Environmental Adaptations
Mammals can be found in
a variety of habitats, some of which fluctuate in temperature by extreme
amounts during the seasons. The ability
to cope with temperature fluctuations is one of the primary adaptations that enable
mammals to colonize a vast array of habitats and ecological niches all over the
world.
Most mammals are homeothermic: the body temperature is
regulated by physiological means
o
The optimal body temperature for most
mammals tends to be between 36 and 38 degrees Celsius.
o
The surface of the skin communicates
with the hypothalamus to regulate body temperature. Heat is maintained around a given set point,
as determined by the hypothalamus.
Some are heterothermic: the body temperature can
vary in different regions of the body or at different times.
Maintaining body
temperature is costly! Why bother?
o
Increased information processing and
quicker CNS functions
o
Enhanced capacity to capture prey and/or
avoid predation
o
Ability to utilize nutritional resources
year-round
Adaptations
to Heat/Dryness
·
Avoidance:
o
Activity patterns
§ Burrows
§ Nocturnal
activity
§ Bimodal
activity and shuttling
§ Heat
shields
§ Dormancy:
estivation
·
Low basal metabolic rates and body
temperatures
·
Ex: pocket mice and kangaroo mice,
cactus mice
o
Insulation
§ Fur
can minimize the rate of heat that is absorbed from the environment by slowing
movement of heat from the environment to the skin and preventing solar
radiation from reaching the skin.
§ Thermal
windows:
o
Appendages
§ Allen’s
Rule:
o
Metabolic Rate
o
Body Size
§ Heat
load (sum of environmental plus metabolic heat gain) is relatively proportional
to body surface area
§ Bergmann’s
Rule:
·
Resistance
o
Evaporation
§ Sweating
§ Panting
§ Saliva
Spreading
o
Cool Brain
o
Respiratory heat exchange
·
Dealing with lack of water
o
Osmoregulation
o
Conservation of urinary and fecal water
o
Diet
Examples: Desert
ungulates
o
Camels=temperature variation, high
tolerance of high body temperature, ability to maintain blood plasma volume
near normal levels during dehydration, concentrated urine, thick pelage,
behavioral modifications
o
Desert antelopes: pelage modifications,
behavioral mechanisms=searching for shade, panting, suppressing of sweating
mechanisms
o
Gazelles: low evaporative water loss
Adaptations
to Cold
·
Avoidance:
o
Body size
o
Insulation
o
Appendages
o
Coloration
o
Modification of microclimatic regime
§ Communal
nesting
§ Construction
of elaborate nests
§ Foraging
zones
o
Food hoarding
o
Reduction in level of activity
o
Reduction in body mass
o
Dormancy
·
Resistance:
o
Increase in thermogenic capacity
§ BMR
§ NST
§ Shivering
Adaptations
to Marine Living
o
Insulation
o
Deep diving ability
o
Countercurrent heat exchangers