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Biomes of the World: Tropics and Deserts

Explore the distinct characteristics of tropical and desert biomes, including their physiognomy, misconceptions, and unique adaptations. Learn about the diverse vegetation, wildlife, and environmental factors that shape these major ecosystems.

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Biomes of the World: Tropics and Deserts

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  1. Biomes Major ecosystems found in large geographic regions characterized by a distinct vegetative community --primarily a result of abiotic processes Physiognomy The overall appearance of a biome or community based on the relative density, height, and shape of its dominant vegetation

  2. Six major biomes: 1. tropics 2. grasslands/savannah 3. temperate forests 4. coniferous forests or taiga 5. tundra 6. deserts

  3. Fig. 24.3 Minor biomes: 1. chaparral 2. temperate rain forest 3. polar regions

  4. Fig. 24.4

  5. Tropical Biomes: • Most occur within 10° latitude • Defined by rainfall > 240 cm per year • Temperature and moisture not limiting factors, nutrients and light are

  6. Amazon (Neotropics) SE Asia Congo Old World New World

  7. Misconceptions about tropics: • Soils are rich • Climate is stable • Jungles are dense

  8. Physiognomy of Tropics • high diversity of trees • 400-700 trees per hectare • 100-200 species represented • low population densities for each • dense canopy, stratified up to four levels

  9. High light attenuation Humidity ~70% Temperature gradient Humidity 90-95% Fig. 25.6

  10. Leaf litter accumulates rapidly, but decays rapidly Plants in competition for nutrients released in decay

  11. Physiognomy of Tropics • shallow, spreading roots and leaves with drip tips

  12. Physiognomy of Tropics • shallow, spreading roots and leaves with drip tips • Mycorrhiza fungi and hyphae • buttress and prop roots

  13. Physiognomy of Tropics • shallow, spreading roots • Mycorrhiza fungi and hyphae • buttress and prop roots • epiphytes, lianas

  14. Gaps and patch dynamics

  15. Nurse tree with successional stages of growth to obtain nutrients released from decaying wood

  16. Semi-aquatic herbivores Nocturnal frugivores Diurnal herbivores Nocturnal herbivores Ant eaters Parallel Evolution

  17. Quiz • How would you describe the physiognomy of tropical • biomes? • 2. What are three misconceptions about the tropics and • why? • 3. What is the function of Mycorrhiza fungi in tropical soils? • 4. What is patch dynamics and its relationship to biodiversity? • 5. What is the function of prop and buttress roots?

  18. Deserts are defined by rainfall: • true desert has < 12 cm/yr • extreme desert < 7 cm/yr • semi-desert has up to 40 cm/yr • evaporation exceeds rainfall

  19. Deserts also characterized by: • hot days, cool nights from high albedo • sparse plant life • C4 and CAM photosynthesis • xerophytes • more living plant biomass below ground than above, sometimes 1:10 difference

  20. Four major North American Deserts • Sonoran • Mohave • Chihuahuan • Great Basin

  21. Sonoran Desert Lowest, hottest desert up to 120° F in summer Bi-annual rainfall ~18 cm/yr Most diverse desert in NA Saguaro Cactus limited by temperature

  22. Sonoran Desert, AZ cholla cactus ocotilla palo verde trees

  23. Most precipitation in winter 5-12 cm/yr Higher elevation than Sonoran Plants adapted to cooler temperatures Mohave Desert

  24. Joshua Trees

  25. Cholla cactus and yucca

  26. Most precipitation in summer 15-20 cm/yr Dominated by low shrubs and cactus Chihuahuan desert and creosote

  27. Prickly Pear Cactus

  28. Largest U.S. desert, considered a cold desert Elevations range from 5000-6000 feet Caused by a series of rainshadow effects Precipitation 15-25 cm/yr Dominated by sagebrush Great Basin Desert

  29. Sagebrush dominates

  30. All deserts are characterized by slow growth by plants, but also slow decay of litter Very fragile ecosystems because of this Disturbances, even a single car track, may last decades to centuries Archaeological roads, clearings still visible after 1000+ years

  31. Kangaroo Rat: Endemic to North America

  32. Kangaroo Rat Adaptations No sweat glands and never drink water Kidneys concentrate urine 5X more than humans Nocturnal behavior, with large auditory bulla Stay in burrows during day, plug entrance and cache seeds Use torpor for brief periods, have bare feet to radiate heat, or cover with tail to retain heat Rostrum long, with complex nasal bones, convoluted surfaces cooled by evaporation to capture water in air leaving body

  33. Ants in Deserts • high diversity, granivores • Chihuahuan desert: 23 spp. in 30 m2 • 50 spp. in 3 km transect • Australia: 150 spp. in < 1 ha • Sonoran desert exclosure experiment show keystone effect desert grasses dominate

  34. Quiz • How would you describe the physiognomy of desert • biomes? • Describe how the Kangaroo Rat is adapted to desert • environments? • Why are deserts considered ‘fragile’ ecosystems? • 4. Give three examples of parallel evolution in deserts. • What are the major differences among the four • deserts in the western U.S.?

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