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

http://www.life.uiuc.edu

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

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