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Ecology: Biomes, Atmospheric Circulation, and Aquatic Systems (VOCAB)

Core Concepts for Today

  • All Achieve Homework Questions are fair game for the exam; make sure you understand the answers to each of them.
  • Topics to master:
    • Hadley Cells
    • Rain Shadow
    • Reading climate diagrams and matching them to terrestrial biomes
    • Summarizing terrestrial biomes in a couple of sentences
    • Describing aquatic environments and differences among aquatic biomes
    • Explaining convergent evolution
  • Key terms and definitions from the slides
    • ITCZ — Intertropical Convergence Zone: the region where the two Hadley cells converge and cause large amounts of precipitation.
    • Lotic — flowing water.
    • Riparian zone — a band of terrestrial vegetation alongside rivers/streams influenced by seasonal flooding and elevated water tables.
    • Littoral, Limnetic, Profundal zones — lake zone classifications with specific habitats.
    • Permafrost — permanently frozen soil; melting due to global warming has ecological and structural consequences.
    • Convergent evolution — unrelated species evolving similar forms due to similar selective pressures.

Hadley Cells and ITCZ

  • Hadley cells are two large atmospheric circulation cells between the equator and 30°N and 30°S.
  • Mechanism of formation (four steps):
    • 1. At the ITCZ, the Sun heats moist tropical air, causing it to rise. ext{location: ITCZ}
    • 2. The rising air cools, causing water vapor to condense into rain and fall back to Earth.
    • 3. After rising to altitudes >10 km, the now cool, dry air circulates back toward Earth and sinks at approximately 30^\circ N and 30^\circ S.
    • 4. The cool, dry air sinks and begins to warm, flowing back toward the equator as warm, dry air.
  • Primary consequence: warm, moist air rises at the equator, creating heavy rainfall in the ITCZ and dry subtropics at around 30° latitude.
  • ITCZ: the geographic area where the two Hadley cells converge, driving large-scale precipitation and climate patterns.
  • Quiz reference: Primary reason Hadley cells form where they do — option d: The Earth is warmest near the equator, and the warm, moist air rises. T_{eq} ext{ is highest at } ext{0° latitude}.

Rain Shadow

  • Rain shadow a region with dry conditions found on the leeward side of mountain ranges.
  • Mechanism: humid winds from the ocean rise over mountains, releasing much of their moisture as precipitation on the windward side; by the time air descends on the leeward side, it is dry, creating arid conditions.
  • Visual cues:
    • Windward side: moist, rainy region.
    • Leeward side: arid/desert conditions.
  • Practical implications: creates contrasting ecosystems within relatively short geographic distances.

Climate Diagrams and Biomes

  • Climate diagram definition: graphs plotting average monthly temperature and precipitation for a location.
  • Reading rules from the slides:
    • When the precipitation line is above the temperature line, plant growth is generally limited by temperature (growing season follows when temperatures exceed 0°C and there is sufficient rainfall).
    • When the precipitation line is below the temperature line, plant growth is limited by precipitation.
    • The shaded region indicates the growing season (months when temperature is above 0°C).
  • Example months shown: J, F, M, A, M, J, J, A, S, O, N, D (labels on climate diagrams).
  • Climate diagrams help match climate to terrestrial biomes, and to understand how temperature and precipitation drive biome structure.

Terrestrial Biomes: Overview and Convergent Evolution

  • Biome (definition): a geographic region containing communities of organisms with similar adaptations. ext{Biome} = ext{region with characteristic climate and life forms}.$$
  • Terrestrial biomes are categorized by major plant growth forms (e.g., trees, shrubs, grasses) and climate.
  • Convergent evolution (definition): two species descended from unrelated ancestors look similar because they evolved under similar selective pressures.
    • Example from slides: two desert plant species do not share a recent common ancestor but both evolved water-conserving growth forms due to arid conditions.
  • Nine categories of terrestrial biomes (as listed in the slides):
    • Tropical rainforest
    • Tropical seasonal forest / savanna
    • Woodland / shrubland (Mediterranean climate)
    • Temperate rainforest
    • Temperate seasonal forest
    • Temperate grassland / cold desert
    • Boreal forest (Taiga)
    • Tundra
    • Subtropical desert
  • Key takeaway: climate (precipitation and temperature) largely determines biome distribution; plant form adapts to water availability and temperature regime.

Global Distribution of Biomes

  • Tropics: tropical rainforest, tropical seasonal forest / savanna, woodland/shrubland.
  • Subtropics / mid-latitudes: deserts, temperate grasslands, temperate forests (seasonal and evergreen), temperate rainforest.
  • Northern latitudes: boreal forest (taiga), tundra.
  • Polar regions: tundra, polar ice cap.
  • The distribution is driven by gradients in temperature and precipitation.

Climate and Biomes: Reading Temperature and Precipitation Data

  • Climates determine temperate biomes: biome boundaries shift with changes in average annual temperature and precipitation.
  • Climate diagrams help visualize these relationships and predict biome type for a location.
  • Shifting climate (e.g., increased temperature, altered precipitation) can move biomes geographically over time.

Permafrost and Its Implications

  • Permafrost definition: soil that remains permanently frozen.
  • Global warming is melting permafrost, leading to several potential outcomes:
    • Decomposition of soils releases CO2 and methane (greenhouse gases).
    • Meltwater can pool and form new aquatic ecosystems.
    • Melting soil enables plant growth and nutrient/water uptake, altering community composition.
    • Possible structural impacts: buildings and infrastructure on permafrost may collapse.
  • These changes illustrate feedbacks in climate systems and potential rapid shifts in Arctic ecosystems.

Boreal Forest (Taiga) and Soil Fertility

  • Boreal forest — dominated by evergreen needle-leaved trees; long, severe winters and short growing seasons.
  • Soils are acidic with low fertility due to slow decomposition rates; this constrains nutrient availability.
  • Also known as Taiga.

Temperate Biomes: Temperate Seasonal Forest and Temperate Rainforest

  • Temperate seasonal forest:
    • Moderate temperatures and precipitation.
    • Dominated by deciduous trees.
    • Distinct seasons with a cold winter and warm summer.
  • Temperate rainforest:
    • Mild temperatures with abundant precipitation.
    • Dominated by evergreen forests; high humidity supports lush understory.

Tropical Rainforest and Other Tropics Biomes

  • Tropical rainforest:
    • Warm temperatures year-round and high rainfall.
    • Multilayered forest structure; extremely high biodiversity.
    • Soils often nutrient-poor but rapid nutrient cycling supports dense communities.
  • Tropical seasonal forest / savanna:
    • Warm year-round temperatures with pronounced wet and dry seasons.
    • Fire and grazing influence vegetation; grassland can dominate in the absence of frequent fires.
  • Subtropical desert and woodland/shrubland:
    • Hot summers, mild to wet winters (Mediterranean climates in some regions).
    • Drought-tolerant grasses and shrubs predominate.

Open-Ended Questions and Key Takeaways about Biomes

  • Tropical rainforest question (quiz sample): Correct description — forests in this biome contain the highest species diversity of any habitat on Earth. [[Correct]]
  • Tropical rainforest characteristic summary: high biodiversity, multilayered structure, warm and wet climate, nutrient cycling influenced by rapid decomposition in some soils but low fertility per unit soil due to leaching.
  • Convergent evolution example: unrelated species in similar climates evolve similar growth forms (e.g., desert plants). [[Correct]]

Aquatic Biomes: Classification and Zones

  • Aquatic biomes categorized by flow, depth, and salinity.
  • Lotic systems: flowing water (streams and rivers).
  • Riparian zone: vegetation along rivers/streams influenced by seasonal flooding and elevated water tables.
  • Freshwater systems include:
    • Streams and rivers (flowing freshwater; width varies).
    • Ponds and lakes (standing freshwater; some depths too deep for rooted plants).
  • Lake zones (distinct ecological zones):
    • Littoral zone — near shore with rooted vegetation.
    • Limnetic zone — open water where light penetrates and photosynthesis occurs.
    • Profundal zone — deep water; low or no sunlight; low oxygen zones in some lakes.
  • Profundal zone definition: the deeper waters of a lake that do not receive sunlight. Correct answer on the quiz: option d.
  • Circulation and turnover in temperate lakes (seasonal dynamics):
    • Spring turnover: epilimnion (warm surface layer) sinks as temperature drops; nutrients mix downward.
    • Summer stratification: epilimnion (warm, well-lit surface) above thermocline; hypolimnion is cold, dark, nutrient-rich but low oxygen can occur.
    • Autumn turnover: cooling surface leads to mixing, redistributing nutrients.
    • Winter: ice cover and reduced mixing; water column becomes isothermal at 0–4°C depending on conditions.
  • Terms to know: epilimnion, thermocline, hypolimnion.

Freshwater Wetlands and Estuaries

  • Freshwater wetlands: standing freshwater or soils saturated with water for part of the year; shallow enough for emergent vegetation throughout.
  • Examples include swamps, marshes, and bogs.
  • Estuaries: zones where freshwater rivers meet and mix with saltwater from oceans; highly productive and highly variable conditions.

Marine and Coastal Biomes

  • Salt marshes: salt-tolerant, nonwoody emergent vegetation in coastal saltwater systems.
  • Mangrove swamps: salt-tolerant trees with roots submerged in water; occur along tropical and subtropical coasts.
  • Intertidal zone: zone along coast between high and low tides; highly dynamic and supports specialized organisms.
  • Coral reefs: marine biomes in warm, shallow waters that stay around ~20°C year-round; high biodiversity and productivity.
  • Open ocean: the vast expanse away from shore and reefs; covers the largest portion of the Earth's surface; contains a large portion of marine life but biodiversity distribution is patchy and many areas have lower biomass compared to coastal ecosystems.
  • Open ocean quiz takeaway (as shown in slides): the open ocean is described as covering a large portion of Earth and housing significant biodiversity; the slides present option a as the correct statement. [[Correct]]

Notable Connections and Real-World Implications

  • Climate change impacts:
    • Melting permafrost releases greenhouse gases (CO2, methane), alters hydrology, and reshapes Arctic ecosystems.
    • Shifts in Hadley cell dynamics and ITCZ position can alter precipitation patterns, impacting tropical and subtropical biomes.
  • Biodiversity and ecosystem services:
    • Tropical rainforests host the highest biodiversity; loss threatens ecological services (carbon storage, water cycling, species interactions).
    • Wetlands and estuaries provide flood control, water purification, and nursery habitats.
  • Human infrastructure and climate feedbacks:
    • Infrastructure on thawing permafrost faces collapse risks.
    • Desertification and altered rainfall patterns affect agriculture and habitability.

Quick Reference: Key Terms and Concepts (glossary-style)

  • ITCZ: Intertropical Convergence Zone; convergent zone of Hadley cells causing heavy rainfall near the equator.
  • Hadley cell: tropical atmospheric circulation between the equator and ~30° latitude, driving trade winds and desert belts.
  • Rain shadow: dry area on leeward side of mountains due to moisture loss on windward side.
  • Convergent evolution: independent evolution of similar traits in species of different lineages due to similar environmental pressures.
  • Lotic: flowing freshwater systems (streams, rivers).
  • Littoral: near-shore lake zone with emergent vegetation.
  • Limnetic: open-water lake zone with photosynthesis by phytoplankton.
  • Profundal: deep-water zone with little or no light.
  • Permafrost: permanently frozen ground; melting alters ecosystems and infrastructure.
  • Biome: broad regional classification of ecosystems based on climate and dominant life forms.
  • Biodiversity gradient: highest species diversity typically in tropical rainforests; varies by habitat and depth in oceans.

Practice Q&A (from slides for quick recall)

  • Q: What is the primary reason that Hadley cells form where they do? A: The Earth is warmest near the equator, and the warm, moist air rises. Correct option: d.
  • Q: Why do unrelated plant species show similar growth forms in areas with similar climates? A: Convergent evolution. Correct option: b.
  • Q: Which statement best describes the tropical rainforest biome? A: Forests in this biome contain the highest species diversity of any habitat on earth. Correct option: d.
  • Q: Which accurately describes the open ocean? A: This biome covers a relatively large portion of the Earth and houses most of its biodiversity. Note: the slides mark option a as correct in the provided material. Acknowledging potential debate here, the slides label this as the correct choice. [[Correct]]

Summary Takeaway

  • Climate patterns (Hadley cells, ITCZ, rain shadows) are primary drivers of where biomes occur and how they function.
  • Biomes reflect adaptations to temperature and precipitation regimes; convergent evolution explains why distant regions can look ecologically similar.
  • Aquatic systems are structured by flow, depth, and salinity, with distinct zones in lakes and oceans that support different communities and processes.
  • Permafrost dynamics illustrate strong climate feedbacks with broad ecological and societal consequences.