Chapter 4 and 5
 Variations in the Physical
Environment
 Biomes
Organisms: constant tension with P.E.
A.
Variations in physical environment
 adaptation  diversity of life.
•
B.
To understand diversity of life:
•
Ecologists and Evolutionary Biologists:
1.
2.
C.
physical environment.
biology of their study organisms.
Climate is perhaps the most important
element of environmental variation.
Adaptation Defined
Adaptation:
the pre-Darwinian idea:
the evolutionary process by which
organisms become better suited to their
environments
Darwin – 1850’s
Bits of inheritance (Mendel) – end of 19th century
Genetics – 1920’s
Modern definition: genetically determined characteristic
that enhances the ability of an individual to cope with its
environment.
Background, Cont’d
A.
The physical environment varies widely over the
earth’s surface.
Conditions of temperature, light, substrate,
moisture, and other factors shape:
B.
•
•
C.
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)
Focus on Climate - Spatial Variation
A.
Climate has predictable and unpredictable
components of spatial variation:
•
predictable:
1.
2.
•
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.)
Focus on Climate - Temporal
Variation
A.
Climate has predictable and unpredictable
components of temporal variation:
•
predictable:
1.
2.
•
seasonal variation
diurnal variation
unpredictable:
1.
2.
large-scale events (El Niño, cyclonic storms)
small-scale events (variable weather patterns)
Levels of Variability
A.
Global scale
•
B.
Regional scale
•
C.
Earth – Hemisphere (i.e. “Northern Hemisphere”)
continent – region within (i.e. “Great Basin” or
“Southwestern U.S.”
Local scale
Global
Earth as a Solar-powered Machine
A.
Earth’s 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:
•
1.
2.
latitudinal variation in temperature and precipitation
general patterns of circulation of winds and oceans
Global
Global Patterns in Temperature and
Precipitation
A.
From the equator poleward, we encounter
dual global trends of:
•
•
B.
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
Global
Temporal Variation in Climate with
Latitude
A.
Temporal patterns are predictable (diurnal,
lunar, and seasonal cycles).
Earth’s rotational axis is tilted 23.5o relative
to its path around the sun, leading to:
B.
•
•
seasonal variation in latitude of most intense
solar heating of earth’s surface
general increase in seasonal variation from
equator poleward, especially in N hemisphere
Global
1) Solar beam is spread over a greater area
2) Solar beam travels a longer path through the
Global
*
a
b
61
81
Why a > b?
Global
Hadley Cells
A.
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 (3060o N and S of equator), which, in turn, drive
polar cells (60-90o N and S of equator)
Global
“Intertropical convergence”
Solar equator and weather (I.C. shifts)
Surface wind patterns and Hadley cells
Surface wind patterns and ocean currents
Global
Effects of solar equator
(shifting intertropical convergence)
Mérida, Mex.
Bogotá, Columbia
Rio de Janeiro, Brazil
Global
Figure 4.5
Global
Figure 4.6
• Surface wind patterns and Hadley cells
Global
Ocean currents redistribute heat and
moisture.
A.
B.
Ocean surface currents propelled by winds.
Deeper currents established by gradients of
temperature and salinity.
Ocean currents constrained by basin
configuration, resulting in:
C.
•
•
clockwise circulation in N hemisphere
counterclockwise circulation in S hemisphere
D. Warm tropical waters carry heat poleward.
Global
A.
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
Regional
Rain Shadows
A.
Moisture content of air masses is recharged
when they flow over bodies of water:
B.
Air masses forced over mountains cool as a
result of adiabatic cooling (air expands,
performs work, and therefore cools) and lose
moisture as precipitation.
C.
Air on lee side of mountains is warmer and
drier (causing rain shadow effect).
Regional
Figure 4.7
Regional
Figure 4.10
NE trades
Regional
Proximity to bodies of water determines
regional climate.
A.
B.
Downwind of large mountain ranges - arid
Continental interiors - arid:
•
Why?
1.
2.
C.
distant from source of moisture
air reaching interior previously lost moisture
Coastal areas have less variable maritime
climates than continental interiors.
Local
Topographic and Geologic Features
A.
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
Local
Seasonal Cycles in Temperate Lakes
1
A.
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
Local
Seasonal Cycles in Temperate Lakes
2
•
Summer: warming of surface
1.
•
“Layers”
1.
2.
3.
•
stable layering of water column - thermal stratification,
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
Local
Figure 4.13
Fall overturn
Spring overturn
Epilimnion
Thermocline
Hypolimnion
Thermal stratification
The Biome Concept
A.
Character (plant and animal life) of natural
communities is determined by climate,
topography, and soil (or parallel influences in
aquatic environments).
B.
Because of convergence, similar dominant plant
forms occur under similar conditions.
C.
Biomes are categories that group communities by
dominant plant forms.
Convergence (Convergent Evolution)
A.
Convergence is the process by which unrelated
organisms evolve a resemblance to each other in
response to common environmental conditions:
•
Examples
1.
Arid climate plants (cactaceae, euphorbaceae)
2.
Mangroves worldwide typically have thick, leathery leaves, root
projections, and viviparity
3.
Seed-cracking birds, running birds (animals)
Convergence (cont.)
Viviparity in mangroves
Climate is the major determinant of plant
distribution.
A.
B.
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:
1.
2.
3.
cold winter temperatures to the north
hot summer temperatures to the south
summer drought to the west
Figure 5.3
Figure 5.4
black: drier, better-drained soils lots of calcium
silver: moist, well-drained soils
red: wet and swampy or dry, (opportunists)
Limitations define distributions (cont.)
N. Coastal region of CA
Waring and Major (1964)
“The optimum”
Form and function match the
environment.
A.
Adaptations match each species to the
environment where it lives:
•
all species are to some extent specialized:
1.
2.
•
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
1.
2.
Niangua darter – Osage River basin
Wondering albatross
Biomes - Terrestrial Examples
A.In North America:
• tundra, boreal forest, temperate seasonal forest,
temperate rain forest, shrubland, grassland, and
subtropical desert
B.In Mexico and Central America:
• tropical rain forest, tropical deciduous forest,
and tropical savanna
*
Climate defines the boundaries of terrestrial
biomes.
A.
Attempts to define Biomes:
•
•
Heinrich Walter
Robert Whittaker
Whittaker scheme
A.
The biomes fall in a triangular area with
corners representing following conditions:
•
•
•
warm-moist
warm-dry
cool-dry
Whittaker’s
diagram