Chp. 34 - The Biosphere: An Introduction to Earth’s Diverse Environments

Introduction to Ecology and the Biosphere

• Definition of Ecology: Ecology is defined as the scientific study of the interactions that occur between organisms and their respective environments.

• Energy Sources in the Biosphere:

  • For the vast majority of life forms on Earth, the Sun serves as the primary and main source of energy.

  • In specific environments like hydrothermal vents, life does not rely on solar energy but depends on chemoautotrophic sulfur bacteria.

• Scope of the Biosphere: Earth’s diverse environments are teeming with life, ranging from the "roof of the world" (high altitude mountains) to the deepest parts of the oceans.

Environmental Factors and Levels of Organization

• Variable Groupings: Organisms are affected by two major types of environmental variables:

  1. Biotic Factors: These include all living organisms within a specific area, representing the living component of the environment.

  2. Abiotic Factors: These constitute the environment’s nonliving component, including all physical and chemical factors (e.g., temperature, light, water, minerals).

• Habitat: This term refers to the specific surroundings of an organism, including both the biotic and abiotic factors present there.

• Ecological Hierarchy: Ecologists study interactions across several structured levels:

  • Organism: An individual living thing.

  • Population: A group of individuals belonging to the same species that live in a particular geographic area.

  • Community: An assemblage consisting of all the populations of organisms living close enough to one another for potential interaction.

  • Ecosystem: A level that includes both the biotic (community) and abiotic components of the environment.

  • Landscapes: Arrays of ecosystems, typically characterized as distinctive patches visible from an aerial perspective.

  • Biosphere: This is the global ecosystem, encompassing all of the Earth that is inhabited by life. It extends from the atmosphere several kilometers above the Earth to the depths of the oceans.

Ecology and Environmental Awareness

• Human Impact: Human activities significantly alter all parts of the biosphere through the construction of cities, farms, and highways, which change the physical landscape.

• Chemical Use: The widespread application of chemicals, such as fertilizers and pesticides, creates environmental problems affecting both humans and other organisms.

• The DDT Controversy: Two specific factors raised public and scientific questions regarding the long-term effects of widespread DDT (Dichlorodiphenyltrichloroethane) usage:

  1. The evolution of pesticide resistance in insect populations.

  2. Rachel Carson’s 1962 book Silent Spring, which is credited with playing a central role in awakening global environmental awareness.

Fundamental Abiotic Factors Influencing Life

• Energy Source: Most ecosystems rely on solar energy (photosynthesis), though some rely on chemical energy.

• Temperature: Impacts metabolic rates; most organisms function within a specific narrow range of temperatures.

• Water: The abundance and type (salinity) of water are critical for survival.

• Nutrients: The availability of inorganic nutrients (like nitrogen and phosphorus) affects the distribution of photosynthetic organisms.

• Other Aquatic Factors: Includes the availability of dissolved oxygen, salinity, and tides.

• Other Terrestrial Factors: Includes wind (which increases water loss) and fire (which can be a disturbance or a necessity for some species).

Adaptation and Natural Selection Case Study: The Pronghorn

• Species Distribution Explanations: A species exists in a specific location because it either evolved from ancestors in that location or dispersed there and survived.

• The Pronghorn (Antilocapra americana):

  • It is a highly successful herbivorous running mammal found in North American open country.

  • It descended from ancestors that roamed North American plains and shrub deserts more than $1,000,000$ years ago.

  • It is not found anywhere else and is only distantly related to African antelopes.

• Environmental Adaptations:

  • Climate: Adapted to arid, windswept environments with extreme temperature fluctuations.

  • Alleles: Survival and successful reproduction under these conditions ensured that adaptive alleles were passed to subsequent generations.

  • Predation History: Until approximately $12,000$ years ago, its major predator was likely the now-extinct American cheetah, which was similar to modern African cheetahs.

  • Selection Pressure: Ecologists hypothesize that the pursuit speed of the cheetah drove the selection for the pronghorn’s extraordinary speed. Its current speed far exceeds that of its modern predator, the wolf.

  • Social Protection: Like many large grassland herbivores, the pronghorn gains protection by living in herds.

Regional Climate and Global Patterns

• Climate Determinants: Global climate patterns are primarily determined by solar energy input and the Earth’s movement in space.

• Solar Radiation: Sunlight intensity varies with latitude. Equatorial regions receive direct sunlight, while higher latitudes receive sunlight at a slant.

• Seasons: Caused by the Earth’s permanent tilt of $23.5^{\circ}$.

  • June Solstice: Northern Hemisphere tilts toward the sun.

  • December Solstice: Northern Hemisphere tilts away from the sun.

  • Equinoxes: Occur in March and September when the equator faces the sun directly.

• Tropics: The region between latitudes $23.5^{\circ}N$ (Tropic of Cancer) and $23.5^{\circ}S$ (Tropic of Capricorn). This area has the greatest annual solar input and least seasonal variation.

• Air Circulation and Precipitation:

  • Doldrums: Areas of calm or light winds near the equator created by rising moist air.

  • Rainfall: As moist air rises in the tropics, it cools and releases water as abundant precipitation.

  • Dry Air Movement: High-altitude dry air spreads toward $30^{\circ}N$ and $30^{\circ}S$, where it descends, absorbs moisture, and creates desert conditions.

• Wind Patterns:

  • Trade Winds: Blow from east to west in the tropics due to Earth’s rotation deflecting vertically circulating air.

  • Westerlies: Blow from west to east in temperate zones.

• Ocean Currents: Created by prevailing winds, planet rotation, unequal heating, and continental shapes. These currents greatly affect regional climates (e.g., the Gulf Stream).

• Landforms and Microclimates:

  • Air temperature drops by approximately $6\,^{\circ}C$ for every $1,000\,m$ increase in elevation.

  • Rain Shadows: Mountains can block moist air, causing heavy rain on the windward side and creating a desert (rain shadow) on the leeward side (e.g., East of the Sierra Nevada).

Aquatic Biomes

• Marine Zonation:

  • Pelagic Realm: All open water.

  • Benthic Realm: The seafloor, from the continental shelf to the deep-sea bottom.

  • Photic Zone: The upper layer (down to approximately $200\,m$) where light is sufficient for photosynthesis. Home to phytoplankton and coral reefs.

  • Aphotic Zone: Includes the "twilight" zone ($200\,m$ to $1,000\,m$) and the "no light" zone ($1,000\,m$ to $10,000\,m$).

  • Intertidal Zone: Where ocean meets land; submerged at high tide and exposed at low tide.

  • Estuaries: Productive regions where freshwater rivers meet the ocean.

  • Wetlands: Transitional areas between aquatic and terrestrial ecosystems.

• Freshwater Biomes:

  • They cover < 1\% of Earth’s surface and contain < 0.01\% of its water, yet harbor $6\%$ of all described species.

  • Standing Water: Lakes and ponds.

  • Flowing Water: Rivers and streams.

Terrestrial Biomes

• Overview: There are nine major types of terrestrial biomes, distinguished mainly by predominant vegetation. Distribution is dictated by temperature and precipitation.

• Tropical Forest: Near the equator; warm temperatures; $11-12$ hour days; variable rainfall. Tropical rain forests are highly complex and species-rich.

• Savanna: Warm year-round; $30-50\,cm$ annual rainfall; seasonal variation; dominated by grasses and scattered trees; large grazing mammals.

• Desert: Driest biome; low and unpredictable rainfall. Desertification (conversion of semiarid land to desert) is a major environmental issue.

• Chaparral: Shrubland; cool/rainy winters and hot/dry summers; vegetation is fire-adapted.

• Temperate Grassland: Mostly treeless (North American prairie); $25-75\,cm$ annual rain; periodic droughts and cold winters; historical home of bison and pronghorn.

• Temperate Broadleaf Forest: Requires moisture for large trees; temperatures from $-30\,^{\circ}C$ to $30\,^{\circ}C$; high precipitation ($75-150\,cm$).

• Coniferous Forest (Taiga): Largest terrestrial biome; dominated by cone-bearing evergreens (spruce, pine, fir); long, cold winters and short, wet summers. Includes temperate rain forests.

• Tundra: Arctic region between taiga and polar ice; characterized by permafrost (continuously frozen subsoil); little precipitation; treeless.

• Polar Ice: Land north of tundra, parts of the Arctic Ocean, and Antarctica; extremely cold with very low precipitation; closely linked to marine biomes.

The Global Water Cycle

• Connectivity: Biomes are linked by the water cycle and nutrient cycles.

• Movement: Water moves via precipitation and evaporation.

  • Over oceans: Evaporation exceeds precipitation.

  • Over land: Precipitation exceeds evaporation.

• Human Impact on Water Cycle:

  • Destruction of tropical rain forests reduces atmospheric water vapor.

  • Pumping groundwater for irrigation increases evaporation rates over land.

• Components of the Cycle: Movement involves solar heat, net movement of water vapor by wind, transpiration from plants, and surface/groundwater flow from land back to the sea.", "title": "Chapter 34: The Biosphere - An Introduction to Earth’s Diverse Environments"}