Winter: An Ecologic Handbook
Chapter 1
Winter Ecology
The science of ecology
Study of organisms and how they react with the environment and other organisms therein
Coined in 1866 (first study 1940)
The dynamic necessity of budgeting energy to meet interconnected stresses
Based on energetics
Winter is a period of decreased energy
Solar
Thermal
Nutritional
Chapter 2
What and Where is Winter
Stevenson screens
White, slotted, weather box
2 Levels
Sensuous
Emotional
Winter is:
cold
Windy
Wind chill
Mechanical erosion
Snow
Isoplex (isolating level)
Shorter days
Timing device for organisms
Less sunshine
Less incoming solar radiation (energy)
Selective pressures for each environment
mean value
Extreme value
Timing of occurrence
Duration
Seasonality
Repeatability
How do organisms sense and respond to winter?
Ermine color change
Genetically fixed
Elliptical orbit
Perihelion in winter (Earth is closest to the sun)
Aphelion in the summer
Energy types
Radiant
Thermal
Gravitational
Chemical
Electrical
Conduction
direct contact transfer
Radiation
non-contact energy exchanges
Electro Magnetic Spectrum (EMS)
30% of sunlight is reflected by the atmosphere
1,360 watts per square meter hits the earth (70%)
Known as the solar constant
Food Calories
protein 3.1 calories per gram
Fat 9.0 calories per gram
Carbohydrates 3.8 calories per gram
Energy Transfer
Radiation- moves through the medium without affecting it
Conduction- molecule-to-molecule transfer
Convection- transfer of movement of the medium around an object
Evaporation- Latent heat of evaporation
Insulation: property of a material which slows or impedes the transfer of heat by conduction
Energy balance:
Energy in = energy out
If not negative consequences occur
Important for both plants and animals
Temperature inversion
driven by radiative cooling
Still, cold, nights
Warmer air gives energy to colder ground
Cools more than overlying air
Cold air sinks in a positive feedback loop
Sunny/ warm days break the inversion
A major cause of winter pollution
Winter Weather
Change in global weather patterns
Canadian Arctic from shifts down
Snow
Massive radiation reflector
Biggest winter factor?
Snow
Snow classification
Surface generated features
Falling snow
Snow on the ground
Falling snow: Snowflakes
Temperature vs. vapor supply
10 types (1-10)
Plate, stellar crystal, column, needle, spatial dendrite, capped column, irregular crystal, grapple, ice pellet, hail
Snow on the ground
It can remain unchanged for just a short time
Change very slowly when the air is cold (-40)
Change = metamorphism
Crystals can grow as vapor moves
4 Major Types of Metamorphism
Destructive metamorphism
Low/ no temperature differential (<.1 C per cm)
Rounds off crystal edges
Compacts the snowpack
Constructive metamorphism
Large temperature gradients (>.1 C per cm)
The largest crystals near the base
Increased avalanche risk
Easy access to subnivean
Depth Hoar
Firnication
Freeze-melt cycles
Pressure metamorphism
Very wet snow
Surface generated features
Rime frost
Freezing of supercooled droplets
Grow into the wind
Hoar frost
Sublimation changes to deposition
Extremely cold nights
Needle ice
Form in saturated snow-free ground
Destroys roots and burrows
Verglas
Thin ice layer underwater
“Water ice”
Melt-freeze layers
Ice lenses
Wind crusts and Sun crusts
Snow Properties
Density
Age
Density increases over time
Plasticity
Thermal conductivity
Generally great insulator
Wet materials conduct heat
10x faster than dry
Temperature gradient
Generally warmer at the bottom
Spring melt
Isothermal point: all snow is the same temperature
Albedo
Clean snow reflects 85%-90%
Dirty snow reflects ~40% of sunlight
Attenuation
Sunlight penetration
Dark at 30-50cm
Transmission
3 factors
Grain size: larger = greater transmission
Density: Greatest at medium density
Wavelength: Blue has the deepest penetration
Absorption
Elephant traps created around trees
Puddles on lakes even in extreme temperatures
Chapter 3
Life, Winter, and Adaptations
All effects relate directly or indirectly to lower or negative energy balance
Vectors of Winter (SCREW)
Snow
Cold
Radiation
Energy
Wind
Acclimation and Adaptation
Snow and wind reduce access to food
Lower temperatures increase metabolic demands
Animals that suffer may not reproduce
Energy is the currency of life
Short-term physiological and behavioral changes = acclimation
Adaptations evolve over a long time
Responses to winter
decision tree
Some plants and insects avoid winter by dying
Moose lower their body temperature
Reduce energy demands
Stay active
Badgers enter torpor
SCREW affects all levels of biology
Strategies for coping
size limits migration length
Size limits access to microhabitats
Bulkier animals have a better ability to stay warm
Increased surface area to volume ratio
Bergmann’s Rule
Body size increases with increased latitude
Allen’s Rule
Shortened limbs in colder environments
Tiny creatures don’t have enough fuel to maintain body temperature over winter
Lower body temperatures = minimal energy demand
Make antifreeze to keep from cell damage
Small creatures
Ability to be more active
It cannot store a lot of energy
Reproductive shutdown
Changes in posture/ huddling
Maintain 2 temperatures
Core vs Limbs
Moderately sized animals
Ability to store food
Large furnace capacity
Can migrate (vertical and horizontal)
Often burrow
Carnivores active, herbivores hibernate
Large animals
Best insulation and most fat
Most options for leaving
The Nivean Environment
Snow is the key to survival and the worst enemy
3 layers in nivean
Supranivian
Intranivean
Subnivean
Formozov Classification
Chinophobes
Unable to adjust to the cold
Ocelots and opossums
Chrinophores
Live but don’t thrive
Foxes, voles, and Elk
Chionophiles
Only live in wintery areas
Snowshoe hare, ptarmigan
Helps identify levels of adaptation
Supranivean
Snow can severely impede movement
Deer yard up
Foot load or snow load
Total weight divided by the number of feet divided by foot area
Snow coping index
Chest height plus foot load plus behavior
6 important behavioral traits
Trail making
Snow selection
Feeding above the snow
Digging for forage
Migration
Special locomotion
Intranivean and Subnivean
Critical periods
Fall: when daily temperatures fall below ground temperature
Need 6-10 inches of snow to insulate
Hiemal threshold
Freezeouts can harm plants and animals if ground temp drops before snowfall
Governs animal biological clocks
When weasels turn white
When plants “harden”
Over winter period
Stable but slowly decreases population
The least critical “critical period”
Spring
Vernal overturn: air temperature warmer than ground temperature
Flooding
Refreezing and ice lenses
Needle ice: highly destructive to plant roots
Animals at their weakest
Temperature
Affects snow density
Decreases gas exchange and insolation
Light
Critical signal for plant growth
Some plants grow under 50cm of snow and can germinate at 6 feet
“Spring ephemerals” tend to have bulbs
Synthesis of chlorophyll appears to be a function of light
Plant phenols signal reproduction in voles
Atmospheric gasses
Carbon dioxide accumulates
Influences plants and animal physiology
Low levels of photosynthesis
Fungi, plants, and animal sources of carbon dioxide
Variable with topography and plant community
Animals move away from high carbon dioxide
Subnivean Food Web
Complex and multileveled
Shrews are major predators
Eat twice body weight each day
Temperature, Life, and Biochemistry
Biochemicals: molecules constructed by a living system
Temperature affects the organization of the body and the function of enzymes and proteins
Membranes composed of features are extremely sensitive to temperature
Water changes at low temperatures
Viscosity
pH
Electrostatic charge
Effects cascade up the living system
Bonds and the cold
Covalent bonds are stable at room temperature
Too stable at lower temperatures
Weak bonds more affected by cold
Unpredictable
Shape and cold
Shape, movement, and bending all depend on weak bonds
Transport systems are strongly affected
Hemoglobin cannot dump oxygen in the cold
Rate and Temperature
Very temperature dependent
Reaction coordination occurs in a narrow range
Generally, slow down
Phase changes
Frostbite
Freezing of water in the cells
Do not rub
Cells intentionally dehydrate to protect from freezing
Plants tolerate freezing better due to having a cell wall
Strategies for Combatting Cold
4time scales
Long, slow changes
Ice ages
Seasonal changes
Daily changes
Very short term
Seconds to minutes
Human hands can be 59F but the core is still 98.6*F
Proteins must function at both
Quantitative responses
Adding more of the same enzyme
Purely hypothetical
Qualitative responses
Manufacture new, better enzymes or improve existing enzymes
Take apart old enzymes and make new ones
Hot and cold enzyme suit
Can day hours or even days
Energy-intensive
Isoenzymes
Modulation
Slight alteration of existing enzymes so they work under various conditions
As cells cool body allows itself to become more acidic
Protection against freezing
Chemical anti-freeze
Large amounts of glycogen in livers
Mobilized to glucose and pumped to cells
1,000g/ml (.00004g/ml normally)
Some plants use alcohol
Many use glycerols
Prevent water molecules from touching
All require lots of molecules
Glycoproteins
Interrupts ice crystal growth
Work at low concentrations
The combination of molecules most effective
Arctic ground squirrels 26.8*F and still safe
Insects take advantage of the latent heat of freezing
Buys time to make anti-freeze
Neatsfoot oil- ungulate legs have more unsaturated fats
So do wolf foot pads
Physiological responses
Keeping warm
2 types of heat
Acute
Chronic
Mechanisms
More food
Muscular activity
Shivering
Non-shiver thermogenesis
Muscles contract but don’t grab
Enzymes for splitting and forming glucose are present in the same cell
“Futile cycle”
Heat generation determined by mitochondria
Fuel is a limiting factor
Need carbohydrates
At 60% capacity can use fats
Need oxygen as well
Chronic heat production
Increased mitochondria
Brown adipose tissue
Present in most newborn mammals
Produces heat, not ATP
Used by animals < 20 lbs
Winter acclimation
Increase survival
Increased fur and feathers
Increased mitochondria
Changes in enzyme makeup
Heat production in humans
To use fats there must be carbohydrates
Theobromine helps stimulate mitochondria
Cod increases appetite
Constriction of peripheral vessels
Thyroid hormone is an amplifier
Winter dormancy
Body temperature drop
Body size determines fuel storage
The smallest animals have the lowest temperature
Moderate size animals spend more time awake
The largest only have a slight temperature decrease
Can awaken for several days at a time
Hibernation reduces metabolism to 1/80th
Energy is rarely the limiting factor
Timing hibernation
2 level system
Internal cycle: tends to drift
Synchronized by environmental cues
Day length
Temperature changes
Allow animals to come out of hibernation at different, more appropriate times
Allows for age, sex, and physiological variation
All animals arouse during hibernation
Feeders vs non-feeders
Arouse daily to weekly
Arousal uses 90% of energy
Proteins are the limiting factor
Waste disposal is another factor
Cycle urea to prevent a build-up
Concentrated in the liver then excreted in saliva swallowed and converted into bicarbonate
Water loss during hibernation
Can be metabolized by fat and protein synthesis
Any animal threatened with freezing will arouse itself
Control of hibernation
Breathing
2 peptide hormones
Hibernation induction trigger
Pulse drops 50%
Breathing slows and blood acidity increases
Drops all heat production
Increases PFK phosphofructokinases
PFK is an arousal sign
Bears!
Temperature drops to 86*F
Burn nearly pure fat
Other animals use 10% protein
Leave hibernation with 100% of lean body mass
Energy and mass balance
Total energy partitioned into
Maintenance
Growth
Storage
Reproduction
Metabolism is the process of chemical burning of food or stored energy for use by the body
Discretionary energy is energy left after metabolic needs have been met
Mass Balance
“Balancing the energy checkbook”
Chemical energy stored in the body as fat, protein, or carbs
Excreted in urine and feces
Used as work and heat
Balance over time = 0
Heat balance
Metabolic heat - produced by burned energy
Shortwave radiation
Longwave radiation
Heat losses
Conduction
Convection
Long wave radiation
Evaporation
Humans intuitively understand this balance
Move, add clothes, dry off
Thermal transfers
Melanin controls radiation absorption
Sources of longwave radiation
Sun! Rocks and trees
Small temperature changes = delta 4 radiation
Warmer nights under tree canopy
Ungulates know
Insulators slow heat transfer
Heat is lost through convection when a medium (air or water) passes over the skin
The air close to the ground is slowed by friction
Creates a boundary layer
Evaporation happens rapidly in the lungs
Energy is lost from the core of the body to the periphery by skin conduction
Larger animals take advantage of solar radiation
Minimal effects of wind
Smaller animals cannot
2 environmental temperatures
Radiant temperature
Important for large animals
Air temperature
Important for small animals
4 modes of energy transfer
Radiation
Conduction
Convection
Evapotranspiration
The quality of fur as an insulator depends upon length, density, diameter, color, and piloerection
Black fur is not the best
White fur “escorts” light to skin
Black radiates in all directions
Animal Energetics and Nutrition
Any aspect of life may be optimized to provide the energy necessary to survive
Decrease in body mass
Social structures
Diet switching
Microhabitat selection
Lowered body mass
Lower mass requires fewer calories
Less effective at retaining heat
Is this an energy-saving technique or the effect of lower nutrition
Diet
Summer 25 lbs per day of high-quality food (moose)
Winter 11lbs per day of low-quality food (moose)
Increased digestion time
Increased fermentation
Increased heat production
30% calorie deficit
Lower food intake due to
Winter!
Depleted range
Congregation (moose)
Deep snow
30% weight reduction
8% metabolic savings
Social structure
Winter aggregation
Small animals form huddles or balls
Increased Surface area to Volume ratio
“Winter- social” species
Segregated rest of the year
Territorial, foraging strategies, high aggression levels
Inter-species aggregation
Deer and mice
Winter solitary
Small and insectivorous
Shrews and lemmings
Only the “least shrew” know to be winter social
Activity switching
Decreased foraging time
Difficult to get food
Increased rumination time
Increased bedding time
Decreased travel time
Elk save 800 kcal per day
2 strategies
Increased foraging effort
Decrease energy expenditure
Avoid the thermoregulatory penalty of standing in the cold
Activity costs about twice the cost of sitting still
Yarding makes activity easier
Foraging stops under harsh conditions
Selection of Wintering Sites
Selection for habitat
Preferred varied habitat access
Selection for site location
Insolation
Gophers expand range under deep snow
Elevated sites under the snowpack
Thermal features
Human influences
Site selection for food
Nearby or clumped foods require less energy for travel and foraging
Bald eagles switch to carrion
Always found within 2 miles of carrion source
Preparation of sites
Animals often improve their sites
Nest building
Cuts heat loss in half
Bigger nests are often preferable
Food Selection
Diet Switching
Changes to available food sources
Concentrated at lower elevations
Not easy to find grasses and forbs
Switch to browsing
Poor-quality food increases rumination time
Supplemental feed goes against NPS natural population maintenance
Gradual switching is important
Avoid pine needles!
High terpenes
Terpenes are natural abortives
Food quality
Select the highest quality food
Target buds with female catkins
Plant defenses
Chemical defenses
Phenol and triterpenes feeding deterrents
Plants selectively defend certain parts and certain stages
browsing --induced resistance
Compensatory growth
Response to browsing pressure
Larges shoots and leaves
More chlorophyll
Less protein and salts
Advantageous to browsers
Conclusions
Natural selection favors those animals that have adopted maximized strategies of conserving energy
Only 2 sources of nutrition
Food
Mobilizing fats
Animal populations
Winter kill is the number 1 controller of animal populations
Migration, starvation, predation
Hunting
Useful management tool
Reduces herd to levels that can be supported by winter range
3%-28% of species harvested
3% sheep
28% deer
20% elk
Tend to reduce young (naive) animals and old, trophy animals
Migration
Vertical or horizontal
Most in GYE are vertical (easy to travel 4,000 feet
Bats are the biggest horizontal migrators
300 miles N:S = 1,000 vertical feet
Shorter land use migration
Moose 25-30 miles
Spruce forests to willow banks
Sheep similar distance
Pronghorn to Green River Valley
Timing is critical
Snow depth is key
Reaches mid-calf height before becoming a pain to travel in
Slow when the weather is nice, travel fast when it’s harsh
2-6 week migration time
Diet switching
Bighorn sheep add high percent sagebrush
Tend to be lower in nutrition in the winter