BIO 461 - Exam 3 - Dry (Xeric) Environments PowerPoint

Question 1

Definition of a desert.

Answer 1

evaporation potential exceeds precipitation (i.e., dry)

Question 2

3 biotic challenges in a desert.

Answer 2

water balance
thermoregulation
energy balance

Question 3

How do species deal with extreme seasonal challenges? (3 E’s)

Answer 3

1. Expire (die): typically, in invertebrates (palavered beetles). No adults. Hatch and last if the pool of water does. Can wait 15 years to hatch.
2. Evade (avoid): Be nocturnal or crepuscular; it refers to the twilight hours, meaning just before sunrise and after sunset, when animals considered “crepuscular” are most active. Borrow where it is cooler or moisture (evading extreme weather (heat) by selecting a micro environment at a certain time. Birds migrate out of the desert.
3. Endure (tolerate): camels, lizards, round tail ground squirrels. Come out during the hot time of day to avoid predation.
   ∙ use less
   ∙ store more
   ∙ cope with imbalance

Question 4

What is homeothermy?

Answer 4

heat in = heat out (temperature does not change)

Question 5

(1) What 3 things do animals use to cope with intense environmental heat and maintain homeothermy?

Answer 5

1. Reduce heat gain
   ∙ behaviorally – microhabitat, temporally (time they come out -nocturnal), posture (squirrel with big, bushy tail – hairs are getting a lot of heat but does not transfer to the body).
   ∙ anatomically/physiologically – insulation, color (reflect light when white), sight.
   ∙ How can adaptations to sight help limit heat gain? Owls are nocturnal – sense the world at night.
   ∙ Insulation: minimize heat transfer (heat going out and in)
   ∙ combination of behavior and anatomy/physiology

Question 6

(2) What 3 things do animals use to cope with intense environmental heat and maintain homeothermy?

Answer 6

2. Increase heat dissipation
   ∙ evaporation (but requires water expenditure) – lose water balance. Very few species use this approach (birds use it but they cheat).
   ∙ regional reduced insulation (when body T > air T)
   ∙ If air temperature is higher than body temperature, it is going to go into the animal. Thick insulation helps this issue. Cover up the short haired areas to reduce surface area where there is poor insulation.

Question 7

(3) What 3 things do animals use to cope with intense environmental heat and maintain homeothermy?

Answer 7

3. Tolerate higher body temperature (Tb)
   ∙ higher preferred Tb - (104°) vs cottontails (101°) By being 3° warmer in body temperature, that is 3° you do not have to eliminate all day through evaporation or insulator heat. Prefer higher body temperatures.
   ∙ allow for considerable heterothermy (i.e., broaden performance curve) – by allowing your body to heat up during the day, you do not need to come up with mechanisms to cool yourself off.

Question 8

What is the other advantage to letting your body go down in temperature at night?

Answer 8

You do not need to worry about the body producing heat if you allow your body to cool off. Metabolism is going to go down. As soon as the day heats up, you have more of a buffer before you get to the critical thermal max is. You are starting at a lower thermal temperature.

Question 9

If it takes an animal longer to heat up, why would that be advantageous, when it is a cost to performance?

Answer 9

Their performance curve is flatter without a dramatic cost to performance. The advantage is they do not have to evaporatively cool for longer – body temperature can go up 2-3 degrees before they get to their preferred temperature, which does set them back.

Question 10

Allen’s rule - revisited and in reverse

Answer 10

Endotherms from colder climates usually have shorter limbs than the equivalent animals from warmer climates. As it gets hotter, it is going to be the reverse of this.
∙ Longer legs and longer ears are good for losing heat, unless the air is hotter than they are, you are going to gain heat. Can use countercurrent heat exchange. Which is going to heat up faster, the rabbit or the poorly insulated rabbit ears? The rabbit ears (will get much warmer than the body temperature) – if you have arteries that are relatively cooler than the blood in the ears, the cooler blood from the body is going pass the warmer blood in the vein coming back from the ear, heat is going to transfer from vein to artery, and hot blood is going to circulate and keep the core cooler.
∙ Ears are made from cartilage, muscle, and skin – is not doing a lot of work.
∙ Countercurrent heat exchange isolates the temperature of the blood in the extremities from the temperature of the blood in the core. Blood circulates between the two, but heat gets transferred.

Question 11

What is Bermann’s rule?

Answer 11

In colder places, animals are bigger; more cells to generate more heat, more thermal inertia (total heat in the body is more), and more surface-to-volume ratio so that the rate heat leaves is slower.

Question 12

How do animals conserve water?

Answer 12

∙ behaviorally
 avoid heat
 find humidity/moisture
∙ anatomically/physiologically
∙ reduce water in urine, feces, ventilation
∙ reduce transcutaneous water loss
 reduce surface area (but reduces heat dissipation)
 skin lipids
 Animals that come from dry environments tend to have more lipids in their skin (fat). Lipids are hydrophobic; they do not like water. A thin lipid layer under the skin is not a great insulator, but is a barrier for water to move across. Snakes in the desert have thicker lipid layer and much lower evaporative water loss across the skin. Reduces the amount of surface area you have and through evaporative water loss and less sweat glands. Harder to get water than avoid heat.
 sweat gland reduction

Question 13

How do animals deal with short-term water imbalance?

Answer 13

∙ store water – must be outside circulation
 typically, in GI tract
 urinary bladder
∙ tolerate hyperosmolality
 typically, >10% change is detrimental but some xeric species can tolerate 50-100% increase