Final Exam Carbon Cycle Web Sites…. • Thurs May 11h 11-1 Koffler 204 • Vehicle C emissions and wind credits: • 100 multiple choice questions http://www.participate.net/terrapass – Cumulative – ~10-15% will be on Natural History of the Sonoran Desert • Carbon quiz: • You already have a study guide (outlines and key http://www.wired.com/wired/archive/14.05/carbon.html concepts) • Review session: Wed the 10th 11 AM Koffer 204 Natural History of the Sonoran Natural History of the Sonoran Desert Desert 1. What is a desert? 2. Desert regions and desert habitats 3. 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? What is a desert? • Communities are a continuum • Deserts: – dry places with virtually no plant life • Tucson Basin ‘moist’ ends of desert – Saguaro National Park that’s teaming with plant life • We don’t need to worry too much about • Deserts are extremely hot, others not where the exact cut-off point is on the continuum (except that we live in an ‘iffy’ desert) 1 What is a What is a desert? desert? • Rainfall alone doesn’t capture aridity • Also – how easily water is lost by plants A dry place with drought adapted plants and Potential Evapotranspiration (PET): how animals and an open canopy much water evaporates and is transpired Often defined by annual precipitation: from plant leaves when it is not limiting • Old World Ecologists: < 125 mm An Index of aridity – evaporative strength of air • New World Ecologists: < 250 mm (Tucson has 300 mm! San Diego has the same The ratio of PET:Precip is what climatologists precip as Tucson) use to define a desert What is a desert? Where is a desert? Ratio higher than 3 as semi-arid Primary determinants of where deserts are: Tucson – 300 mm precip/ 1,524 mm PET A. Sunlight falls perpendicular to the axis of the The air can evaporate 5x more water than spherical planet actually falls in precip – so even if we had B. 3 Laws of air and water: 1,524 mm of precip it could all be evaporated! 1. Hot air rises, cool air sinks 2. Rising air expands and cools, sinking air For comparison: compresses and heats up Yuma PET/P = 30 3. Warm air can hold more water than cool Sahara PET/P = 600 air Where is a desert? Where is a desert? • Warmest in tropics – • Creates convection near vertical sunlight cells - Hadley Cells • • Hot air rises from • Rising air spreads towards the poles the tropics, cools, and drops rain in • Eventually cools and then sinks, flowing storms back toward the surface • Air sinks around 30 degrees N and S 2 Where is a desert? Where is a desert? Thus deserts are found mostly at 30 degrees N • Cool air sinks Æ Can it hold more or less water? and S latitude • No rain AND absorbs moisture Where is a desert? There are 4 North American Deserts Great Basin Desert – northern most, highest Rain shadows exacerbate the dryness of the elevation. Very cold winters (in the Old World desert Southwest – would be called a steppe) There are 4 North American Deserts There are 4 North American Deserts Great Basin Desert – Summer growing season Mojave Desert – winter rain. Hard freezes (but isnt always rain!) Many species of low shrubs & winter annual Small leaved shrubs. Poor in trees, succulents plants (only seen in wet years) Few and annuals. succulents and trees Dominants: big sagebrush (Artemisia) Joshua tree is a tree yucca 3 There are 4 North American Deserts There are 4 North American Deserts Chihuahuan Desert – high elevation and arctic Sonoran Desert – Biseasonal rainfall. air causes winter freezes. Northern 2/3 gets winter storms, southern 2/3 gets summer Many species of low shrubs, leaf succulents, thunderstorms and small cacti. Few trees. • The only NA desert with mild Summer rainfall – summer annuals 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 Subdivisions of the Sonoran Desert Sonoran Desert Lower Colorado River Valley Hottest driest part of the desert 1. Lower Colorado River Valley 2. Arizona Upland • Temperature: just like Death Valley in the Mojave 3. Plains of Sonora – Over 120 F (49 C), soil temperatures to 180 F (82 C) 4. Central Gulf Coast • Rainfall: low as 76 mm (3 in) but doesn’t rain every 5. Vizcaino year 6. Magdalena Plains Subdivisions of the Sonoran Desert Subdivisions of the Sonoran Desert Lower Colorado River Valley Lower Colorado River Valley Valleys: creosote bush and white bursage Mountains – have more shrubs and cacti (Very drought tolerant perennials) Few columnar cacti (they are restricted to valley • Trees grow along larger washes floors) 50% or more of the plants are annuals, mostly winter annuals, and abundant only in wet years 4 Subdivisions of the Sonoran Desert Subdivisions of the Sonoran Desert Arizona Upland Arizona Upland Highest, coldest part of the Sonoran Desert • Hard frosts exclude some species found in other • More trees and succulents parts of Sonoran Desert • Trees on rocky slopes and drainageways • Two equal rainy seasons • Saguaros on slopes above valley floors • Palo Verde is a common tree • Many plants and animals – 630 plant species in the Tucson Mountains alone Subdivisions of the Sonoran Desert Subdivisions of the Sonoran Desert Vizcaino Vizcaino • Pacific side of Baja California • Many stem succulents: Boojum (Fouquiera • Less than 125 mm rain, but humid breezes and columnaris), Baja elephant tree (Pachycormus fog discolor), strangler figs Subdivisions of the Sonoran Desert Vizcaino Desert Adaptation Concepts • Also Blue Palms (Brahea armata) The main stressors are aridity and heat: •Aridity? water is needed for physiological functions (e.g. photosynthesis, transport) • Heat? 5 Desert Adaptation Concepts Desert Adaptation Concepts • Heat – Van’t Hoff’s Rule for every temperature rise of 10o C, rate of Options? biochemical reactions double (up to a point) 1. EXPIRE: when the going gets tough…die – Have annual lifecycle and be a tough egg/seed This is why it is bad to get too hot or too cold during harsh times – Too cold = body functions slow due to Van’t Hoff’s Rule. e.g. annual wildflowers – Too hot = proteins break down and body functions slow Desert Adaptation Concepts Torpor: a resting state • lowering of body temp below activity temp Options? 1. EXPIRE • Reduces water needs – less evaporation, less respiration, less excretion 2. EVADE: when the going gets tough…avoid – Store Water. Example: cactus • Also reduces energy needs – – Spatial – migrate, select comfortable – Slower heat loss microhabitat – Less tissue demand (Van’t Hoff’s Rule) – Temporal – nocturnal, CAM, torpor Endure: Temperature Desert Adaptation Concepts Stress Options? 1. Reduce Heat Input 1. EXPIRE Ex. Use orientation/posture, shading from spines/hairs, small surface area 2. EVADE 3. ENDURE: when the going gets tough, tough What’s going on with the toes? it out. Several adaptations: – Temperature Stress – Water Stress 6 Endure: Water Stress Endure: Temperature Stress 1. Store Water 1. Reduce Heat Input • Animals – in fatty deposits 2. Dissipate Heat Ex. Small size, long extremities, evaporative cool • Plants - roots, stems, and/or leaves of plants (plants that 3. Tolerate Hyperthermia (High do this are called Body Temp) succulents) Ex. C4 photosynthesis, Harris’ Antelope Squirrel (up to 105 F!) Endure: Water Stress Endure: Water Stress 2. Conserve Water 3. Tolerate Dehydration • Minimize loss through skin • Many plants (prickly pear) e.g. waxes, small surface area and animals (desert toads) • Minimize excretory loss can tolerate great losses of concentrate urine, dry feces water without dying • Minimize respiratory loss C4/CAM photosynthesis, e.g. Humans: ~12% loss drought deciduous leaves, torpor Prickly pear: ~80% loss Notable Plants and Animals Notable Plants and Animals Ambrosia – major cause of hay fever Ambrosia • Different Species are very common throughout Drought deciduous shrubs the Sonoran desert • Avoid drought by loosing leaves in hot, dry season •Critical nurse plants • Usually have 2 leaf cohorts per year – monsoon and cool winter • Downside: it takes several weeks to re-deploy their leaves (the photosynthetic machinery) 7 Notable Plants and Animals Notable Plants and Animals Ambrosias vary in leaf size and drought tolerance • Smaller leaves, divided leaves - smaller Larger leaves have more photosynthesis and boundary layer and loose heat more can evaporatively cool (need plenty of water effectively by convection to keep stomata open) • Don’t overheat Boundary layer of stagnant air at the surface and can overheat when stomata are closed Which type of leaf do you think is the most drought tolerant (large vs. small)? Notable Plants and Animals Notable Plants and Animals Ambrosia ambrosiodes - Canyon Ragweed Ambrosia deltoidea – Triangleleaf bursage • A large broadleaf shrub • Shrub with smaller leaves • Confined to washes and canyon bottoms – • Same range as canyon ragweed, but is on • Where it can get enough water to plains evaporatively cool • Dominant plant in Arizona Upland (with the Palo Verde and Saguaro) Notable Plants and Animals Notable Plants and Animals Ambrosia dumosa - White Bursage Defining life forms of the Sonoran Desert: • Small shrub with smallest leaves • Columnar Cacti and Legume trees • Dominant in driest areas of the Lower • Columnar cacti are found in arid tropical Colorado River habitats throughout Mexico, Central and • Leave size