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. 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 their effects on community structure and organization. Example: What factors influence the diversity of species at an African lake?

• Ecosystem Ecology: Focuses on energy flow and chemical cycling among organisms and their environment within an ecosystem. Example: What factors control 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 organisms in a lake?

• Global Ecology: Studies the biosphere as a whole, analyzing how global exchanges of energy and materials influence the distribution and function of organisms. Example: How do global air circulation patterns affect the distribution of organisms?

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

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

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

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

• Seasonal wind changes can cause upwelling of nutrient-rich water in oceans, boosting productivity.

Bodies of Water and Mountains

• Oceans and 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. Every 1,000 m increase in elevation drops temperature by ~6°C.

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) 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.

• Species ranges are shifting; some expand, others contract or go extinct.

• Range shifts can disrupt existing communities and lead to extinctions.

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 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, constant or seasonal rainfall; warm	Broadleaf evergreen (rain), deciduous (dry)	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 rainfall; 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	Significant precipitation all seasons	Deciduous trees, vertical layers	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, including salinity, depth, and water flow.

• Marine biomes: ~3% salt concentration; include oceans, coral reefs, estuaries.

• Freshwater biomes: <0.1% salt; include lakes, rivers, wetlands.

• Oceans cover ~75% of Earth's surface, regulate climate, and support most of the planet's photosynthesis.

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; inhabited by benthos (organisms).

• 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	Key Features	Producers	Animals	Human Impact
Lakes	Oligotrophic (nutrient-poor, O2-rich) vs. 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, headwaters (cold, clear), downstream (warm, turbid)	Phytoplankton, rooted plants	Fish, invertebrates	Pollution, damming
Estuaries	Transition between river and sea, variable salinity	Saltmarsh grasses, algae	Fish, invertebrates, birds	Filling, pollution
Intertidal Zones	Submerged/exposed by tides, variable conditions	Algae, seagrass	Sponges, mollusks, crustaceans	Pollution, construction
Oceanic Pelagic Zone	Open water, mixed by currents	Phytoplankton	Zooplankton, fish, marine mammals	Overfishing, pollution
Coral Reefs	Calcium carbonate skeletons, warm shallow water	Coral, algae	Fish, invertebrates	Overfishing, warming, acidification
Marine Benthic Zone	Seafloor, deep cold water, hydrothermal vents	Seaweeds (shallow), chemoautotrophs (vents)	Tube worms, echinoderms, fish	Overfishing, dumping

Factors Limiting Species Distribution

Ecological and Evolutionary Factors

• Species distributions are shaped by 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 may disrupt local ecosystems.

Biotic Factors

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

• Example: Grazing by sea urchins prevents seaweed establishment.

Abiotic Factors

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

• Water: Essential for life; availability limits distribution, especially in deserts.

• Oxygen: Low in deep water, sediments, or flooded soils; affects aquatic and wetland organisms.

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

• Sunlight: Limits photosynthesis; too much can cause stress or UV damage.

• Soil/Rocks: pH, mineral content, and structure affect plant growth and animal burrowing/attachment.

Ecological and Evolutionary Feedback

Interactions Over Time

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

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

• Feedback can be rapid (e.g., guppy color and predation) or gradual (e.g., plant-animal coevolution).

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.

• Benthos: Organisms living on/in aquatic substrate.

• 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.

• Osmoregulation: Regulation of water and salt balance.

• Convergent Evolution: Similar traits in unrelated lineages due to similar environments.

Example Application: The northward shift of European butterfly species and the movement of Pacific diatoms into the Atlantic are real-world examples of how climate change and dispersal affect species distributions.

Additional info: For further study, students should review climographs, biome maps, and case studies of species range shifts in response to climate change.