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 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

• Solar energy and Earth's movement: The sun's energy and Earth's rotation and tilt create temperature variations, air and water circulation, and evaporation patterns, leading to latitudinal climate differences.

• Latitudinal variation in sunlight: Sunlight is most direct at the tropics (23.5º N to 23.5º S), resulting in higher temperatures. At higher latitudes, sunlight is less direct, making these regions cooler.

• Global air circulation: Warm, moist air rises at the equator, cools, and releases precipitation. Dry air descends at 30º N/S, creating deserts. Air rises again at 60º N/S, causing precipitation, and descends at the poles, creating cold, dry climates.

• Wind patterns: Earth's rotation causes trade winds (east to west in tropics) and 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 air belts cause seasonal changes in precipitation, influencing the growth of tropical forests and other biomes.

• Seasonal wind changes can cause ocean upwelling, bringing nutrient-rich water to the surface and supporting marine life.

Bodies of Water and Mountains

• Oceans and lakes: Moderate climate due to water's high specific heat. Ocean currents transport heat, affecting coastal climates.

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

Vegetation and Microclimate

• Vegetation: Forests absorb more solar energy, but transpiration cools and moistens the local climate. Deforestation leads to hotter, drier conditions.

• 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) increase greenhouse gases, causing climate change.

• Earth has warmed by ~0.9°C since 1900; further warming is expected.

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

• Range shifts can disrupt existing communities and lead to extinctions, especially for species with poor dispersal abilities.

Biomes: Major Life Zones

Terrestrial Biomes

Biomes are major life zones defined by vegetation type (terrestrial) or physical environment (aquatic). Climate is the primary determinant of biome distribution.

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

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

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

• Convergent evolution: Similar adaptations in unrelated species in similar 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, constant (rain forest); seasonal (dry forest); 25–29ºC	Broadleaf evergreen/deciduous trees, layered	Highest 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, 24–29ºC	Grasses, fire-adapted forbs	Large herbivores, insects	Ranching, overhunting
Chaparral	Midlatitude coasts	Rainy winters, dry summers; hot summers	Shrubs, small trees, fire-adapted	Amphibians, reptiles, small mammals	Agriculture, urbanization
Temperate Grassland	Continents, interiors	Seasonal; cold winters, hot summers	Grasses, forbs, fire/drought-adapted	Grazers, burrowers	Agriculture, overgrazing
Northern Coniferous Forest (Taiga)	N. America, Eurasia	30–70 cm precipitation; cold winters	Evergreen conifers	Birds, large mammals	Logging
Temperate Broadleaf Forest	Midlatitudes, N. Hemisphere	70–200+ cm precipitation; 0ºC winters, hot summers	Deciduous/evergreen trees, layered	Mammals, birds, insects	Settlement, recovery
Tundra	Arctic, alpine	20–60 cm (arctic), >100 cm (alpine); cold	Mosses, grasses, dwarf shrubs	Large mammals, migratory birds	Oil/mineral extraction

Aquatic Biomes

Aquatic biomes are defined by their physical and chemical environment, including salinity, depth, and water movement. Oceans cover about 75% of Earth's surface and play a major role in climate and nutrient cycling.

• Marine biomes: ~3% salt concentration (e.g., oceans, coral reefs, estuaries).

• Freshwater biomes: <0.1% salt concentration (e.g., lakes, rivers, wetlands).

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 living on/in the substrate).

• Abyssal zone: Deepest part (2,000–6,000 m).

• Thermocline: Temperature boundary separating warm upper water from 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
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	Invertebrates, fish	Pollution, construction
Oceanic Pelagic Zone	Open water, low nutrients, high O2	Phytoplankton	Zooplankton, fish, mammals	Overfishing, acidification
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

Factors Limiting Species Distribution

Ecological and Evolutionary Factors

• 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 (e.g., cattle egrets, Hawaiian silverswords).

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

Biotic Factors

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

• Example: Grazing by sea urchins prevents seaweed establishment.

Abiotic Factors

• Temperature: Affects metabolism, enzyme function, and survival. Most organisms have a narrow optimal range.

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

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

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

• Sunlight: Required for photosynthesis; limited in deep water or shaded environments. Excess light can cause stress or UV damage.

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

Ecological Change and Evolution

Feedback Between Ecology and Evolution

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

• Evolutionary changes can alter ecological interactions (e.g., guppy color patterns and predation levels affect algal abundance).

• Feedbacks can be rapid or occur over long timescales.

Example: Trinidadian guppies evolve different traits under different predation pressures, which in turn affects the ecosystem's algal community.

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