Endothermy and Ectothermy

Endothermy and Ectothermy Ch. 6.7, Bush

Outline • Effects of temperature on life • Thermoregulation • Ecological aspects of thermoregulation

Effects of extreme temperatures • Cold -- the effects of freezing • physical damage to structures caused by the formation of ice; the membrane bound structures are destroyed or damaged. • Heat • inadequate O2 supply for metabolic demands (especially in areas where O2 is low, such as water) • Heat and Cold • reduced activity or denaturation of proteins -- the inactivation of certain proteins with the result that metabolic pathways are distorted.

Optimal temperature for enzyme functioning

Body Temperature • Law of Tolerance: • for most requirements of life, there is an optimal quantity, above and below which the organism performs poorly • There is much variation in the range of temperatures that a species can tolerate

Thermoregulation • maintenance of internal temperature within a range that allows cells to function efficiently • Two main types • ectothermy • endothermy

Endothermy versus ectothermy

Ectothermy • an animal that relies on external environment for temperature control instead of generating its own body heat • “cold-blooded” • e.g., invertebrates, reptiles, amphibians, and most fish • the majority of animals are ectotherms

Metabolism and temperature • ectotherms cannot move very much unless the ambient temperature allows • roughly, for each 10 degree increase in temperature, there is a 2.5 increase in metabolic activity

Ectothermy Desert iguanas are active only when ambient temperature is close to optimal for them

Ectothermic animals

Endothermy • a warm-blooded animal that controls its body temperature by producing its own heat through metabolism • evolved approximately 140 mya • E.g., birds, mammals, marsupial, some active fish like the great white shark and swordfish

Endothermic animals

Outline • Endothermy versus ectothermy • Behavioural adaptations to thermoregulation • Physiological adaptations to thermoregulation

Behavioural adaptations for thermoregulation • animals often bathe in water to cool off or bask in the sun to heat up

Shivering, sweating, and panting • honeybees survive harsh winters by clustering together and shivering, which generates metabolic heat • Inefficient – 75% of energy is lost in mechanical movement

Torpor • metabolism decreases • heart and respiratory system slow down • body temperature decreases • conserves energy when food supplies are low and environmental temps are extreme E.g., hummingbirds on cold nights

Hibernation • Long-term torpor • adaptation for winter cold and food scarcity • E.g., ground squirrels

Aestivation • summer torpor • adaptation for high temperatures and scarce water supplies • E.g., mud turtles, snails

Endothermy and the evolution of sleep? • evolutionary remnant of torpor of our ancestors • the body needs sleep in order to offset the high energy costs of endothermy: • When animals fall asleep their metabolic rates decrease by approximately ten percent

Colour and Posture • Change coloration (darker colors absorb more heat) • E.g., lizards, butterflies, crabs • Posture: • Change shape (flatten out to heat up quickly) • Orientation changes

Chemical adaptations • Many Canadian butterflies overwinter here and hibernate • they produce sugar-like substances as antifreeze • E.g., Mourning Cloak butterfly

Advantages & Disadvantages of Endothermy • Advantages: • external temperature does not affect their performance • allows them to live in colder habitats • muscles can provide more sustained power • e.g., a horse can move for much longer periods than a crocodile can • Disadvantage: • energy expensive • an endotherm will have to eat much more than an ectotherm of equivalent size

Where can endotherms thrive? • Higher latitudes and deserts • Terrestrial environments have more variation in daily and seasonal temperature which contributes to more endotherms in terrestrial environments • endotherms (mammals and birds) generally outcompete ectotherms if they are after the same food source

Size and thermoregulation • Small mammals (such as mice and shrews) have a greater dependence on internally-generated heat than big mammals (such as elephants and hippos) • leads to: • presence of insulation (fur - large mammals generally have less hair) • voracious appetites of small mammals (a shrew eats more per unit body weight than an elephant does)

Surface area to volume ratios

Ectothermy vs. endothermy • Many more ectotherms are small in size versus endotherms • Ectotherms typically have no insulation • Posture is different

Where do ectotherms thrive? • Where food items are: • scarce • small • In environments low in O2

Ecosystem functioning and ectothermy • Production Efficiency: -can be seen as the ratio of assimilation between trophic levels = biomass of predator biomass of food species • Ectotherms are more efficient than endotherms (up to 15% versus 7%)

Thermoregulation and food chains • Endotherms are often the top predator in food chains • Food chains with lots of ectotherms are often longer in length

Summary • Endothermic animals regulate their body heat to stay within the optimal range for performance while the temperature of ectothermic animals fluctuates with that of the surrounding environment • Both endotherms and ectotherms have a variety of behavioural and physiological adaptations to deal with environmental extremes

Climate Ch. 4, Bush

Outline • Climate and ecology • Solar energy and air circulation • Oceanic influences • Cycles of climate change

Climate affects ecology

Temperature and precipitation

Outline • Climate and ecology • Solar energy and air circulation • Oceanic influences • Cycles of climate change

Solar energy • Solar energy distribution is not balanced across the globe in • intensity • constancy • Together, these differences explain the distribution of tropical and temperate climates

Intensity of Solar energy • Solar energy is more intense at lower latitudes (that is, closer to the equator) because: • the “footprint” of the beam of energy is smaller at tropical latitudes • beams have shorter passage through the atmosphere

Intensity of solar energy more energy per square meter in the tropics than at the poles

Differences in daylength

Differences in Day Length • caused by the constant tilt of Earth as it orbits around the sun • the reason why temperate environments have four seasons while tropical environments do not

Heat and air circulation • The disparity in energy input across the globe drives all our weather systems • This is because heat energy must flow from warm to cold

Hadley cells – the effect of heat transfer • Hot air rises and, as it rises, it cools • Cool air cannot hold as much moisture as heated air, so it rains • This cool, dry air must go somewhere so it pushes towards the poles, where it slows and descends • As it descends, it is warmed

Hadley cells

Hadley cells and climate • The downdraft of hot dry air causes the formation of the desert regions of Earth: E.g., Sahara Sonoran Australian Gobi Atacama

Endothermy and Ectothermy