Campbell Biology Tenth Edition Chapter 34 and Chapter 37 Notes

Introduction to Ecology and the Biosphere

• Definition of the Biosphere: The biosphere encompasses all of Earth that is inhabited by life. It extends from the atmosphere several kilometers above the Earth down to the depths of the ocean floors.

• Properties of the Biosphere:

  • Vast yet finite realm housing all global living ecosystems.

  • Significantly modified by human activity across the globe, including visible alterations such as urbanization, agricultural land conversion, and highway networks, as well as invisible global chemical and environmental impacts.

• Ecology Analogy:

  • Just as effective human healthcare relies on understanding human anatomical structure and physiological function, environmental preservation and ecological health rely on understanding the structure and dynamics of populations, communities, and ecosystems.

Scope and Levels of Ecological Hierarchy

• Ecology: The scientific study of the interactions of organisms with each other and with their chemical and physical environment.

• Environmental Factors:

  • Biotic Factors: All living components within an area, including animals, plants, fungi, protists, and microorganisms.

  • Abiotic Factors: The nonliving physical and chemical components of an environment, such as temperature, light, water, minerals, nutrients, wind, and soil composition.

  • Habitat: The specific environment in which an organism lives, encompassing both its local biotic and abiotic factors.

• Subfields and Levels of Ecological Organization:

  • Organismal Ecology: Focuses on the evolutionary adaptations, behavior, and physiology of individual organisms that enable them to meet environmental challenges.

  • Population Ecology: Analyzes factors affecting population size, density, structure, and growth over time for a group of individuals of the same species living in a defined area.

  • Community Ecology: Examines interactions between species—such as predation, competition, mutualism, and parasitism—across all populations inhabiting a defined geographic area.

  • Ecosystem Ecology: Investigates energy flow and biogeochemical cycling involving all living organisms alongside the abiotic environment within a given area.

  • Landscape Ecology & Biosphere Studies: Addresses spatial patterns and ecological processes spanning multiple ecosystems or the entire planet.

Scientific Thinking and Environmental History: Pesticides and Rachel Carson

• Mid-20th Century Perspective (1950s):

  • The prevailing societal view held that nature was a force to be controlled, dominated, and engineered for human economic benefit.

  • Synthetic chemical pesticides were embraced enthusiastically as modern agricultural innovations to eradicate pests and vector-borne diseases.

  • Dichlorodiphenyltrichloroethane (DDT) became the most extensively manufactured and broadcast chemical pesticide.

• Emergence of Environmental Concerns (Late 1950s):

  • Public concern grew over synthetic pesticide residues detected in food supplies.

  • Ecological research revealed that DDT persists in soil and aquatic environments without breaking down rapidly.

  • Top predators, particularly birds of prey (e.g., peregrine falcons, eagles, and ospreys), suffered severe population declines due to eggshell thinning caused by bioaccumulation of DDT.

• Rachel Carson and Silent Spring (1962):

  • Rachel Carson, a marine biologist and writer for the U.S. Fish and Wildlife Service, compiled comprehensive scientific evidence on the ecological hazards of nonselective pesticide use.

  • The publication of Silent Spring in 1962 transformed public environmental consciousness and exposed the unintended consequences of chemical pollution.

  • Carson's work triggered nationwide pesticide regulatory revisions and spawned the modern environmental movement.

Abiotic Factors Influencing the Biosphere

• Solar and Chemical Energy:

  • Sunlight powers photosynthetic primary producers in terrestrial and photic aquatic systems.

  • In dark aquatic realms (e.g., hydrothermal vents), chemoautotrophic bacteria synthesize organic compounds using inorganic chemicals such as hydrogen sulfide ($H_2S$).

• Temperature:

  • Controls metabolic rates due to enzyme temperature sensitivity.

  • Most organisms operate within narrow temperature ranges; extreme temperatures cause protein denaturation or tissue freezing.

• Water Availability and Osmoregulation:

  • Essential for cellular solvent processes and metabolic pathways.

  • Terrestrial organisms require physical structures to prevent desiccation; aquatic organisms require osmoregulatory mechanisms to maintain solute balance.

• Inorganic Nutrients:

  • Inorganic elements such as nitrogen ($N$) and phosphorus ($P$) limit primary productivity in aquatic and terrestrial ecosystems.

  • Soil structure and mineral composition dictate plant species composition.

• Aquatic and Terrestrial Environmental Factors:

  • Aquatic: Dissolved oxygen levels, salinity, water currents, and tide levels.

  • Terrestrial: Wind patterns (increasing rate of evaporative water loss) and natural fire regimes.

Climate Dynamics and Global Distribution of Biomes

• Global Climate Drivers:

  • Climate patterns dictate the geographical distribution of terrestrial communities.

  • Climate variations stem primarily from solar energy input differentials, planetary rotation, ocean currents, and land topography.

• Latitudinal Solar Energy Differentials:

  • Solar radiation strikes the Equator ($0^\circ$) directly, concentrating heat per unit area.

  • High latitudes ($60^\circ\text{N}$ and $60^\circ\text{S}$) receive solar light at oblique angles, spreading solar energy over larger surface areas and traveling through thicker atmospheric layers.

• Axial Tilt and Seasonality:

  • Earth maintains a constant axial tilt of $23.5^\circ$ relative to its orbital plane.

  • June Solstice: Northern Hemisphere tilts toward the sun, causing longer summer days and higher solar intensity in the north, while the Southern Hemisphere experiences winter.

  • December Solstice: Northern Hemisphere tilts away from the sun (winter), while the Southern Hemisphere tilts toward the sun (summer).

  • March & September Equinoxes: Solar ray strikes perpendicular to the Equator; equal day and night durations globally.

• Global Air Circulation and Rainfall Patterns:

  • Intense equatorial solar heating warms surface air, causing moist tropical air masses to ascend.

  • Rising warm air expands and cools, precipitating out atmospheric moisture over equatorial regions (yielding tropical rain belts).

  • High-altitude dry air masses stream north and south toward latitudes $30^\circ\text{N}$ and $30^\circ\text{S}$, descending to absorb moisture from the land surface and forming major global desert belts.

• Wind Patterns:

  • Trade Winds: Prevailing easterly winds in tropical regions ($0^\circ$ to $30^\circ$ latitude) formed as air flows back toward the Equator and is deflected westward by Earth's rotation.

  • Westerlies: Prevailing westerly winds in temperate regions ($30^\circ$ to $60^\circ$ latitude) blowing from west to east.

• Ocean Circulation Currents:

  • Formed by a combination of prevailing wind currents, Earth's rotation, and continental boundaries.

  • Warm ocean streams (e.g., the Gulf Stream) transport equatorial heat north to moderate coastal North American and European climates.

  • Cold ocean currents (e.g., the California Current and Labrador Current) bring polar water south, cooling coastal land margins.

• Topographic Mountain Effects (Rain Shadow Effect):

  • Prevailing ocean winds drive humid air inland and upward along the windward side of mountain ranges (e.g., Coast Range, Sierra Nevada).

  • Air cools as it rises, losing moisture as rain/snow on the mountain's windward slope, supporting dense forest growth.

  • Dry air descends along the leeward slope, absorbing moisture from the landscape and creating arid rain shadow deserts on the inland side.

Marine Biomes and Ecosystem Zonation

• Oceanic Realms and Light Zones:

  • Pelagic Realm: All open ocean water from the surface to the abyssal seafloor.

  • Benthic Realm: The seafloor substrate extending from coastal continental shelves to deep oceanic trenches.

  • Photic Zone: The shallow illuminated surface layer (depth down to $-200\,\text{m}$) where light intensity permits autotrophic photosynthesis by phytoplankton and multicellular algae.

  • Aphotic Zone: Undersea layers below $-200\,\text{m}$ where light is insufficient for photosynthesis.

  • Twilight Zone: Semi-dark layer ($-200\,\text{m}$ to $-1,000\,\text{m}$).

  • Abyssal Dark Zone: Pitch-black depths ($-1,000\,\text{m}$ to $-10,000\,\text{m}$) characterized by low temperatures, high pressures, and specialized fauna (anglerfish, gulper eels, tripod fish, hydrothermal vent tube worms).

• Coastal Marine and Interface Biomes:

  • Intertidal Zone: Coastal shoreline exposed to ambient air and solar radiation during low tide, and pounded by wave turbulence during high tide. Home to barnacles, sea stars, and attached algae.

  • Estuaries: Highly productive coastal transitional zones where freshwater rivers merge into the salty ocean. Serve as critical breeding grounds and nurseries for fish, waterfowl, and crustaceans.

  • Wetlands: Transitional biomes covered permanently or seasonally by shallow water. Filter pollutants, reduce coastal storm surge erosion, and store excess runoff water.

  • Coral Reefs: Warm photic marine biomes built over long periods by invertebrate coral polyps secreting calcium carbonate exoskeletons. Feature extremely high biodiversity.

Freshwater Ecosystems

• Freshwater Biome Categories:

  1. Standing Water (Lentic) Biomes: Lakes, ponds, and inland marshes. Stratified into photic/aphotic zones and a benthic floor.

  2. Flowing Water (Lotic) Biomes: Rivers and streams.

• Dynamics of Lotic Ecosystems:

  • Headwaters (Source): Cold, low in nutrients, clear, narrow channel, swift current; supporting primary producers adapted to attachment (mosses, algae) and high-oxygen organisms (trout).

  • Downstream Outlets: Warmer, wider channel, turbid/murky sediment, slower velocity, higher nutrient content; supporting emergent vegetation, warm-water fish, and phytoplankton.

• Ecological Interconnectedness: Freshwater environments receive inorganic nutrients, organic matter, and pollutants from surrounding terrestrial river basin landscapes.

Terrestrial Biomes

• Overview: Nine distinct terrestrial biome categories distributed globally based on mean annual temperature, total annual precipitation, and seasonal climatic variations.

1. Tropical Forests

• Distribution: Equatorial regions ($0^\circ$ latitude).

• Climatic Profile: Warm year-round temperatures, uniform day length ($11-12\,\text{hours}$), variable annual rainfall (dry tropical forest vs. wet tropical rain forest).

• Vegetation & Biodiversity: Multilayered structural canopy, high vertical stratification, highest species biodiversity on Earth.

• Soil Characteristics: Highly leached, nutrient-poor soils. Rapid decomposition rates ensure nutrients are absorbed almost immediately by plant biomass rather than accumulated in topsoil.

• Threats: Deforestation for agriculture and cattle ranching endangers vast numbers of endemic species.

2. Savannas

• Climatic Profile: High temperatures year-round, annual precipitation of $30-50\,\text{cm}$, distinct wet and dry seasons.

• Flora & Fauna: Dominated by grasses and sparse, scattered fire-resistant trees. Dominant herbivores are insects (termites), accompanied by large grazing mammals and predators.

• Ecological Driver: Frequent natural fires prevent woody plant succession and maintain grassland structure.

3. Deserts

• Climatic Profile: Extremely dry environment; annual rainfall under $30\,\text{cm}$. Can be hot (Sahara) or cold (Gobi).

• Adaptations: Plant reproduction and seed germination cycles are tied to rainfall events. Succulents (cacti) store water; animals exhibit nocturnal behavior and physiological water preservation adaptations.

• Environmental Impact: Desertification—the conversion of semi-arid margins into desert lands due to overgrazing and climate change—is a major environmental hazard.

4. Chaparral

• Distribution: Coastal regions moderated by cool offshore ocean currents (e.g., California coast, Mediterranean Basin).

• Climatic Profile: Mild, rainy winters and hot, dry summers.

• Vegetation: Dense, spiny evergreen shrubs with thick leaves.

• Fire Regime: Adapted to periodic lightning fires. Seeds germinate following fire exposure, utilizing nutrient-rich ash.

5. Temperate Grasslands

• Distribution: Continental interiors (e.g., North American prairies, Eurasian steppes).

• Climatic Profile: Cold winters, warm summers, precipitation ranges from $25\,\text{cm}$ to $75\,\text{cm}$ per year with periodic droughts.

• Flora & Fauna: Treeless landscapes (except along waterways). Historically grazed by large migratory mammals (bison, pronghorns).

• Soil & Use: Deep, nutrient-rich soils created by decomposing grass roots. Most original grasslands have been converted into agricultural farmland.

6. Temperate Broadleaf Forests

• Distribution: Mid-latitude regions in the Northern Hemisphere.

• Climatic Profile: Wide seasonal temperature variations (cold winters, hot summers), high precipitation ($75-150\,\text{cm}$ annually), 5-6 month growing season.

• Vegetation: Deciduous trees (oak, hickory, maple, beech) that drop leaves in autumn.

• Soil Profile: Richer in organic leaf litter nutrients and inorganic minerals than tropical forest soils due to slower seasonal decomposition rates.

7. Northern Coniferous Forest (Taiga)

• Distribution: High latitudes across North America and Eurasia below the Arctic Circle; also temperate rain forests along coastal Pacific Northwest.

• Climatic Profile: Long, bitterly cold winters and short, wet summers.

• Vegetation: Cone-bearing evergreen conifers (spruce, fir, pine, hemlock). Represents the largest terrestrial biome on Earth.

• Soil Profile: Thin, acidic, low-nutrient soils with slow decomposition due to cold temperatures and waxy needle composition.

8. Tundra

• Distribution: Expansive Arctic region between the taiga and permanently frozen polar ice.

• Climatic Profile: Bitter cold, strong winds, brief summer season, low annual precipitation ($< 25\,\text{cm}$).

• Key Feature: Permafrost—a continuously frozen layer of subsoil that prevents deep root growth and water drainage.

• Vegetation: Dwarf shrubs, grasses, mosses, and lichens; large trees cannot grow.

9. Polar Ice

• Distribution: High northern and southern latitudes (covering Arctic Ocean ice sheets and the continent of Antarctica).

• Climatic Profile: Extremely cold year-round; low precipitation.

• Ecosystem Connection: Terrestrial land is mostly bare rock or ice sheet with little to no plant growth. Highly interconnected with the rich surrounding marine biome (supporting seals, penguins, polar bears, and invertebrates).

Global Water and Biogeochemical Cycles

• The Global Water Cycle:

  • Connects all ecosystems across the biosphere through physical transport.

  • Key Mechanisms:

  • Solar heat drives evaporation from ocean and land surfaces.

  • Transpiration (evaporative loss of water from plant leaves) contributes moisture to the atmosphere.

  • Water vapor undergoes atmospheric condensation, producing precipitation over ocean and land ecosystems.

  • Surface runoff, groundwater flow, and rivers return terrestrial fresh water to the ocean.

• General Principles of Biogeochemical Cycling:

  • Life on Earth depends on chemical recycling because Earth is a closed system for matter.

  • Biogeochemical cycles involve biological (biotic) pathways, abiotic geological processes, and non-living chemical reservoirs.

• The Carbon Cycle:

  • Atmospheric reservoir: Carbon dioxide ($CO_2$).

  • Photosynthesis: Terrestrial plants, algae, and cyanobacteria absorb $CO_2$ to synthesize organic compounds.

  • Cellular Respiration: Consumers, producers, and decomposers release $CO_2$ back into the atmosphere.

  • Combustion: Burning of wood and fossil fuels adds excess $CO_2$ into the atmosphere.

• The Phosphorus Cycle:

  • No Atmospheric Component: Phosphorus cycles primarily through geological rock reservoirs and soil solutions as inorganic phosphate ions ($PO_4^{3-}$).

  • Weathering: Physical/chemical breakdown of rocks releases phosphate into soil and aquatic environments.

  • Assimilation: Plants absorb inorganic phosphate from soil; animals obtain organic phosphorus by consuming plants.

  • Decomposition: Soil decomposers break down organic detritus, returning inorganic phosphate to soil.

  • Sedimentation: Phosphates wash into water bodies, precipitate into solid sediment, and form rock over geological timescales.

• The Nitrogen Cycle:

  • Essential constituent of amino acids, proteins, and nucleic acids.

  • Major Abiotic Reservoir: Atmospheric nitrogen gas ($N_2$), making up roughly $80\%$ of the atmosphere.

  • Nitrogen Fixation: Specialized nitrogen-fixing bacteria (free-living in soil or symbiotic in legume root nodules) convert atmospheric $N_2$ into usable compounds (e.g., ammonium, $NH_4^+$).

  • Nitrification: Nitrifying bacteria in soil oxidize ammonium into nitrates ($NO_3^-$).

  • Assimilation: Plants take up $NH_4^+$ and $NO_3^-$ to synthesize organic nitrogen molecules.

  • Decomposition & Ammonification: Soil decomposers return nitrogen from detritus back into ammonium ($NH_4^+$).

  • Denitrification: Denitrifying bacteria convert soil nitrates ($NO_3^-$) back into gaseous nitrogen ($N_2$), returning it to the atmosphere.

Ecosystem Services and Human Well-Being

• Ecosystem Services: Functions performed by natural ecosystems that directly or indirectly benefit human society.

  • Provisioning of fresh drinking water, oxygen, and food resources.

  • Natural cycling of essential biochemical elements and decomposition of organic waste products.

  • Climate and air quality regulation.

• Wetlands & Forests:

  • Wetlands buffer coastal communities against hurricane storm surges and tidal waves, moderate inland flooding, and filter chemical pollutants from water.

  • Vegetation roots hold topsoil in place, preventing severe soil erosion, landslides, and mudslides.

Concept Check Questions & Answers

• Why isn't "cold desert" an oxymoron?

  • Deserts are defined by aridity and low precipitation ($< 30\,\text{cm}/\text{year}$), not by warm air temperatures. Cold deserts (such as Antarctica or the Gobi Desert) receive almost no annual precipitation.

• How can homeowners in chaparral areas protect their neighborhoods from fire hazards?

  • Homeowners can reduce brush density surrounding structures, clear dead vegetation to maintain defensible space around homes, and use fire-resistant building materials.

• What factors prevent woody plants and trees from dominating temperate grasslands?

  • Low annual rainfall, periodic dry droughts, frequent natural fires, and extensive grazing by large herbivores inhibit tree growth.

• How does the soil of a temperate broadleaf forest differ from that of a tropical rain forest?

  • Temperate broadleaf forest soil is richer in organic matter and nutrients because leaf litter accumulates and decomposes slowly over winter, storing nutrients in topsoil. In tropical rain forests, rapid warm decomposition and immediate uptake by dense vegetation leave the soil thin and nutrient-poor.

• How and why does the soil of northern coniferous forests differ from that of broadleaf forests?

  • Coniferous forest soil is thinner, acidic, and nutrient-poor because cold temperatures slow decomposition and evergreen needles contain waxy, acidic compounds.

• What three abiotic factors account for the rarity of trees in the arctic tundra?

  • Permafrost (preventing root penetration), extremely cold ambient temperatures during a brief growing season, and intense dry winds.

• How does the vegetation found in polar ice regions compare with tundra vegetation?

  • Polar ice regions have virtually no vascular plant growth (only sparse lichens and mosses on exposed rock), whereas tundra supports dwarf shrubs, grasses, sedges, mosses, and lichens.

• What is the main way that living organisms contribute to the global water cycle?

  • Transpiration—the evaporative loss of water through plant stomata into the atmosphere.

• Why does oil pollution in estuaries affect non-resident animal species?

  • Estuaries serve as nursery grounds, feeding stops, and spawning habitat for migratory birds, marine fish, and crustaceans that reside elsewhere during adulthood.

• Why does sewage release cause massive algal blooms in freshwater lakes?

  • Sewage delivers rich loads of inorganic nutrients (nitrogen and phosphorus) that eliminate nutrient limitations, stimulating rapid algal growth.

• Which biome will most likely replace arctic tundra as global temperatures continue to rise?

  • Northern coniferous forest (taiga).

• Why are soils in most tropical rain forests nutrient-poor?

  • High temperature and humidity cause rapid decomposition, and nutrients released into soil are immediately reabsorbed by dense plant growth or leached away by heavy rain.

• How do periodic fires help maintain savannas as grassland ecosystems?

  • Fires kill young tree saplings before they mature, while perennial grasses survive via underground root crowns.