mass specific metabolic rate – THE REPTIPAGE
Sep 15, Mass-specific metabolic rate, the rate at which organisms consume as the ratio between the basal metabolic rate of an organism and its body mass . 47], and in cylindrically-shaped objects volume is proportional to length. Mammals and birds have substantially greater metabolic rates than . MASS. Body size clearly affects metabolic rate: a chihuahua eats and requires relationship between body size and metab- of an object with an exponent of , and. Body size and metabolic rate both fundamentally constrain how species our temporal perception are apparent when tracking fast-moving objects such as the .. the relationship between both physiology and the effects of body mass on the .
That is to say they rely on bacterial degradation of cellulose in order to extract nutrients from their food. Because of this, the digestive phase for ruminants can last for a substantially long time.
Typically, artiodactyls are fasted for 72 hours before having their BMR measured, yet data on digestion in ruminants suggests that they can last as long as 7 days before entering a postabsorptive state White and Seymourif at all McNab When this is not taken into account, one winds up measuring RMR instead of BMR, which raises the overall exponent to the mass specific metabolic rate equation.
Now, to be fair, Kleiber did note that his extensive use of artiodactyls three cows and a sheep could have an unwanted effect on his data if they were not being measured in a postabsorptive state. Thus, he performed an analysis with and without his ruminants. White and Seymour argued that the reason behind this still high exponent might be due to the relatively high BMRs of domestic carnivores Kleiber used dogs and humans.
Another aspect of BMR studies that tends to get overlooked when researchers attempt MSMR calculations is the need to measure animals in a thermoneutral environment. This is an environment in which the animal is not actively thermoregulating, otherwise known as the thermoneutral zone. Automatic endotherms are often lauded for their ability to maintain body temperatures regardless of the external environment.
This seems to have lead to the assumption that the environmental temperature should not matter, which results in experiments that grab metabolic rate data from animals that are in fact, rather stressed e. White and Seymour noted that mass and body temperature showed an intimate relationship in mammals White and Seymourand that in order to get a useful comparative estimate of BMR for mammals that encompasses the full range of masses seen in this group, BMR should be standardized to a common body temperature.
As mentioned previouslyautomatic endotherms do not escape the Q10 effect, but instead keep it at bay by keeping their cells encased in a bubble of stable temperatures. That temperature turned out to be White and Seymour discovered that when BMR was standardized to a universally comparable temperature, the mass specific exponent for metabolic rate was approximately 0. So it appears that Rubner had it right all along.
For seventy years we have been using a formula that suffered from some hefty methodological errors. One power law to rule them all? This violates a fundamental assumption of practically every statistical analysis.
Basal Metabolic Rate
Namely that data points are independent. Savage et al pointed out that most BMR data exists for mammals that are less than 1kg in size. This is going to bias the regression statistic indeed, Dodds et al.
The authors cited a lack of data for larger taxa as a likely cause of this strangeness. Savage et al decided to repeat the statistical analyses of White and Seymour, as well as a few other authors.
In the process they found various errors in each analysis that resulted in some major discrepancies e. The idea being that by separating mass into sections like this, they could turn mass into a treatment effect, which should allow the statistical analysis to better analyze the effect of BMR as described by body mass. The authors noted this unexpected result, but quickly pointed out that this was for data that was heavily biased for small size mostly rodents.
By essentially forcing a uniform distribution across the mass ranges available the authors results revealed an exponent of 0. The authors took this a step further by looking for exponents to describe field metabolic rate and maximal metabolic rate. Their reasoning being that these are more easily obtained measurements that have more biologically meaningful results to them. Further, I would argue that the benefits of BMR is that they indicate what the bare minimum energy requirements of an organism should be.
That has the potential to be extremely useful for paleontology.
Especially if one is looking to figure out how much food at minimum an organism would need to eat to survive in some environment and thus, infer something about thermophysiology. And this is where we come to the punchline in all of this.
While the arguments had previously focused on automatic endotherms, data started to appear in both those groups, and especially the groups outside Figure 1 from White et al illustrates the mess likely represents a more accurate look of how metabolism scales with mass. Note how the automatic endotherms actually scale up slower than everyone else. Mammalia and Aves, that a universal metabolic exponent appeared not to exist. This was tackled more formally by White et al. This was followed up by a final analysis by the authors on published allometric exponents for taxa that spanned the range of animal classes.
Following Felsenstein they incorporated independent contrasts to remove the effects of phylogeny which has a tendency to screw the pooch for independence of data points. The authors then assigned the exponents found to one of three categorical variables: This suggests that a true discrepancy between these modes of thermophysiology ultimately affect metabolic rate. However there is still considerable sway around these exponents. So much so that White et al. The authors do offer some alternatives that might be used such as statistics that incorporate multiple exponent models, accounting for body mass by using it as a variable in an analysis of covariance ANCOVA model, or just choosing the right exponent for the job e.
Where are we now? So here we are, finally at the end of this long winded blog entry, and what do we have to show for it? Another thing to take away from this is just how complicated metabolic physiology studies really are. They have to account for so many unexpected variables that is amazing we can say anything at all about extant animals.
One thing I did not touch upon was the fact that all MSMR equations use regression as their model of choice. A severe limit to this approach and one that is violated all the time is that regression models can really only predict — with any certainty — the estimated MSMR of an animal that falls within the size range measured. Once one starts to extrapolate beyond the maximum, or minimum size of the available data, one is practically just speculating. Regression graph showing trend line for a range of predicted values bold line and possible real distributions that exist beyond the measured data grey dotted lines.
In the case of above, the animal now has eight times the biologically active tissue to support, but the surface area of its respiratory organs has only increased fourfold, creating a mismatch between scaling and physical demands. Similarly, the organism in the above example now has eight times the mass to support on its legs, but the strength of its bones and muscles is dependent upon their cross-sectional area, which has only increased fourfold.
Therefore, this hypothetical organism would experience twice the bone and muscle loads of its smaller version. This mismatch can be avoided either by being "overbuilt" when small or by changing proportions during growth, called allometry.
Isometric scaling is often used as a null hypothesis in scaling studies, with 'deviations from isometry' considered evidence of physiological factors forcing allometric growth. Allometric scaling[ edit ] Allometric scaling is any change that deviates from isometry. The skeletal structure becomes much stronger and more robust relative to the size of the body as the body size increases. If, after statistical analyses, for example, a volume-based property was found to scale to mass to the 0.
Conversely, if a surface area-based property scales to mass to the 0. One example of positive allometry occurs among species of monitor lizards family Varanidaein which the limbs are relatively longer in larger-bodied species. Determining if a system is scaling with allometry[ edit ] To determine whether isometry or allometry is present, an expected relationship between variables needs to be determined to compare data to.
This is important in determining if the scaling relationship in a dataset deviates from an expected relationship such as those that follow isometry. The use of tools such as dimensional analysis is very helpful in determining expected slope.
For example, different sized frogs should be able to jump the same distance according to the geometric similarity model proposed by Hill  and interpreted by Wilson but in actuality larger frogs do jump longer distances. Now, the rate at which heat energy is radiated from an object is proportional to the difference in temperature between the surface of the object and the temperature of the surroundings.
This is usually called Newton's Law of Cooling. This means that if we are in a cold room we radiate away energy faster than in a warm room, and start feeling cold.
- Metabolic rate
The body will begin to shiver, which increases the metabolic rate. Metabolic rates of W or more are possible for people who are shivering. Julius Robert Mayer was a German-born physician.
In the early 's he noticed that people who lived in Indonesia had blood which was a deeper red than people living in Europe. This indicated that they had less oxygen in their blood, which meant their metabolic rate was lower than Europeans.
He reasoned that this was because to maintain equilibrium with their warmer environment required a lower metabolic rate.
This was one of the very first realisations the heat is just another form of energy. Mayer's first paper on this realisation was rejected, largely because he was a physician and largely ignorant about physics.
Although disappointed, Mayer took up the study of physics, learned about kinetic energy, and his second paper was published in