26.0 Introduction

1. The Biosphere Includes All Communities
1. Distribution of Life Reflects Environmental Variations
2. Earth Can Be Viewed as a Whole Through Satellite Images fig 26.1

26.1 Organisms must cope with a varied environment

1. The Environmental Challenge
1. How Environments Vary
1. Temperature
1. Most organisms live within narrow temperature range
2. Growing season of plants influenced by temperature

2. Water
1. All organisms require water
2. Water may be scarce on land, patterns of rainfall are important

3. Sunlight
1. Nearly all ecosystems require sunlight to produce energy via photosynthesis
2. Sunlight influences the amount of life supported

4. Soil
1. Physical consistency, pH and mineral content may limit plant growth
2. Nitrogen and phosphorous are particularly important

2. Range and Grain of Environmental Variation
1. Environmental grain
1. Key element in variation
2. Spatial size of variation, relative to organism's size and mobility

2. "Coarse-grained" environment
1. Patches are large, individuals can select among them
2. Example: Plants in a field to a bee
3. Bee can select clover while ignoring other plants

3. "Fine-grained" environment
1. Varying patches are small, relative to how the organism uses them
2. May be small enough that organism ignores them
3. Example: Plants in field to a cow
4. Cow may ignore difference between clover and other plants, eats both

4. Temporal variation also exhibits differences in grain
1. Daily variation may be fine-grained for long-lived animals
2. Can be coarse-grained for insects with adult life span of only hours
3. Seasonal variation in climate is coarse-grained in most all cases

3. Active and Passive Approaches to Coping with Environmental Variation
1. Coarse-grained environment may elicit homeostasis in an individual
1. Animals use various mechanisms to maintain homeostasis
2. Example: Beetle behavior to cope with water availability fig 26.2

2. Other animals simply conform to environment

4. Resource Allocation
1. No organism can do everything optimally
1. Not enough available resources
2. With limited resources, organisms forced to make compromises
3. Must allocate resources to various tasks to ensure survival

2. Homeotherms expend 80% of energy to generate heat
3. Conforming organisms do not make a similar expenditure

2. Adaptations to Environmental Change
1. Physiology
1. Changes used to help organisms adapt to coarse-grained environment
2. Examples
1. Body constricts facial blood vessels in a cold day
1. Reduces heat loss
2. Produces characteristic "flush"

2. Frogs exposed to low temperature fig 26.3
1. Shift temperature response downward
2. Rate of metabolism depends on temperature to which they are acclimated

3. Insects avoid freezing with presence of glycerol antifreeze in blood
4. Others convert body glycogen to protective alcohols

2. Morphology
1. Endotherms in cold climates minimize energy expenditures
1. Mammals have shorter ears and limbs, larger bodies
2. Both minimize heat loss by reducing surface area

2. Some animals hibernate, in effect, behave like conformers
3. Some animals use fur to insulate themselves and retain body heat
1. Thicker fur provides greater insulation fig 26.4
2. Wolf's fur is three times thicker in winter, insulates more than twice as well

3. Behavior
1. Many animals deal with coarse-grained environment by avoiding it
2. Example: Tropical lizards fig 26.5
1. Open habitat, maintain even temperature by basking in sun
2. Shaded habitat, become conformers, adapt temperature of surroundings

3. Behavior adaptations can be extreme
1. Spadefoot frogs burrow under surface
2. Remain for nine moths of a year
3. Reduced metabolic rate, survive on fat reserves
4. Emerge and breed with coming of cool period
5. Young mature rapidly and burrow

26.2 Climate shapes the character of ecosystems

1. Distribution of Biomes Are a Result of the Earth's Features
1. Interaction of Various Factors
1. Features of earth include soil type, presence of mountains or valleys
2. Two key physical factors
1. Amount of solar heat reaching surface, and its seasonal variations
2. Global atmospheric circulation

3. Dictate local climate, determine amount and distribution of precipitation

2. The Sun and Atmospheric Circulation
1. Earth Receives Heat from Sun
1. Heat energy transferred in various forms
1. Receives short-wave radiation from sun
2. Radiates long-wave radiation back into space

2. Ultraviolet radiation absorbed by oxygen and ozone in atmosphere

2. Why the Tropics Are Warmer
1. Climate depends on amount of energy received from sun's rays
1. Variation results from spherical shape of earth
2. Perpendicular at equator, more intense over given area
3. Greater angle at poles, energy spread over greater area fig 26.6a

2. Earth's rotation on axis and annual orbit affect climate fig 26.6b
1. Inclination of axis tilted 23.5c
2. Orbit and angle of inclination produce seasons

3. Major Atmospheric Circulation Patterns
1. Warms air holds more moisture than cold air
2. Equatorial north/south pattern of air flow fig 26.7
1. Warm air at equator rises and flows to poles
2. Air cools as it rises, thus loses moisture to tropics
1. Rising low pressure air pattern called doldrums
2. Draws air from north and south latitudes

3. Air sinks at 30° latitude, is reheated at surface
4. Results in zone of lesser precipitation
5. Warm air continues northward to poles
6. Rises at 60° latitude and flows to equator
7. Produces polar front zone of high precipitation
8. Descends near poles, producing zone of very low precipitation

4. Air Currents Generated by the Earth's Rotation
1. Earth's rotation causes an east/west air flow
1. Trade winds at 30° latitude
1. From east-southeast in southern hemisphere
2. From east-northeast in northern hemisphere

2. Prevailing westerlies at 30 to 60° latitude
1. Blow from west to east
2. Dominate climate patterns fig 26.8

3. Weak zones of east to west winds at extreme latitudes in north and south

3. Atmospheric Circulation, Precipitation, and Climate
1. Comparing Regions of Precipitation
1. Low at 30° north and south air falling and warming
2. Higher at 60° north and south, air rising and cooling
3. All great deserts lie near 30° north or south
4. Other large deserts in continental interiors, away from oceans

2. Rain Shadows
1. Other deserts result from mountain ranges intercepting rainfall
1. Air rises, ability to hold moisture decreases
2. Increased precipitation windward side of mountain ranges
3. Air descends on other side, warms, and holds water better, blocking precipitation

2. Rain shadow effect: Drier on leeward side of mountain fig 26.9

3. Regional Climates
1. Areas with climate resembling the Mediterranean
1. Small, isolated and widely separated areas fig 26.10
1. Baja, California, southwestern Oregon
2. Central Chile
3. Southwestern Australia
4. Cape region of South Africa

2. Prevailing westerlies blow from cool ocean to warm land
3. Air holds moisture, thus precipitation limited during summer

2. Great deserts lie on western sides of continents due to prevailing westerlies
3. Monsoon conditions of India and southern Asia
1. Winter trade winds blow east-northeast off cool land onto warm ocean
2. Summer winds blow east-southeast from water onto land
3. Results in heavy rains in certain regions

4. Latitude
1. Higher temperatures in tropical regions due to more sunlight
1. Most intense when sunlight strikes equator perpendicularly
2. Highest global temperatures at 0° latitude fig 26.11
3. No seasonal variation in temperature

2. Light strikes earth at oblique angle at greater latitudes
1. Less sunlight falls on a given area, lower mean temperatures
2. Greater variation due to marked seasons

5. Elevation
1. Temperature also varies with elevation, cooler at higher altitudes
2. Changes in altitude mimic changes in latitude fig 26.12
3. Timberline (no tree growth) occurs at lower elevations as latitude increases

6. Microclimate
1. Climate varies on a fine scale within an environment
2. Considerable variation in local temperature, rate of evaporation
1. Can be very different from conditions of overhead atmosphere
2. Used advantageously by gardeners

26.3 Biomes are widespread terrestrial ecosystems

1. The Major Biomes
1. Biomes Are Major Communities Occurring Over Wide Areas
1. Recognized by characteristic appearance
2. Associated with characteristic climates

2. Distribution of Major Biomes fig 26.13
1. Eight major biomes presented in this chapter
2. Six lesser biomes described, often considered subsets of major categories
3. Each biome by convention named for its dominant vegetation
4. Also characterized by particular animals, fungi and microorganisms

3. Biomes and Climate
1. Many environmental factors influence location of biomes
2. Key parameters are moisture and temperature fig 26.14
1. Productivity greatly influenced by both
2. Other important factors like soil structure, minerals
3. Readily predict what biomes will occur where fig 26.15

3. Mountains, climatic effects due to continental irregularities shape biome distribution
4. Distance from oceans and elevation also provide major impact

4. Tropical Rain Forests fig 24.16
1. Receive 140 to 450 centimeters of rain per year
2. Richest biome in terms of number of species ^_ more than 2 million
3. Great diversity of life forms, represented by few individuals
4. Life forms highly specialized and unusual
5. Substantial rainfall throughout year
6. Found in South America, Africa, Southeast Asia
7. Most nutrients concentrated in trees and other life forms
8. Destruction accompanied by loss of vast diversity of life

5. Savannas fig 26.17
1. Dry climates that border the tropics
2. Open grassland with scattered shrubs and trees
1. Rainfall is seasonal, 75 to 125 centimeters per year
2. Animals and plants may be active only in rainy season

3. Characteristic large grazing mammals
4. Increasingly being converted to agricultural uses

6. Desert fig 26.18
1. Often found on interior of continents
2. Extremely low rainfall, less than 25 centimeters per year
3. Plant and animal life may limit activity to specific seasons
1. Live in moist, deep burrows and emerge at night
2. Drink water when available, survive long periods of drought
3. Many simply leave during dry season

7. Temperate Grasslands fig 26.19
1. Halfway between equator and each pole
2. Once common in Eurasia, South America, and North America
1. Highly productive when converted to agriculture due to rich soil
2. Grasslands also called prairies
3. Roots of perennial plants penetrate deep, rich soil

3. Populated by herds of grazing mammals

8. Temperate Deciduous Forests fig 26.20
1. Warm summers, cool winters, plentiful rains
2. Exemplified by forests of Eurasia, northeastern U.S., eastern Canada
1. Deciduous trees drop leaves in winter
2. Deer, bears, beaver, raccoons are familiar animals

3. Remnants of more extensive forests
1. Share animals and plants that were once widespread
2. Alligators now found only in China and southeastern U.S.

4. Many areas possess rapidly growing perennial herbs

9. Temperate Evergreen Forests fig 26.21
1. Winters cold, strong seasonal dry period
2. Include pine forests of U.S., California oak woodlands, Australian eucalyptus forests
1. Evergreen trees mixed with deciduous trees
2. Characteristic of regions with more nutrient-poor soils

3. Broad transitional zone between deciduous forests and taiga

10. Taiga fig 26.22
1. Northern coniferous forests of Eurasia and North America
1. Conifers have needle-like leaves that are retained year-round
2. Long, cold dry winters with most precipitation in summers

2. Short growing season, not good for agriculture, low human populations
3. Variety of animal life
1. Large mammals: Elk, moose, wolves
2. Small mammals: Rodents

4. Willows, birches common around lakes and marshes

11. Tundra fig 26.23
1. Farthest north, excluding regions of polar ice
2. Grassland is open, windswept and often boggy
1. Very low precipitation
2. Permanent ice, permafrost near surface
3. Small trees around open water

3. Large grazing mammals, various carnivores

2. Other Biomes
1. Polar Ice fig 26.24
1. Ice caps at north (Arctic) and south (Antarctic) poles
2. No precipitation, ice abundant, fresh water scarce, life limited to coasts
3. Antarctic interior not warmed by heat from circulating ocean
4. Only bacteria, algae, small insects in Antarctic interior

2. Mountain Zone (Alpine) fig 26.25
1. Same temperature and moisture as northern latitudes
2. Wind swept vegetation similar to tundra, few trees
3. Most growth in summer

3. Chaparral fig 26.26
1. California chaparral derived from deciduous forests
2. Found in regions with mediterranean, summer-dry climate
3. Examples: Mediterranean area, California, Central Chile, South African Cape, southwestern Australia
4. Consists of evergreen shrubs and low trees
5. Shrub communities adapted to periodic fires

4. Warm, Moist Evergreen Forest fig 26.27
1. Occur where winters are mild, rain is plentiful
2. Examples: Central China, south-eastern U.S. pine forests, northern California coastal redwood forests

5. Tropical Monsoon Forest fig 26.28
1. Also called tropical upland forests
2. Occur in tropics at higher latitudes or drier climates than rain forests
3. Trees are deciduous, lose leaves in dry season
4. Rainfall seasonal, from very wet to nearly drought conditions
5. Example: Central India

6. Semidesert (Tropical Dry Forest) fig 26.29
1. Occur in tropical regions with less rain than monsoon forests, but more than savannas
2. Also known as thornwood forests, bushes and trees have thorns and spikes
3. Brief rainy period of growth followed by long dry period with no growth

26.4 Aquatic ecosystems cover much of the earth

1. Patterns of Circulation in the Ocean
1. Ocean Circulation Depends on Atmospheric Circulation
1. Oceanic air circulation modified by land masses
2. Surface gyrals dominate ocean circulation fig 26.30
1. Clockwise in north, counterclockwise in south
2. Redistribute heat and affect continental climates
3. Gulf Stream carries warmth to western Europe

3. Western sides of continents generally warmer than eastern sides in north hemisphere
1. Opposite occurs in southern hemisphere
2. Winds from cold water onto warm land hold water

4. Humboldt Current carries cold water up the west U.S. Coast
1. Contains high concentration of phosphorus brought up from ocean depths
2. Phosphorous provides resources for abundant marine life in coast of South America

2. El Niño Southern Oscillations and Ocean Ecology
1. Current sweeps along coast of Peru and Ecuador at Christmas fig 26.31
1. Reduces fish population
2. Term now used only for catastrophic version of the current
3. Occurs every two to seven years, has global consequences

2. How El Niño happens
1. Trade winds normally push warm surface waters away from ocean's east side
2. Cold water takes its place
3. Carries nutrients and plankton-rich waters to feed fish
4. Surface water around Australia and Philippines is several degrees warmer
5. Warm water sloshes back if winds don't blow strong enough
6. As the water warms, it stays at surface and warms even more
7. Easterly trade winds weaken even further

3. End result: Western Pacific weather patterns shift 6,000 km eastward
1. Indonesia and Philippines don't receive yearly rainstorms, experience drought
2. Western edge of South America receives rains instead
3. Commercial fisheries off South America are vastly less productive
4. Midwest U.S. And Israel experience heavier than normal rainfall
5. When severe, may cause drought in Oregon and Washington

4. Trigger for El Niño is still a mystery

2. Life in the Oceans
1. Oceans Dominate Earth's Surface Composition
1. Three quarters of surface covered by water
2. Average depth of three kilometers
3. Photosynthetic organisms limited to upper surface
4. Water density affects mineral and gas solubility
1. Warm water holds less oxygen than cold
2. Carbon dioxide not limited in oceans
3. Mineral distribution more uniform than on land

2. Sea Floors Once Considered to be Nearly Devoid of Life
1. New studies show ocean floor teems with life fig 26.32
1. Estimates of diversity have soared to millions of species
2. Rivals diversity of tropical rain forests
3. Lack of migration of individuals may encourage speciation
4. Fine but formidable resource barriers exist in sea

2. Additional time for evolution may also contribute to biological richness
3. More than 90% of all described species though, occur on land
1. Barriers between habitats are sharper on land
2. Few deep sea taxonomists are actively classifying the profusion of organisms

4. Most of the major phyla of organisms originated in the sea
1. Almost every one is represented there
2. Only a few phyla are successful on land or in freshwater
3. Phyla on land evolved into a myriad of described species

3. Marine Ecosystems
1. Three Major Kinds of Oceanic Habitats fig 26.33
1. Neritic zone: Shallow waters along coasts
2. Pelagic zone: Top layer of open ocean
3. Benthic zone: Actual ocean floor
4. Abyssal zone: Deep-water areas of ocean, no light penetrates

2. The Neritic Zone
1. Small in area, but inhabited by comparatively large number of species
2. Intense, violent interactions between land and sea
3. Intertidal (littoral) region exposed when tide recedes
1. Provided transition from ocean to land habitats
2. Inhabitants generally well-secured
3. Preadaptation to terrestrial life with greater stresses
4. Organisms adapted to resist desiccation

4. Abundant nutrients from land support great continental shelf fisheries
5. Heavily populated areas, like Chesapeake Bay, damaged fig 26.35
1. Runoff from farms contains large amount of nutrients
2. Allows some organisms to thrive, use oxygen in water
3. Disturbs population of other organisms

6. Three-fourths of ocean waters occur in tropical regions
1. Successful growth of coral reefs at 21º C
2. Highly-productive ecosystems concentrate nutrients in nutrient-poor waters

3. The Pelagic Zone
1. Composed of microscopic plankton and macroscopic nekton
1. Photosynthetic plankton accounts for 40% of all photosynthesis on earth
2. Heterotrophic organisms abundant
3. Largest animals (whales) feed directly on plankton

2. Great fluctuations in populations of plankton
1. Results in rapid turnover of nutrients
2. Productivity of region may be grossly underestimated

4. The Benthic Zone
1. Area of sea floor twice that of exposed land masses
2. Sea floor covered by thick layer of fine mud
3. Initially expected to contain little life
1. High pressures, low temperature
2. Absence of light and lack of food sources

4. Recent discovery of wide array of life
1. Free-swimming frequently bioluminescent animals fig 26.36a
2. Sampled via examination of cubes of mud from sea floor

5. Clusters of organisms around deep-sea thermal vents
1. Superheated water rich in reduced compounds fig 26.36b
2. Depend on chemosynthesis rather than photosynthesis
3. Bacteria contained in animal tissue provides food

4. Fresh Water Habitats
1. Limited in Area, About 2% of Earth's Surface
1. Strongly connected to terrestrial habitats
2. Marshes and swamps constitute intermediate zones
3. Supplied with nutrients from nearby land communities fig 26.37
4. Freshwater organisms generally restricted to that habitat fig 26.38

2. Ponds and Lakes
1. Divided into two layers by light penetration
1. Photic zone: Photosynthetic organisms limited to this region
2. Aphotic zone: Strictly heterotrophic organisms, no light penetrates

2. Three zones in which organisms occur
1. Littoral zone: Shallow waters along shore
2. Limnetic zone: Top layer of open water away from shore
3. Profundal zone: Deep-water areas with no light penetration

3. Thermal Stratification fig 26.40
1. Summer conditions
1. Upper epilimnion layer
2. Lower, cooler hypolimnion layer
3. Layer of temperature change separating the two called thermocline

2. Fall conditions
1. Epilimnion temperature drops; layers mix
2. Called fall overturn

3. Winter conditions
1. Water most dense at 4º C, thus cooler surface water freezes
2. Water below ice remains between 0º and 4º
3. Organisms can survive readily

4. Spring conditions
1. Water warms and mixes with cool water below
2. Called spring overturn

5. Mixing in fall and spring mixes nutrients and oxygen into upper and lower layers

5. Productivity of Freshwater Ecosystems
1. Productivity of Lakes
1. Eutrophic lakes
1. Abundant minerals, organic matter
2. In summer oxygen is depleted below the thermocline
3. Overturns redistribute nutrients and oxygen
4. Harmless sulfate and nitrate convert into toxic hydrogen sulfide and ammonia

2. Oligotrophic lakes fig 26.41
1. Organic matter and nutrients relatively scarce
2. Frequently very deep, clear blue color
3. Deep water always rich in oxygen
4. More drastically affected by phosphate pollution and algal blooms

2. Productivity of Wetlands
1. Support wide variety of water-tolerant hydrophytes plants
2. Possess rich diversity of invertebrates, birds, other animals
3. Among the most productive ecosystems tbl 26.1
4. Key role in water storage to moderate flooding
1. Human development of "useless land" disrupting wetlands
2. Government efforts to preserve remaining wetlands