• most life processes occur within the temperature range of liquid water, 0o-100oC

• few living things survive temperatures in excess of 45oC

• freezing is generally harmful to cells and tissues

2

Most life processes are dependent on water in Most life processes are dependent on water in its liquid state (0-100its liquid state (0-100ooC).C).

Typical upper limit for plants and animals is Typical upper limit for plants and animals is 4545ooC (some cyanobacteria survive to 75C (some cyanobacteria survive to 75ooC and C and some archaebacteria survive to 110some archaebacteria survive to 110ooC).C).

Good: high temp -> organisms develop Good: high temp -> organisms develop quickerquicker

The bad: High temperatures:The bad: High temperatures:• denature proteinsdenature proteins• accelerate chemical processesaccelerate chemical processes• affect properties of lipids (including affect properties of lipids (including

membranes)membranes)

3

Temperature has consistent effects on a range of processes important to ecology and evolution (Univ of New Mexico ecologists)• Rates of metabolism• Rates of development of individuals• Productivity of ecosystems• Rates of genetic mutation• Rates of evolutionary change• Rates of species formation

Temperatures rarely exceed 50 degrees C (except….)

Temperatures below freezing point of water are common• On land• In small ponds which may become solid

during winter So: adaptation is necessary

• Freezing disrupts life processes and ice crystals can damage delicate cell structures.

• Adaptations among organisms vary:• maintain internal temperature well above freezing• activate mechanisms that resist freezing

•glycerol or glycoproteins lower freezing point effectively (the “antifreeze” solution)

•glycoproteins can also impede the development of ice crystals, permitting “supercooling”

• activate mechanisms that tolerate freezing

8

Pure water: freezes at 0 degrees C Seawater: freezes at -1.9 degrees C

• Contains about 3.5% dissolved salts

Another physical solution to freezing is the process of lowering the temperature

of a liquid or gas below its freezing point w/o it becoming a solid

Liquids can cool below the freezing point w/o ice crystals development• Ice generally forms around some object (a seed)• In a seed’s absence, pure water may cool more than

20C below its freezing point w/o freezing• Recorded to -8C in reptiles and to -18 in

invertebrates• Glycoproteins in the blood impede ice formation by

coating developing crystals

…under a restricted range of temperatures (but of course!)

Optimum: narrow range of environmental conditions to which organism x is best suited

Temperature! One such example. Put a tropical fish in cold water and it becomes

sluggish and soon dies; put an Antarctic fish in temperatures warmer than -5C, and it won’t tolerate it

but Many fish species from cold environments swim

as actively as fish from the tropics

Different temperatures result in different enzyme formation (in quantity or in qualitative difference of the enzyme itself)

Rainbow trout: • Low temp in its native habitat during the

winter• Higher temp in the summer

Many organisms accommodate to predictable environmental changes through their ability to “tailor” various attributes to prevailing conditions:• rainbow trout are capable of producing two

forms of the enzyme, acetylcholine esterase: winter form has highest substrate affinity

between 0 and 10oC summer form has highest substrate affinity

between 15 and 20oC

14

The heat, water, food and salt budgets of animals (including us) are coupled by diet, evaporative water loss and excretion

Although few animals sweat the way that we do, all lose heat by evaporation from their respiratory surfaces

When water is scarce…stay out of the sun

Why then do several species of seabirds nest in full sun on bare sand, while wedge-tailed shearwater builds it nests under-sand?

Sooty terns can tolerate a hot nesting environment

Theories?• Predators?

• Diets and feeding regimes• Sooty Terns feed on fish and squid – close to the nesting

sites; male and female cooperation in incubation duty• Shearwaters, similar diet, but feed hundreds of

km from their nesting sites• So:

• Sooty terns have stomach full of water-laden food water for evaporative heat loss (remember: fish provide supply of free water)

• Shearwaters plenty of fat for fast but little water (fat has less water than fresh fish)

24

Use scientific literature (what is that?) Read 1 article (no older than 2007) on the

issue of: impact of climate change. Send me the article for approval by March 10 Summarize the article.

• Grammar. Reference. Logic. Etc. no cut and paste. Email me the summary. Present the material during class (5-7 min) Due: March 25 (PDHP). No late papers accepted.

An organism’s ability to maintain constant internal conditions in the face of a varying environment is called homeostasis:• homeostatic systems consist of sensors, effectors, and a condition maintained constant

• all homeostatic systems employ negative feedback -- when the system deviates from set point, various responses are activated to return system to set point

32

33

Principal classes of regulation:• homeotherms (warm-blooded animals) -

maintain relatively constant internal temperatures

• poikilotherms (cold-blooded animals) - tend to conform to external temperatures some poikilotherms can regulate internal

temperatures behaviorally, and are thus considered ectotherms, while homeotherms are endotherms

34

As the difference between internal and external conditions increases, the cost of maintaining constant internal conditions increases dramatically:• in homeotherms, the metabolic rate

required to maintain temperature is directly proportional to the difference between ambient and internal temperatures

35

Homeotherms are limited in the extent to which they can maintain conditions different from those in their surroundings:• beyond some level of difference between

ambient and internal, organism’s capacity to return internal conditions to norm is exceeded

• available energy may also be limiting, because regulation requires substantial energy output

36

Some animals (and plants!) may only be homeothermic at certain times or in certain tissues…

pythons maintain high temperatures when incubating eggs

large fish may warm muscles or brain some moths and bees undergo pre-flight warm-

up hummingbirds may reduce body temperature at

night (torpor)

37

38

Oxidative metabolism releases energy. Low O2 may thus limit metabolic

activity:• animals have arrived at various means of

delivering O2 to tissues: tiny aquatic organisms (<2 mm) may rely on

diffusive transport of O2

insects use tracheae to deliver O2

other animals have blood circulatory systems that employ proteins (e.g., hemoglobin) to bind oxygen

40

Opposing fluxes of fluids can lead to efficient transfer of heat and substances:• countercurrent circulation offsets tendency

for equilibration (and stagnation)• some examples:

in gills of fish, fluxes of blood and water are opposed, ensuring large O2 gradient and thus rapid flux of O2 into blood across entire gill structure

similar arrangement of air and blood flow in the lungs of birds supports high rate of O2 delivery

41

Countercurrent fluxes can also assist in conservation of heat; here are two examples:• birds of cold regions conserve heat through

countercurrent circulation of blood in legs warm arterial blood moves toward feet cooler venous blood returns to body core heat from arterial blood transferred to venous blood

returns to core instead of being lost to environment

• kangaroo rats use countercurrent process to reduce loss of moisture in exhaled air

42

43

44