Part 1 of 5
The Biosphere: An Introduction to
Earth's Diverse Environments
A Mysterious Giant of the Deep
• Ecology is the scientific study of the interactions of
organisms with their environment
• The ocean is Earth’s largest and least explored
ecosystem
• Recent explorations
of the deep sea have
brought previously
unknown species to
light, such as this
“mystery squid”
• Scientists have found
seafloor life whose
ultimate energy source is
not sunlight, but energy
that comes from the
interior of the planet
– This energy is
emitted from
hydrothermal vents
near the edges of
Earth’s crustal
plates
• Many animals thrive in
the extreme
environment around
hydrothermal vents
– Tube worms were
unknown to science
until hydrothermal
vents were explored
– They live on energy
extracted from
chemicals by
bacteria
Ecologists study how organisms interact with their
environment at several levels
• Ecologists study environmental interactions at the
organism, population, community, and ecosystem
levels
– These clams
that live near
an ocean vent
constitute a
population
• Ecosystem interactions involve living (biotic)
communities and nonliving (abiotic) components
– Abiotic components include energy, nutrients,
gases, and water
• Organisms are affected by their
environment
– But their presence and activities often change
the environment they inhabit
THE BIOSPHERE
The biosphere is the total of all of Earth's ecosystems
• The global ecosystem is called the biosphere
– It is the sum
of all the
Earth's
ecosystems
– The biosphere
is the most
complex level
in ecology
• The biosphere is self-contained
– except for energy obtained
from the sun and heat lost
to space
• Patchiness characterizes
the biosphere
– Patchiness occurs in the
distribution of deserts,
grasslands, forests, and
lakes
– Each habitat has a unique
community of species
Connection: Environmental problems reveal the limits
of the biosphere
• Human activities affect all parts of the biosphere
– One example is the widespread use of chemicals
• Disturbances such as fires, hurricanes, and
volcanic eruptions are also abiotic factors
Physical and chemical factors influence life in the
biosphere
• The most important abiotic factors that determine
the biosphere's structure and dynamics include
– solar energy
– water
– temperature
Organisms are adapted to abiotic and biotic factors
by natural selection
• The presence and success of a species in a
particular place depends upon its ability to adapt
• Natural selection
adapts organisms to
abiotic and biotic
factors
– Biotic factors include
predation and
competition
Regional climate influences the distribution of
biological communities
• Climate often determines the distribution of
communities
• Earth's global climate patterns are largely
determined by the input of solar energy and the
planet's movement in space
• Most climatic variations are due to the uneven
heating of Earth's surface
– This is a result of the variation in solar
radiation at different latitudes
North Pole
60º N
Low angle of
incoming sunlight
30º N
Tropic of
Cancer
Sunlight directly
overhead
0º (equator)
Tropic of
Capricorn
30º S
Low angle of
incoming sunlight
Atmosphere
60º S
South Pole
AQUATIC BIOMES
Oceans occupy most of Earth's surface
• Oceans cover about 75% of the Earth's surface
• Light and the availability of nutrients are the major
factors that shape aquatic communities
• Estuaries are productive areas where rivers meet
the ocean
– The saltiness of estuaries ranges from less than
1% to 3%
– They provide nursery
areas for oysters,
crabs, and
many fishes
– They are often
bordered by
extensive coastal
wetlands
• The intertidal zone is the wetland at the edge of an
estuary or ocean, where water meets land
– Salt marshes, sand and
rocky beaches, and tide
pools are part of the
intertidal zone
– It is often flooded by
high tides and then left
dry during low tides
• Abiotic conditions dictate the kinds of communities
that ocean zones can support
Intertidal zone
Continental zone
Photic
zone
Benthic
zone
(seafloor)
Aphotic
zone
Pelagic
zone
• The pelagic zone is the open ocean
– It supports highly motile animals such as
fishes, squids, and marine mammals
– Phytoplankton and zooplankton drift in the
pelagic zone
• The benthic zone is the ocean bottom
– It supports a variety of organisms based upon
water depth and light penetration
• The photic zone is the portion of the ocean into
which light penetrates
– Photosynthesis occurs here
• The aphotic zone is a vast, dark region of
the ocean
– It is the most extensive part of the biosphere
– Although there is no light, a diverse and
dense population inhabits this zone
• Coral reefs are found in warm tropical waters
above the continental shelf
– They support a huge diversity of invertebrates
and fishes
• Coral reefs are easily degraded by
– pollution
– native and
introduced
predators
– human
souvenir
hunters
Freshwater biomes include lakes, ponds,
rivers, streams, and wetlands
• Lake and pond communities are shaped by
– light
– temperature
– the availability of nutrients and dissolved oxygen
• A river environment
changes greatly between
its source and its mouth
– Temperature,
nutrients, currents,
and water clarity vary
at different points
• Wetlands are among the richest biomes in terms
of species diversity
TERRESTRIAL BIOMES
Terrestrial biomes reflect regional variations in
climate
• Climatic differences, mainly temperature and
rainfall, shape the major biomes that cover Earth's
land surface
• Biomes tend to grade into each other
• Within each biome there is local variation
– This gives vegetation a patchy, rather than uniform,
appearance
• Major terrestrial biomes
30º N
Equator
30º S
Tropical forest
Polar and high-mountain ice
Temperate deciduous forest
Savanna
Chaparral
Coniferous forest
Desert
Temperate grassland
Tundra (arctic and alpine)
Tropical forests cluster near the equator
• Several types of tropical forests occur in the
warm, moist belt along the equator
• The tropical rain forest is the most diverse
ecosystem on Earth
• Large-scale human destruction of tropical
rain forests continues to endanger many
species
– It may also alter world climate
Savannas are grasslands with scattered trees
• Drier, tropical areas and some nontropical areas
are characterized by the savanna
Deserts are defined by their dryness
• Deserts are the driest of all terrestrial biomes
– They are characterized by low and unpredictable rainfall
– Desertification
is a significant
environmental
problem
–
the rapid depletion of
plant life and the loss of
topsoil at desert
boundaries and in
semiarid regions, usually
caused by a combination
of drought and the
overexploitation of
grasses and other
vegetation by people.
Spiny shrubs dominate the chaparral
• The chaparral
biome is a
shrubland with
cool, rainy winters
and dry, hot
summers
• Chaparral
vegetation is
adapted to
periodic fires
Temperate grasslands include the North American
prairie
• Temperate grasslands are found in the interiors of
the continents, where winters are cold
– Drought, fires, and grazing animals prevent trees from
growing
– Farms have
replaced
most
of North
America's
temperate
grasslands
Deciduous trees dominate temperate forests
• Temperate deciduous forests grow where there is
sufficient moisture to support the growth of large
trees
– Nearly all of
the original
deciduous
forests in North
America have
been drastically
altered by
agriculture and
urban
development
Coniferous forests are often dominated by a
few species of trees
• The northern
coniferous
forest,
or taiga, is the
largest
terrestrial
biome on Earth
• The taiga is characterized by long, cold winters
and short, wet summers
• Coastal coniferous forests of the Pacific
Northwest are actually temperate rain
forests
Long, bitter-cold winters characterize the
tundra
• The arctic tundra lies between the taiga and the
permanently frozen polar regions
– It is a treeless
biome
characterized
by extreme
cold, wind,
and permafrost
– Permafrost is
continuously
frozen subsoil
Part 2 of 5
Population Dynamics
The Spread of Shakespeare's Starlings
• In the 1800s and early 1900s, introducing foreign
species of animals and plants to North America
was a popular, unregulated activity
• In 1890, a group of Shakespeare enthusiasts
released about 120 starlings in New York's Central
Park
– It was part of a project to
bring to America every
bird species mentioned
in Shakespeare’s works
• Today, the starling range extends from Mexico to
Alaska
• Their
population
is estimated
at well over
100 million
Current
1955
Current
1955
1945
1935
1925
1945
1905
1915
1935
1925
1925
1935
• Over 5 million starlings have been counted in a
single roost
• Starlings are omnivorous, aggressive, and
tenacious
• They cause
destruction and
often replace
native bird species
• Attempts to
eradicate starlings
have been
unsuccessful
• The starling population in North America has some
features in common with the global human
population
– Both are expanding and are virtually
uncontrolled
– Both are harming other species
• Population ecology is concerned with
changes in population size and the factors
that regulate populations over time
Populations are defined in several ways
• Ecologists define a population as a singlespecies group of individuals that use common
resources and are regulated by the same
environmental factors
– Individuals in a population have a high likelihood of
interacting and breeding with one another
• Researchers must define a population by
geographic boundaries appropriate to the
questions being asked
POPULATION STRUCTURE AND DYNAMICS
Density and dispersion patterns are important
population variables
• Population density is the number of individuals in
a given area or volume
• It is sometimes possible to count all the
individuals in a population
– More often, density is estimated by sampling
• One useful sampling technique for estimating
population density is the mark-recapture method
Total population = No. animals in 1st sample X Total no. animals in 2nd sample No.
marked animals in 2nd sample
• The dispersion pattern of a population refers to
the way individuals are spaced within their area
– Clumped
– Uniform
– Random
• Clumped dispersion is a pattern in which
individuals are aggregated in patches
– This is the most
common
dispersion
pattern in nature
– It often results
from an unequal
distribution of
resources in the
environment
• A uniform pattern of dispersion often results from
interactions among individuals of a population
– Territorial behavior and competition for water
are examples of such interactions
• Random dispersion is characterized by individuals
in a population spaced in a patternless,
unpredictable way
– Example: clams living in a mudflat
– Environmental conditions and social
interactions make random dispersion rare
Idealized models help us understand population
growth
• Idealized models describe two kinds of
population growth
– exponential growth
– logistic growth
• Exponential growth is the accelerating increase
that occurs during a time when growth is
unregulated
• A J-shaped growth curve, described by
the equation G = rN, is typical of
exponential growth
– G = the population growth rate
– r = the intrinsic rate of increase, or an
organism's maximum capacity to reproduce
– N = the population size
• Logistic growth is slowed by population-limiting
factors
– It tends to level off at
carrying capacity
– Carrying capacity
is the maximum
population size
that an environment
can support at a
particular time
with no degradation
to the habitat
• The equation G = rN(K - N)/K describes a logistic
growth curve
– K = carrying capacity
– The term
(K - N)/K
accounts
for the
leveling
off of the
curve
• The logistic growth model predicts that
– a population's growth rate will be low when
the population size is either small or large
– a population’s growth rate will be highest
when the population is at an intermediate
level relative to the carrying capacity
Multiple factors may limit population growth
• Increasing population density directly influences
density-dependent rates
– such as declining birth rate or increasing death rate
• The regulation of growth in a natural population is
determined by several factors
–
–
–
–
limited food supply
the buildup of toxic wastes
increased disease
predation
• Most populations are probably regulated by a
mixture of factors
– Density-dependent birth and death rates
– Abiotic factors such as climate
and disturbances
• Populations often
fluctuate in number
– A natural population
of song sparrows
often grows rapidly
and is then drastically
reduced by severe
winter weather
Some populations have "boom-and-bust" cycles
• Some populations go through boom-and-bust
cycles of growth and decline
• Example: the population cycles of the lynx and
the snowshoe hare
– The lynx is one of the main predators of the snowshoe
hare in the far northern forests of Canada and Alaska
– About every 10 years, both hare and lynx populations
have a rapid increase (a "boom") followed by a sharp
decline (a "bust")
• Recent studies suggest that the 10-year cycles of
the snowshoe hare are largely driven by excessive
predation
– But they are also influenced by fluctuations in
the hare's food supply
• Population cycles may also result from a
time lag in the response of predators to
rising prey numbers
LIFE HISTORIES AND THEIR EVOLUTION
Life tables track mortality and survivorship in
populations
• Life tables and survivorship curves predict
an individual's statistical chance of dying or
surviving during each interval in its life
• Life tables predict how long, on average, an
individual of a given age can expect to live
– This table was compiled using 1995 data from
the U.S. Centers for Disease Control
Evolution shapes life histories
• An organism's life history is the series of
events from birth through reproduction to
death
• Life history traits include
– the age at which reproduction first occurs
– the frequency of reproduction
– the number of offspring
– the amount of parental care given
– the energy cost of reproduction
THE HUMAN POPULATION
Connection: The human population has been
growing exponentially for centuries
• The human population as a whole has
doubled three times in the last three
centuries
• The human population now stands at about
6.7 billion and may reach 10 billion by the
year 2050
• Most of the increase is due to improved
health and technology
– These have affected death rates
• The history of human population growth
• The ecological footprint represents the
amount of productive land needed to support
a nation’s resource needs
• The ecological capacity of the world may
already be smaller than its ecological
footprint
Connection: Waiting for the “Crash”
• When the population
of a species grows
beyond the capacity
of its environment to
sustain it, it reduces
that capacity below
the original level,
ensuring an eventual
population crash
• The exponential growth of the human
population is probably the greatest crisis
ever faced by life on Earth
Connection: Principles of population ecology
have practical applications
• Principles of population ecology may be
used to
– manage wildlife, fisheries, and forests for
sustainable yield
– reverse the decline of threatened or
endangered species
– reduce pest populations
• Renewable resource management is the
harvesting of crops without damaging the
resource
– However, human economic and political
pressures often outweigh ecological concerns
– There is frequently insufficient scientific
information
Part 3 of 5
Communities and Ecosystems
Energy supply limits the length of food chains
• Biomass is the amount of living organic material
in an ecosystem
• Primary production is the rate at which producers
convert sunlight to chemical energy
– The primary production of the entire biosphere is about
170 billion tons of biomass per year
• A pyramid of production reveals the flow of energy
from producers to primary consumers and to
higher trophic levels
Tertiary
consumers
10 kcal
Secondary
consumers
100 kcal
Primary
consumers
1,000
kcal
Producers
10,000 kcal
1,000,000 kcal of sunlight
• Only about 10% of the energy in food is stored at
each trophic level and available to the next level
– This stepwise energy loss limits most food
chains to 3 - 5 levels
– There is simply not enough energy at the very
top of an ecological pyramid to support another
trophic level
Food Chains & Food Webs
Food chains
follow a single
path of energy as
it moves through
an ecosystem.
Food webs are
more complex
and more
realistic.
The Food Web of an Owl
• http://www.coolclassroom.org/cool_windows/home.html
Connection: A production pyramid explains why meat
is a luxury for humans
• The dynamics of energy flow apply to the human
population as much as to other organisms
– When we eat grain or fruit, we are primary consumers
– When we eat beef or other meat from herbivores, we are
secondary consumers
– When we eat fish like trout or salmon (which eat insects
and other small animals), we are tertiary or quaternary
consumers
• Because the production pyramid tapers so
sharply, a field of corn or other plant crops can
support many more vegetarians than meat-eaters
TROPHIC LEVEL
Secondary
consumers
Primary
consumers
Producers
Human
meat-eaters
Human
vegetarians
Cattle
Corn
Corn
Chemicals are recycled between organic matter and
abiotic reservoirs
• Ecosystems require daily infusions of energy
– The sun supplies the Earth with energy
– But there are no extraterrestrial sources of water or
other chemical nutrients
• Nutrients must be recycled between organisms
and abiotic reservoirs
– Abiotic reservoirs are parts of the ecosystem where a
chemical accumulates
• There are four main abiotic reservoirs
– Water cycle
– Carbon cycle
– Nitrogen cycle
– Phosphorus cycle
Water moves through the biosphere in a global cycle
• Heat from the sun drives the global water cycle
– Precipitation
– Evaporation
– Transpiration
Solar
heat
Water vapor
over the sea
Precipitation
over the sea
(283)
Net movement
of water vapor
by wind (36)
Evaporation
from the sea
(319)
Water vapor
over the land
Evaporation
and
transpiration
(59)
Precipitation
over the land
(95)
Oceans
Flow of water
from land to sea
(36)
Surface water
and groundwater
The carbon cycle depends on photosynthesis and
respiration
• Carbon is taken from the atmosphere by
photosynthesis
– It is used to make organic molecules
– It is returned to the atmosphere by cellular respiration
CO2 in atmosphere
Burning
Cellular respiration
Plants,
algae,
cyanobacteria
Photosynthesis
Higher-level
consumers
Primary
consumers
Wood and
fossil fuels
Decomposition
Detritivores
(soil microbes
and others)
Detritus
The nitrogen cycle relies heavily on bacteria
• Nitrogen is plentiful in the atmosphere as N2
– But plants cannot use N2
• Various bacteria in soil (and legume root nodules)
convert N2 to nitrogen compounds that plants can
use
– Ammonium (NH4+) and nitrate (NO3–)
• Some bacteria break down organic matter and
recycle nitrogen as ammonium or nitrate to plants
• Other bacteria return N2 to the atmosphere
Nitrogen (N2) in atmosphere
Assimilation
by plants
Denitrifying
bacteria
Amino acids
and proteins in
plants and animals
Nitrogen
fixation
Detritus
Nitrogen-fixing
bacteria in root
nodules of legumes
Nitrates
(NO3–)
Detritivores
Nitrifying
bacteria
Decomposition
Nitrogen
fixation
Ammonium (NH4+)
Nitrogen-fixing
bacteria in soil
The phosphorus cycle depends on the weathering of
rock
• Phosphates (compounds containing PO43-) and
other minerals are added to the soil by the
gradual weathering of rock
• Consumers obtain phosphorus in organic form
from plants
• Phosphates are returned to the soil through
excretion by animals and the actions of
decomposers
Uplifting
of rock
Phosphates
in organic
compounds
Weathering
of rock
Phosphates
in rock
Animals
Plants
Runoff
Detritus
Phosphates
in solution
Phosphates
in soil
(inorganic)
Decomposition
Rock
Precipitated
(solid) phosphates
Detritivores
in soil
ECOSYSTEM ALTERATION
Connection: Ecosystem alteration can upset chemical
cycling
• Experimental studies have been performed to
determine chemical cycling in ecosystems
• A study to monitor nutrient dynamics has been
ongoing in the Hubbard Brook Experimental
Forest since 1963
• Environmental changes caused by humans can
unbalance nutrient cycling over the long term
– Example: acid rain
• Conservation biology is a goal-oriented science
that seeks to counter the biodiversity crisis
• Conservation biology relies on research
from all levels of ecology, from
populations to ecosystems
THE BIODIVERSITY CRISIS: AN OVERVIEW
Habitat destruction, introduced species, and
overexploitation are the major threats to
biodiversity
• Human alteration of
habitats poses the
single greatest threat to
biodiversity
– The loss of tropical rain
forests and marine
habitats are especially
devastating
• Competition with introduced species also threatens
many species in their native habitats
– Introduced species are those that have been
transferred to an area where they did not
occur naturally
– Examples: European starlings, pigeons, and
house sparrows
• Overexploitation of wildlife also threatens many
species
– Excessive commercial harvest or sport hunting
has reduced the numbers of many species
– Examples: whales, American bison, Galápagos
tortoises, and numerous fish
Biodiversity is vital to human welfare
• Preservation of biodiversity is
important to humans for
aesthetic, ethical and
practical reasons
• Biodiversity provides humans
with food, clothing, shelter,
oxygen, soil fertility, etc.
• We evolved in Earth's
ecosystem
– Large-scale changes in the
ecosystem threaten us as well
as other species
• Oil spills, acid rain,
ozone depletion, and
chemical pesticides
affect the entire world
• Chemical
pesticides are
concentrated in
food chains by
biological
magnification or
“bioaccumulation”
DDT concentration:
increase of
10 million times
DDT in
fish-eating birds
25 ppm
DDT in
large fish
2 ppm
DDT in
small fish
0.5 ppm
DDT in
zooplankton
0.04 ppm
DDT in water
0.000003 ppm
Connection: Rapid global warming could alter the
entire biosphere
• Burning of fossil fuels is increasing the amount of
CO2 and other greenhouse gases in the air
Light
CO2
Heat
CO2
CO2
• An increase in global temperature could have
many negative effects
– Change in climate patterns
– Melting of polar ice
– Flooding of coastal regions
– Increase in the rate of species loss
CONSERVATION OF POPULATIONS AND
SPECIES
• Habitat degradation can lead to population
fragmentation
– Portions of populations
are split and
subsequently isolated
– It often results in species
being designated as
threatened or endangered
• The Endangered Species Act (ESA) defines an
endangered species as one that is in danger of
extinction throughout all or a significant portion of
its range
– Example: the northern
spotted owl
• The ESA defines a
threatened species as one
that is likely to become
endangered in the
foreseeable future
Part 5 of 5
Symbiosis
&
Succession
Population – group of individuals of the same species
living in the same area, potentially interacting
Community – group of populations of different species
living in the same area, potentially interacting
What are some ecological interactions?
Why are ecological interactions important?
Interactions can affect distribution and abundance.
Interactions can influence evolution.
Think about how the following interactions can affect
distribution, abundance, and evolution.
Types of ecological interactions
competition
predation
parasitism
mutualism
commensalism
symbiosis
Competition – two species share a requirement for a
limited resource  reduces fitness of one or both species
Predation – one species feeds on another  enhances
fitness of predator but reduces fitness of prey
herbivory is a form of
predation
Symbiosis – two species live together  can include
parasitism, mutualism, and commensalism
Parasitism – one species feeds on another  enhances
fitness of parasite but reduces fitness of host
Mutualism – two species provide resources or services
to each other  enhances fitness of both species
Commensalism – one species receives a benefit from
another species  enhances fitness of one species; no
effect on fitness of the other species
Changes in Ecosystems:
Ecological Succession
Definition:
• Natural, gradual changes in the types of
species that live in an area; can be
primary or secondary
• The gradual replacement of one plant
community by another through natural
processes over time
Primary Succession
• Begins in a place without any soil
– Sides of volcanoes
– Landslides
– Flooding
• Starts with the arrival of living things such
as lichens that do not need soil to survive
• Called PIONEER SPECIES
http://botit.botany.wisc.edu
http://www.saguaro-juniper.com/
Primary Succession
• Soil starts to form as lichens and the
forces of weather and erosion help break
down rocks into smaller pieces
• When lichens die, they decompose,
adding small amounts of organic matter to
the rock to make soil
http://www.life.uiuc.edu
Primary Succession
• Simple plants like mosses and ferns can
grow in the new soil
http://www.uncw.edu
http://uisstc.georgetow
n.edu
Primary Succession
• The simple plants die, adding more
organic material
• The soil layer thickens, and grasses,
wildflowers, and other plants begin to take
over
http://www.cwrl.utexas.edu
Primary Succession
• These plants die, and they add more
nutrients to the soil
• Shrubs and tress can survive now
http://www.rowan.edu
Primary Succession
• Insects, small birds, and mammals have
begun to move in
• What was once bare rock now supports a
variety of life
http://p2-raw.greenpeace.org
Secondary Succession
• Begins in a place that already has soil and
was once the home of living organisms
• Occurs faster and has different pioneer
species than primary succession
• Example: after forest fires
http://www.geo.arizona.edu
http://www.ux1.eiu.edu
http://www.agen.ufl.edu
Climax Community
• A stable group of plants and animals that
is the end result of the succession process
• Does not always mean big trees
– Grasses in prairies
– Cacti in deserts