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Lecture 21
INTRODUCTION TO
ECOLOGY
Overview: Discovering Ecology
• Ecology is the scientific study of the interactions
between organisms and the environment
– what environmental factors limit the geographic
distribution of an organism?
– what factors can affect the size of its population?
• interactions of an organism with its environment
(e.g. other organisms, food supply, pathogens)
determine the distribution of organisms and their
abundance
Global ecology
Landscape ecology
Ecosystem ecology
The Scope of Ecological
Research
• ecologists work at levels
ranging from individual
organisms to the planet
Community ecology
Population ecology
Organismal ecology
Global Ecology
• The biosphere is the global ecosystem
– the sum of all the planet’s ecosystems and landscapes
• Global ecology examines the influence of how the
regional exchange of energy and materials
influences the function and distribution of
organisms across the biosphere
Global ecology
Landscape Ecology
• A landscape or seascape is a mosaic of
connected ecosystems
• Landscape ecology focuses on the factors
controlling the exchanges of energy, materials,
and organisms across multiple ecosystems
Landscape ecology
Ecosystem Ecology
• An ecosystem is the community of organisms
in an area and the physical factors with which
they interact
• Ecosystem ecology emphasizes energy flow
and chemical cycling between organisms and
the environment
Ecosystem ecology
Community Ecology
• A community is a group of populations of different
species in an area
• Community ecology examines how interactions
between species affect community structure and
organization
– e.g. predation, competition
Community ecology
Population Ecology
• A population is a group of individuals of the same
species living in an area
• Population ecology analyzes factors that affect
population size and how and why it changes with time
Population ecology
Organismal Ecology
• Organismal ecology studies how an organism’s
structure, physiology, and behavior meet
environmental challenges
• Organismal ecology includes physiological,
evolutionary, and behavioral ecology
Organismal ecology
Earth’s climate varies by latitude and
season and is changing rapidly
• the most significant influence on the distribution of
organisms on land and in the water is climate
• climate = the long-term prevailing weather conditions
in an area
• four major physical components of climate are
temperature, precipitation, sunlight, and wind
• climate can be described on two scales
– Macroclimate consists of patterns on the global, regional,
and landscape level
– Microclimate consists of very fine patterns,
•
such as those encountered by the community of organisms
underneath a fallen log
Global Climate Patterns
• determined largely by solar energy and the
planet’s movement in space
• The warming effect of the sun causes
temperature variations
– variations in temperature drive evaporation and the
circulation of air and water
– causes latitudinal variations in climate
Latitudinal Variation in Sunlight Intensity
• Earth’s curved shape causes latitudinal variation in the intensity of
sunlight
– due to the angle
• the angle at which sunlight hits Earth affects its intensity
– intensity determines the amount of heat and light per unit of surface area
• The intensity of sunlight is strongest in the tropics (between 23.5 north
latitude and 23.5 south latitude)
Atmosphere
Low angle of incoming sunlight
90°N (North Pole)
60°N
30°N
23.5°N (Tropic of
Cancer
Sun overhead at equinoxes
0° (Equator)
23.5°S (Tropic of
Capricorn)
30°S
Low angle of incoming sunlight
60°S
90°S (South Pole)
Latitudinal variation in sunlight intensity
Global Air Circulation and Precipitation Patterns
•
•
•
•
•
•
•
solar radiation near the equator sets up a global pattern of air circulation
and precipitation
high temperature in the tropics: water evaporates and warm, wet air masses flow
toward the poles
rising air masses release water and causes high precipitation, especially in the
tropics
release of water dries the air – air begins to descend
dry, descending air masses create arid climates - near 30 degrees north and
south
flows back toward the poles – picking up moisture
as the air reaches 60 degrees in latitude – air mass rises again and the cycle
repeats
66.5°N (Arctic Circle)
60°N
30°N
Westerlies
30°N
Northeast trades
0°
Southeast trades
30°S
Westerlies
60°S
66.5°S (Antarctic Circle)
Global air circulation and precipitation patterns
0°
Descending
dry air
absorbs
moisture.
Ascending
moist air
releases
moisture.
Global Air Circulation and Precipitation Patterns
•
•
•
•
•
air flowing close to Earth’s surface creates predictable global wind patterns
as the Earth rotates – land near the equator moves faster than at the poles
this deflects the wind from their vertical pattern – creates westerly and easterly
flowing wind patterns
cooling trade winds blow from east to west in the tropics
prevailing westerlies blow from west to east in the temperate zones
66.5°N (Arctic Circle)
60°N
30°N
30°N
Westerlies
Northeast trades
Ascending
moist air
releases
moisture.
0°
Southeast trades
30°S
Westerlies
60°S
66.5°S (Antarctic Circle)
circulation
and precipitation patterns
© 2011Global
Pearson air
Education,
Inc.
Descending
dry air
absorbs
moisture.
0°
Regional and Local Effects on Climate
• Climate is affected by: seasonality, large
bodies of water, and mountains
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Seasonality
• Seasonal variations of light and temperature
increase steadily toward the poles
– Seasonality seen from the middle to high latitudes
– is caused by the tilt of Earth’s axis of rotation and its annual
passage around the sun
– as a result, belts of wet and dry air straddling the equator shift
throughout the year with the changing angle of the sun
– also changing wind patterns affect ocean currents
March equinox
December
solstice
60°N
30°N
0° (equator)
30°S
Constant tilt
of 23.5°
June solstice
September equinox
Bodies of Water
• Oceans currents, and large lakes moderate the climate of nearby
terrestrial environments
– by heating and cooling overlying air masses that pass across the land
• coastal areas are generally wetter than inland areas at the same
latitude
– the cool climate produced by the California current flowing southward
supports the coniferous and redwood forest of the Pacific coast
Labrador Current
California Current
30°N North Pacific
Subtropical Gyre
Gulf Stream
North Atlantic
Subtropical
Gyre
Equator
Indian
Ocean
Subtropical
Gyre
Antarctic Circumpolar Current
30°S
South Pacific
Subtropical Gyre
South
Atlantic
Subtropical
Gyre
• oceans and large lakes tend to moderate the climate of nearby
land
• during a hot day, air over the land heats up and rises draws a cool breeze from the water across the land
• as the land cools at night, air over the warmer water rises and
draws cooler air from land back over the water, which is
replaced by warm air from offshore
Leeward side
of mountains
Air flow
Mountain
range
Ocean
Mountains
• when moist air approaches a mountain – air rises and cools and
releases its moisture on the windward side of a peak
• this creates a “rain shadow” as it absorbs moisture on the
leeward side
• the leeward rain shadow determines where many deserts are found
• mountains can also affect the amount of sunlight and temperature in
an area
• in the Northern Hemisphere, south-facing slopes receive more
sunlight than north-facing slopes
• every 1,000 m increase in elevation produces a temperature drop of
approximately 6C
Leeward side
of mountains
Air flow
Mountain
range
Ocean
© 2011 Pearson Education, Inc.
Microclimate
• in addition to regional and local effects on
climate – have microclimates
• a microclimate is determined by fine-scale
differences in the environment that affect
light and wind patterns
• every environment is characterized by smallscale differences in:
– Abiotic (non-living) factors - temperature,
light, water, and nutrients
– Biotic (living) factors - organisms that are part
of an individual’s environment
Global Climate Change
• changes in Earth’s climate can profoundly affect the biosphere
– by changing the distribution of plants and animals
• one way to predict the possible effects of future global climate
change is to study previous changes – since the last ice age
• as glaciers retreated 16,000 years ago and the climate warmed tree distribution patterns expanded northward
– seen as a fossilized pollen record
• the current climatic limits of current distributions of organisms can be
used to predict how these distributions might change in the future
– e.g. models predict the American beech may move 700-900 km further north with
warming and will shift even further south
Current
range
Predicted
range
Overlap
(a) 4.5°C warming over next
century
(b) 6.5°C warming over next
century
Biome structure and distribution are
controlled by climate and disturbance
• Biomes = major life zones characterized by
vegetation type (terrestrial biomes) or physical
environment (aquatic biomes)
• Climate is very important in determining why
terrestrial biomes are found in certain areas
© 2011 Pearson Education, Inc.
Climate and Terrestrial Biomes
• terrestrial biomes show strong latitudinal
patterns
• one way to highlight the important of climate on
a terrestrial biome – to create a climograph
30°N
Tropic of
Cancer
Equator
Tropic of Capricorn
30°S
Tropical forest
Savanna
Desert
Chaparral
Temperate grassland
Temperate broadleaf forest
Northern coniferous forest
Tundra
High mountains
Polar ice
• climograph – a plot of the annual average
temperature and precipitation in a region
• biomes are affected not just by average temperature
and precipitation, but also by the pattern of
temperature and precipitation through the year
– e.g. wet and dry seasons in addition to rainfall amounts
Annual mean temperature (°C)
Desert
Temperate grassland
Tropical forest
30
Temperate
broadleaf
forest
15
Northern
coniferous
forest
0
Arctic and
alpine
tundra
15
0
100
200
300
Annual mean precipitation (cm)
400
General Features of Terrestrial Biomes
• most terrestrial biomes are named for major physical or
climatic factors and for their predominant vegetation
– e.g. temperate grasslands in the middle latitudes – moderate
climates, dominated by various grass specific
• each biome is also characterized by specific
microorganisms, fungi and animals that have adapted to
its environment
• terrestrial biomes usually grade into each other, without
sharp boundaries
• where biomes overlap – area of intergradation or an
ecotone
– may be wide or narrow
• Vertical layering is an important feature of
terrestrial biomes
• in a forest, it might consist of an upper canopy, lowtree layer, shrub understory, ground layer of
herbaceous plants, the forest floor, and root layer
• non-forest biomes also have layers – not as
pronounced
– grasslands – grass layer, a litter layer and a root layer
• layering of vegetation in the biomes provides
diverse habitats for animals
Disturbance and Terrestrial Biomes
• biomes are dynamic and usually exhibit
extensive patchiness due to disturbances
• disturbance is an event such as a storm, fire, or
human activity that changes a community
• even the dominant plants in a biome need
disturbances from time to time
– frequent fires can kill woody plants and keep a
savanna from becoming a woodland that the
environment would support
– fires and outbreaks of pests create gaps in
forests that allow different species to grow
– fire are rare across the Great Plains due to the
change into agricultural fields
Terrestrial Biomes
• Terrestrial biomes can be characterized by:
–
–
–
–
distribution
precipitation
temperature
plants & animals
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Tropical Forest
• distribution: equatorial and subequatorial regions
• precipitation: tropical rain forests, rainfall is relatively
constant, while in tropical dry forests precipitation is highly
seasonal
• temperature: high year-round with little seasonal variation
• plants: vertically layered, and competition for light is
intense
• animals: home to millions of animal species, including an
estimated 5–30 million still undescribed species of insects,
spiders, and other arthropods
A tropical rain forest in Borneo
Desert
• distribution: occur in bands near 30 north and south of
the equator, and in the interior of continents
• precipitation: is low and highly variable, generally less
than 30 cm per year
• temperature: hot or cold
• plants: adapted for heat and desiccation tolerance, water
storage, and reduced leaf surface area
• animals: include many kinds of snakes and lizards,
scorpions, ants, beetles, migratory and resident birds, and
seed-eating rodents; many are nocturnal
A desert in the southwestern
United States
Savanna
• distribution: equatorial and subequatorial regions
• precipitation: seasonal rainfall with a long dry season
• temperature: warm year round
– averages (24–29C) - more seasonally variable than in the tropics
• plants: grasses and forbs (broad-leaf plants) make up most
of the ground cover
– The dominant plant species are fire-adapted and tolerant of seasonal
drought
• animals: include insects and mammals such as wildebeests,
zebras, lions, and hyenas
• Fires set by humans may help maintain this biome
A savanna in Kenya
Chaparral
• Distribution: mid-latitude coastal regions on several continents
• Precipitation: is highly seasonal with rainy winters and dry
summers
• Temperature: summer is hot (30C+); fall, winter, and spring are
cool (10–12C)
• Plants: dominated by shrubs, small trees, grasses, and herbs
– many plants are adapted to fire and drought
• Animals: include amphibians, birds and other reptiles, insects,
small mammals, and browsing mammals
• Humans have reduced chaparral areas through agriculture and
urbanization
An area of chaparral
in California
Temperate Grassland
• Distribution: on many continents
– e.g. plains and prairies of North America
• Precipitation: highly seasonal
• temperature: seasonal - winters are cold and dry;
summers are hot and wet
• plants: grasses and forbs
– are adapted to droughts and fire
• animals: include large grazers such as bison and wild
horses and small burrowers such as prairie dogs
• Most grasslands have been converted to farmland
Grasslands National Park,
Northern Coniferous Forest
• distribution: northern North America and Eurasia and is the largest
terrestrial biome on Earth
• Precipitation: varies
– some have periodic droughts and others, especially near coasts, are wet
• temperature: winters are cold; summers may be hot (e.g., Siberia
ranges from –50C to 20C)
• plants: conifers such as pine, spruce, fir, and hemlock dominate
– the conical shape of conifers prevents too much snow from
accumulating and breaking their branches
• animals: include migratory and resident birds and large mammals
such as moose, brown bears, and Siberian tigers
• Some forests are being logged at an alarming rate
A forest in Norway
Temperate Broadleaf Forest
• distribution: mid-latitudes in the Northern Hemisphere
–
smaller areas in Chile, South Africa, Australia, and New Zealand
• precipitation: significant amounts of fall during all seasons as rain or
snow
• Temperature: winters average 0C; summers are hot and humid
• plants: vertical layers
– dominated by deciduous trees in the Northern Hemisphere and evergreen
eucalyptus in Australia
• animals: Mammals, birds, and insects make use of all vertical layers in
the forest
– in the Northern Hemisphere, many mammals hibernate in the winter
• These forests have been heavily settled on all continents but are
recovering in places
Great Smoky Mountains
National Park in
North Carolina, in autumn
Tundra
• distribution: expansive areas of the Arctic
– alpine tundra also exists on high mountaintops at all latitudes
• Precipitation: is low in arctic tundra and higher in alpine tundra
•
Permafrost, a permanently frozen layer of soil, prevents water infiltration
• Temperature: winters are cold (below –30C); summers are relatively cool
(less than 10C)
• plants: herbaceous (mosses, grasses, forbs, dwarf shrubs and trees, and
lichen) and supports birds, grazers, and their predators
• animals: musk oxen, caribou, reindeer, bears, wolves, and foxes; many
migratory bird species nest in the summer
• Settlement is sparse, but tundra has become the focus of oil and mineral
extraction
Denali National Park, Alaska,
in autumn
Aquatic biomes
• Aquatic biomes account for the largest part of the
biosphere in terms of area
• show less latitudinal variation than terrestrial biomes
• marine biomes have salt concentrations of about 3%
– the largest marine biome is made of oceans, which cover about 75%
of Earth’s surface and have an enormous impact on the biosphere
• freshwater biomes have salt concentrations of less than
0.1%
– freshwater biomes are closely linked to soils and the biotic
components of the surrounding terrestrial biome
Zonation in Aquatic Biomes
• Many aquatic biomes are stratified into zones
or layers - defined by light penetration,
temperature, and depth
• upper photic zone has sufficient light for
photosynthesis
(b) Marine zonation
Intertidal zone
Neritic
zone Oceanic zone
• lower aphotic zone receives little light
– Deep in the aphotic zone lies the abyssal zone with a
depth of 2,000 to 6,000 m
• The photic and aphotic zones make up the
pelagic zone
•
•
0
200 m
Continental
shelf
Pelagic
zone
The organic and inorganic sediment at the
bottom of all aquatic zones is called the benthic
zone
Detritus, dead organic matter, falls from the
productive surface water and is an important
source of food to animals in the lower zones
Photic
zone
Benthic
zone
Aphotic
zone
2,000
6,000 m
Abyssal
zone
(b) Marine zonation
Intertidal zone
Neritic
zone
0
200 m
(a) Zonation in a lake
Littoral
zone
Limnetic
zone
Continental
shelf
Oceanic zone
Photic
zone
Pelagic
zone
Photic
zone
Benthic
zone
Benthic
zone
Pelagic
zone
Aphotic
zone
Aphotic
zone
2,000
6,000 m
Abyssal
zone
-lake environment is classified on the basis of three criteria: light penetration
(i.e. photic and aphotic), distance from shore (littoral and limnetic) and open water
(pelagic) or the bottom (benthic).
-the marine environment is classified the same way but distance from shore is
intertidal, neretic/coastal and oceanic
-also there is an abyssal zone in addition to the benthic zone
• In oceans and most lakes, a temperature
boundary called the thermocline separates the
warm upper layer from the cold deeper water
• Many lakes undergo a semiannual mixing of their
waters called turnover
• Turnover mixes oxygenated water from the
surface with nutrient-rich water from the bottom
Winter
Spring
Summer
0°
2°
4°C
4°
4°
22°
18°
8°
4°C
4°C
Thermocline
© 2011 Pearson Education, Inc.
Autumn
4°C
• Communities in aquatic biomes vary with depth, light
penetration, distance from shore, and position in the pelagic
or benthic zone
• Most organisms occur in the relatively shallow photic zone
• The aphotic zone in oceans is extensive but harbors little life
30°N
Tropic of
Cancer
Equator
Tropic of
Capricorn
30°S
Oceanic pelagic and benthic zones
Intertidal zones
Estuaries
Coral reefs
Rivers
Lakes
Aquatic Biomes
• Major aquatic biomes can be characterized
by their:
– physical environment
– chemical environment
– geological features
– photosynthetic organisms
– heterotrophs
© 2011 Pearson Education, Inc.
Lakes
• size can vary from small ponds to very large lakes
• temperate lakes may have a seasonal thermocline
• tropical lowland lakes have a year-round thermocline
• littoral zone had rooted and floating aquatic plants
– littoral zone is shallow and well-lighted and close to shore
– good for rooted plants
• limnetic zone has small drifting animals called zooplankton
– water is too deep in the limnetic zone to support rooted aquatic plants
– zooplankton are drifting heterotrophs that graze on the phytoplankton in
the limnetic zone
• invertebrates live in the benthic zone
• fishes live in all zones with sufficient oxygen
Lakes
• two kinds:
– Oligotrophic
– Eutrophic
• Oligotrophic lakes:
nutrient-poor and generally
oxygen-rich
An oligotrophic lake in Grand
Teton National Park, Wyoming
Lakes
• Eutrophic lakes: nutrientrich
• are often depleted of
oxygen if ice covered in
winter
• have more surface area
relative to depth than
oligotrophic lakes
A eutrophic lake in the Okavango
Delta, Botswana
Wetlands
• among the most productive biomes on Earth
• wetland = a habitat inundated by water at least some of the
time
– supports plants adapted to water-saturated soil
• high organic production and decomposition and have
low dissolved oxygen
• can develop in shallow basins, along flooded river banks, or
on the coasts of large lakes and seas
•Plants: water lilies, cattails, sedges,
tamarack, and black spruce
•animals: diverse invertebrates and birds,
otters, frogs, and alligators
•Humans have destroyed up to 90% of
wetlands; wetlands purify water and reduce
flooding
A basin wetland in the United Kingdom
Streams and Rivers
• most prominent physical
characteristic of streams and
rivers is a current
• headwaters: generally cold,
clear, turbulent, swift, and oxygenrich
– often narrow and rocky
• downstream waters: form rivers
and are generally warmer, more
turbid, and more oxygenated
A headwater stream in the Great
Smoky Mountains
– often wide and meandering and have
silty bottoms
– may contain phytoplankton or rooted
aquatic plants
• diversity of fishes and
invertebrates inhabit unpolluted
rivers and streams
The Loire river (in France) far
from its headwaters
Estuaries
• estuary = transition area
between river and sea
• include a complex network of tidal
channels, islands, natural levees,
and mudflats
• nutrient-rich and highly productive
– algae are the base of the “food-chain”
• abundant supply of food attracts
marine invertebrates, fish,
waterfowl, and marine mammals
– e.g. oysters, crabs and fish
• salinity can vary with the rise
and fall of the tides
An estuary in the southeastern United States
Intertidal Zones
• intertidal zone = periodically
submerged and exposed by the tides
• animals include: sponges, sea anemones,
echinoderms, and small fishes
• organisms are challenged by variations
in temperature and salinity and by the
mechanical forces of wave action
• Oxygen and nutrient levels are high
• sandy intertidal zones support sea grass
and algae
– worms, clams, and crustaceans bury
themselves in sand
• rocky intertidal zones support attached
marine algae
– many animals have structural adaptations for
attaching to the hard substrate
• Oil pollution has disrupted many intertidal
areas
Rocky intertidal zone on the Oregon coast
Oceanic Pelagic Zone
•
•
•
•
covers approximately 70% of Earth’s surface
constantly mixed by wind-driven oceanic currents
high oxygen levels
temperate oceans have a lot of turnover
– renews nutrients in the photic zones
• tropical oceans exhibit year-round stratification
– leads to lower nutrient concentrations
• dominant organisms: phytoplankton and zooplankton
– zooplankton includes protists, worms, copepods, krill, jellies, and
invertebrate larvae
Open ocean off the island of Hawaii
Coral Reefs
• formed from the calcium carbonate skeletons of cnidarians
(i.e. corals)
• shallow reef-building corals: live in the photic zone in warm,
clear water
• deepsea corals: live at depths of 200–1,500 m
• require high oxygen concentrations and a solid substrate for
attachment
• progresses from a fringing reef to a barrier reef to a coral
atoll
A coral reef in the Red Sea
Marine Benthic Zone
• known as the seafloor
• found below the surface waters of the coastal/
neritic zone and the offshore pelagic zone
• deep benthic zone – known as the abyssal zone
– organisms here are adapted to continuous cold and
extremely high water pressure
• substrate is mainly soft sediments
• some areas can be rocky
Interactions between organisms and the
environment limit the distribution of species
•
•
•
•
Species distribution is the result of ecological and evolutionary
interactions through time
Ecological time: minute-to-minute time frame of interactions between
organisms and the environment
– events in ecological time can lead to evolution
– adaptations from one generation to another increases their fitness
Evolutionary time: spans many generations and captures adaptation
through natural selection
both biotic and abiotic factors influence species distribution
– e.g. climate, predation
• Ecologists ask questions about where species
occur and why species occur where they do
Why is species
X absent
from an area?
Yes
Does dispersal
limit its
distribution?
No
Area inaccessible
or insufficient time
Does behavior
limit its
distribution?
Yes
Habitat selection
Yes
No
Do biotic factors
(other species)
limit its
distribution?
Predation,
parasitism,
competition,
disease
No
Do abiotic
factors limit its
distribution?
Physical
factors
Temperature
Light
Soil structure
Fire
Moisture, etc.
Chemical
factors
Water
Oxygen
Salinity
pH
Soil nutrients,
etc.
Dispersal and Distribution
• Dispersal: movement of
individuals away from
centers of high population
density or from their area of
origin
• contributes to the global
distribution of organisms
• natural range expansions
show the influence of
dispersal on distribution
Current
1970
1966
1965
1960
1961
1958
1943
1951
1937
1956
1970
cattle egret range expansion
Dispersal and Distribution
• biotic & abiotic factors affect the distribution of
organisms
• Biotic factors may include:
– Predation
– Herbivory
• e.g. sea urchins can limit the distribution of seaweeds
– Competition
• abiotic factors include:
–
–
–
–
–
Temperature
Water
Sunlight
Wind
Rocks and soil
Factors affecting species distribution
• Behavior and Habitat Selection: some organisms do not
occupy all of their potential range
• Environmental temperature: has an effect on biological
processes
• Water and O2 availability: water affects oxygen availability
as oxygen diffuses slowly in water
– Oxygen concentrations can be low in deep oceans and deep lakes
• Salinity: salt concentration affects the water balance of
organisms through osmosis
• Sunlight: light intensity and wavelength affect photosynthesis
– water absorbs light - aquatic environments most photosynthesis occurs
near the surface
– deserts, high light levels increase temperature and can stress plants
and animals
• Rocks and Soil: characteristics of soil limit the distribution of
plants and thus the animals that feed on them
– Physical structure
– pH
– Mineral composition
Why is species X absent from an area?
Does dispersal limit its distribution?
Yes
Area inaccessible or
insufficient time
No
Does behavior limit its distribution?
Yes
Habitat selection
No
Do biotic factors (other species)
limit its distribution?
No
Yes
Chemical
factors
Do abiotic factors limit
its distribution?
Physical
factors
Predation, parasitism,
competition, disease
Water, oxygen, salinity,
pH, soil nutrients, etc.
Temperature, light, soil
structure, fire, moisture,
etc.
Species Transplants
• include organisms that are intentionally
or accidentally relocated from their
original distribution
• can disrupt the communities or
ecosystems to which they have been
introduced