Terrestrial Biomes and Climate Adaptations Study Guide

The Rain Shadow Effect

• The rain shadow effect refers to consistent differences in precipitation observed on each side of a mountain range.
• On the windward side of the mountain, moisture is released as air rises and cools, leading to orographic precipitation.
• As the air descends on the leeward side, it becomes drier, creating a rain shadow, which is characterized by a dry climate.
• Global rain shadows are determined by the combination of prevailing winds and the geographical location of mountains.
• Key locations influenced by these climatic patterns include Vancouver, New York, New Orleans, Mexico City, Lima, Santiago, Rio de Janeiro, Cape Town, Moscow, Istanbul, Nairobi, Jakarta, Calcutta, Beijing, Tokyo, and Sydney.
• Regional example: In Oregon, the rain shadow effect is visible across a transect from the Pacific Border (Oregon Coast Range) through the Puget Trough, the Cascade Sierra Mountains (Middle Cascade Mountains), and onto the Columbia Plateau (Walla Walla, Harney, and Payette sections) and the Blue Mountain section.

Defining Biomes and Terrestrial Ecosystems

• A biome is a distinct physical environment inhabited by ecologically similar organisms that possess similar adaptations.
• Global terrestrial biomes include:
  • Tropical rain forest
  • Tropical seasonal forest/savanna
  • Subtropical desert
  • Temperate grassland/desert
  • Woodland/shrubland
  • Temperate seasonal forest
  • Temperate rain forest
  • Boreal forest
  • Tundra
  • Alpine (mountains)
  • Ice cap
• The Arctic and Antarctic differ significantly; Antarctica is a continent where ice sheets cover approximately $97.6\%$ of the land.

The Whitaker Biome Diagram

• The Whitaker diagram classifies biomes based on two primary variables: annual precipitation and average temperature.
• Annual precipitation scale: $0$ to $400\,cm$.
• Average temperature scale: $-10\,^\circ C$ to $30\,^\circ C$.
• The Tropical rain forest occupies the highest precipitation and temperature bracket ($>200\,cm$ and $>20\,^\circ C$).
• Tundra and Boreal forest occupy the lowest temperature brackets (below $0\,^\circ C$ to $10\,^\circ C$).

Temperature Conversions and Benchmarks

• Temperature conversion formulas:
  • Celsius to Fahrenheit: $T(^\circ F) = T(^\circ C) \times 9/5 + 32$
  • Fahrenheit to Celsius: $T(^\circ C) = (T(^\circ F) - 32) \times 5/9$
• Standard Temperature Comparisons:
  • Home freezer: $0\,^\circ F$ ($-18\,^\circ C$)
  • Freezing/Melting point of water: $32\,^\circ F$ ($0\,^\circ C$)
  • Home refrigerator: $40\,^\circ F$ ($4\,^\circ C$)
  • Room temperature: $70\,^\circ F$ ($21\,^\circ C$)
  • Human body temperature: $98.6\,^\circ F$ ($37\,^\circ C$)
  • Boiling point of water: $212\,^\circ F$ ($100\,^\circ C$)

Walter Climate Diagrams

• Walter climate diagrams, devised by Heinrich Walter, summarize climate in an ecologically relevant way by plotting monthly averages of temperature and precipitation.
• The scaling follows a rule of thumb: $20\,mm$ of precipitation corresponds to $10\,^\circ C$ of temperature above freezing.
• Growing Season: The period during the year when the precipitation line remains above the temperature line on the diagram.

Detailed Biome Characteristics

Tropical Rain Forest

• Location: Found near the equator (roughly $0^\circ$ latitude).
• Climate: Temperature varies little, averaging around $23\,^\circ C$. Annual rainfall exceeds $2000\,mm/yr$.
• Vegetation: Characterized by tall trees (up to $55\,m$) forming large canopies. High species diversity is a hallmark.
• Soils: Old and highly weathered; low in nutrients, carbon, and fertility.

Temperate Seasonal Forest

• Climate: Characterized by warm, moist summers and cold, dry winters.
• Vegetation: Large tree biomass including a mix of deciduous and evergreen trees.

Tundra

• Climate: Severe winters and cool summers, resulting in a very short growing season. Experience 24-hour light during the summer and short winter days.
• Vegetation: No trees or very sparse tree cover. Dominated by short vegetation such as sedges, low shrubs, mosses, and lichens.
• Soils: Permafrost (permanently frozen soil). These soils are high in organic matter, carbon, and nutrients. Tundra soils contain approximately half of the global soil carbon, which is double the amount of carbon found in the entire atmosphere.

Boreal Forest (Taiga)

• Climate: Often shows great temperature variation. Proximity to the sea can moderate temperatures. The growing season is limited.
• Charts for locations like Dawson, Canada ($324\,m$), Ume, Sweden ($7\,m$), and Verkhoyansk, Russia ($137\,m$) show modified scales to reflect cold, dry conditions.

Temperate Rain Forest

• Example: Sitka, Alaska elevation $5\,m$. Average temperature is $6.9\,^\circ C$. Annual precipitation is high at $2,514\,mm$.

Temperate Grassland

• Soils: Rich and fertile.
• Environmental stressors: Shaped primarily by drought, fire, and grazing.

Deserts

• Temperate Deserts (e.g., Salt Lake City, Utah): Higher elevation ($1,300\,m$), moderate average temperature ($10.6\,^\circ C$), precipitation around $414\,mm$.
• Tropical/Subtropical Deserts (e.g., Brawley, California): Low elevation ($-36\,m$), high average temperature ($22.0\,^\circ C$), and very low precipitation ($58\,mm$).

Biological Adaptations to Biomes

Adaptations to Tropical Rain Forests

• Plants - Drip Tips: Leaf structures that allow high rainfall to runoff quickly. This sheds excess water and prevents the growth of fungi and bacteria.
• Root Buttresses: Large, shallow root systems that lend support for tall trees ($55\,m$) in nutrient-poor soil where the fertile layer is only at the surface.
• Animal Specialization: Tropical rain forests hold over $50\%$ of all terrestrial species. Adaptations include high diversity, camouflage, and the use of poisons with aposematic (warning) coloration.
• Arboreal Life: Adaptations for living in trees include long limbs and prehensile tails, as seen in the two-toed sloth (Choloepus hoffmanni), Geoffroy spider monkey (Ateles geoffroyi), and the Solomon Island prehensile-tailed skink.

Adaptations to Deserts

• Plant Drought Avoidance:
  • Annual leaf cycles (e.g., California poppy, Eschscholzia californica).
  • Perennial adaptations (e.g., Creosote bush, Larrea tridentata).
  • Leaf structures: Thick cuticles, trichomes, spines, and a reduced number of stomata.
  • Physiology: CAM (Crassulacean Acid Metabolism) photosynthesis.
  • Storage: Fleshy stems and leaves (succulence) and deep tap roots to increase water uptake.
• Animal Adaptations:
  • Behavioral: Avoiding heat during the day and living in burrows.
  • Physiological: Low rates of evaporation through skin, concentrated urine, production of dry feces, and large ears for heat dissipation (e.g., Desert fox, Vulpes zerda).
  • Specific examples: Desert Kangaroo Rat (Dipodomys ordii), the Sidewinder snake (slithering at $18\,MPH$ to reduce contact with hot sand), use of moist food in the diet, salt glands, and nocturnal torpor as seen in roadrunners.

Adaptations to Tundra and Ice Caps

• Insulation: Blubber layers, thick insulating fur, and oils on skin/coats.
• Morphology: Shorter legs and ears to minimize surface area and heat loss.
• Physiology:
  • Countercurrent heat exchange: A mechanism where heat flows from warm arterial blood to cooler venous blood to maintain core temperature.
  • Antifreeze proteins: Proteins produced to prevent internal ice crystal formation. This has arisen through convergent evolution at least four times, occurring in species like the winter flounder (Pseudopleuronectes americanus) and the Notothen family (cod icefishes).
• Seasonal Adaptations: Hibernation (e.g., BC Spirit Bears) and winter coats with thick underfur that are shed when temperatures rise.

Questions & Discussion

• Identification from Walter Diagrams:
  • Locality with greatest seasonality in rainfall: Diagram A.
  • Locality in Northern Hemisphere: Diagram A (indicated by temperature peak in July/August).
  • Locality with shortest growing season: Diagram C.
• Diagram Analysis:
  • Diagram B represents the Tropical rain forest biome based on the Whitaker diagram (high constant temp and high precip).
  • In comparison of locations at similar latitudes (~5 degrees longitudinally), vast differences in climate occur due to the rain shadow effect (e.g., Portland vs. areas east of Mt. Hood).
• Adaptation Matching:
  • Organisms living in a tropical rain forest biome (Diagram C) would be likely to have prehensile tails, drip tips, and root buttresses.
  • They would NOT typically have fleshy stems and leaves, which is an adaptation for desert environments to store water.