Lecture 2: The Physical Environment

What Determines Where Organisms Live?

• The physical environment determines where organisms can live, the resources available, and the rate at which populations can grow

• Understanding the physical environment is they key to understanding all ecological phenomena

Biomes

• Biomes are large-scale biological communities shaped by the physical environment, particularly climate

• They are categorized by dominant plant forms, not taxonomic relationships

Plants and What They Indicate

• Plants occupy sites for a long time and are good indicators of climatic conditions and disturbances

• Plant form responds to selection pressures such as aridity, extreme temperatures, etc.

• Terrestrial biomes are characterized by growth forms of the dominant plants, such as leaf deciduousness or succulence (shedding of leaves and storing of water in leaves)

Convergence

• Evolution of similar growth forms along distantly related species in response to similar selection pressures

Temperature and Precipitation on Plants

• Temperature has direct physiological effects on plant growth form

• Precipitation and temperature act together to influence water availability and water loss by plants

• Water availability and soil temperature determine the supply of nutrients in the soil

Climate Controls Where and how Organisms Live

• Climate is characterized by average conditions, but extreme conditions are also important to organisms because they can contribute to mortality

Evapotranspiration (ET)

• Water transfers from the Earth’s surface to the atmosphere through evaporation from the soil and transpiration by plants

Climate Graphs (PET, AET)

• Find PET by using the temperature curve and precipitation axis

• When precipitation exceeds the PET, AET = PET

  • This means use the temperature curve and precipitation axis for AET

• When precipitation is less than PET, AET < PET

  • Find AET by using the precipitation curve, not temp. curve

• When temperature is less than 0C, both PET and AET are 0

Difference Between Weather and Climate

Weather

• Short-term state of the atmosphere

• Can change within minutes or hours

Climate

• Long-term pattern of weather

• It is the average weather over many years in one specific place

Upwelling Zones

• Upwellings bring up nutrients from the deep sediments to the photic zone, where light penetrates and phytoplankton grow

Effects of Mountains on Temperature

• Increasing elevations = decreasing temperatures

Effects of Water Bodies on Temperature

• Water has high heat capacity, so it can absorb and release heat slowly, moderating temperatures

• Land heats up quickly but also cools off quickly. Water is a heat sink

Global Energy Balance

• Equilibrium between incoming solar radiation (sunlight) and outgoing thermal radiation emitted by Earth

• When perfectly balanced, the planet maintains a stable average temperature