Ecology: The Biosphere and the Distribution of Life

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 on Earth.

• Biotic factors: Living components such as other organisms (predators, competitors, symbionts).

• Abiotic factors: Nonliving components such as temperature, water, sunlight, wind, and soil.

Ecologists investigate questions at multiple levels of biological organization, from individuals to the entire biosphere.

Levels of Ecological Research

• Organismal Ecology: Examines how an organism's structure, physiology, and behavior enable it to survive in its environment. Includes physiological, evolutionary, and behavioral ecology.

• Population Ecology: Studies groups of individuals of the same species, focusing on factors that affect population size and changes over time.

• Community Ecology: Investigates interactions between species in a community and how these affect community structure and organization.

• Ecosystem Ecology: Emphasizes energy flow and chemical cycling among organisms and their environment within a defined area.

• Landscape Ecology: Explores how ecosystems are arranged in a geographic region and the exchanges of energy, materials, and organisms among them.

• Global Ecology: Considers the biosphere as a whole, focusing on global patterns and processes that affect the distribution of life.

Climate and the Distribution of Life

Climate: Definition and Components

Climate is the long-term prevailing weather conditions in a region and is the most significant factor influencing the distribution of terrestrial organisms. The four major physical components of climate are:

• Temperature

• Precipitation

• Sunlight

• Wind

Global Climate Patterns

• Determined largely by solar energy and Earth's movement in space.

• Solar energy drives temperature variations, air and water circulation, and evaporation.

• Latitudinal variation in sunlight intensity: Most direct at the tropics (23.5°N to 23.5°S), more diffuse at higher latitudes.

Global Air Circulation and Precipitation

• Intense sunlight at the equator causes warm, wet air to rise, leading to high precipitation in the tropics.

• Dry, descending air at ~30° N/S creates arid climates (deserts).

• Air rises again at ~60° N/S, causing precipitation, and descends at the poles, creating cold, dry climates.

• Earth's rotation causes predictable wind patterns: trade winds (east to west in tropics), westerlies (west to east in temperate zones).

Seasonality

• Caused by Earth's axial tilt and orbit around the sun.

• Results in variations in day length, solar radiation, and temperature, especially at higher latitudes.

• Shifts in wet/dry belts and wind patterns affect local climates and ocean currents.

Bodies of Water and Mountains

• Oceans and large lakes moderate climate due to water's high specific heat.

• Ocean currents transport warm or cold water, influencing coastal climates.

• Mountains affect air flow, precipitation (rain shadow effect), and sunlight exposure; temperature drops about 6°C per 1,000 m elevation.

Vegetation and Microclimate

• Forests absorb more solar energy but also cool via transpiration.

• Deforestation leads to hotter, drier climates; reforestation has the opposite effect.

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

Global Climate Change

• Human activities (fossil fuel burning, deforestation) increase greenhouse gases, causing global warming and climate change.

• Earth has warmed ~0.9°C since 1900; further warming projected.

• Species ranges are shifting; some species cannot keep pace and may decline or go extinct.

Biomes: Major Life Zones

Terrestrial Biomes

Biomes are major life zones characterized by vegetation type (terrestrial) or physical environment (aquatic). Climate is a key determinant of biome distribution.

• Climograph: Plots annual mean temperature and precipitation for a region.

• Biomes often grade into each other at ecotones (transition areas).

• Vertical layering of vegetation provides diverse habitats.

• Similar adaptations can arise in distant biomes via convergent evolution.

• Disturbance (e.g., fire, storms, human activity) shapes biome structure and species composition.

Summary Table: Major Terrestrial Biomes

Biome	Location	Climate	Vegetation	Animals	Human Impact
Tropical Forest	Equatorial, subequatorial	High temp, high rainfall (rainforest); seasonal (dry forest)	Broadleaf evergreens, deciduous trees	Highest animal diversity	Deforestation
Desert	30° N/S, continental interiors	Low, variable precipitation; hot/cold extremes	Succulents, C4/CAM plants	Nocturnal, water-conserving animals	Urbanization, agriculture
Savanna	Equatorial, subequatorial	Seasonal rainfall, warm	Grasses, fire-adapted forbs	Large herbivores, insects	Ranching, overhunting
Chaparral	Midlatitude coasts	Rainy winters, dry hot summers	Shrubs, small trees	Amphibians, birds, small mammals	Agriculture, urbanization
Temperate Grassland	Continents, midlatitudes	Cold winters, hot summers, seasonal rain	Grasses, forbs	Grazers, burrowers	Agriculture, overgrazing
Northern Coniferous Forest (Taiga)	Northern N. America, Eurasia	Cold winters, hot summers, moderate rain	Evergreen conifers	Moose, bears, migratory birds	Logging
Temperate Broadleaf Forest	Midlatitudes, N. Hemisphere	Cold winters, hot humid summers, year-round rain	Deciduous trees, vertical layers	Mammals, birds, insects	Settlement, recovery
Tundra	Arctic, alpine	Cold, low precipitation	Mosses, grasses, dwarf shrubs	Caribou, migratory birds	Resource extraction

Aquatic Biomes

Aquatic biomes are defined by physical and chemical characteristics, such as salinity, depth, and water flow. Oceans cover about 75% of Earth's surface and have a major impact on the biosphere.

• Marine biomes: ~3% salt concentration

• Freshwater biomes: <0.1% salt concentration

Zonation in Aquatic Biomes

• Photic zone: Sufficient light for photosynthesis

• Aphotic zone: Little or no light

• Pelagic zone: Open water (photic + aphotic)

• Benthic zone: Bottom substrate

• Abyssal zone: Deep ocean (2,000–6,000 m)

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

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

Summary Table: Major Aquatic Biomes

Biome	Physical/Chemical Features	Producers	Animals	Human Impact
Lakes	Oligotrophic (nutrient-poor, O2-rich), Eutrophic (nutrient-rich, O2-poor)	Phytoplankton, aquatic plants	Zooplankton, fish, invertebrates	Eutrophication, fish kills
Wetlands	Water-saturated soil, high productivity	Lilies, cattails, mosses	Birds, amphibians, invertebrates	Draining, filling
Streams & Rivers	Current, O2-rich, nutrient increases downstream	Phytoplankton, rooted plants	Fish, invertebrates	Pollution, damming
Estuaries	Transition zone, variable salinity	Saltmarsh grasses, algae	Fish, invertebrates, birds	Filling, pollution
Intertidal Zones	Submerged/exposed by tides, high O2	Algae, seagrass	Crustaceans, mollusks, fish	Pollution, construction
Oceanic Pelagic Zone	Open water, high O2, low nutrients	Phytoplankton	Zooplankton, fish, marine mammals	Overfishing, pollution
Coral Reefs	Warm, clear, shallow water, high O2	Coral, algae	Fish, invertebrates	Overfishing, warming, acidification
Marine Benthic Zone	Seafloor, cold, high pressure	Seaweeds (shallow), chemoautotrophs (deep)	Tube worms, echinoderms, fish	Overfishing, dumping

Factors Limiting Species Distribution

Ecological and Evolutionary Influences

• Species distributions are shaped by both ecological factors (current environment) and evolutionary history (origin, dispersal).

• Dispersal is the movement of individuals or gametes away from their origin, influencing global distribution.

• Natural range expansions and adaptive radiation can result from dispersal events.

• Species transplants test whether dispersal limits distribution; successful transplants may disrupt local ecosystems.

Biotic Factors

• Predation, herbivory, competition, presence/absence of pollinators, food resources, parasites, and pathogens can limit species distribution.

• Example: Grazing by sea urchins prevents seaweed establishment.

Abiotic Factors

• Temperature: Affects biological processes; extremes can be lethal or denature proteins.

• Water and Oxygen: Water availability and oxygen concentration (especially in aquatic or waterlogged environments) are critical.

• Salinity: Affects osmoregulation; most organisms are restricted to either freshwater or saltwater.

• Sunlight: Limits photosynthesis; too much or too little can be harmful.

• Rocks and Soil: pH, mineral content, and structure affect plant growth and, indirectly, animal distribution.

Ecological and Evolutionary Feedback

Interactions Over Time

• Ecological interactions can drive evolutionary change (e.g., new habitats, food sources).

• Evolutionary changes (e.g., new adaptations) can alter ecological relationships and community structure.

• Feedback between ecology and evolution can be rapid, as seen in predator removal experiments with guppies.

Key Terms and Concepts

• Ecotone: Transition area between biomes.

• Turnover: Seasonal mixing of water in lakes.

• Thermocline: Temperature gradient in aquatic environments.

• Osmoregulation: Regulation of water and salt balance.

• Adaptive radiation: Rapid evolution of many species from a common ancestor.

Example: The expansion of the long-spined sea urchin's range due to warming waters led to the destruction of seaweed communities, illustrating how abiotic change can have cascading biotic effects.

Additional info: This summary integrates and expands upon the provided notes to ensure a self-contained, exam-ready study guide for college-level biology students.