Transcript Slide 1
The full size range (extant) Mycoplasma Average bacterium < 10 -13 g < 0.1 pg 10 -10 g 0.1 ng Large amoeba 0.1 mg 10 -4 g Bee 100 mg 10 -1 g Hamster 100 g 10 2 g Human 100 kg 10 5 g Elephant Blue Whale Sequoia 5,000 kg (5 tons) 100 tons 5000 tons10 10 g 5 x 10 6 g 10 8 g 1. Dimensions % of body mass that is skeleton Sorex (shrew) 3.8% Human 18.8% elephant 27% 3. Design Short bridge Long bridge Compressive support, stone Tensile support, steel Oxygen Delivery—design changes with size Unicellular organism 0.1 mm = 5 sec Diffusion Problem!: Time to diffuse is proportional to the square of the distance 1 mm = 500 sec Diffusion 10 cm =~ 55 days Scaling Relationships Physiological parameter of interest Y = a Mb A “power” function a = proportionality constant b = scaling exponent (describes strength and direction of the effect of mass on Y) Body Mass (M) • allow for huge range of body sizes •generate a straight line •slope of line = b b = 0.75 Body mass Log E O2 consumption (E) Physiologists often use log-log plots log Body mass Y-intercept E = a Mb slope log E = log a + b log M How does mass-specific O2 consumption scale with body size? (02 consumption per gram of tissue) Mass-specific MR Y = a Mb Log O2/g*hr Take log: So b = -0.25 Slope = -0.25 log Body mass b: describes relationship of X to Y as Y gets bigger If b = 0 If 0 < b < 1 If b = 1 b = 0.75 No relationship e.g. [hemoglobin] Isometric relationship e.g., blood volume in mammals -constant fraction of body mass If b > 1 e.g. whole animal metabolic rate If b < 0 b = -0.25 e.g., bone thickness e.g., mass specific metabolic rate = 65 mya Mammals diversified in the Cretaceous, between 144 and 65 mya Dinosaurs disappear here (except for lineage leading to birds). Why did dinosaurs go extinct? Artist rendition of early mammal Fish and Reptiles Mammals and Birds Primates From Jerison 1969 Reptiles Mammals From Jerison 1969 But wait a second… What if dinosaurs were endothermic? • Dinosaur trackways reveal that dinosaurs may have been able to travel up to 27 mph… • Some large dinosaurs had erect posture and a vertical distance between the heart and head to require a high blood pressure, like the giraffe. • Where do we draw the line between ectothermic dinosaurs and endothermic ancestors to birds? • Dinosaur bone is more similar to mammalian or avian (bird) bone in cross section than it is to typical ectothermic "reptilian" bone Big antlers on Irish Elk—10 – 12 feet across! Two outstanding questions: Why the enormous antlers? Did the large antlers contribute to its extinction? Megaloceros giganteus Stood 2.1 m tall Went extinct 10,600 years ago Found across Eurasia Most of dots represent extant species of deer Irish elk Maximum length of antler Two species of moose Antler length = 0.064 * Shoulder height1.68 Height of shoulder Gould 1974 But, not the last word on Irish Elk? *New study by Moen et al 1999: what about nutrient requirements? *Irish elk antlers weighing 40 kg at the end of velvet shedding would have contained 2.1 kg nitrogen, 7.6 kg calcium and 3.8 kg phosphorus. *to grow 40 kg antlers in 150 days, need: 60 g calcium, 30 g phosphorous daily for 60 days *In the model, 6% of calcium, 10% of phosphorous taken from skeleton because dietary intake of minerals insufficient to meet requirements of antler mineralization *climate change!!!