BiomesMajor ecosystems found in large geographicregions characterized by a distinct vegetative community

--primarily a result of abiotic processes

PhysiognomyThe overall appearance of a biome or communitybased on the relative density, height, and shape of its dominant vegetation

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

Fig. 24.3

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

Fig. 24.4

Tropical Biomes:

• Most occur within 10° latitude

• Defined by rainfall > 240 cm per year

• Temperature and moisture not limiting

factors, nutrients and light are

Amazon(Neotropics)

Congo SE Asia

New World

Old World

Misconceptions about tropics:

• Soils are rich

• Climate is stable

• Jungles are dense

• dense canopy, stratified up to

four levels

Physiognomy of Tropics

• high diversity of trees

• 400-700 trees per hectare

• 100-200 species represented

• low population densities for each

Humidity ~70%

Humidity 90-95%

Temperature gradient

Fig. 25.6

High light attenuation

Leaf litter accumulates rapidly, but decays rapidlyPlants in competition for nutrients released in decay

Physiognomy of Tropics• shallow, spreading roots and

leaves with drip tips

Physiognomy of Tropics

• shallow, spreading roots and leaves with drip tips

• Mycorrhiza fungi and hyphae

• buttress and prop roots

Physiognomy of Tropics

• shallow, spreading roots

• Mycorrhiza fungi and hyphae

• buttress and prop roots

• epiphytes, lianas

Gaps and patch dynamics

Semi-aquatic herbivores

Nocturnal frugivores

Diurnal herbivores

Nocturnal herbivores

Ant eaters

Parallel Evolution

Hammocks in south Florida

Temperate rain forest: Olympic National Park, WA

Longleaf Pine community of the Southeast

http://www.worldwildlife.org/

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

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

Four major North American Deserts

1. Sonoran2. Mohave3. Chihuahuan4. Great Basin

Sonoran DesertLowest, hottest desert up to 120° F in summerBi-annual rainfall ~18 cm/yrMost diverse desert in NA

Saguaro Cactus limited by temperature

SonoranDesert, AZ

cholla cactus ocotilla palo verde trees

Mohave Desert

Most precipitation in winter 5-12 cm/yrHigher elevation than SonoranPlants adapted to cooler temperatures

Joshua Trees

Cholla cactus and yucca

Chihuahuan desert and creosote

Most precipitation in summer 15-20 cm/yrDominated by low shrubs and cactus

Prickly Pear Cactus

Great Basin Desert

Largest U.S. desert, considered a cold desertElevations range from 5000-6000 feetCaused by a series of rainshadow effectsPrecipitation 15-25 cm/yrDominated by sagebrush

Sagebrush dominates

All deserts are characterized by slow growth by plants, but also slow decay of litterVery fragile ecosystems because of thisDisturbances, even a single car track, may last decades to centuriesArchaeological roads, clearings still visible after 1000+ years

Kangaroo Rat: Endemic to North America

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

Jerboa

• Sonoran desert exclosure experiment show keystone effect

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

desert grassesdominate