The Biology of Winter

• Snow Virtue

• Surface Area to Volume Ratio

– Metabolic rate

– Heat loss

– Bergmann’s Rule

• Survival strategies

– Huddling

– Hibernation

– Freeze tolerance

– Freeze avoidance

– Other?

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Snow Virtue

• Excellent insulator

– Ground remains close to 32ºF

• Predator protection

• May improve food availability

• Light transmission & spring

Winter Coloration in the Arctic

Why White?

Photos on this page are taken from www.junglewalk.com

Why white?

• Crypticity

• If true, then

– Why do weasels which hunt under the snow turn white, while the Fisher remains brown and hunts above the snow?

– Why does the Arctic Hare remain white in Greenland and some northern islands during the summer (even in the absence of snow)?

Why white?

• White pelage and plumage are highly vacuolated (i.e., air spaces)

– Melanin (dark pigment) and other pigments replaced

by air spaces

– Air spaces lower the thermal conductivity of plumage

and pelage (thermal conductivity—think window glass versus Styrofoam)

Surface Area and Volume Ratios

In Explaining Biology

Gas Exchange

Heat Exchange

Water Loss

Nutrient Absorption

1 cm

2 cm

4 cm

A = 6 cm2

V = 1 cm3

R = 1:6

A = 24 cm2

V = 8 cm3

R = 1:3

A = 96 cm2

V = 64 cm3

R = 1:1.5

Smaller cubes have greater surface area

relative to volume, therefore, a faster

rate of exchange with environment

As length and width dimensions double,

Volume increases 8X, but

Surface area only increases 4X.

Smaller animals lose heat more quickly

than large animals.

This has important implications for how

animals eat, forage, and survive the winter.

Application of Surface Area

to Volume Ratio

• Metabolic Rates

• Human examples

• Organs

– Lungs, Kidney, GI mucosa

• High Metabolic Rate of small

animals?

– Shrews, H-birds, etc

– Consumer higher caloric food

– Higher food requirement per body mass

– Consume more oxygen per body mass

– Higher body temperature

Bergman’s Rule Warm-blooded animals from northern latitudes have

larger bodies relative to those closer to equator

http://www.mun.ca/biology/scarr/Bergmann's_rule_in_Odocoileus.htm

Golden-crowned Kinglet

(Regulus satrapa)

• TINY

• Insectivorous

• Northern winter climate

• Adaptive response

– Continuous daylight foraging

– Social calling

• Buddy Huddling

Emperor Penguins Extremes in Winter Survival

• What are the physical and behavioral adaptations that allow

Emperor Penguins to survive Antarctic winters?

– Feather design

– Contact with ice-snow

– Insulation

– Interesting use of feathers

– Minimize extremities

– Heat conservation

– Energy storage

http://www.amnh.org/exhibitions/water/?section=lifeinwater&page=lifeinwater_b

Emperor Penguins Extremes in Winter Survival

• What are the physical and behavioral adaptations that allow

Emperor Penguins to survive Antarctic winters?

– Feather design

– Contact with ice-snow

– Insulation

– Interesting use of feathers

– Minimize extremities

– Heat conservation

– Energy storage

http://phys.org/news/2013-03-emperor-penguins-outer-feathers-colder.html

Hibernation Questions

• Adaptive value?

• Equal opportunity activity?

• Disadvantages?

• Waking to sleep?

Woodchuck (Marmota monax) (A larger mammal with more volume)

• Hibernation—complex control—gene regulation, circ-annual

rhythm, environment

• Hyperphagia in Aug./Sept.

• Brown fat deposited over internal organs— generates heat

• Underground burrows-dens

• Hibernation induction trigger

– Role of CO2 & O2

Woodchuck (Marmota monax) (A larger mammal with more volume)

• Metabolic Rest

– Heart rate to 5 bpm

– Body temperature drops to 43°F

• Despite the extra fat, reduce

respiration, temperate climate,

and insulation of underground

– Weight loss of 37-48% (170 days)

• Periodic Arousal

C. mimicking female insects ready for sex C. mimicking female insects ready for sex

Body Temperature & Arousal of Three

Populations of Marmota monax

Zervanos et al. 2009. Physiological and Biochemical Zoology 83:135-141.

Alpine Marmots versus

Temperate Marmots

• Alpine and tundra species

hibernate in social groups

• Why do alpine and tundra

marmots form social

huddles?

Photo from http://webecoist.com/2009/06/28/high-nature-amazing-mountain-wildlife/

Freeze Avoidance in Mammals

• Arctic ground squirrel

“Supercools” two degrees

below freezing

• Hibernates 8 months in year

• Soil temperature goes well

below 0ºC

Gray Squirrel (Sciurus carolinensis)

• Active throughout winter

• Cache-stores—nuts individually stored throughout territory

• Spatial memory

Wood Frog (Rana sylvatica)

& Spring Peeper (Pseudacris crucifer)

• Freeze tolerant frogs

• Winter near soil surface

• Early breeding competition

• Mechanism

– High blood solute concentration

– Decreased cell water

– Freezing restricted to intercellular spaces

Summary-Winter Adaptations

• Plumage & Pellage Adaptations

• Physical properties of volume & surface area

• Torpor & hibernation

• Freeze tolerance & avoidance

• Case Histories – Emperor Penguin

– Golden-crowned Kinglet

– Woodchuck

– Gray Squirrel

– Arctic Ground Squirrel

– Wood Frog & Spring Peeper

– Painted Turtle