Environmental Adaptations: Feldhamer Chap 9 Temps on Earth can range from -65 degrees C to +55 degrees C That is 120 degrees C or 216 degrees F Animals must have adaptations to avoid overheating and overcooling

Environmental Adaptations Mammals are able to regulate their body temps using physiological mechanisms as well endothermy Regulation of body temp through behavioral adjustments is called ectothermy Mammals can maintain a relatively constant body temp homeothermic

Environmental Adaptations physiological mechanismsendothermy behavioral adjustmentsectothermy homeothermic:maintain relatively constant body temp = = +

Prototherians Metatherians Eutherians Internal temperature variability most variable least variable Fluctuation of internal body temperature in mammals best thermoregulators

Fluctuation of internal body temperature in mammals Ambient temperature

Mammals have a thermoneutral zone -a range of environmental temperatures within which the metabolic rate is minimal lower critical temp upper critical temp thermoneutral zone need to increase heat loss through panting (increases metabolism), evaporative heat loss (sweating), behavioral means need to increase metabolic heat production and reduce heat loss (or go into torpor or hibernation)

If the core body temperature drops below the lower critical temperature HYPOTHERMIADEATH If the core body temperature rises above the upper critical temperature HYPERTHERMIADEATH

How do mammals deal with cold? AVOIDANCE RESISTANCE Methods of Energy Conservation Methods of Energy Expenditure

Total E required increases with mass But E per kg of body mass decreases with increasing mass Why? Kcal/day Body mass (kg) Mass-specific energy use Total Energy use BODY SIZE

volume increases as a cubed measure, whereas surface area increases as a square measure area = length * width volume = length * width * height X 2 X 3 BODY SIZE -metabolic rate related to ability to retain heat -heat loss related to body size

area = length * width volume = length * width * height X X 2 3 The larger an animal gets the lower its surface area to volume ratio surface area = volume denominator increases much faster than numerator X 2 X 3

Large animals lose heat less quickly than small animals Which would you rather knit a sweater for: 1 deer that weighs 200 kg or 100 monkeys that weigh 2 kg each?

Bergman’s Rule -body size should increase with latitude (within a species) 0º90ºN body size lattitude Empirical data are mixed: McNab (1971): of 47 species, only 32% followed the trend predicted by Bergman’s Rule

-might have same volume but very different surface area Shape also very important

Example: torpedo weasel shape Weasels have metabolic rates % higher when cold-stressed than woodrats of similar mass Evolutionary trade-off Body plan great for hunting, poor for heat retention

Allen’s Rule -appendages are shorter in colder climates, longer in warmer climates -ears -tails -rostrum -legs -probably holds for many groups, but generality is debated hares-yes rabbits-no Ear length

Exceptions to Allen’s Rule -appendages may be long in cold climates to deal with heavy snowfall -need other mechanisms to reduce heat loss

Countercurrent Heat Exchange 10-12ºC 38ºC

Insulation hair & fat -help keep core body temp high -retain heat

Insulation -effectively allows the lower critical temperature to be extended -arctic fox has a LCT of -40ºC! -even at -70ºC, metabolic rate only has to be raised 50% terrestrial mammals

Insulation aquatic mammals -hair loses much of it’s insulative properties when wet -have specialized hairs that trap a layer of air -skin stays dry, shielded by a layer of air

Insulation marine mammals -most have a thick layer of fat (blubber) -58% blubber! -42% muscle, bones, organs etc. -some also have fur -sometimes overheating can be a problem during high activity

some extremely elaborate Construction of nests: -inside of snow-covered beaver lodge may be as much as 35ºC (63ºF) warmer than the outside air in winter most mammals construct nests also benefit from communal nesting

Communal Nesting -decrease surface area relative to volume -change places periodically

Foraging zones: zones which have a much higher temperature than the outside air snow ground air subnivean zone heat water vapor condenses & freezes SUBNIVEAN ZONE -pockets form between snow and ground

Foraging zones: mammals often forage in zones which have a much higher temperature than the outside air snow ground air subnivean zone will be much colder if snow cover is light More snow can be better than less snow for small mammals

Food Hoarding Easily accessible food source during cold periods -cuts down search time (time outside of nest etc.) Scatter-hoarders -scatter food around (use scent, memory etc. to find) example: southern flying squirrel

Food Hoarding Easily accessible food source during cold periods -cuts down search time (time outside of nest etc.) Larder-hoarder -make one or few big stashes (need to protect this) -example: chickaree

Food Hoarding Easily accessible food source during cold periods -cuts down search time (time outside of nest etc.) Predators -may stash big kills in snow for later

Torpor -can occur on a daily basis -form of dormancy lowering of: -body temp -metabolic rate -respiration -heart rate (not as drastic as hibernation) metabolic rate and body temp of Peromyscus during daily torpor Torpid by day, active by night

prolonged winter torpor Richardson’s ground squirrel Up to 8 months of hibernation Normal body temp = 38ºC hibernation: probably accomplished by supercooling, where solutes build up in blood, lowering freezing temp of the blood hibernating body temp= 3º- 4ºC

How do mammals deal with cold? AVOIDANCE Body size Insulation Modification of microclimate regime -communal nesting -foraging zones Food hoarding Reduction in body mass Reduction in level of activity Dormancy Increase in thermogenic capacity RESISTANCE Energy Conservation Energy Expenditure

Resistance to Cold Shivering thermogenesis Non-shivering thermogenesis (NST) Brown adipose tissue -lots of mitochondria -miniature internal blanket that overlies parts of the vascular system & heats blood Brown adipose (fat) tissue -Using energy to generate more body heat

Flying squirrels