Ecology: The Biosphere, Climate, and Biomes

Ecology and the Biosphere

Introduction to Ecology

Ecology is the scientific study of the interactions between organisms and their environment, including 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 nutrients.

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

Levels of Ecological Study

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

• Population Ecology: Studies factors that affect population size and how and why it changes over time. Example: What environmental factors affect the reproductive rate of flamingos?

• Community Ecology: Investigates interactions between species and how these affect 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. Example: What factors control photosynthetic productivity in an aquatic ecosystem?

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

Climate and the Biosphere

Climate: Definition and Components

Climate is the long-term prevailing weather conditions in a region. It is the most significant factor influencing the distribution of terrestrial organisms.

• Major components of climate: Temperature, precipitation, sunlight, and 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: Sunlight is most direct in the tropics (23.5º N to 23.5º S), less intense at higher latitudes.

Global Air Circulation and Precipitation

• Intense sunlight at the equator causes warm, moist air to rise, releasing precipitation (tropical rain belts).

• Dry, descending air at ~30º N and S creates deserts.

• Air rises again at ~60º N and S, causing precipitation; 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 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, supporting phytoplankton growth.

Bodies of Water and Mountains

• Oceans and lakes: Moderate climate of nearby land due to water's high specific heat; influence air temperature and precipitation patterns.

• Mountains: Affect air flow, precipitation (rain shadows), sunlight exposure, and temperature (temperature drops ~6ºC per 1,000 m elevation).

Vegetation and Microclimate

• Forests absorb more solar energy but cool the environment via transpiration.

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

• Microclimate: Localized climate patterns influenced by features like shade, windbreaks, and soil moisture.

Global Climate Change

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

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

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

Biomes

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 through ecotones (transition areas).

• Vertical layering of vegetation provides diverse habitats (e.g., forest canopy, understory, shrub layer, forest floor).

• 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 year-round	Broadleaf evergreen (rain), deciduous (dry)	High animal diversity	Deforestation
Desert	~30º N/S, interior continents	Low, variable precipitation; hot or cold	Cacti, succulents, CAM/C4 plants	Nocturnal, water-conserving	Urbanization, agriculture
Savanna	Equatorial, subequatorial	Seasonal rainfall; warm, more variable than tropics	Grasses, fire-adapted forbs	Large herbivores, insects	Ranching, overhunting
Chaparral	Midlatitude coasts	Rainy winters, dry hot summers	Shrubs, small trees, fire-adapted	Amphibians, reptiles, small mammals	Agriculture, urbanization
Temperate Grassland	Continents, midlatitudes	Dry winters, wet summers; hot/cold extremes	Grasses, forbs, fire/drought-adapted	Grazers, burrowers	Agriculture, overgrazing
Northern Coniferous Forest (Taiga)	N. North 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	Urbanization, recovery in some areas
Tundra	Arctic, alpine	Low precipitation, cold winters/summers	Herbaceous, mosses, lichens	Large mammals, migratory birds	Oil/mineral extraction

Aquatic Biomes

Aquatic biomes are classified by physical and chemical environment, less by latitude. Oceans cover 75% of Earth's surface and have a major impact on climate and 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 light

• Pelagic zone: Open water (photic + aphotic)

• Benthic zone: Bottom substrate

• Abyssal zone: Deep benthic (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	Consumers	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, sedges	Invertebrates, birds, amphibians	Draining, filling, pollution
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, dredging, pollution
Intertidal Zones	Submerged/exposed by tides, high O2/nutrients	Algae, seagrass	Invertebrates, fish	Oil pollution, construction
Oceanic Pelagic Zone	Open water, low nutrients, high O2	Phytoplankton	Zooplankton, fish, marine mammals	Overfishing, pollution
Coral Reefs	Calcium carbonate skeletons, warm clear water	Corals (with algae), algae	Fish, invertebrates	Overfishing, warming, pollution
Marine Benthic Zone	Seafloor, cold, high pressure	Seaweeds, chemoautotrophs (vents)	Tube worms, echinoderms, fish	Overfishing, dumping

Species Distribution and Limiting Factors

Factors Affecting Distribution

• Species distributions are shaped by both ecological factors and evolutionary history.

• Dispersal, biotic interactions, and abiotic factors all play roles.

Dispersal

• Movement of individuals or gametes away from origin or high-density areas.

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

• 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 metabolism, enzyme function, and survival. Most organisms have a limited temperature range.

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

• Oxygen: Diffuses slowly in water; low in deep or stagnant waters.

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

• Sunlight: Required for photosynthesis; too little or too much can be limiting.

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

Ecological and Evolutionary Feedback

Interactions Between Ecology and Evolution

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

• Evolutionary changes can alter ecological interactions (e.g., new adaptations affecting resource use).

• Feedbacks can be rapid (e.g., guppy color and predation) or occur over long timescales (e.g., plant diversification and animal speciation).

Example: Trinidadian guppies evolve different color patterns and feeding preferences depending on predation pressure, which in turn affects algal abundance in streams.

Additional info: Understanding the interplay between ecological and evolutionary processes is crucial for predicting responses to environmental change, including climate change and habitat alteration.