Today Calculate metabolic rate using different methods indirect

Today • Calculate metabolic rate using different methods – indirect calorimetry and respirometry. • Examine the effects of size on metabolic rate • Examine the effects of temperature on metabolic rate.

A Roach Ate Chicago ?

Isometry = body dimensions scale exactly i. e. as the height doubles the arm length doubles. Note that the surface to volume ratio changes, however. 96(16 x) Surface: volume 6: 1 3: 1 2: 1 1. 5: 1

With allometric change the proportions vary. Note the size of the head and eyes.

If the large roach ( 8 inches)were 4 x as long as the small one (2 inches) its surface area would be 42 times greater and its volume would be 43 time greater. The small roach would have a surface to volume ratio of 4: 1 and the large roach 2: 1. The small roach would have a much more efficient absorbtive surface for digestion and respiration. If there were isometric scaling of the body, legs of the large roach would have a cross sectional area 16 x greater but a volume or density 64 x greater. Legs would be carrying 4 x as much weight.

Metabolic Rate = a Mb (1) where a is the log/log intercept, M is mass and b is the rate of change of metabolic rate with mass. For Mass specific rate MR/M = a. M b-1(2) Expressing these equations as logs gives a straight line where b= the slope. For (1) log MR = log a + b(log M) For (2) log MR/M = log a +( b-1) log M

• In general large animals live slower than small animals. Chicken heart rate = 300 beats/minute. Elephant heart rate = 30 beats/minute. Elephant mass = 10, 000 chicken mass. Warm blooded animals die after 1 -2 billion heart beats so elephant lives longer.

For metabolic rate b =. 75

For surface area b =. 63

For a single species (I. e. small range) b =. 67

Rubner rule: Metabolic rate varies with mass 2/3 If length = l 1; then area is proportional to l 2 and volume is proportional to l 3 ; so the surface to volume ratio is l 2: l 3 or l 2/3 Problems : shouldn’t there be differences between ectotherms and endotherms ? Between plants and animals ? Kleibner’s Rule == Metabolic rate = mass 3/4