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Energetics
Employ a variety of methods to evaluate costs & benefits of specific life processes
Involves costs of acquiring resourcesevolution of adaptations to aquatic
existence - seawaterHow resources are allocated
cost benefit interactionsenergy-flow models
Energetics
Allocate energy across three uses: - burned in metabolism - allocated to growth - used in reproduction
Metabolic Fuels
Substrates used in metabolism fat, protein, carbohydrate, combination
2X energy metabolized from lipid than amount from protein or carbohydrate
Lipids > proportion of metabolic fuel
Greater proportion of lipids in diet
Metabolic Rate
Cellular mechanics similar to other verts
Typically other mechanisms when diving
Standardized units
Biological state of an organisms can affect metabolic rate
Basal Metabolic Rate (BMR)
Measure of the metabolic rate of mature (sex & phys), postabsorptive individuals at rest in a thermoneutral environment
BMR – used for comparison across groups
Ambient Temperature
Met
abo
lic
Rat
eLower lethal temp.
Lower critical temp.
Upper lethal temp.
Upper critical temp.
Thermo neutral zone (TNZ)
BMR
High and constant body tempcan be maintained at rest over a fluctuationof temperatures of 5-10 C with littleExtra metabolic work—this is the TNZ.
Most birds/mammals spend time in environments that fall within the TNZ
BMR & Body MassKleiber Curve – BMR to body mass to the 0.75 power (BMR = aM0.75)
Do marine mammals have higher metabolic rates??? – continues debate
Live in cold, highly conductive media
Heat capacity of water 25X air
Several adaptations to reduce heat loss:large body size – reduced SVRincreased insulationconserving counter-current systems
Provide broad thermoneutral zones
Thermoregulation
Body Mass – SAV Ratios
Marine mammals span a body-mass range 4X from sea otters (5kg) to blue whales (10x104)
Surface area of a body ↑ proportionally to the square of its lengthVolume (≈mass) ↑ proportional to its cube
Marine mammals capable of producing considerable heat with relatively little loss
Body Mass – SAV Ratios
Reduce heat loss by streamlining body form – reducing surface area
Surface area of pinnipeds, cetaceans, & sea otters are 23% < terrestrial mammals of similar body mass
Insulation
Use dense fur or blubber
Fur: depends upon capacity to trap air
Blubber functions: thermoregulation, energy storage, buoyancy control, streamlining
Non-shivering thermogenesis – brown fatlarge amounts in pups
Fur
Fur – extreme sea otter (150,000 hairs/cm2)
In air: impedes thermoregulation
In water: works well in shallow water environment
Deep divers – air squeezed out (pressure)
Blubber
Insulative value a function of thickness, lipid content, & peripheral blood flow
Cetaceans – mostly lipid content
Very efficient in cetaceans & pinnipedsless so in sirenians
manatees thinner than dugongs
Blubber
Sirenians – 2 blubber layers
Functionally cuts insulatory capability in half
Cetacean Manatee
Skin
Blubber
Muscle
SkinBlubber
Muscle
BlubberMuscle
Peripheral Blood Circulation
Conserve heat in water (cold) – inhibits heat dissipation on land (warm)
Counter current heat exchangers – conserve heat by maintaining a heat differential between oppositely directed flows of blood
Counter Current Heat Exchangers
39°C 37°C 35°C 33°C 31°C 29°C27°C
38°C 36°C 34°C 32°C 30°C 28°C
Heat is conserved before it is lost at the extremity
Veins
Artery
Parallel intermingling vessels (in contact)
= vascular bundles (rete)
Counter Current Heat Exchangers
Pinnipeds & cetaceans - Flippers & fins (flukes)Use hindflippers & forsal fin to cool gonads
Sirenians – vascular bundles throughout body – expel heat in warm waters
Right & Gray whales – in mouths; when feeding in cold waters
Energetics of Locomotion
Up to 80% of daily activity budget
Frictional resistance of water has large effect – 800x more dense than air, 30x more viscous
Must overcome hydrodynamic drag
What a Drag
Frictional & Pressure Drag – associated with physical prcesses of water surrounding the body surface
Induced Drag – associated with water flow around the flippers, fins, & flukes
Wave Drag – moving at or near the surface
Transport Adaptations
Wave Riding – large energetic savings - bow or stern of ships & whales
Surfacing only to breathe
Porpoising – removes animal from high drag environment at surface while breathing; mammals < 10m Crossover – velocity at which porpoising becomes more efficient (5m/s)
Osmoregulation
Hyposmotic – body fluids have a lower ionic content than surrounding water
losing water to hyperosmotic seawater
Larger kidneys than terrestrial mammals
Multi-lobed kidneys – reniculihuman & horses – single lobecetaceans – 450 to 3,000 reniculi
Osmoregulation
Cetaceans can concentrate urine to a greater extent than any other mammals
Allow them a net-gain to drinking seawater
In cetaceans: 1L seawater = 0.5L water gain
In humans: 1L seawater = 0.5L water loss