Comprehensive Ecology and Biosphere Study Guide

Levels of Ecological Organization and Ecosystem Dynamics

• Hierarchical Organization of Matter and Biological Systems:

  • Matter and biological complexity are structured across a continuous spectrum of scale: $\text{Atoms} > \text{Molecules} > \text{Protoplasm} > \text{Cells} > \text{Tissues} > \text{Organs} > \text{Organisms} > \text{Populations} > \text{Communities} > \text{Ecosystems} > \text{Biomes} > \text{Biosphere} > \text{Earth} > \text{Solar Systems} > \text{Galaxies} > \text{Universe}$
  • Ecology focuses specifically on interactions spanning six key levels: Organisms, Populations, Communities, Ecosystems, Biomes, and the Biosphere.

• Ecosystem Structure and Component Classification:

  • Ecosystems are dynamic functional units consisting of plants, animals, and microorganisms interacting with each other and their non-living physical environment.
  • Biotic Components: Living factors that shape and alter the environment (e.g., animals, fungi, plants, bacteria). Dead organic matter (detritus) remains categorized as biotic.
  • Abiotic Components: Non-living physical and chemical factors influencing organismal survival and environmental architecture (e.g., rainfall, temperature, weather patterns, soil and aquatic nutrients).
  • Biotic-Abiotic Interactivity: Reciprocal loops connect abiotic and biotic factors. Abiotic conditions govern energy and nutrient supply, while biological processes (e.g., photosynthesis, respiration, decomposition) continuously alter abiotic chemistry.

• Ecosystem Balance, Carrying Capacity, and Ecological Niches:

  • Functional Equilibrium: Ecosystems must maintain dynamic balance. Failure to sustain equilibrium leads to ecosystem degradation or breakdown.
  • Carrying Capacity: No biological community can support population densities exceeding available resources such as food, water, and shelter.
  • Population Regulators: Natural events and biotic controls—including wildland fire, disease outbreaks, territorial behavior, and predator-prey dynamics—regulate population density within environmental bounds.
  • Ecological Niche: The functional role, biological requirements, and habitat utilization strategy of a specific organism within an ecosystem.

Ecosystem Boundaries and Spatial Delimitation

• Defining Ecosystem Boundaries:

  • Boundaries are defined by distinct transitions in landforms, vegetation patterns, microclimates, and organismal habits that delineate abiotic/biotic interactions and energy cycles.

• Comparison of Confined vs. Unconfined Ecosystem Boundaries:

  • Confined Ecosystems (e.g., Caves): Possess clear physical boundaries, making it simple to delineate energy budgets and separate distinct species assemblages.
  • Unconfined Ecosystems (e.g., Yellowstone National Park): Display open boundaries because wildlife frequently ranges across official park borders, requiring scientists to expand boundary definitions over landscape scales.

Community Ecology and Species Competition

• Community Ecology: The study of biological interactions among coexisting species within a shared habitat.

• Resource Competition:

  • Defined as the active struggle among individuals to obtain shared, limiting resources (e.g., food, water, light, nesting sites, mates).
  • Intraspecific Competition: Competition occurring between individuals of the same species.
  • Interspecific Competition: Competition occurring between individuals of different species.

• Mechanisms Resolving Competition:

  • Gause's Competitive Exclusion Principle: States that two species competing for the exact same limiting resource cannot coexist indefinitely. The species with a competitive advantage in capturing prey or nutrients will out-reproduce the other, ultimately driving the inferior competitor to local extinction.
  • Resource Partitioning: An evolutionary strategy where competing species divide environmental resources by space, time, or morphology to minimize direct competition and enable stable coexistence.

Predation, Adaptations, and the Evolutionary Arms Race

• Predation: An interaction where one animal consumes another organism.

• Trophic Consumption Categories:

  • True Predation: Organisms actively hunt, kill, and consume prey individuals.
  • Herbivory: Animals feed on living plants or algae.
  • Parasitism: Parasites live on or inside a host body, deriving nutrition and shelter over time, negatively impacting the host without causing immediate death.
  • Parasitoidism: Specialized organisms deposit eggs inside a host organism; developing larvae feed on the host's body and food reserves, ultimately killing the host upon emergence.

• The Evolutionary Arms Race:

  • Reciprocal co-evolutionary adaptations occurring over extended timeframes:
  • Predator Adaptations: Evolution of specialized hunting physical traits, acute senses, speed, stealth, venom, and specialized anatomical appendages.
  • Prey Adaptations: Evolution of defensive adaptations, such as chemical deterrence, warning odors, camouflage, physical protective armor, and evasive behaviors.

Symbiotic Relationships: Mutualism and Commensalism

• Symbiosis: A close, long-term biological interaction between two distinct species coexisting within an ecosystem.

• Mutualism ($+ / +$ Interaction):

  • Interactions where both participating species derive a net fitness benefit.
  • Examples: Coral polyps harboring photosynthetic algae; large megafauna (e.g., rhinoceroses) associating with cleaner organisms that feed on ectoparasites.

• Commensalism ($+ / 0$ Interaction):

  • Interactions where one species benefits while the other species remains unaffected.
  • Examples: Transport phoresy, where one organism hitches a ride on another without impacting its host.

Native and Invasive Species Dynamics

• Native Species: Species that have evolved over extended periods within a specific ecosystem, fully integrated into local arms races, food webs, and ecological cycles.

• Invasive / Exotic / Alien Species: Non-native organisms introduced to environments outside their evolutionary range.

  • Ecological Impacts: Invasive species disrupt ecosystems because they lack co-evolved predators or pathogens. Unchecked population growth allows them to outcompete native flora and fauna, alter food web structure, and destabilize nutrient cycling.

Atmospheric Structure, Solar Energy, and Earth's Seasons

• Latitudinal Variations in Solar Insolation:

  • Equatorial Regions ($0^\circ$ Latitude): Solar radiation strikes Earth at a perpendicular ($90^\circ$) angle, concentrating solar energy over a small surface area and passing through minimal atmosphere, resulting in intense heating.
  • High Latitudes / Polar Regions ($60^\circ-90^\circ$): Solar radiation strikes at an oblique angle, spreading energy across a larger surface area and traversing thicker atmospheric layers, leading to significant energy loss and lower temperatures.

• Earth's Surface Albedo:

  • Measured as the percentage of incoming light reflected by a surface. Earth's global average albedo is approximately $30\,\%$.
  • Albedo Values by Surface Type:
  • Fresh Snow: $80-95\,\%$
  • Sea Ice: $50-90\,\%$
  • Clouds: $10-90\,\%$
  • Water: $10-60\,\%$ (dependent on solar angle)
  • Cropland and Grassland: $10-25\,\%$
  • Forest Cover: $10-20\,\%$
  • Asphalt: $5-10\,\%$

• Axial Tilt and Seasonal Solstices/Equinoxes:
  • Earth's axis is tilted at an angle of $23.5^\circ$ relative to its orbital plane.

• March Equinox: Sun is directly overhead at the equator. All global regions receive $12\,\text{hours}$ of daylight and $12\,\text{hours}$ of darkness. Marks the start of Spring in the Northern Hemisphere and Fall in the Southern Hemisphere.

• June Solstice: Northern Hemisphere is maximally tilted toward the Sun, experiencing the longest day length of the year. Marks the start of Summer in the Northern Hemisphere and Winter in the Southern Hemisphere.

• September Equinox: Sun is directly overhead at the equator. All global regions receive $12\,\text{hours}$ of daylight and $12\,\text{hours}$ of darkness. Marks the start of Fall in the Northern Hemisphere and Spring in the Southern Hemisphere.

• December Solstice: Northern Hemisphere is maximally tilted away from the Sun, experiencing the shortest day length of the year. Marks the start of Winter in the Northern Hemisphere and Summer in the Southern Hemisphere.

  • Atmospheric Thermal Stratification:

• Troposphere ($0-16\,\text{km}$): Innermost layer containing most atmospheric gas and water vapor. Site of weather events. Temperature decreases with altitude down to $-60^\circ\text{C}$.
• Stratosphere ($16-50\,\text{km}$): Contains the peak ozone layer ($\text{O}_3$) between $20-40\,\text{km}$. Ozone absorbs ultraviolet (UV) light, causing temperature to increase with altitude up to roughly $0^\circ\text{C}$.
• Mesosphere ($50-85\,\text{km}$): Atmospheric pressure drops significantly. Temperature decreases with altitude down to $-100^\circ\text{C}$.
• Thermosphere ($85-600\,\text{km}$): Absorbs high-energy X-rays and UV radiation, driving temperatures up to $1,750^\circ\text{C}$, though gas density is near vacuum.
• Exosphere ($>600\,\text{km}$): Upper boundary transitioning into outer space.

Global Atmospheric Circulation and Wind Patterns

• Hadley Cell Circulation Steps:

  1. Intense solar heating at the Intertropical Convergence Zone (ITCZ) warms moist tropical air, causing it to expand and rise.
  2. Rising air experiences adiabatic cooling (expansion under lower atmospheric pressure), causing water vapor to condense into intense tropical precipitation.
  3. Condensation releases latent heat, causing air to expand further and ascend higher into the atmosphere.
  4. Warm, rising air displaces cooler, drier air above it, forcing it poleward toward $30^\circ\text{N}$ and $30^\circ\text{S}$.
  5. Cold, dry air sinks at $30^\circ\text{N}$ and $30^\circ\text{S}$, undergoing adiabatic heating (compression under higher atmospheric pressure). Sinking air reaches Earth's surface as warm, dry air, generating major subtropical desert belts, then flows back toward the equator.

• Ferrel and Polar Cells:

  • Polar Cells: Cold, dry air sinks at the poles ($90^\circ$), flows equatorward to $60^\circ\text{N}$ and $60^\circ\text{S}$, warm air rises along the polar front, and completes the cell.
  • Ferrel Cells: Mid-latitude circulation cells ($30^\circ-60^\circ$) driven by interactions between Hadley and Polar cells.

• Coriolis Effect and Prevailing Wind Belts:

• Earth's rotational speed is highest at the equator and decreases poleward. Objects and air moving across latitudinal gradients are deflected relative to Earth's surface:
  • Northern Hemisphere: Moving fluids deflect to the RIGHT.
  • Southern Hemisphere: Moving fluids deflect to the LEFT.
• Global Wind Patterns:
  • Northeast Trade Winds: Blow from northeast to southwest in the Northern Hemisphere tropics ($0^\circ-30^\circ\text{N}$).
  • Southeast Trade Winds: Blow from southeast to northwest in the Southern Hemisphere tropics ($0^\circ-30^\circ\text{S}$).
  • Westerlies: Prevailing mid-latitude winds ($30^\circ-60^\circ$) blowing from west to east in both hemispheres.
  • Polar Easterlies: High-latitude winds ($60^\circ-90^\circ$) blowing from east to west.

Ocean Circulation, Thermohaline Currents, and Upwelling Phenomena

• Surface Ocean Gyres and Coastal Upwelling:

  • Driven by prevailing winds, trade winds, Westerlies, and the Coriolis effect.
  • Coastal Upwelling: Trade winds push warm surface water offshore (westward). Cold, nutrient-rich deep water moves upward to replace surface water, creating highly productive fisheries along western continental margins.

• El Niño-Southern Oscillation (ENSO):

• Normal Years: Strong trade winds push surface waters westward across the Pacific toward Australia. Deep cold water upwells along the western coast of South America.

• El Niño Years: Trade winds weaken or reverse direction (flowing west to east). Warm surface water accumulates along South America, preventing upwelling of cold, nutrient-rich deep water and altering global weather.

  • Thermohaline Circulation (Global Conveyor Belt):

1. Warm surface water flows from the Gulf of Mexico via the Gulf Stream into the North Atlantic, transferring heat toward northwestern Europe.
2. In the cold North Atlantic, surface water loses heat, and a portion freezes into sea ice while evaporation occurs, leaving remaining unfrozen water saltier and denser.
3. Dense, cold, saline water sinks to the ocean floor in the North Atlantic.
4. Deep cold water moves along the ocean floor, connecting the Atlantic, Southern, Indian, and Pacific oceans.
5. Cold deep water gradually rises (upwells) in the Pacific and Indian oceans and circulates back to the North Atlantic as shallow warm currents.

Terrestrial Biomes and Climate Characteristics

• Determinants of Biome Distribution:

  • Climate parameters—specifically Precipitation and Temperature—determine dominant Flora (plant species).
  • Flora determines Fauna (animal species) by structuring habitat and food availability.
  • Local Geology creates physical landscapes.

• Reading and Interpreting Biome Climate Graphs:

• Growing Season: Marked by months where average temperature remains above freezing ($>0^\circ\text{C}$).
• Temperature Limitations: When the precipitation line lies ABOVE the temperature curve, plant growth is limited by temperature.
• Precipitation Limitations: When the precipitation line lies BELOW the temperature curve, plant growth is limited by precipitation (drought).

Detailed Analysis of the Nine Terrestrial Biomes

• 1. Tundra Biome:

  • Climate & Growing Season: Cold, treeless biome with low precipitation. Short growing season ($2-3\,\text{months}$) during summer when Earth tilts toward the Sun, providing extended daylight.
  • Soil & Vegetation: Upper soil layer thaws in summer, forming pools of water for insects. Deeper soil remains permanently frozen as permafrost, preventing deep root systems. Dominated by dwarf woody shrubs, mosses, and lichens adapted to shallow, waterlogged soil. Cold temperatures slow decomposition, leading to organic matter accumulation.
  • Location Example: Egedesminde, Greenland.

• 2. Boreal Forest (Taiga) Biome:

  • Extent & Characteristics: Makes up $27\,\%$ of global forest cover, situated in high northern latitudes between $52^\circ\text{N}$ and $66^\circ\text{N}$ (extending up to $70^\circ\text{N}$).
  • Climate: Subfreezing winters and short growing seasons limited by cold temperatures rather than precipitation.
  • Soil & Vegetation: Dominated by needle-leafed coniferous evergreen trees (spruce, fir, pine) adapted to drop needles incrementally (needlecast). Waxy needles and cold climate slow decomposition, producing acidic, nutrient-poor soil rich in organic matter. Unsuited for agriculture; utilized for timber and pulp.
  • Fauna Example: Inhabited by the American Black Bear (North America's smallest and most common bear species).
  • Location Example: Thunder Bay, Ontario, Canada.

• 3. Temperate Rainforest Biome:

  • Climate: Coastal mid-latitude biome ($30^\circ-50^\circ$) featuring mild winters and warm summers regulated by ocean currents. High annual precipitation and year-round growing season.
  • Soil & Vegetation: Supports giant trees (e.g., coastal redwoods, Douglas fir). Soil decomposition is slow, and heavy rainfall leaches nutrients or drives rapid uptake by large trees; forest floor is dominated by shade-tolerant ferns and mosses.
  • Location Example: Nanaimo Departure Bay, British Columbia, Canada.

• 4. Temperate Seasonal Forest (Deciduous Forest) Biome:

  • Climate: Mid-latitude biome with hot summers and cold winters.
  • Soil & Vegetation: Dominated by broadleaf deciduous trees (beech, maple, oak, hickory) alongside conifers. Warm summer temperatures encourage rapid decomposition; broadleaf foliage breaks down faster than coniferous needles, producing highly fertile soil. Extensively converted for agriculture worldwide.
  • Location Example: Stuttgart, Germany.

• 5. Tropical Rainforest Biome:

  • Global Significance: Covers $6\,\%$ of Earth's land surface but contains $40-70\,\%$ of all terrestrial species. The Amazon Rainforest alone generates $20\,\%$ of global atmospheric oxygen. Deforestation claims an estimated $137$ plant, animal, and insect species daily.
  • Climate: Equatorial ($20^\circ\text{N}-20^\circ\text{S}$). Warm ($>20^\circ\text{C}$) and wet year-round with minimal seasonal temperature variation.
  • Soil & Structure: High primary productivity and complex vertical canopy layering create diverse ecological niches. Rapid decomposition occurs, but intense vegetation uptake and leaching leave soils severely nutrient-depleted. Slash-and-burn agriculture yields short-term fertility before soil exhaustion.
  • Location Example: Basco, Philippines.

• 6. Tropical Seasonal Forest / Savanna Biome:

  • Climate: Warm tropical temperatures with distinct wet and dry seasons driven by seasonal shifts of the Intertropical Convergence Zone (ITCZ).
  • Soil & Vegetation: Deciduous trees shed leaves during dry periods to conserve moisture. Savannas consist of open grasslands with scattered trees; frequent fires and large herbivore grazing prevent forest establishment. High decomposition during warm wet seasons and reduced dry-season leaching create fertile soil used for agriculture and grazing.
  • Location Example: Kabwe, Zambia.

• 7. Subtropical Desert (Hot Desert) Biome:

  • Global Extent: Covers $33\,\%$ of land surface, supporting $13\,\%$ of the human population. Major deserts include the Sahara ($>3,320,000\,\text{sq mi}$), Arabian ($900,000\,\text{sq mi}$), Gobi ($500,000\,\text{sq mi}$), Kalahari ($360,000\,\text{sq mi}$), Patagonian ($260,000\,\text{sq mi}$), Great Victoria ($250,000\,\text{sq mi}$), Great Basin ($190,000\,\text{sq mi}$), Thar ($200,000\,\text{sq mi}$), Antarctic ($5,339,573\,\text{sq mi}$), and Arctic ($>5,300,000\,\text{sq mi}$).
  • Climate: Located around $30^\circ\text{N}$ and $30^\circ\text{S}$. Summer temperatures reach $113^\circ\text{F}$ ($45^\circ\text{C}$), dropping to $32^\circ\text{F}$ ($0^\circ\text{C}$) in winter.
  • Plant Adaptations: Thick cuticles, spines, reduced leaves, and stem photosynthesis. Saguaro cacti take up to $75\,\text{years}$ to grow a side branch, live over $150\,\text{years}$, and reach heights of $15-50\,\text{ft}$. Annual plants sprout and bloom rapidly after rare rains; perennials grow opportunistically.
  • Location Example: Arica, Chile.

• 8. Woodland / Shrubland (Chaparral) Biome:

  • Climate: Hot, dry summers and mild, rainy winters. Year-round growing season constrained by summer drought.
  • Vegetation & Land Use: Plants are adapted to fire and drought (sprouting from root crowns or requiring heat for seed germination). Agricultural use is limited to drought-tolerant, deep-rooted crops (e.g., grapevines for viticulture) and livestock grazing.

• 9. Temperate Grassland / Cold Desert Biome:

  • Extent: Covers vast interior plains; grasslands globally cover $31\,\%$ of land mass (and nearly $50\,\%$ of Africa).
  • Climate: Cold winters and hot, dry summers. Growth is limited by cold in winter and drought in summer. Wildfires are frequent.
  • Vegetation & Soil: Dominated by grasses and non-woody flowering plants. Tallgrass prairies ($8\,\text{ft}$ tall grasses) receive sufficient rainfall for trees, but fire prevents forest establishment; mostly converted to crop production. Shortgrass prairies receive less rain and are used for grazing. Cold deserts experience lower rainfall and subfreezing winter conditions. Soils are extremely fertile due to dense root networks and rapid seasonal decomposition.

Aquatic Ecosystems: Freshwater Systems

• Global Water Distribution Metrics:

  • Oceans hold $97\,\%$ of all global water.
  • Glaciers and polar ice caps hold $2.4\,\%$.
  • Surface freshwater (lakes, rivers, ponds) holds $0.6\,\%$.
  • Atmosphere holds $0.009\,\%$.
  • Freshwater biomes cover $0.8\,\%$ of aquatic habitats.

• Unique Freshwater Features:

  • Lake Baikal (Russia): Deepest lake on Earth, holding $1/5$ ($20\,\%$) of world unfrozen surface freshwater. Home to over $2,500$ plant and animal species ($2/3$ endemic), including the Baikal seal (world's only freshwater seal).
  • Great Lakes & Lake Baikal Combined: Contain $7/8$ of Earth's unfrozen surface freshwater.

• Classification of Freshwater Habitats:

  • Lentic Systems: Slow-moving or standing water bodies (pools, ponds, lakes).
  • Lotic Systems: Rapidly-moving freshwater systems (rivers, streams).
  • Freshwater Wetlands: Inundated or saturated by water for part of the year. Divided into Swamps (dominated by emergent trees), Marshes (dominated by non-woody plants), and Bogs (acidic wetlands dominated by sphagnum mosses and spruces). Wetland ecosystem services include floodwater retention, groundwater recharge, pollutant filtration, and critical habitat for migratory birds.

• Ecological Zonation of Lakes and Ponds:

• Littoral Zone: Shallow perimeter water where light penetrates to the sediment, supporting emergent rooted plants and high rates of photosynthesis.

• Limnetic Zone: Open surface water away from shore extending as deep as light penetrates, dominated by floating phytoplankton and algae.

• Profundal Zone: Deep water column below light penetration depth. Lacks photosynthetic primary production; exhibits lower dissolved oxygen (DO) and high concentrations of settling organic nutrients.

• Benthic Zone: Sediment substrate covering the lake bottom.

  • River and Stream Dynamics:

• Allochthonous Energy Inputs: Fast-moving streams lack rooted plants; primary energy input comes from terrestrial organic matter (riparian leaf litter).

• Aeration & Dissolved Oxygen: Water flowing over steep gradients forms rapids that entrain air, providing high dissolved oxygen (DO) levels vital for aquatic life.

• Stream Channel Evolution:

* **Youthful Stream**: High gradient, steep V-shaped valley, high friction, rough channel bed, large bed load.
* **Mature Stream**: Moderate gradient, developing floodplain, meandering channel.
* **Old Age Stream**: Broad floodplain, oxbow lakes, tributary streams, low gradient.

• Longitudinal Profile Dynamics:

* Downstream reaches near the river mouth exhibit the largest cross-sectional area, greatest hydraulic radius, highest flow velocity, and maximum total discharge.

Aquatic Ecosystems: Marine Systems and Coastal Habitats

• Ocean Extent and Chemical Salinity:

  • Oceans cover $71\,\%$ of Earth's surface. Seawater contains ~$3.5\,\%$ dissolved salts, with sodium ($\text{Na}^+$) and chlorine ($\text{Cl}^-$) ions making up $85\,\%$ of dissolved materials.

• Marine Depth Zonation:

• Intertidal Zone: Narrow coastline band between high tide and low tide. Subject to extreme fluctuations in drying, temperature, solar exposure, and wave shock.

• Photic Zone: Upper water column where sunlight penetrates (~$200\,\text{m}$ / $650\,\text{ft}$). Phytoplankton generate over $50\,\%$ of atmospheric oxygen and form the base of marine food webs.

• Aphotic Zone: Deep water column below $200\,\text{m}$ devoid of sunlight.

  • Chemosynthesis: Chemoautotrophic bacteria oxidize hydrogen sulfide ($\text{H}_2\text{S}$) and methane ($\text{CH}_4$) at hydrothermal vents to synthesize organic matter, forming the food base for deep-sea communities.
  • Bioluminescence: Deep-sea organisms produce light chemically for communication, predation, and defense.

• Benthic Zone: Ocean floor sediment and rock substrate.

• Abyssal Zone: Deep benthic region beneath the pelagic zone.

  • Coastal Habitat Types and Ecosystem Services:

• Salt Marshes: Temperate coastal wetlands in nutrient-rich estuaries where rivers deposit sediment. Dense non-woody plants filter pollutants and act as spawning nurseries for fish.

• Mangrove Swamps: Tropical and subtropical coastal wetlands dominated by salt-tolerant trees with aerial prop roots. Protect shorelines against storm surges and erosion while sheltering juvenile marine life.

• Coral Reef Systems:

  • Structure & Symbiosis: Found in warm, shallow photic waters ($<200\,\text{m}$). Corals secrete calcium carbonate ($\text{CaCO}_3$) skeletons. Over $500\,\text{million}$ people depend on coral reefs for food and income.
  • Biodiversity: Reefs cover $1\,\%$ of aquatic habitats but support $25\,\%$ of marine species and over $4,000$ fish species.
  • Reef Types: Fringing Reefs (attached directly to shore), Barrier Reefs (separated from land by a deep lagoon), and Atoll Reefs (circular reefs enclosing a lagoon without a central island).
  • Bleaching & Threats: Ocean warming, acidification, and pollution cause corals to expel mutualistic algae, leading to coral death. Out of $845$ reef-building coral species, $27\,\%$ are threatened and $20\,\%$ are near-threatened.

• Ocean Dead Zones: Hypoxic marine areas depleted of dissolved oxygen where aerobic life cannot survive. Sizes range from $0.4\,\text{km}^2$ to $70,000\,\text{km}^2$ ($27,000\,\text{sq mi}$).

Global Biodiversity and Vascular Plant Distribution

• Vascular Plant Diversity Patterns:
  • Plant species richness increases dramatically from polar regions toward equatorial tropical regions.
  • Diversity Zones (DZ) measured as species count per $10,000\,\text{km}^2$:
  • DZ 1: $<100\,\text{species}$ (Polar / High Tundra)
  • DZ 2: $100-200\,\text{species}$
  • DZ 3: $200-500\,\text{species}$
  • DZ 4: $500-1,000\,\text{species}$
  • DZ 5: $1,000-1,500\,\text{species}$
  • DZ 6: $1,500-2,000\,\text{species}$
  • DZ 7: $2,000-3,000\,\text{species}$
  • DZ 8: $3,000-4,000\,\text{species}$
  • DZ 9: $4,000-5,000\,\text{species}$
  • DZ 10: $>5,000\,\text{species}$ (Equatorial Rainforest Hotspots, e.g., Neotropics, Southeast Asia)