temperature fluctuations, ecto and endotherms, homeotherms, heterotherms and thermo-conferms
Temperature
fluctuations:
They can occupy
a place in the environment where the temperature remains constant and
compatible with their physiological processes. Physiological processes may have
adapted to the range of temperature in which the animals are capable of living
or they can generate and trap heat internally to maintain constant body
temperature, despite fluctuation in the temperature of external environment.
Ectotherms:
They derive most
of their body heat from the environment rather than from their own metabolism.
They have low rates of metabolism and are poorly insulated. In general,
reptiles, amphibians, fishes and invertebrates are ectotherms, although few
reptiles, insects and fishes can raise their internal temperature. Eclotherms
tend to move about the environment and find places that minimize heat or cold
stress to their bodies.
Endotherms:
Birds and
Mammals are endotherms because they obtain their body heat from cellular
processes. A constant source of internal heat allows them to maintain nearly
constant core temperature, despite the fluctuating environmental temperature.
Core means body’s internal temperature as opposed to the temperature near its
surface. Most endotherms have bodies insulated by fur of feathers or hairs and
large amount of fat. This insulation enables them to retain heat more
efficiently and to maintain high core temperature. Endothermy allows animals to
stabilize their core temperature so that biochemical processes and nervous
system functions can proceed at steady high levels. Endothermy
allows some animals to colonize habitats derived to ectotherms.
Homeotherms and
heterotherms:
Most endotherms
are homeotherms (maintain constant body temperature) and most ectoderms are
heterotherms (have variable body temperature) there are many exceptions. Some
endotherms vary their body temperatures seasonally (e.g. hibernation), others
vary it on daily basis. For example some birds (e.g. humming birds) and mammals
(e.g. Shrews) can only maintain high body temperature for a body mass so small
that they cannot generate enough heat to compensate for the heat lost across
their large surface area.
Humming birds must devote much of the day to locating
and sipping nector (a very high calorie food source) as a constant energy
source for metabolism. When not feeding, humming birds rapidly run out of
energy unless their metabolic rates decrease considerably. At night humming
birds enter a sleep like state called daily torpor and their body temperature
approaches that of cooler surroundings, some bats also undergo daily torpor to
conserve energy. Some ectotherms like some reptiles that can maintain fairly
constant body temperatures by changing position and location during the day to
equalize heat gain and loss.
Thermoconformers:
Many
invertebrates have low metabolic rates and have no thermoregulatory mechanisms,
thus, they passively confirm to the temperature of their external environment.
These invertebrates are termed thermoconformers. Zoologists know that many
arthropods such as insects, crustaceans and horse shoe crab (limulus) can sense
thermal variation e.g. ticks of warm blooded vertebrates can sense the ‘warmth
of a nearby meal’ and drop on the vertebrate most.
Comments
Post a Comment