Ecology: The Biosphere and Biomes – Distribution, Climate, and Interactions

Ecology and the Biosphere

Introduction to Ecology

Ecology is the scientific study of interactions between organisms and their environment, encompassing both living (biotic) and nonliving (abiotic) components. These interactions determine the distribution and abundance of organisms across the planet.

• Ecology: Study of relationships between organisms and their environment.

• Distribution: Where organisms are found.

• Abundance: How many organisms are present in a given area.

Levels of Ecological Research

Ecologists investigate questions at multiple levels of biological organization:

• Organismal Ecology: How an organism’s structure, physiology, and behavior meet environmental challenges. Example: How do flamingos select a mate?

• Population Ecology: Factors affecting population size and changes over time. Example: What environmental factors affect flamingo reproductive rates?

• Community Ecology: Interactions between species and their effects on community structure. Example: What influences species diversity at an African lake?

• Ecosystem Ecology: Energy flow and chemical cycling between organisms and the environment. Example: What controls photosynthetic productivity in aquatic ecosystems?

• Landscape Ecology: Exchanges of energy, materials, and organisms across multiple ecosystems. Example: How do terrestrial nutrients affect lake organisms?

• Global Ecology: Function and distribution of organisms across the biosphere. Example: How do global air circulation patterns affect organism distribution?

Climate and the Distribution of Life

Earth’s Climate: Components and Patterns

Climate, the long-term prevailing weather conditions, is the most significant factor influencing terrestrial organism distribution. The four major physical components of climate are:

• Temperature

• Precipitation

• Sunlight

• Wind

Global Climate Patterns

• Solar energy and Earth’s movement in space drive global climate patterns.

• Sun establishes temperature variations, air/water circulation, and evaporation.

• Latitudinal variation: Sunlight is most intense in the tropics (23.5ºN to 23.5ºS); more diffuse at higher latitudes.

Air Circulation and Precipitation

• Intense sunlight in tropics causes evaporation and rising warm, wet air.

• Rising air releases water, causing high precipitation in tropics.

• Dry, descending air creates arid climates near 30ºN/S.

• Global wind patterns: Trade winds (east to west in tropics), westerlies (west to east in temperate zones).

Seasonality

• Caused by Earth’s tilt and orbit; increases toward poles.

• Seasonal changes affect day length, solar radiation, and temperature.

• Shifts in wet/dry air belts cause wet/dry seasons in tropics.

• Seasonal wind changes alter ocean currents, causing nutrient upwelling.

Bodies of Water and Mountains

• Oceans moderate climate via high specific heat; currents transfer heat.

• Mountains affect air flow, precipitation, and sunlight; create rain shadows and temperature gradients.

Vegetation and Microclimate

• Forests absorb more solar energy, but transpiration cools and increases precipitation.

• Microclimate: Localized climate patterns influenced by shade, evaporation, and wind.

Global Climate Change

• Burning fossil fuels and deforestation increase greenhouse gases.

• Earth has warmed 0.9°C since 1900; projected to warm 1–6°C by 2100.

• Range shifts: Many species move northward or to higher elevations; some decrease or go extinct.

Terrestrial Biomes

Definition and Distribution

Biomes are major life zones characterized by vegetation (terrestrial) or physical environment (aquatic). Climate and disturbance are key factors controlling biome distribution.

• Climograph: Plots annual mean temperature and precipitation.

• Ecotone: Area of intergradation between biomes.

• Vertical layering: Provides diverse habitats (e.g., canopy, understory, forest floor).

• Convergent evolution: Similar traits in distant biomes (e.g., cacti vs. euphorbs).

Disturbance

• Events like fire, storms, or human activity change communities.

• Many biomes depend on periodic disturbance for maintenance.

Major Terrestrial Biomes

• Tropical Forest: Equatorial; high rainfall (rain forest: 200–400 cm, dry forest: 150–200 cm); high temperature; broadleaf evergreen or deciduous trees; high animal diversity; threatened by deforestation.

• Desert: 30ºN/S or continental interiors; low precipitation (<30 cm); variable temperature; plants adapted for water conservation (C4/CAM photosynthesis); nocturnal animals; biodiversity reduced by urbanization/agriculture.

• Savanna: Equatorial/subequatorial; seasonal rainfall (30–50 cm); warm, fire-adapted grasses/forbs; large herbivores; threatened by ranching/overhunting.

• Chaparral: Midlatitude coastal; seasonal precipitation (30–50 cm); hot summers, cool winters; fire/drought-adapted shrubs; reduced by agriculture/urbanization.

• Temperate Grassland: Many continents; seasonal precipitation (30–100 cm); cold winters, hot summers; drought/fire-adapted grasses; converted to agriculture; overgrazing leads to desertification.

• Northern Coniferous Forest (Taiga): Largest biome; 30–70 cm precipitation; cold winters, hot summers; evergreen conifers; migratory/resident birds, large mammals; threatened by logging.

• Temperate Broadleaf Forest: Midlatitudes; 70–200+ cm precipitation; cold winters, hot/humid summers; vertical layers; deciduous trees; mammals hibernate, birds migrate; heavily settled but recovering.

• Tundra: Arctic/alpine; low precipitation (20–60 cm arctic, >100 cm alpine); cold winters, cool summers; herbaceous vegetation; permafrost restricts roots; migratory birds, large mammals; sparse settlement, focus of resource extraction.

Aquatic Biomes

Characteristics and Zonation

Aquatic biomes cover most of Earth and are characterized by physical and chemical environment, including salt concentration, light penetration, and depth.

• Marine biomes: 3% salt; cover 75% of Earth; major impact on biosphere.

• Freshwater biomes: <0.1% salt; influenced by surrounding terrestrial biome.

• Zonation: Photic (light for photosynthesis), aphotic (little light), pelagic (open water), benthic (bottom), abyssal (deep benthic).

• Thermocline: Temperature boundary separating warm upper and cold deeper water.

• Turnover: Seasonal mixing of lake waters, redistributing oxygen and nutrients.

Major Aquatic Biomes

• Lakes: Oligotrophic (nutrient-poor, O2-rich), eutrophic (nutrient-rich, O2-poor); rooted plants in littoral zone, phytoplankton in limnetic zone; human-induced nutrient enrichment causes algal blooms.

• Wetlands: Water-saturated soil; high productivity; lilies, cattails, bald cypress; diverse invertebrates/birds; purify water, reduce flooding; threatened by drainage/filling.

• Streams and Rivers: Current is key; headwaters cold/clear, downstream warm/turbid; O2-rich; pollution and damming degrade ecosystems.

• Estuaries: Transition between river and sea; variable salinity; saltmarsh grasses/algae; abundant invertebrates/fish; disrupted by filling, dredging, pollution.

• Intertidal Zones: Submerged/exposed by tides; rocky/sandy substrates; high oxygen/nutrients; structural adaptations for attachment/burrowing; oil pollution and construction disrupt zones.

• Oceanic Pelagic Zone: Open water; covers 70% of Earth; mixed by currents; phytoplankton/zooplankton dominate; overfishing, pollution, acidification threaten biome.

• Coral Reefs: Calcium carbonate skeletons; photic zone, warm water; mutualism with algae; high diversity; threatened by collection, overfishing, warming, pollution.

• Marine Benthic Zone: Seafloor below neritic/pelagic zones; cold, high pressure; hydrothermal vents with chemoautotrophic prokaryotes; diverse invertebrates/fishes; overfishing and waste dumping deplete populations.

Species Distribution and Limiting Factors

Ecological and Evolutionary Influences

Species distributions are shaped by ecological factors and evolutionary history. Both biotic and abiotic factors limit where species can live.

• Dispersal: Movement of individuals/gametes away from origin; influences global distribution.

• Adaptive Radiation: Rapid evolution of ancestral species into diverse forms after long-distance dispersal.

• Species Transplants: Used to test if dispersal limits distribution; successful transplants indicate potential range is larger than actual range.

Biotic Factors

• Interactions with other species (predators, herbivores, pollinators, pathogens, competitors) can limit survival and reproduction.

Abiotic Factors

• Temperature: Affects biological processes; cells freeze below 0ºC, proteins denature above 45ºC; mammals/birds regulate internal temperature.

• Water and Oxygen: Water availability critical; oxygen diffuses slowly in water; deep waters and organic-rich sediments may be oxygen-poor.

• Salinity: Affects water balance via osmosis; most organisms restricted to freshwater or saltwater habitats; salmon can osmoregulate between both.

• Sunlight: Limits photosynthetic species; competition for light in forests; aquatic photosynthesis near surface; high light/UV can stress organisms.

• Rocks and Soil: pH, mineral composition, and structure limit plant distribution; substrate affects water chemistry and organism attachment/burrowing.

Ecological Change and Evolution

Feedback Between Ecology and Evolution

Ecological interactions can drive evolutionary change, and evolutionary change can alter ecological dynamics. These feedbacks can occur rapidly or over long periods.

• Example: Diversification of plants provided new habitats for animals, stimulating speciation and further ecological change.

• Rapid feedback: Trinidadian guppies evolve color patterns and feeding preferences in response to predation, affecting algal abundance.

Summary Table: Terrestrial Biomes

Biome	Location	Precipitation	Temperature	Dominant Vegetation	Human Impact
Tropical Forest	Equatorial/Subequatorial	Rain: 200–400 cm; Dry: 150–200 cm	High, little variation	Broadleaf evergreen/deciduous trees	Deforestation
Desert	30ºN/S, continental interiors	<30 cm	Variable, hot/cold	C4/CAM plants, spines	Urbanization, agriculture
Savanna	Equatorial/Subequatorial	30–50 cm, seasonal	Warm, variable	Fire-adapted grasses/forbs	Ranching, overhunting
Chaparral	Midlatitude coastal	30–50 cm, seasonal	Hot summers, cool winters	Shrubs, small trees	Agriculture, urbanization
Temperate Grassland	Continents	30–100 cm, seasonal	Cold winters, hot summers	Grasses, forbs	Agriculture, overgrazing
Northern Coniferous Forest	North America, Eurasia	30–70 cm	Cold winters, hot summers	Evergreen conifers	Logging
Temperate Broadleaf Forest	Midlatitudes	70–200+ cm	Cold winters, hot/humid summers	Deciduous trees	Settlement, recovery
Tundra	Arctic, alpine	20–60 cm (arctic), >100 cm (alpine)	Cold winters, cool summers	Herbaceous plants, permafrost	Resource extraction

Summary Table: Aquatic Biomes

Biome	Salinity	Key Features	Dominant Organisms	Human Impact
Lakes	Freshwater (<0.1%)	Oligotrophic/eutrophic, thermocline	Phytoplankton, zooplankton, fish	Nutrient enrichment, algal blooms
Wetlands	Freshwater	Water-saturated soil, high productivity	Lilies, cattails, birds, invertebrates	Drainage, filling
Streams/Rivers	Freshwater	Current, headwater vs. downstream	Fish, invertebrates	Pollution, damming
Estuaries	Variable	Transition zone, tidal channels	Saltmarsh grasses, fish, invertebrates	Filling, pollution
Intertidal Zones	Variable	Submerged/exposed, rocky/sandy	Algae, worms, clams, crustaceans	Oil pollution, construction
Oceanic Pelagic Zone	Marine (3%)	Open water, wind-driven mixing	Phytoplankton, zooplankton, fish	Overfishing, pollution, acidification
Coral Reefs	Marine	Calcium carbonate skeletons, photic zone	Corals, algae, diverse invertebrates/fish	Collection, overfishing, warming
Marine Benthic Zone	Marine	Seafloor, hydrothermal vents	Chemoautotrophic prokaryotes, tube worms	Overfishing, waste dumping

Key Equations and Concepts

• Specific Heat of Water: Water moderates climate due to high specific heat. $C = \frac{Q}{m \Delta T}$ Where $C$ is specific heat, $Q$ is heat added, $m$ is mass, $\Delta T$ is temperature change.

• Photosynthesis: Key process in aquatic and terrestrial biomes. $6CO_2 + 6H_2O \rightarrow C_6H_{12}O_6 + 6O_2$

• Osmosis: Movement of water across membranes, affected by salinity. $\pi = iMRT$ Where $\pi$ is osmotic pressure, $i$ is ionization constant, $M$ is molarity, $R$ is gas constant, $T$ is temperature.

Additional info: Academic context was added to clarify definitions, examples, and to expand brief points into full explanations. Tables were inferred and constructed to summarize biomes and their features. Equations were provided for relevant physical and biological processes.

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