Terrestrial Biomes

Reminders

  • Lecture assignment 9 and makeup lecture assignment due Friday.
  • Issue with images in assignment 9 RESOLVED.
  • Final exam on THURSDAY MAY 8 at 2:00pm

Biomes

  • At least eight major terrestrial biomes:
    • Forest
    • Temperate grasslands
    • Tropical savanna
    • Chaparral
    • Shrubland
    • Tundra
    • Desert
  • A major terrestrial or aquatic zone, characterized by vegetation type in terrestrial biomes or the physical environment in aquatic biomes.

What Determines Biome Distribution?

  • Terrestrial biomes are primarily determined by climate.
    • Temperature
    • Rainfall
  • Topography, soil type, and disturbance exposure.
  • Boundaries between biomes are broad and can be indistinct.

Figure 23.2

  • Mean annual precipitation (cm) vs. Mean annual temperature (°C)
  • Biomes plotted based on temperature and rainfall:
    • Tropical rain forest
    • Temperate rain forest
    • Tropical seasonal forest
    • Temperate forest
    • Thorn forest (Savanna)
    • Woodland
    • Thorn scrub (Grassland)
    • Taiga
    • Shrubland
    • Tundra
    • Desert
  • Temperature scale: Tropical → Subtropical → Warm temperate → Cold temperate → Arctic–Alpine

Plant Life-Forms

  • Trees
    • Woody tissue (lignin) → better light access
    • High investment in stems
    • “Cost” of leaf production
    • Deciduous vs. evergreen
  • Shrubs
    • Woody tissue (lignin)
  • Grasses
    • High biomass in leaves

Deciduous Leaves

  • Deciduous leaves live for only a single year or growing season; are shed at the end of a growing season and regrown at the beginning of the next.
    • Winter-deciduous leaves lost in response to low temperatures.
    • Drought-deciduous leaves lost in response to dry conditions.

Evergreen Leaves

  • Evergreen leaves live > 1 year.
    • Needle-leaf evergreen leaf – environments where the growing season is very short (higher latitudes) or nutrient availability severely constrains photosynthesis and plant growth.
    • Broadleaf evergreen leaf – environments with no distinct growing season, growth continues year-round.

Tropical Forest

  • Equatorial
  • Warm temperatures
  • 11-12 hrs of daylight year-round
  • 6-15 ft of rain annually
  • Layered structure provides many habitats
  • High NPP (Net Primary Productivity)
  • High rates of litter input to the forest floor
  • Almost no accumulation because of high decomposition rate

Figure 23.8

  • Tropical rain forests can be divided into five vertical layers:
    • Emergent canopy (trees widely spaced)
    • Upper canopy (medium-spaced crowns)
    • Lower canopy
    • Understory (shrubs and saplings)
    • Ground cover (herbs and ferns)

Tropical Dry Forests

  • Slightly above/below equator
  • Seasonality in precipitation
  • Farther from equator → more seasonality
  • Broadleaf evergreen forests replaced by dry tropical forests
  • Tropical dry forests predominate in lowland areas that have a prolonged dry season or scarce rainfall at any time.

Diversity in Tropical Forests

  • Highest biodiversity
  • 6% of land surface but >50% plant and animal species
  • Buttresses

Tropical Savanna

  • Grasses and scattered trees
  • Warm climate
  • Wet/dry seasonality
  • High ungulate diversity
  • High herbivorous insect diversity
  • Dry season associated with frequent fires
    • Lightning
    • Human activity
  • Termite mound

Temperate Grassland

  • Mostly treeless
  • Cold winters
  • Frequent droughts
  • Periodic fires
  • Dominated by grazers
    • Grasshoppers, nematodes
    • Bison and pronghorn in North America
    • Wild horses and sheep of the Asian steppes
    • Kangaroos in Australia
  • Many birds nest on the ground

Grassland Types

  • Shortgrass prairie
  • Mixed-grass prairie
  • Tallgrass prairie
  • Flint Hills tallgrass prairie
  • mixed-grass prairie
  • shortgrass steppe

Figure 23.13 Soil texture

  • Clay
  • Sand
  • Rainfall (mm) and biome distribution:
    • Grassland
    • Savanna
    • Woodland
    • Forest

Desert

  • Driest of all biomes
  • Temperature can be hot or cold
  • Sparse plant cover → Low NPP
  • Vegetation includes:
    • Water-storing plants (ex: cacti)
    • Deeply rooted shrubs
  • Common animals:
    • Reptiles: snakes, lizards
    • Seed-eating rodents
    • Arthropods (scorpions and insects)

Desert Adaptations

  • Omnivory and generalist diet strategies
  • Drought resistance – adaptations that make them less susceptible to dry conditions
    • Kangaroo rat’s kidneys
  • Drought evasion – inactive periods or forgone reproduction
    • Plants flower only when moisture is present
    • Persist as seeds during drought periods
    • Animals adopt an annual cycle of activities or go into a dormant state (estivation)