citations.
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