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Part 1 of 5The Biosphere: An Introduction to
Earth's Diverse Environments
• 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”
A Mysterious Giant of the Deep
• 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 environmental interactions at the organism, population, community, and ecosystem levels– These clams
that live near an ocean vent constitute a population
Ecologists study how organisms interact with their
environment at several levels
• 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 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 the total of all of Earth's ecosystems
THE BIOSPHERE
• 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
• Human activities affect all parts of the biosphere– One example is the widespread use of chemicals
Connection: Environmental problems reveal the limits of the biosphere
• Disturbances such as fires, hurricanes, and volcanic eruptions are also abiotic factors
• The most important abiotic factors that determine the biosphere's structure and dynamics include– solar energy– water– temperature
Physical and chemical factors influence life in the biosphere
• 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
Organisms are adapted to abiotic and biotic factors by natural selection
• 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
Regional climate influences the distribution of biological communities
• 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
Low angle ofincoming sunlight
Sunlight directlyoverhead
Low angle ofincoming sunlight
Atmosphere
North Pole
60º N
30º N
Tropic ofCancer
0º (equator)
30º S
60º S
South Pole
Tropic ofCapricorn
• Oceans cover about 75% of the Earth's surface• Light and the availability of nutrients are the major
factors that shape aquatic communities
Oceans occupy most of Earth's surface
AQUATIC BIOMES
• 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
Benthiczone(seafloor)
Photiczone
Aphoticzone
Pelagiczone
• 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
• Lake and pond communities are shaped by – light – temperature – the availability of nutrients and dissolved oxygen
Freshwater biomes include lakes, ponds, rivers, streams, and wetlands
• 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
• 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
Terrestrial biomes reflect regional variations in climate
TERRESTRIAL BIOMES
• Major terrestrial biomes
30º N
Equator
30º S
Tropical forest
Savanna
Desert
Polar and high-mountain ice
Chaparral
Temperate grassland
Temperate deciduous forest
Coniferous forest
Tundra (arctic and alpine)
• Several types of tropical forests occur in the warm, moist belt along the equator
Tropical forests cluster near 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
• Drier, tropical areas and some nontropical areas are characterized by the savanna
Savannas are grasslands with scattered trees
• Deserts are the driest of all terrestrial biomes– They are characterized by low and unpredictable rainfall
Deserts are defined by their dryness
– 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.
• The chaparral biome is a shrubland with cool, rainy winters and dry, hot summers
• Chaparral vegetation is adapted to periodic fires
Spiny shrubs dominate the chaparral
• 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
Temperate grasslands include the North American prairie
• 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
Deciduous trees dominate temperate forests
• The northern coniferous forest, or taiga, is the largest terrestrial biome on Earth
Coniferous forests are often dominated by a few species of trees
• The taiga is characterized by long, cold winters and short, wet summers
• Coastal coniferous forests of the Pacific Northwest are actually temperate rain forests
• 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
Long, bitter-cold winters characterize the
tundra
Part 2 of 5Population Dynamics
• 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
The Spread of Shakespeare's Starlings
• Today, the starling range extends from Mexico to Alaska
• Their population is estimated at well over 100 million
Current
1955
1945
1935 1925
1925
1935
19151905
19251935
1945
1955Current
• 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
• Ecologists define a population as a single-species 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
Populations are defined in several ways
• 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
Density and dispersion patterns are important
population variables
POPULATION STRUCTURE AND DYNAMICS
• 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 describe two kinds of population growth– exponential growth – logistic growth
Idealized models help us understand population 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
• 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
Multiple factors may limit population growth
• 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 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
Some populations have "boom-and-bust" cycles
– 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 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
Life tables track mortality and survivorship in populations
LIFE HISTORIES AND THEIR EVOLUTION
– This table was compiled using 1995 data from the U.S. Centers for Disease Control
• 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
Evolution shapes life histories
• 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
Connection: The human population has been growing exponentially for centuries
THE HUMAN POPULATION
• 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
• 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
Connection: Principles of population ecology have practical applications
• 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 5Communities and Ecosystems
• 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
Energy supply limits the length of food chains
• A pyramid of production reveals the flow of energy from producers to primary consumers and to higher trophic levels
Tertiaryconsumers
Secondaryconsumers
Primaryconsumers
Producers
10 kcal
100 kcal
1,000kcal
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
• http://www.coolclassroom.org/cool_windows/home.html
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
• 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
Connection: A production pyramid explains why meat
is a luxury for humans
• Because the production pyramid tapers so sharply, a field of corn or other plant crops can support many more vegetarians than meat-eaters
Secondaryconsumers
Primaryconsumers
Producers
Humanvegetarians
Corn
Humanmeat-eaters
Cattle
Corn
TROPHIC LEVEL
• 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
Chemicals are recycled between organic matter and abiotic reservoirs
• There are four main abiotic reservoirs
– Water cycle– Carbon cycle– Nitrogen cycle– Phosphorus cycle
• Heat from the sun drives the global water cycle – Precipitation– Evaporation – Transpiration
Water moves through the biosphere in a global cycle
Solarheat
Precipitationover the sea(283)
Net movementof water vaporby wind (36)
Flow of waterfrom land to sea(36)
Water vaporover the sea
Oceans
Evaporationfrom the sea(319)
Evaporationandtranspiration(59)
Water vaporover the land
Precipitationover the land(95)
Surface waterand groundwater
• Carbon is taken from the atmosphere by photosynthesis– It is used to make organic molecules– It is returned to the atmosphere by cellular respiration
The carbon cycle depends on photosynthesis and respiration
CO2 in atmosphere
Cellular respiration
Higher-levelconsumers
Primaryconsumers
Plants,algae,
cyanobacteria
Photosynthesis
Wood andfossil fuels
Detritivores(soil microbes
and others) Detritus
Decomposition
Burning
• 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–)
The nitrogen cycle relies heavily on bacteria
• 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
Amino acidsand proteins in
plants and animalsAssimilationby plants
Denitrifyingbacteria
Nitrates(NO3
–)
Nitrifyingbacteria
Detritus
Detritivores
Decomposition
Ammonium (NH4+)
Nitrogenfixation
Nitrogen-fixingbacteria in soil
Nitrogen-fixingbacteria in root
nodules of legumes
Nitrogenfixation
• 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
The phosphorus cycle depends on the weathering of rock
Upliftingof rock
Phosphatesin solution
Weatheringof rock
Phosphatesin rock
Phosphatesin organic
compounds
Detritus
Detritivoresin soil
Phosphatesin soil
(inorganic)
Rock Precipitated(solid) phosphates
Plants
Animals
Decomposition
Runoff
• 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
Connection: Ecosystem alteration can upset chemical cycling
ECOSYSTEM ALTERATION
• 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
• Human alteration of habitats poses the single greatest threat to biodiversity– The loss of tropical rain
forests and marine habitats are especially devastating
Habitat destruction, introduced species, and overexploitation are the major threats to
biodiversity
THE BIODIVERSITY CRISIS: AN OVERVIEW
• 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
• 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
Biodiversity is vital to human welfare
• 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 in water0.000003 ppm
DDT inzooplankton0.04 ppm
DDT insmall fish0.5 ppm
DDT inlarge fish2 ppm
DDT infish-eating birds25 ppm
DDT concentration:increase of10 million times
• Burning of fossil fuels is increasing the amount of CO2 and other greenhouse gases in the air
Connection: Rapid global warming could alter the entire biosphere
Light
Heat
GREENHOUSE EFFECT:CO2 lets sunlight through butretains the heat generatedby the sun
CO2
Adding CO2 to the airincreases the greenhouse effect
Removal of CO2 from the air byphotosynthesizing plants and
algae decreases the greenhouse
effect
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
• 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
CONSERVATION OF POPULATIONS AND SPECIES
• 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 speciesliving in the same area, potentially interacting
Community – group of populations of different speciesliving 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 affectdistribution, abundance, and evolution.
Types of ecological interactions
competition
predation
parasitism
mutualism
commensalism
symbiosis
Competition – two species share a requirement for alimited resource reduces fitness of one or both species
Predation – one species feeds on another enhancesfitness of predator but reduces fitness of prey
herbivory is a form ofpredation
Symbiosis – two species live together can includeparasitism, mutualism, and commensalism
Parasitism – one species feeds on another enhancesfitness of parasite but reduces fitness of host
Mutualism – two species provide resources or servicesto each other enhances fitness of both species
Commensalism – one species receives a benefit fromanother species enhances fitness of one species; noeffect 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
Primary Succession
• Simple plants like mosses and ferns can grow in the new soil
http://uisstc.georgetown.edu
http://www.uncw.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
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
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