Variations in the Physical Environment

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Chapter 4 and 5

• Variations in the Physical Environment
• Biomes

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• Organisms constant tension with P.E.
• Variations in physical environment
• ? adaptation ? diversity of life.
• To understand diversity of life
• Ecologists and Evolutionary Biologists
• physical environment.
• biology of their study organisms.
• Climate is perhaps the most important element of
  environmental variation.

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Adaptation Defined
Adaptation the pre-Darwinian idea the
evolutionary process by which organisms become
better suited to their environments Darwin
1850s Bits of inheritance (Mendel) end of 19th
century Genetics 1920s Modern definition
genetically determined characteristic that
enhances the ability of an individual to cope
with its environment.
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Background, Contd

• The physical environment varies widely over the
  earths surface.
• Conditions of temperature, light, substrate,
  moisture, and other factors shape
• distributions of organisms (see chap 5)
• adaptations of organism (later in semester)
• Earth has many distinctive climatic zones
• within these zones, topography and soils further
  differentiate the environment (local
  environmental variability)

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Focus on Climate - Spatial Variation

• Climate has predictable and unpredictable
  components of spatial variation
• predictable
• large-scale (global) patterns primarily related
  to latitudinal distribution of solar energy
• regional patterns primarily related to shapes and
  positions of ocean basins, continents, and
  mountain ranges
• unpredictable - extent and location of random
  disturbance (fire, tsunami, etc.)

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Focus on Climate - Temporal Variation

• Climate has predictable and unpredictable
  components of temporal variation
• predictable
• seasonal variation
• diurnal variation
• unpredictable
• large-scale events (El Niño, cyclonic storms)
• small-scale events (variable weather patterns)

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Levels of Variability

• Global scale
• Earth Hemisphere (i.e. Northern Hemisphere)
• Regional scale
• continent region within (i.e. Great Basin or
  Southwestern U.S.
• Local scale

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Earth as a Solar-powered Machine
Global

• Earths surface and adjacent atmosphere are a
  giant heat-transforming machine
• solar energy is absorbed differentially over
  planet
• this energy is redistributed by winds and ocean
  currents, and is ultimately returned to space
• there are interrelated consequences
• latitudinal variation in temperature and
  precipitation
• general patterns of circulation of winds and
  oceans

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Global Patterns in Temperature and Precipitation
Global

• From the equator poleward, we encounter dual
  global trends of
• decreasing temperature
• decreasing precipitation
• Why? At higher latitudes
• solar beam is spread over a greater area
• solar beam travels a longer path through the
  atmosphere

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Temporal Variation in Climate with Latitude
Global

• Temporal patterns are predictable (diurnal,
  lunar, and seasonal cycles).
• Earths rotational axis is tilted 23.5o relative
  to its path around the sun, leading to
• seasonal variation in latitude of most intense
  solar heating of earths surface
• general increase in seasonal variation from
  equator poleward, especially in N hemisphere

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Global
1) Solar beam is spread over a greater area 2)
Solar beam travels a longer path through the
atmosphere
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Global

a
b
Why a gt b?
61 81
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Hadley Cells
Global

• Hadley cells constitute the principal patterns of
  atmospheric circulation
• warm, moist air rising in the tropics spreads to
  the north and south
• as this air cools, it eventually sinks at about
  30o N or S latitude, then returns to tropics at
  surface
• this pattern drives secondary temperate cells
  (30-60o N and S of equator), which, in turn,
  drive polar cells (60-90o N and S of equator)

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Global
Intertropical convergence Solar equator and
weather (I.C. shifts) Surface wind patterns and
Hadley cells Surface wind patterns and ocean
currents
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Global
Effects of solar equator (shifting intertropical
convergence)
Mérida, Mex.
Bogotá, Columbia
Rio de Janeiro, Brazil
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Figure 4.5
Global
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Figure 4.6
Global

• Surface wind patterns and Hadley cells

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Ocean currents redistribute heat and moisture.
Global

• Ocean surface currents propelled by winds.
• Deeper currents established by gradients of
  temperature and salinity.
• Ocean currents constrained by basin
  configuration, resulting in
• clockwise circulation in N hemisphere
• counterclockwise circulation in S hemisphere
• Warm tropical waters carry heat poleward.

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Global

• Surface wind patterns and ocean currents
• Clockwise currents in North
• Counter-clockwise in South

• West coasts typically have cool water
• East coasts typically have warm water
• Areas of high productivity

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Rain Shadows
Regional

• Moisture content of air masses is recharged when
  they flow over bodies of water
• Air masses forced over mountains cool as a result
  of adiabatic cooling (air expands, performs work,
  and therefore cools) and lose moisture as
  precipitation.
• Air on lee side of mountains is warmer and drier
  (causing rain shadow effect).

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Figure 4.7
Regional
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Figure 4.10
Regional
NE trades
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Proximity to bodies of water determines regional
climate.
Regional

• Downwind of large mountain ranges - arid
• Continental interiors - arid
• Why?
• distant from source of moisture
• air reaching interior previously lost moisture
• Coastal areas have less variable maritime
  climates than continental interiors.

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Topographic and Geologic Features
Local

• Topography can modify environment on local scale
• steep slopes - drain well - xeric conditions
• Bottomlands - moist (maybe riparian), even in
  arid lands
• N hemisphere, south-facing slopes warmer, drier

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Seasonal Cycles in Temperate Lakes 1
Local

• Four seasons of a small temperate lake each has
  temperature profile
• Winter 0o at surface, 4o near bottom
• Spring surface warms, dense water sinks -
  uniform 4oC profile wind causes spring overturn

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Seasonal Cycles in Temperate Lakes 2
Local

• Summer warming of surface
• stable layering of water column - thermal
  stratification,
• Layers
• epilimnion - warm, less dense surface water
• thermocline - zone of rapid temperature change
• hypolimnion - cool, denser bottom water
• Fall water cools at surface sinks, destroying
  stratification fall overturn

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Figure 4.13
Local
Fall overturn
Spring overturn
Epilimnion Thermocline Hypolimnion
Thermal stratification
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The Biome Concept

• Character (plant and animal life) of natural
  communities is determined by climate, topography,
  and soil (or parallel influences in aquatic
  environments).
• Because of convergence, similar dominant plant
  forms occur under similar conditions.
• Biomes are categories that group communities by
  dominant plant forms.

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Convergence (Convergent Evolution)

• Convergence is the process by which unrelated
  organisms evolve a resemblance to each other in
  response to common environmental conditions
• Examples
• Arid climate plants (cactaceae, euphorbaceae)
• Mangroves worldwide typically have thick,
  leathery leaves, root projections, and viviparity
• Seed-cracking birds, running birds (animals)

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Convergence (cont.)
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Viviparity in mangroves
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Climate is the major determinant of plant
distribution.

• Climatic factors - limits of plant distributions
• Determined by ecological tolerances
• Range of physical conditions within which each
  species (type of plant) can survive. (resource
  utilization curve)
• The sugar maple, Acer saccharum, in eastern North
  America, is limited by
• cold winter temperatures to the north
• hot summer temperatures to the south
• summer drought to the west

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Figure 5.3
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Figure 5.4
black drier, better-drained soils lots of
calcium silver moist, well-drained soils red
wet and swampy or dry, (opportunists)
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Limitations define distributions (cont.)
N. Coastal region of CA Waring and Major (1964)
The optimum
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Form and function match the environment.

• Adaptations match each species to the environment
  where it lives
• all species are to some extent specialized
• insect larvae from ditches and sloughs survive
  without oxygen longer than related species from
  well-aerated streams
• marine snails from the upper intertidal tolerate
  desiccation better than their relatives from
  lower levels
• we recognize both specialists and generalists
• Niangua darter Osage River basin
• Wondering albatross

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Biomes - Terrestrial Examples

• In North America
• tundra, boreal forest, temperate seasonal forest,
  temperate rain forest, shrubland, grassland, and
  subtropical desert
• In Mexico and Central America
• tropical rain forest, tropical deciduous forest,
  and tropical savanna

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Climate defines the boundaries of terrestrial
biomes.

• Attempts to define Biomes
• Heinrich Walter
• Robert Whittaker

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Whittaker scheme

• The biomes fall in a triangular area with corners
  representing following conditions
• warm-moist
• warm-dry
• cool-dry

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Whittakers diagram