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Carbon Cycle Web Sites….
• Vehicle C emissions and wind credits:http://www.participate.net/terrapass
• Carbon quiz:http://www.wired.com/wired/archive/14.05/carbon.html
Final Exam
• Thurs May 11h 11-1 Koffler 204
• 100 multiple choice questions– Cumulative – ~10-15% will be on Natural History of the Sonoran
Desert• You already have a study guide (outlines and key
concepts)• Review session: Wed the 10th 11 AM Koffer 204
Natural History of the Sonoran Desert
Natural History of the Sonoran Desert
1. What is a desert?2. Desert regions and desert habitats3. Adaptation in deserts (generally)4. Plants and animals of the Sonoran Desert
Connections between the detail of the Sonoran Desert and general concepts you have been learning
What is a desert?• Communities are a continuum• Deserts:
– dry places with virtually no plant life– Saguaro National Park that’s teaming with plant
life• Deserts are extremely hot, others not
What is a desert?
• Tucson Basin ‘moist’ ends of desert
• We don’t need to worry too much about where the exact cut-off point is on the continuum (except that we live in an ‘iffy’ desert)
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What is a desert?
A dry place with drought adapted plants and animals and an open canopy
Often defined by annual precipitation:• Old World Ecologists: < 125 mm• New World Ecologists: < 250 mm(Tucson has 300 mm! San Diego has the same
precip as Tucson)
What is a desert?• Rainfall alone doesn’t capture aridity• Also – how easily water is lost by plantsPotential Evapotranspiration (PET): how
much water evaporates and is transpired from plant leaves when it is not limiting
An Index of aridity – evaporative strength of air
The ratio of PET:Precip is what climatologistsuse to define a desert
What is a desert?Ratio higher than 3 as semi-aridTucson – 300 mm precip/ 1,524 mm PET The air can evaporate 5x more water than
actually falls in precip – so even if we had 1,524 mm of precip it could all be evaporated!
For comparison:Yuma PET/P = 30Sahara PET/P = 600
Where is a desert?Primary determinants of where deserts are:A. Sunlight falls perpendicular to the axis of the
spherical planetB. 3 Laws of air and water:
1. Hot air rises, cool air sinks2. Rising air expands and cools, sinking air
compresses and heats up3. Warm air can hold more water than cool
air
Where is a desert?
• Warmest in tropics –near vertical sunlight
•• Hot air rises from
the tropics, cools, and drops rain in storms
Where is a desert?• Creates convection
cells - Hadley Cells
• Rising air spreads towards the poles
• Eventually cools and then sinks, flowing back toward the surface
• Air sinks around 30 degrees N and S
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Where is a desert?
• Cool air sinks Can it hold more or less water?• No rain AND absorbs moisture
Where is a desert?Thus deserts are found mostly at 30 degrees N
and S latitude
Where is a desert?
Rain shadows exacerbate the dryness of the desert Southwest
There are 4 North American DesertsGreat Basin Desert – northern most, highest
elevation. Very cold winters (in the Old World – would be called a steppe)
There are 4 North American DesertsGreat Basin Desert – Summer growing season
(but isnt always rain!)Small leaved shrubs. Poor in trees, succulents
and annuals.Dominants: big sagebrush (Artemisia)
There are 4 North American DesertsMojave Desert – winter rain. Hard freezesMany species of low shrubs & winter annual
plants (only seen in wet years) Few succulents and trees
Joshua tree is a tree yucca
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There are 4 North American DesertsChihuahuan Desert – high elevation and arctic
air causes winter freezes.Many species of low shrubs, leaf succulents,
and small cacti. Few trees.Summer rainfall – summer annuals
There are 4 North American DesertsSonoran Desert – Biseasonal rainfall.
Northern 2/3 gets winter storms, southern 2/3 gets summer thunderstorms
• The only NA desert with mild winters (only a few hard freezes)
• Allows tropical plants and animals to edge up here
• Dominants: legume trees and columnar cacti. (Also many shrubs and annuals)
There are 6 Subdivisions of the Sonoran Desert
1. Lower Colorado River Valley2. Arizona Upland3. Plains of Sonora4. Central Gulf Coast5. Vizcaino6. Magdalena Plains
Subdivisions of the Sonoran Desert Lower Colorado River ValleyHottest driest part of the desert• Temperature: just like Death Valley in the Mojave
– Over 120 F (49 C), soil temperatures to 180 F (82 C)• Rainfall: low as 76 mm (3 in) but doesn’t rain every
year
Subdivisions of the Sonoran Desert Lower Colorado River Valley
Valleys: creosote bush and white bursage(Very drought tolerant perennials)• Trees grow along larger washes
Subdivisions of the Sonoran Desert Lower Colorado River ValleyMountains – have more shrubs and cacti
Few columnar cacti (they are restricted to valley floors)
50% or more of the plants are annuals, mostly winter annuals, and abundant only in wet years
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Subdivisions of the Sonoran Desert Arizona UplandHighest, coldest part of the Sonoran Desert• More trees and succulents• Trees on rocky slopes and drainageways• Saguaros on slopes above valley floors• Palo Verde is a common tree
Subdivisions of the Sonoran Desert Arizona Upland• Hard frosts exclude some species found in other
parts of Sonoran Desert• Two equal rainy seasons
• Many plants and animals – 630 plant species in the Tucson Mountains alone
Subdivisions of the Sonoran Desert Vizcaino• Pacific side of Baja California• Less than 125 mm rain, but humid breezes and
fog
Subdivisions of the Sonoran Desert Vizcaino• Many stem succulents: Boojum (Fouquiera
columnaris), Baja elephant tree (Pachycormus discolor), strangler figs
Subdivisions of the Sonoran Desert Vizcaino• Also Blue Palms (Brahea armata)
Desert Adaptation Concepts
The main stressors are aridity and heat:• Aridity?water is needed for physiological functions (e.g.
photosynthesis, transport)
• Heat?
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Desert Adaptation Concepts
• Heat – Van’t Hoff’s Rulefor every temperature rise of 10o C, rate of biochemical reactions double (up to a point)
This is why it is bad to get too hot or too cold– Too cold = body functions slow due to Van’t
Hoff’s Rule.– Too hot = proteins break down and body
functions slow
Desert Adaptation Concepts
Options?1. EXPIRE: when the going gets tough…die
– Have annual lifecycle and be a tough egg/seed during harsh times
e.g. annual wildflowers
Desert Adaptation Concepts
Options?1. EXPIRE2. EVADE: when the going gets tough…avoid
– Store Water. Example: cactus– Spatial – migrate, select comfortable
microhabitat– Temporal – nocturnal, CAM, torpor
Torpor: a resting state• lowering of body temp below activity temp
• Reduces water needs – less evaporation, less respiration, less excretion
• Also reduces energy needs –– Slower heat loss– Less tissue demand (Van’t Hoff’s Rule)
Desert Adaptation Concepts
Options?1. EXPIRE2. EVADE3. ENDURE: when the going gets tough, tough
it out. Several adaptations:– Temperature Stress– Water Stress
Endure: Temperature Stress
1. Reduce Heat InputEx. Use orientation/posture, shading from spines/hairs, small surface
area
What’s going on with the toes?
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Endure: Temperature Stress
1. Reduce Heat Input2. Dissipate Heat
Ex. Small size, long extremities, evaporative cool
3. Tolerate Hyperthermia (High Body Temp)Ex. C4 photosynthesis, Harris’
Antelope Squirrel (up to 105 F!)
Endure: Water Stress
1. Store Water• Animals – in fatty deposits
• Plants - roots, stems, and/or leaves of plants (plants that do this are called succulents)
Endure: Water Stress
2. Conserve Water• Minimize loss through skin
e.g. waxes, small surface area• Minimize excretory loss
concentrate urine, dry feces• Minimize respiratory loss
C4/CAM photosynthesis,drought deciduous leaves,torpor
Endure: Water Stress
3. Tolerate Dehydration• Many plants (prickly pear)
and animals (desert toads) can tolerate great losses of water without dying
e.g. Humans: ~12% lossPrickly pear: ~80% loss
Notable Plants and AnimalsAmbrosia – major cause of hay fever• Different Species are very common throughout
the Sonoran desert
• Critical nurse plants
Notable Plants and AnimalsAmbrosiaDrought deciduous shrubs• Avoid drought by loosing leaves in hot, dry
season• Usually have 2 leaf cohorts per year – monsoon
and cool winter• Downside: it takes several weeks to re-deploy
their leaves (the photosynthetic machinery)
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Notable Plants and AnimalsAmbrosias vary in leaf size and drought
toleranceLarger leaves have more photosynthesis and
can evaporatively cool (need plenty of water to keep stomata open)
Boundary layer of stagnant air at the surface and can overheat when stomata are closed
Notable Plants and Animals
• Smaller leaves, divided leaves - smaller boundary layer and loose heat more effectively by convection
• Don’t overheat
Which type of leaf do you think is the most drought tolerant (large vs. small)?
Notable Plants and AnimalsAmbrosia ambrosiodes - Canyon Ragweed• A large broadleaf shrub • Confined to washes and canyon bottoms –• Where it can get enough water to
evaporatively cool
Notable Plants and AnimalsAmbrosia deltoidea – Triangleleaf bursage• Shrub with smaller leaves • Same range as canyon ragweed, but is on
plains • Dominant plant in Arizona Upland (with the
Palo Verde and Saguaro)
Notable Plants and AnimalsAmbrosia dumosa - White Bursage• Small shrub with smallest leaves• Dominant in driest areas of the Lower
Colorado River• Leave size matches aridity of habitat
Notable Plants and AnimalsDefining life forms of the Sonoran Desert:• Columnar Cacti and Legume trees• Columnar cacti are found in arid tropical
habitats throughout Mexico, Central and South America
• 41 Species in Mexico
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Notable Plants and AnimalsThere’s 4 big ones in the Sonoran Desert:• Cardon• Senita• Organ Pipe• Sagauro
Final Exam
• Thurs May 11h 11-1 Koffler 204• 100 multiple choice questions
– Cumulative – ~10-15% will be on Natural History of the Sonoran
Desert• You already have a study guide (outlines and key
concepts)• Review session:
– Michod Tues 9th 1PM location TBA– P-Z and Hunter Wed the 10th 11 AM BSE 100
Mean top points so far:282 out of 300 (roughly 94)
So (roughly):A: 253-282B: 225-252C: 197-225D: 155-197E: <154
ExI ExII ExIII Total
94 96 96 286
96 94 96 286
92 96 98 286
98 92 96 286
94 96 94 284
100 90 92 282
92 94 96 282
98 92 90 280
92 94 92 278
98 94 86 278
Exam III –
Top score 98
Mean 75
Natural History of the Sonoran Desert
Notable Plants and AnimalsSaguaro • The only columnar cactus cold-
hardy enough to grow in the Arizona Upland
• Largest cactus in the USA
Notable Plants and AnimalsCAM succulents (like Saguaro) have shallow but
extensive root system• 4 in deep & extend out as far as the plant is tall
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Notable Plants and Animals
CAM metabolism ‘idles’ during drought
Close their stomata –• Recycle CO2 to photosynthesis• Recycle O2 to respiration
Notable Plants and AnimalsIt never really goes dormant• Can resume full growth 24-48
hrs after rain
• Uses shallow roots and idling photosynthesis to take advantage of frequent small rains
Notable Plants and Animals
• Only under nurse plantsdo they get protection from temperature, drought and predators
• Grow very very slowly
Notable Plants and Animals
• Takes several wetter than average years
• Only occurs several times a century in the AZ Upland
= there is episodic recruitment
Notable Plants and AnimalsThe Sonoran Desert is dominated by
columnar cacti and legume treesLegume trees: Palo Verde, Mesquite,
Ironwood
Notable Plants and AnimalsPalo Verde - stem photosynthetic trees• 72% of growth is from stem photosynthesis• More chlorophyll in stems than leaves• More photosynthesis with less water loss
(higher WUE)
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Notable Plants and AnimalsPhotosynthetically active all year – but drought
deciduous• Produces leaves only in response to heavy
rains• Intermediate in function between drought
avoiding deciduous shrubs and drought resistant evergreens
Notable Plants and AnimalsOcotillo – FouquieriaDrought deciduous C3 plants that behave like
CAM plants
Notable Plants and Animals• Short shoots allow rapid leaf deployment• Very shallow roots allow rapid uptake • Behaves like a CAM plant (but is C3)• Idling - parenchyma layer under the bark,
but no stomata
Notable Plants and AnimalsInvasive grasses are threatening the Sonoran
Deserte.g. Bufflegrass (Pennisetum ciliare) was
extensively introduced to AZ and Sonora for livestock forage since the 1960s
Expanding along highways and is invading the desert
Notable Plants and Animals• In Sonora more than 1,000,000 hectares of desert
have been purposely converted to Bufflegrass• ‘Grassification’ of the desert• Results in drastic habitat reduction and reduction
in species diversity• It is big and burns easily
Notable Plants and AnimalsBark Scorpion• Most poisonous of the 30 in AZ• Not likely to kill a human (but it sure hurts)• Orients upside down (people often get stung
picking up rocks)
• Strong venom paralyzes prey
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Notable Plants and AnimalsGiant Hairy Scorpion• Biggest in the USA – 6 inches!• Uncommon, only out a few weeks in summer• Eats what ever it wants!• Mild venom (it doesn’t need much!)
Notable Plants and AnimalsGiant desert centipede (Scolopendra heros) • True giant at 6-8 in long• Aposematic coloration –
• Bite is painful but not dangerous to humans• Won’t bite if you don’t pick them up
Notable Plants and AnimalsKissing bugs – our local
nightmare• 1 in long Bloodsuckers• Fly around in May and June
• Inject anesthetic and an anticoagulant
• Wake up with a large hard itchy welt
Notable Plants and AnimalsBees• Tucson has more species of bees
than anywhere else in the world:• Sonoran Desert: 1,000 species in
45 genera in 7 families• Bees are the pollinators of most
desert plants
Notable Plants and AnimalsMost bees in the Sonoran Desert dig burrows in
the ground for their broodMost are solitary
A few bees are socialHoney bees and bumble bees are highly social,
they have queens that are larger than the workers
Notable Plants and AnimalsTarantula hawk – a wasp• Huge – 2 inches• Very painful sting • Tarantula is eaten alive by larvae
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Notable Plants and AnimalsRattlesnakes • 11 species of rattlesnakes in Sonoran Desert• Usually diurnal• “Extra” senses:
– Pit organ: ‘heat vision’ – Jacobson's Organ: augments smell
Notable Plants and Animals• Fangs are like retractable hypodermic
needles• Hemolytic venom - breaks down blood and
vessels, useful for subduing prey and beginning the digestive process
Notable Plants and AnimalsRattlesnake bites are NOT always fatal
You are more likely to die in a car accident than from a snakebite
Most rattler bites are ‘dry’
Most rattlesnake bite victims are young men - bitten while handling the snake. Called “illegitimate” bites.
Notable Plants and AnimalsBats – 25% of all mammals are bats • Eat lots of insects.• Pollinate flowers and disperse seeds for
ecologically and economically important plants.
• Protect Gotham City from criminal elements.• Many are threatened or endangered.
Notable Plants and AnimalsCalifornia leaf-nosed bat can live for months
without water.• Large eyes as good as the best military
night vision goggles.• They pluck tiny sleeping insects from foliage
without even landing.• Don’t migrate
Notable Plants and AnimalsLesser long-nosed bat - feed on nectar of
columnar cacti.• Migratory – follow the flowering of cardon and
organ pipe north in late spring.• Feed on agave at higher elevations during the
summer.• Return south feeding on agaves in the fall.
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Notable Plants and AnimalsCoevolved relationship with cacti:• Plants provide copious nectar at night.• Light colored flowers with strong musty odor • Sturdy flowers arranged for easy bat access.• Bat has long slender snout with extensible
tongue with a brush tip for lapping nectar.
Notable Plants and AnimalsHummingbirds - birds with:• Most iridescent colors.• Fastest wing beat (80 beats per second).• Fastest heart beat (500/min. resting, 1260
flying).• World’s smallest species (< 2 gm).
Notable Plants and AnimalsHummingbird Metabolism
• Eat mostly nectar and insects.• It requires lots of energy to be a hummingbird (fast heart and wings, high body temp:105-109F).• It’s like driving a car with a one-gallon gas tank: constant need to refuel.• They consume 70% of body weight in solid foodper day, 4-8 times their body weight in H2O.
