1 Animal Adaptations for Desert Living 2 Challenges of Desert Living
High temperatures keeping cool
Low humidity conserving water
3 Heat Balance Hs Hc Hr He Hs Heat stored in body Hc Heat exchange due to conduction convection conduction transfer between bodies in contact convection acceleration of conduction by motion Hr Heat exchange due to radiation radiation electromagnetic emission or absorption He Heat exchange due to evaporation evaporation exchange due to heat changing water from liquid to vapor 4 Keeping Cool 1. Heat Avoidance Behavior javelina stay in shady area during midday heat rodents tarantulas scorpions active at night Reduced Hc and Hr 5 Relative Heat Load (kcal) Body Mass (kg) Heat load is greater for small animals. Being nocturnal pays big if youre small! 6 Exception which proves the rule Antelope ground squirrel Out at midday returns repeatedly to burrow where it lays body flat against cool ground. Sparse fur on belly promotes conduction. Increased Hc 7 Figure 41.8 8 Keeping Cool 2. Long Appendages Desert ant and beetle have long thin legs Which lifts body higher from the ground. Stenocara a beetle Namib Desert Cataglyphis the desert ant Saharan Desert Reduced Hc 9 Keeping Cool 3. Passive Radiators
large ears act as passive radiator flat ears have high SV
blood close to surface and lots of surface
Increased Hr (meaning animal increases radiation) 10 Arizona cottontail rabbit species has bigger ears than cool-weather species. Sylvilagus auduboni Sylvilagus floridanus 11 Mule deer a desert-adapted deer also has big ears. White-tailed deer for comparison Herd of mule deer 12 Also kit fox of American Southwest. 13 Knut Schmidt-Nielsen fennec fox lives in still-hotter Saharan desert 14 Keeping Cool 4. Evaporative Cooling
Sweating (mammals one insect)
Gular fluttering (birds)
Increased He and Hc via convection 15 Evaporative Cooling Heat lost when liquid H2O is converted to vapor. Works best when humidity is low! swamp cooler 16 Evaporative Cooling Is Best for Large Animals body water loss per hour at 35oC 0.1kg K-rat 12 70kg human 2.5 500kg camel 1 10-20 body water loss is lethal. Small animals cannot survive heat stress by sweating or panting alone 17 The exception which proves the rule. Diceroprocta apache cicadas emerge as adults in hottest time of summer (mid-June). Males sing midday. Singing can raise thorax T by 12oC. 18 HOW They sweat! Sweating cicadas lose 20-35 of body water every hour. Cicadas can afford H2O loss because they feed on xylem fluid of plants. Xylem fluid is mostly H2O. 19 Honeybee spit An evaporative cooling trick
Hot bee regurgitates drop of nectar ( sugary water) while flying.
Some H20 in the bubble evaporates.
Remainder of drop re-ingested.
Increased He 20 Keeping Cool 5. Countercurrent Heat Exchange Thomsons Gazelle escape behavior can generate copious heat brain must work effectively premium on keeping brain cool 21 Selective Brain Cooling (SBC) In Gazelles Veins Carry deoxygenated blood towards heart Arteries Carry oxygenated blood away from heart 22 Venous blood cooled in nose via panting. Warm arterial blood flows through cool venous blood resulting in countercurrent heat exchange. Cool arterial blood goes to brain. Increased He and Hc by convection 23 Brain Temperature (oC) Body Temperature (oC) Brain T increases more slowly than body T. 24
Challenges of Desert Living
High temperatures keeping cool
Low humidity conserving water
25 Conserving Water 1. Estivation Behavior spade-foot toad Most of the year estivates underground covered in mucus until monsoon rains estivation a state of reduced metabolism that functions to survive drought and heat stress 26 Conserving Water 2. Reduced Water Loss in Excretion Kangaroo Rat All of the water they need to survive is metabolized from the dry seeds they eat. 27 Knut Schmidt-Nielsen 1960s Studied Merriams Kangaroo Rat in Santa Rita Mountains near Tucson. Suspected that excretion was key. 28 Nitrogen Excretion and Water Loss 29 Nitrogen Excretion and Water Loss K-rats might excrete uric acid BUT DONT! 30 K-rat urine is 3-4xs more concentrated than our own urine! HOW
What Kidneys Do
maintain ion concentration
maintain water volume
remove metabolic end products (like urea)
remove foreign substances
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