Deserts Study Guide- EVERYTHING PDF

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QUIZ 1

1.

Why is there a temperature gradient on Earth from the equatorial regions to the

poles? -

This occurs because the earth is round, so the sun’s rays hit the earth at different angles depending on the curvature of the earth at a certain point. At the equator, the sun’s rays hit the earth directly at a 90º angle; thus, the surface area that the ray reaches is approximately the same as the cross section of the ray itself. Therefore, there is more heat per unit of volume in that region than at the poles, where the sun’s rays hit at an angle, causing it to reach a larger surface area of the earth given the same size of the ray. Thus, there is less heat per unit of volume as we tend towards the poles.

2.

Main reasons: earth is round, angle of sun Why are there deserts at 30 degrees N and S latitudes? Describe the processes that

produce them. -

At equator, cooler air pushes warmer, moist air up. As it ascend to atmosphere, the air expands and loses moisture, causing it to become more cold and dry. At 30 degrees N and S this air coming from equator meets with air from 60 degrees N and S high altitude, causing the colder dry air to descend because of rotation of earth and conservation of momentum. As air descends, it gains heat from the ground, thus allowing it to gain moisture from the ground. Ground becomes dry and air is hotter, causing deserts.

3.

(copied this answer from grassroots answer key) List and describe (in brief) the remaining physical causes of deserts.

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(1) Descending cold, dry air at 30’ North and South poles.

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(2) The centers of continents are dry, therefore there is less precipitation as the air passes through the continent; because the ground is heated, the low density air is pushed upward by the cooler air and the electrons are sucked up and lead to convection which causes the air to lose precipitation. The climate is also more variable here because there is no water to force the heat to sink.

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(3) Mountains cause rainshadow effect; the other side of a mountain is arid and causes a dry region. Hot humid air rises hits the mountain gets higher and then expands and cools and the descends on the other side of the mountain which results in hotter drier air.

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(4) Cold ocean currents; cold dry wind from the shore comes onto the warm land which then changes the temperature easily. Then the cold, dry wind becomes warm and dry and is therefore able to absorb moisture.

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(5) Non-physical causes; the non physical causes such as Humans are one of the physical causes of deserts. (feel free to edit this, I was going off of Emma’s notes)

4.

State which deserts you would be in if you observed the following:

a.

Majority of precipitation in summer, no columnar cacti, lots of leaf succulents such

as agave. b.

Chihuahan ← yes -Hannah Columnar cacti, leguminous trees

c.

Sonoran Desert Arborescent yucca (Joshua Trees)

d.

Mojave Desert Bimodal rainfall, gentle winter rains, local thunderstorms in summer

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Sonoran

e.

Mostly shrubs, few succulents, few annuals. -

5.

The Great Basin Why are plants better indicators of local climate than animals?

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Animals can migrate, hibernate, and adapt, but plants cannot move and thus must survive in the climate year round. Thus, vegetation is a much more reliable measure of the local climate.

6.

Why do biomes along an elevation gradient mimic similar changes in vegetation

along latitudinal gradient? -

As air rises, it expands due to less pressure above it. As a result, the air cools. Thus, an increase in elevation causes the temperature to decrease in the same manner as an increase in latitude. As a result, similar biome spreads occur as one increases in elevation and latitude, leading to similar types of vegetation that are adapted to the temperature and rainfall in the area.

7.

List two fire climax biomes. For each, what trait in morphology or growth habit

allows them to survive fire or perhaps even thrive with frequent fires? Grassland, chaparral, and Ponderosa – or – Upper Sonoran and Transition In Grasslands, when the aboveground portions are burned away, they resprout from roots. In the case of grasses, fire stimulates growth. Ponderosa pine – protected from intense heat by thick bark, with frequent fires there is little fuel to maintain a locally intense fire that could burn through the bark or heat the bark sufficiently to kill the living (meristem)

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Grasslands

8.

In mountains of the SW, bands of vegetation (Merriam’s Life Zones or Biomes)

extend higher on one side of mountains than on the other. Which side? Why ? Explain the pattern.

Plants have adaptations that allow them to live successfully in some range of climate – they can live where it is hot (lower on mts) or can survive freezing temps for some particular period of time (higher on mts). As the S facing slopes of mts in the North Hemisphere receive more sunlight than N facing slopes, for any given elevation it will be warmer/hotter than at that same elevation on the N slope. In the case of species limited by freezing temps, frost intolerant species can live higher up the S slope than they can on the N slope. Whatever the limiting factor – temperature or plant available soil moisture – there is a similar limitation that applies to their distribution on the S facing vs. N facing slopes resulting in particular vegetation type extending farther up the S slope than the N. Conversely, you could consider that higher elevation vegetation types find suitable growing conditions farther down the N side than on the S side.

● Gene flow: movement of individuals into/out of a population; must be reproducing members or must become reproducing members ■ Maintained gene flow between two populations can lead to a combination of the two gene pools, reducing the genetic differentiation between the two groups ○ First four foster heterogeneity, last one leads to homogeneity ● Local adaptation ● Speciation ● Ecological issues: species species interactions ● Character displacement: dwarfism

● Gradients in the deserts ● Adaptations for different water stress ○ Drought avoiders: annual plants ○ Water spenders vs. water savers/collector ○ Adaptations to reduce heat load vs. to conserve water

QUIZ 2

1. Sky islands: sky islands are cradles of diversity that are isolated by seas of inhospitable conditions. -Species: 5 things, sky islands, -Size change (dwarfism) -Ecological factors vs. evolutionary factors Ecological: population growth, species interaction, predators/prey, competition (exclusion and development) Evolutionary: mutation, natural selection, mate choice, genetic drift, gene flow a. What are “Sky Islands”? What conditions produced them? -Isolation & divergence -Isolated populations on mountaintops that used to be joined together but are now separated by xeric/dry basins that create separate ecological niches -Born during the Pleistocene between glaciation and de-glaciation.

b. Many of the endemic species of the SW reside in these Sky Islands. List and briefly describe the contribution of evolutionary factors that have lead to the production of these endemic species. ● Mutation ● Natural selection ● Non-random mating ● Genetic drift ● Gene flow 2. Why might some species exhibit dwarfism on islands when compared to their mainland counterpart? Some species may exhibit dwarfism on islands when compared to their mainland counterpart because on islands there are limited resources (and a need to conserve energy more) and limited land area. The species must adapt and become small so that they can live off less resources while still maintaining a large population size.

There may also be a predator on the island that isn't on the mainland and being small helps the species hide from the predator. 3. a. How are annual plants “drought escapers”? Annual plants produce dormant seeds that germinate when there is just enough rainfall to promote growth. When there is rainfall, water leeches into the seed and leeches out a germination inhibitor. This allows the seed to germinate and grow. Annual plants also grow during a short period of time - they go from seed to flowering in one growing season, meaning they only need one good season to flower and seed. They avoid the drought season by only growing and germinating in the rainy season. b. How is this adaptation different/the same for annuals in the Chihuahuan and Sonoran deserts? Sonoran desert – bimodal rain pattern, has annuals that germinate after summer rains as well as annuals that germinate after winter rains; the summer annuals are adapted to the quick torrential downpours that occur and have built up drought tolerance. Winter annuals can take longer. Chihuahuan desert has most of its precipitation in the summer so it will mainly have summer annuals. 4. List two different physical leaf characteristics that help a plant deal with heat stress and describe how they do so. 1. 2. 3. 4. 5. 6.

Orientation: less direct sunlight Waxy cuticle: prevents water loss and reflects heat Fuzz/salt deposits: increased albedo to lower heat absorption Size: smaller leaf area makes it not absorb as much heat (less absorption of photons) Stomata: open at night, put inside a pit Folding of leaf: less surface area, also traps some hit inside the fold

5. Describe two reasons why islands of the same size in the Sea of Cortez might have more lizard species than mammals. 1. Lizards don’t need as many nutrients as mammals they have lower metabolic rates so they can survive on smaller islands with fewer resources 2. Lower metabolic rates and water resistant skin (more able to resist salt water) so they can survive the journey across the water 6. Water Collectors vs. Water Savers Water Collectors: -Do photosynthesis while retaining water • CAM photosynthesis- photosynthesis during that day with stomates closed to reduce water loss • Shallow root system -- doesn’t compete w deep root system bc at different levels

of the soil Water Savers (have a lower metabolic rate): • Sunken stomates to reduce water loss o Water in pit so it's not blown away by wind, it stays there o Pubescence- small hairs all over the plant • White • Increase insulation layer (keeps heat in)=bad • To counteract insulation, these hairs are white so they reflect sunlight • Increase albedo- (the fraction of solar energy (shortwave radiation) reflected from the Earth back into space) o Smaller leaves- less surface area to lose water from o Leaf orientation 7. How have the annual plants of the Sonoran desert adapted to the rainfall pattern for that desert? Sonoran desert is bimodal (both summer & winter rains) -plants must adapt to two rainy seasons -still both summer and winter annuals that must now adapt to survive in late spring and fall to persevere to the next summer or winter rainfall, when in non-bimodal desert they would die -germination based-precipitation and temperature (winter >20C, Summer particle size gets smaller 9. How does particle size affect species diversity of plants along gradient? -As particle size decreases, SA/V ratio increases-->increases adhesion of the water making it harder for plants to pull out water -This is why it goes from higher bajada to lower playa valley, species diversity drastically decreases (why??) because there are fewer physiological adaptations for water retrieval from soil of higher SA/V ratio

QUIZ 3 1. a) Two aspects of life history strategies are how much and how often to spend

energy on reproduction. One strategy is labeled iteroparity. What is this? ITEROPARITY=multiple reproductive bouts It is when a plant goes through its reproductive cycle several times throughout its life. Usually about once a year depending on the season, it gets ready to reproduce. It limits the amount of seed it produces and does not release them all in one big event. Iteroparity involves producing a limited number of seeds every year. Therefore, in each reproductive cycle, iteroparous plants expend relatively little energy, but they have more reproductive cycles than semelparous plants.

b) What are the advantages and disadvantages of an iteroperous strategy? advantages - the risks are spread apart. It has a good chance of survival, if there is one bad season, it is not so bad because it can reproduce later in a better climate. disadvantages- It will attract seed predators because it produces seeds for many seasons. There may not be a good season for many years. The plant might die early. Adv: It does not put all its eggs in one basket. Thus it limits loss in the bad years and secures benefit in the good years. Disadv: If the plant dies early it does not reproduce as much, although this is not as big of an issue as it is for semelparous plants. It does not swamp its predators with seeds, meaning its predators may eat lots of its offspring according to the cycle. Due to the fact that it produces few seeds, it never really has a huge reproductive success, even in the good years.

1. Why is C3 photosynthesis inefficient in comparison to C4 photosynthesis at high leaf temperatures? -high temperatures: more O2 and less CO2 -C3 uses a RUBISCO enzyme, which fixes CO2 to carbon the plant can use and photorespiration which uses O2 and does not fix carbon -At high temperatures, with less CO2 available, it performs more photorespiration which is not very useful for the plant -C4 photosynthesis has an enzyme called PEPCarboxylase which has very high affinity for CO2 and low affinity for O2 -In high temperatures, the PEPCarboxylase is in the outer mesophyll cell; it fixes CO2 into a C4 molecule and sends it to the inner bundle sheath cell where Rubisco converts CO2 from this C4 molecule into C the plant can use.

2. If CAM photosynthesis fixes far less carbon dioxide per day than C3 and C4 photosynthesis, then why is it present at all in some desert plants? What is the

benefit? Because the C3 photosynthesis enzyme has an affinity for both C02 and 02, but when it grabs O2, it does not result in any carbon chains. At an increased temperature, the concentration of C02/O2 decreases in a plant, however, CO2 decreases at a faster rate, leaving more O2 behind and less CO2. Furthermore, at a higher temperature plants close their stomata to save water, but this also lets in less CO2. Thus, in higher temperatures, there is less CO2 for C3 and more O2 for the C3 process to be wasted on. For C4, however, the enzyme PCP carboxylase does not have an affinity for O2, so it is more likely to produce more carbon chains. CAM Photosyntheses allows for the use of CO2 at night when stomata are open, tis when gradient for water loss is lower. at night, CO2 can be converted to malice acid and stored. During the day, the CO2 from the malice acid can be used for photosynthesis when the stomata are closed, thus with no water loss. Overall, it provides more CO2 and photosynthesis.

3. What is a “pollination syndrome”? A pollination syndrome is a collection of characteristics exhibited by flowers in order to attract and to accommodate a particular pollinator. Elements of a pollination syndrome include flower color, structure, odor, particular inducements and rewards for pollinators, etc.

Describe briefly any two specific pollination syndromes. Bats – ample pollen nectar. The flower will likely be white because bats are noctural and white is most visible at night. It may be wide so the bat can land on it. A hawkmoth will produce a flower with a long thin stalk with pollen to accommodate its long, tubiform tongue. It will be white because the moth is nocturnal too but it need not be wide because the hawkmoth can hover. Birds: go out during day (diurnal), pursue bright red flower, no odor, actinomorphic or zygomorphic. Flower depth is deep, wide area or spur. Reward is nectar, concealed. Bats: Go out at night (nocturnal), go after dull white or green flowers (light colors), like strong, fermented odor. Flower depth is brush or bowl based. Reward is much nectar and pollen, open

4. How does the saguaro maximize the number of flowers it can produce compare to the much larger cardon? The Saguaro opens its flower with sweet, nutritious nectar inside, later int he day than the other cacti. It also specializes as tropical. Also has two peaks of pollination. Bats are nocturnal so they go to plants that open their flowers at night and since the saguaro opens

its flower after sunrise, while still cool, that does not strictly follow the "bat pollination syndrome". Flowers grow on the ribs of the cacti. In an effort to maximize reproductive success, saguaro splits ribs into 2 ribs, thus allowing for more areas for flowers to grow. Cardon is larger and has many more arms, which allows it to grow many flowers on the many arms, thus helping possibility for reproductive success.

What is the evidence that the saguaro does not follow the “bat pollination syndrome” strictly? Bats pollinate at night. They pollinate many types of cacti and the peak pollination level is at night because bats are nocturnal. Saguaro still have a peak at night, but they have a second peak at around 6 AM, suggesting that the Saguaro does not strictly adhere to the bat’s time schedule. Data on the peak times of nectar secretion reveals that the saguaro has two peaks—one at night around 2am and the other in the morning at 5am. Since bats only emerge at night, the morning secretions are targeted towards doves.

Why might the saguaro be doing this? It faces competition for pollination by bats from other cacti. Also, many saguaro live too far north of any bats, and are adapting their characteristics for other pollinators (i.e. the dove) over time. It is being pollinated by the morning dove too, perhaps to combat the fewer bats up north in its region and the stress of character displacement w/ other cactus species pollinated by bats. Thus it can get more pollen and reproduce more by using the dove.

5. Endotherms have a problem regulating body temperature as ambient temperatures increase above the thermal neutral zone. Explain. Above the thermal neutral zone, endotherms’ metabolic rate increases steadily. The metabolic heat produced by attempting to maintain body temperature and greater metabolic function decreases the net benefit of these adaptations to heat stress. Above the thermal neutral zone, endotherms must exert energy to cool themselves, via finding shade, sweating, resting, vasodilation, and various other behaviors and practices that stop thermogenesis. They do not have as many mechanisms to cool themselves as to heat themselves, which is why it is more challenging for them to cool themselves. Also they must work at a high metabolic rate to cool themselves, but this increase creates heat, so they can only cool themselves very slowly.

6. Why do many desert mammals have much longer appendages (ears, nose, limbs) than similar animals at high latitudes? Desert animals have much larger appendages because this allows them a bigger surface area to volume ratio and gives more opportunities for the heat to escape whereas at high altitudes where it is cooler they want to prevent heat loss so they have a lower SA/V ratio. Longer appendages mean more surface area. Desert mammals experience heat stress, while animals at higher latitudes experience cold stress. To handle heat stress, mammals will have adaptations that promote heat loss - since longer appendages have a high surface area/volume ratio, there will be more surfaces by which heat can escape. Inversely, to handle cold stress, animals will have shorter appendages as an adaptation. Shorter appe...