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 Study

• Organismal Ecology: Examines how an organism's structure, physiology, and behavior enable it to survive in its environment. Includes physiological, evolutionary, and behavioral ecology. Example: How do flamingos select a mate?

• Population Ecology: Studies groups of individuals of the same species in an area, focusing on factors that affect population size and changes over time. Example: What environmental factors affect the reproductive rate of flamingos?

• Community Ecology: Investigates interactions between species in a community and how these affect community structure and organization. Example: What factors influence species diversity at an African lake?

• Ecosystem Ecology: Focuses on energy flow and chemical cycling among organisms and their environment. Example: What controls photosynthetic productivity in an aquatic ecosystem?

• Landscape Ecology: Examines exchanges of energy, materials, and organisms across multiple ecosystems (landscapes or seascapes). Example: How do nutrients from terrestrial ecosystems affect lake organisms?

• Global Ecology: Studies the biosphere as a whole, focusing on global patterns and processes. Example: How do global air circulation patterns affect organism distribution?

Climate and the Distribution of Life

Climate: Definition and Components

Climate is the long-term prevailing weather conditions in an area 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 patterns: Warm, wet air rises in the tropics, causing high precipitation; dry air descends at 30° N/S, creating deserts.

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

Seasonality and Local Climate Modifiers

• Seasonality: Caused by Earth's axial tilt and orbit, leading to variations in day length, solar radiation, and temperature, especially at higher latitudes.

• Bodies of Water: Oceans and lakes moderate climate due to water's high specific heat; currents transport heat globally.

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

• Vegetation: Forests absorb more solar energy but also cool via transpiration; deforestation leads to hotter, drier climates.

• Microclimate: Localized climate patterns influenced by shade, wind, and evaporation (e.g., under a forest canopy).

Global Climate Change

• Human activities (burning fossil fuels, deforestation) have increased greenhouse gases, causing global warming and climate change.

• Earth has warmed ~0.9°C since 1900; further warming of 1–6°C projected by 2100.

• Organisms are shifting ranges in response; some species cannot keep pace and face extinction.

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.

• Ecotone: Area of intergradation between biomes, often with high biodiversity.

• Vertical layering: Forests have multiple layers (canopy, understory, shrub, herb, forest floor, root layer), providing diverse habitats.

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

• Disturbance: Events like fire, storms, or human activity that alter communities; many biomes depend on periodic disturbance.

Summary Table: Major Terrestrial Biomes

Biome	Location	Climate	Vegetation	Animals	Human Impact
Tropical Forest	Equatorial, subequatorial	High temp, high precipitation (rain or dry)	Broadleaf evergreen/deciduous trees, layered	Highest animal diversity	Deforestation
Desert	30° N/S, continental interiors	Low, variable precipitation; hot/cold extremes	Heat/drought-adapted plants (C4, CAM)	Nocturnal, water-conserving animals	Urbanization, agriculture
Savanna	Equatorial, subequatorial	Seasonal precipitation, warm	Grasses, fire-adapted forbs	Large herbivores, insects	Ranching, overhunting
Chaparral	Midlatitude coasts	Rainy winters, dry hot summers	Shrubs, small trees, fire-adapted	Amphibians, birds, small mammals	Agriculture, urbanization
Temperate Grassland	Continents, midlatitudes	Seasonal precipitation, cold winters, hot summers	Grasses, forbs, fire/drought-adapted	Grazers, burrowers	Agriculture, overgrazing
Northern Coniferous Forest (Taiga)	Northern N. America, Eurasia	Cold winters, hot summers, moderate precipitation	Evergreen conifers	Birds, large mammals	Logging
Temperate Broadleaf Forest	Midlatitudes, N. Hemisphere	All seasons, moderate to high precipitation	Deciduous/evergreen trees, layered	Mammals, birds, insects	Settlement, recovery
Tundra	Arctic, alpine	Low precipitation, cold	Herbaceous, mosses, permafrost	Migratory birds, large mammals	Resource extraction

Aquatic Biomes

Aquatic biomes cover most of Earth's surface and are classified by physical and chemical environment. Marine biomes have ~3% salt; freshwater biomes have <0.1% salt.

• Oceans cover ~75% of Earth's surface, regulate climate, and are major sources of O2 and CO2 cycling.

• Freshwater biomes are influenced by surrounding terrestrial biomes, water flow, and climate.

Zonation in Aquatic Biomes

• Photic zone: Sufficient light for photosynthesis.

• Aphotic zone: Little or no light.

• Pelagic zone: Open water (photic + aphotic).

• Abyssal zone: Deep aphotic, 2,000–6,000 m.

• Benthic zone: Bottom substrate; inhabited by benthos (organisms).

• 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)	Rooted/floating plants, phytoplankton	Zooplankton, invertebrates, fish	Eutrophication, fish kills
Wetlands	Water-saturated soil, high productivity	Lilies, cattails, sedges, mosses	Invertebrates, birds, amphibians	Draining, filling, pollution
Streams/Rivers	Current, O2-rich, variable nutrients	Phytoplankton, rooted plants	Fish, invertebrates	Pollution, damming
Estuaries	Transition zone, variable salinity	Saltmarsh grasses, algae	Invertebrates, fish, birds	Filling, dredging, pollution
Intertidal Zones	Submerged/exposed by tides, high O2	Algae, seagrass	Sponges, mollusks, crustaceans	Oil pollution, construction
Oceanic Pelagic Zone	Open water, high O2, low nutrients	Phytoplankton	Zooplankton, fish, mammals	Overfishing, pollution
Coral Reefs	Calcium carbonate skeletons, warm, clear water	Corals (with algae), algae	Fish, invertebrates	Overfishing, warming, acidification
Marine Benthic Zone	Seafloor, cold, high pressure	Seaweeds, chemoautotrophs (vents)	Tube worms, echinoderms, fish	Overfishing, dumping

Factors Limiting Species Distribution

Ecological and Evolutionary Factors

• Species distributions result from both ecological factors (current environment) and evolutionary history (origin, dispersal).

• Dispersal: Movement of individuals or gametes away from origin; can lead to range expansion and adaptive radiation.

• Species transplants test whether 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.

• Example: Grazing by sea urchins prevents seaweed establishment.

Abiotic Factors

• Temperature: Affects biological processes; extremes can cause cell damage or protein denaturation. Most organisms have optimal temperature ranges.

• Water and Oxygen: Water availability is crucial; oxygen diffuses slowly in water, limiting aquatic and wetland organisms.

• Salinity: Affects water balance via osmosis; most organisms are adapted to either freshwater or saltwater.

• Sunlight: Limits photosynthesis; too little or too much (UV damage) can be harmful.

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

Ecological and Evolutionary Feedback

Interactions Over Time

• Ecological interactions can drive evolutionary change (e.g., new plant species provide new habitats for animals).

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

• Feedback can be rapid (e.g., guppy color and predation) or gradual (e.g., post-glacial range shifts).

Key Terms and Concepts

• Biome: Major life zone defined by vegetation or physical environment.

• Ecotone: Transition area between biomes.

• Photic/Aphotic Zone: Light/no light in aquatic biomes.

• Thermocline: Temperature boundary in water bodies.

• Turnover: Seasonal mixing of lake waters.

• Dispersal: Movement of organisms from origin.

• Adaptive Radiation: Rapid evolution of diverse species from a common ancestor.

• Disturbance: Event altering community structure.

Example Application: Predicting how climate change will shift the range of a species requires understanding both its physiological tolerances (abiotic factors) and its interactions with other species (biotic factors), as well as its ability to disperse to new suitable habitats.

Additional info: The above notes synthesize and expand upon the provided content, adding definitions, examples, and summary tables for clarity and completeness.