Different strategies for coping with temperature Flashcards
Ectotherm/endotherm
classification based on source of body heat
Ectotherm
depends almost entirely on ambient heat sources
Endotherm
generates its own body heat
Heterotherms
are intermediate between ectotherms and endotherms: they generate their own
heat either some of the time, or in part of their body only. Some insects and fish.
Poikilotherm/homeotherm
terms refer to constancy of body temperature
Poikilotherm
body temperature tends to fluctuate with changes in ambient temperature
Homeotherm
regulates body temperature close to a set point. Nearly all endotherms are
homeotherms
The terms poikilotherm/homeotherm and ectotherm/endotherm are independent
In
principle, any ectotherm can be homeothermic, given a suitable habitat.
Body heat-The rate of change of body heat depends on the rates of three factors:
- heat production through metabolic means
- heat gain from environment
- heat loss to environment
Body heat =
= heat produced + (heat gained- heat lost)
= heat produced + heat transfer
Heat production:
- Basal metabolism: basic metabolic processes necessary for life result in production of
heat. Metabolic rate is the sum of all energy-requiring biochemical reactions over a
given time interval. The basal metabolic rate (BMR) is that of an animal that is at rest, is
not digesting, and is not experiencing stress.
Factors influencing heat production are
- Behavioural mechanisms e.g. exercise
- Autonomic mechanisms such as accelerated metabolism of energy reserves
- Acclimatization (longer term mechanism) : increase basal metabolic rate
Heat transfer (gain and loss)
Heat can be transferred by four means:
Conduction, Convection, Radiation and Evaporation
Conduction
transfer between objects in contact with each other e.g. animal and water or
rocks. Heat flows from warmer to cooler. Conduction is affected by surface area and
temperature gradient.
Convection
transfer of heat contained in a gas or liquid by the movement of the gas or
liquid. Convection e.g. of air can accelerate heat transferred by conduction between a solid
and the air, e.g. wind cools an animal by removing air warmed by its body and replacing it
with cold air. Convection in water results in very rapid cooling. A naked human cannot
thermoregulate in water below 15oC
Radiation
occurs without direct contact between bodies e.g. sun warms an animal.
Evaporation
evaporation of liquid requires heat which is lost from the surface. Sweating
and panting involve evaporative heat loss.
The rate of heat transfer between a body and the environment depends on
Surface area, temp diff, heat conducting properties of an animals surface
Surface area
surface area/g tissue decreases with increase in body size, therefore small
animals lose and gain heat faster than large ones.
Temperature difference
the closer the body temperature to that of the environment the
less heat is lost or gained
Heat conducting properties of animal’s surface (“specific heat conductance”).
Poikilotherms typically have high heat conductance; they gain or lose heat rapidly and
so stay close to environmental temperature. Homeotherms have evolved means of
reducing heat transfer (i.e. insulation), such as feathers, fur or blubber. Fur and feathers
trap air; as air conducts heat poorly, this further retards the loss of heat.
Regulation of heat exchange
Behaviour, autonomic process, longer term adaptations
(1) Behaviour:
: Move to an environment with suitable temperature e.g. sun or shade
Posture: animals curl tightly to reduce heat exchange, spread out to maximise it
(2) Autonomic process
modify blood flow to vertebrate skin
fluffing of hair/feathers (more air increases insulation)
sweating/ panting to increase evaporative cooling
