The hierarchy of life

Species Species: the different kinds of living things

in a community All individuals are like one another, but are

distinct from other groupsSpecies are grouped into ________Which are

grouped into families, orders, classes, phyla, kingdoms, and domains

The official species name is Latin and has two parts:

It is hard to define a species All members that can interbreed and produce

fertile offspring Members of different species generally do not

breed This definition does not work for organisms

that do not mate to produce offspringScientists use other classification methods

New species arise due to evolution Species classifications are changed to reflect

this

Populations and biotic communities Population: a number of individuals that

make up the interbreeding, reproducing group It refers only to individuals of a species in an

area For example, gray wolves in Yellowstone

National ParkA species would be all gray wolves in the world

A biotic community (biota): the grouping of populations in a natural area Includes all vegetation, animals, and

microscopic organisms

Species within a biotic community The biotic community is determined by abiotic

(nonliving chemical and physical) factors Water, climate, salinity, soil

A community is usually named for its plants Vegetation strongly indicates environmental

conditions Species in a community depend on each other

The plant community supports the animalsPopulations of different species within a biotic

community constantly interact With each other and with the abiotic environment

Pine Forest Community

EcosystemsEcosystem: an interactive complex of biota and

the abiotic environment within an area A forest, grassland, wetland, coral reef Humans are part of ecosystems

Ecosystems lack distinct boundaries and are not isolatedSpecies can occupy multiple ecosystems and migrate

between themEcotone: a transitional region between ecosystems

Shares species and characteristics of bothMay have more or fewer species than the ecosystems

Ecotones

Landscapes and biomes Landscape: a cluster of interacting ecosystems Biome: a large area of Earth with the same

climate and similar vegetation For example, grasslands can be predicted by

rainfall and temperature Boundaries grade into the next biome

Biomes describe terrestrial systems Aquatic and wetland ecosystems are determined

by depth, salinity, and permanence of waterBiosphere: one huge system formed by all living

things

Environmental factors Organisms live in the environment with

physical, chemical, and biological factors Some factors vary in space and time but are

not used up (temperature, wind, pH, salinity)Some factors are consumed by organisms

Water, nutrients, light, oxygen, food, spaceFactors determine whether a species

occupies an area

Optimums, ranges and limits of tolerance

A fundamental biological principle Every species has an optimum range and

limits of tolerance for every abiotic factor These characteristics vary between speciesSome species have a broad rangeOther species have a narrower range

The range of tolerance for a factor affects an organism’s growth, health, survival, reproduction

The population density of a species is greatest where all conditions are optimal

Law of limiting factors

Habitat and niche

Energy changes in organismsBreaking bonds in molecules releases energy

to do workOxidation: a loss of electrons

Usually accomplished by the addition of oxygen (which causes burning)

Inorganic compounds are nonflammable They have low potential energy

Production of organic material from inorganic material represents a gain in potential energyBreakdown of organic material releases energy

Producers make organic molecules

Producers: make high-potential-energy organic molecules from low-potential-energy raw materials (CO2, H2O, N, P)Chlorophyll in plants absorbs kinetic light

energy to power the production of organic molecules

Green plants use the process of photosynthesis to make Sugar (glucose—stored chemical energy)Using inputs of carbon dioxide, water, and light

energyReleasing oxygen as a by-product

Within the plant

Glucose serves three purposesIt is the backbone for all other organic

moleculesIt provides energy to run cell activities (e.g.,

growth)It is stored for future use (as starch in

potatoes, grains, seeds) Each stage of the process uses enzymes:

proteins that promote the synthesis or breaking of chemical bonds

Cell respirationConsumers: organisms that live on the

production of othersObtain energy from feeding on and breaking

down organic matter made by producersRespiration: organic molecules are broken

down inside each cell Produces energy for the cell to useThe reverse of photosynthesisOxygen is consumedOccurs in plants and animals

One-way flow of energyMost solar energy entering ecosystems is absorbed

Heats the atmosphere, oceans, and land2–5% is passed through plants to consumers

All energy eventually escapes as heat Entropy is increasedRe-radiated into space

Energy flows in a one-way direction through ecosystemsLight from the Sun is nonpolluting and nondepletableIn contrast, nutrients are recycled and continually

reused

The cycling of matter in ecosystemsBiogeochemical cycles: circular pathways of

elements involving biological, geological, and chemical processes

The carbon cycle: starts with the reservoir of carbon dioxide in the airBecomes organic molecules in organismsCarbon is respired by plants and animals into the

air or is deposited in soilPhotosynthesis in oceans moves CO2 from

seawater into organisms Respiration returns inorganic carbon to seawater

Carbon CycleCO2 in atmosphere

Cellular respiration

Burning

Woodand

fossilfuels

Higher-levelconsumers

5

3

2

4

Decomposition

Decomposers(soil microbes) Detritus

Wastes; death

Primaryconsumers

Plant litter;death

Plants, algae,cyanobacteria

Photosynthesis1

The phosphorus cycleMineral elements originate in rock and soil minerals

A shortage of phosphorus is a limiting factorExcessive phosphorus can stimulate algal growth

As rock breaks down, phosphate is releasedReplenishes phosphate lost through leaching or runoff

Organic phosphate: incorporated into organic compounds by plants from soil or waterCycles through the food chainBroken down in cell respiration or by decomposers

Enters into chemical reactions with other substances

Upliftingof rock Weathering

of rockPhosphates

in rock

Phosphatesin solution

Runoff

Assimilation

RockDecomposition

Phosphatesin soil

(inorganic)

Precipitated(solid) phosphates

Decomposersin soil

Detritus

AnimalsPlants

3

1

2

4

5

6

The nitrogen cycleIs a unique cycle

Bacteria in soils, water, and sediments perform many steps of the cycle

Nitrogen is in high demand by aquatic and terrestrial plants

Air is the main reservoir of nitrogen (N)most organisms can not use it

Plants take up nitrogenPlants in terrestrial ecosystems (“non-N-fixing

producers”)Take up nitrogen as ammonium (NH4) and

incorporate it into proteins and nucleic acid compounds

The nitrogen moves through the food chain to decomposers, releasing nitrogen wastes

Soil bacteria (nitrifying bacteria) convert ammonium to nitrate to obtain energyNitrate is available for plant uptake

Nitrogen fixation: bacteria and cyanobacteria can use N and produce compounds

Means of nitrogen fixation Bacteria (genus Rhizobium) live in legume root nodulesThe legume provides the bacteria a place to live and

foodIt receives a source of nitrogen in returnNitrogen enters the food chain from the legumes

Three other processes “fix” nitrogenAtmospheric nitrogen fixation: lightningIndustrial fixation: in fertilizer manufacturingCombustion of fossil fuels: oxidizes nitrogen

Industrial fixation and fossil fuels release nitrogen oxides, which are converted to nitric acid (acid precipitation)

DenitrificationA microbial process in soils and sediments

depleted of oxygenMicrobes use nitrate as a substitute for oxygen

Nitrogen is reduced (it gains electrons) to nitrogen gasReleased into the atmosphere

Figure 37.21 The nitrogen cycle

Nitrogen (N2) in atmosphere

Plant Animal

Nitrogen-fixingbacteria in

root nodules

Free-livingnitrogen-fixing

bacteria

Detritus

Decomposers

Ammonium (NH4)

in soil

Nitrifyingbacteria

Denitrifiers

Assimilationby plants

Nitratesin soil(NO3

)

8

6

5

3

4 7

2

1

Comparing the cyclesCarbon is mainly found in the atmosphere

Directly taken in by plantsNitrogen and phosphorus are limiting factorsAll three cycles have been sped up by human

actionsAcid rain, greenhouse gases, eutrophication

Other cycles exist for other elements (e.g., water)All go on simultaneouslyAll come together in tissues of living things

Dynamics of natural populationsPopulation: a group of members of the same

species living in an areaCommunity: populations of different species

living together in an areaPopulations grow with births and

immigrationThey decline with deaths and emigration

(Births + Immigration) – (Deaths + Emigration) = Change in population number

Dynamics of natural populationsPopulation: a group of members of the same

species living in an areaCommunity: populations of different species

living together in an areaPopulations grow with births and

immigrationThey decline with deaths and emigration

(Births + Immigration) – (Deaths + Emigration) = Change in population number

Population growthPopulation growth: change in population

Equilibrium: births + immigration are equal to deaths + emigration

Often, population growth is not zeroPopulation growth rate: amount the population

has changed divided by the time it had to changePopulation growth curves: graph how

populations grow; used to findHow fast a population could growHow many individuals there are nowWhat the future population size could be

Exponential growthEach species can increase its population

With favorable conditionsExponential increase: does not add a constant

number of individuals for each time periodThe doubling time remains constantFor example, it takes 2 days to go from 8 to 16

individuals, as well as from 1,000 to 2,000 individuals

Such growth is called an “explosion”The population continues to grow and then dies off

due to limiting resourcesJ-curve: the curve of exponential growth

Exponential growth of rabbits

Time (months)

Pop

ula

tion

siz

e (N

)

0 1 2 3 4 5 6 7 8 9 1011120

50

100

150

200

250

300

350

400

450

500

Logistic Growth and carrying capacityLogistic growth: some process slows growth

so it levels off near carrying capacity (K)Results in an S-shaped curveIt levels off at K

As the population approaches K, growth slowsThe population remains steady and growth = 0The maximum rate of population growth occurs

halfway to K

Logistic growth of a population of fur seals

Year1915 1925 1935 1945

0

2

4

6

8

10B

reed

ing

male

fu

r se

als

(th

ou

san

ds)

Biotic potential vs. environmental resistanceBiotic potential: the number of offspring

(live births, eggs, or plant seeds and spores) produced under ideal situationsMeasured by rate at which organisms

reproduce (r)Varies tremendously from less than 1

birth/year (some mammals) to millions/year (plants, invertebrates)

Recruitment: survival through early growth stages to become part of the breeding populationYoung must survive and reproduce to have any

effect on population size

Environmental resistanceAbiotic and biotic factors cause mortality (death)

Prevents unlimited population growthEnvironmental resistance: the biotic and abiotic

factors that may limit a population’s increaseBiotic: predators, parasites, competitors, lack of foodAbiotic: unusual temperatures, moisture, light,

salinity, pH, lack of nutrients, fireEnvironmental resistance can also lower

reproductionLoss of suitable habitat, pollutionChanged migratory habits of animals

Reproductive strategies: r-strategists

Reproductive strategies: K-strategists

Life historiesLife history: progression of changes in an organism’s

life Age at first reproduction, length of life, etc.Visualized in a survivorship graph

Type I survivorship: low mortality in early lifeMost live the bulk of their life span (e.g., humans)

Type III survivorship: many offspring that die youngFew live to the end of their life (oysters, dandelions)

Type II survivorship: intermediate survivorship pattern (squirrels, coral)

K-strategists have a Type I pattern; r-strategists show Type III

Three types of survivorship curves

Percentage of maximum life span50 1000

0.1

1

10

100

III

II

IP

erc

en

tag

e o

f su

rviv

ors

(lo

g s

cale

)

Predictable pattern in speciesThere is a predictable pattern to the way

human activities affect speciesr-strategists become pests when humans

change an areaHouseflies, dandelions, cockroaches increase

K-strategists become rarer or extinct with changeEagles, bears, and oaks decline

Community interactions

Species interactionsThe most important relationships

Predation, competition, mutualism, commensalism

Amensalism: one species is unaffected, the other is harmed (0−)For example, an elephant stepping on a flower

or plants produce chemicals for defense against herbivory that inadvertently harms other plants

It is theoretically possible to have a (00) relationshipIt has no name

Introduction to ecosystemsIn 1988, lightning started fires in Yellowstone

National Park165,000 acres were burned in one day

National Park Service policies have changed over timeIn the early years, all fires were extinguishedBefore 1988, only fires that threatened human

habitations were extinguishedThis fire started a great controversy over this

policySnow in September finally put the fires out

Fire in Yellowstone

Yellowstone recovered from the 1988 fireThe fires burned 36% of the park

Burned and unburned areas were interspersedWithin 2 weeks, grasses and other vegetation

sproutedWithin a year, vegetation covered the burned

areasBison and elk fed on the new vegetationWithin 25 years, plant and animal diversity will

have completely recovered in the burned areasFire is vital to many ecosystems

It may even impact evolution

Lodgepole pines growing back in the burned area of Yellowstone

Bison in Yellowstone

Characteristics of ecosystemsYellowstone National Park (founded in 1872)

is part of the Greater Yellowstone EcosystemBecause of its unique features, it is a World

Heritage Site and International Biosphere Reserve

Ecosystems contain communities of interacting species and their abiotic factorsThey function on different scalesIt’s hard to delineate fixed boundaries

Scientists study ecosystemsBiomes: ecosystems having similar

vegetation and climactic conditionsGreater Yellowstone Ecosystem belongs to the

northern temperate forest biomeScientists study ecosystem properties

Trophic levelsProductivityConsumption

Trophic levelsDuring photosynthesis, plants use the Sun’s energy

Producing chemicals from carbon dioxide and waterPlants are eaten by predators (a grasshopper, mouse,

etc.)These animals are eaten by other predators

Food chain: describes where energy and nutrients go as they move from one organism to anotherEnergy moves “up” the food chainNot all energy and nutrients are passed to other

levelsFood web: interconnection of food chains to form

complex webs of feeding relationships

Trophic level

Plant

A terrestrial food chainAn aquatic food chain

ProducersPhytoplankton

GrasshopperPrimary

consumers Zooplankton

MouseSecondaryconsumers Herring

TunaSnake

Tertiaryconsumers

Killer whaleHawk

Quaternaryconsumers

Quaternary,tertiary,and secondaryconsumers

secondaryconsumers

Tertiaryand

Secondaryandprimaryconsumers

Primaryconsumers

Producers(plants)

Trophic categories

Producers are essential to every ecosystemThey capture energy from the Sun or chemical

reactionsConverting CO2 to organic matter

Most producers are green plantsChlorophyll: a green pigment that captures light energy

Range in size from microscopic bacteria to gigantic trees Every major ecosystem has producers

Chemosynthesis: some bacteria use energy in inorganic chemicals to form organic matter from CO2 and water

Primary production: production of organic matter through photosynthesis and growth of producers

ConsumersOrganisms feed on organic matter for energy

Animals, fungi (mushrooms, mold, etc.), most bacteriaRange in size from plankton to blue whales

Divided into subgroups according to their food sourcePrimary consumers (herbivores): feed on producers Secondary consumers: feed on primary consumersThird (tertiary), fourth (quaternary), or higher levels

Carnivores: secondary or higher-order meat eatersOmnivores: feed on both plants and animalsAnimals can occupy various levels, depending on the

food

DecomposersDetritus: dead plant material (leaves, etc.),

fecal wastes, dead bodies Most energy in an ecosystem goes through this

food webDetritus is organic and high in potential

energy forDecomposersScavengers (vultures): break down large pieces

of matterDetritus feeders (earthworms): eat partly

decomposed matterChemical decomposers (fungi and bacteria):

break down matter on the molecular scale

Limits on trophic levelsTerrestrial ecosystems usually have three or

four trophic levels and rarely fiveBiomass: the total combined (net dry) weight

of organismsEach higher trophic level has about 90% less

biomassOne acre of grassland has 907 kg (2,000 lbs)

It has 90.7 kg (200 lbs) of herbivoresIt has 9.7 kg (20 lbs) of primary carnivores

Biomass pyramid: the different levels of producer and consumer mass

Tertiaryconsumers

Secondaryconsumers

Primaryconsumers

Producers

10 kcal

100 kcal

1,000 kcal

10,000 kcal

1,000,000 kcal of sunlight

The flow of energy in ecosystemsIn most ecosystems, sunlight is the initial source of

energyPrimary production (production of organic molecules)

is only 2% of the incoming solar energyAlthough small, it’s enough to fuel all lifeOn average 10% energy is available to each trophic

level Standing-crop biomass: the actual biomass of primary

producers in an ecosystem at any given timeNot always a good measure of productivity

Biomass and primary production vary greatlyForests have large biomassGrasslands have high primary production

From ecosystems to biomesBroad ecosystem patterns translate into a

predictable set of organisms that live under particular conditions

Different regions have distinct biotic communitiesCreating variety in ecosystems, landscapes, and

biomesA biome: a large geographical biotic community

Controlled by climateIs named after the dominant vegetationHas fuzzy boundaries

Aquatic areas are not called biomesBut they function similarly

The role of climateClimate: a description of the average

temperature and precipitation (weather) of a region

Climates vary widelyEquatorial areas: warm, high rainfall, no

seasonsAbove and below the equator: temperatures

become seasonal (warm/hot summers, cool/cold winters)

Toward the poles: longer and colder wintersColder temperatures are also found at higher

elevations

30N

Tropic ofCancer

Tropic ofCapricorn

30S

Equator

Key

Tropical forest

Savanna

Chaparral

Desert

Temperate grassland

Temperate broadleaf forest

Coniferous forest

Arctic tundra

Polar ice

High mountains(coniferous forestand alpine tundra)

Effects of precipitation on biomesPrecipitation varies widely in different

regionsFrom almost 0 to over 250 cm (100 in.)/yr

It can be evenly distributed throughout the year or concentrated in certain months (wet and dry seasons)

A given climate supports species that can tolerate the temperature and precipitation levels of the areaHighest densities occur where conditions are

optimalA species is excluded where any condition is

beyond its range of tolerance

Biome examplesIndividual ranges of tolerance to temperature

and precipitation determine where a species can liveSpecies’ distributions describe a biome’s

placementSix major types of biomes exist

Rainfall effects are primary in determining biomesTemperate deciduous forest: rainfall of 72–

200 cm (30–80 in.)/yrGrassland (prairie) biome: rainfall is less or

seasonalDesert biome: rainfall is less than 25 cm (10

in.)/yr

The effects of temperature on biomesTemperature effects are superimposed on

rainfall effectsIt determines the kind of forests in an area

with 75 cm (30 in.) or more of rainfall per yearTropical rain forests have broad-leaved

evergreens that cannot tolerate freezingDeciduous trees tolerate freezing by dropping

their leaves and becoming dormantConiferous forests tolerate the harsh winters

and short summers of northern regions

Biomes with little precipitationPermafrost: permanently frozen subsoil

Prohibits tree growth because their roots cannot penetrate the soil

Tundra biome: has grasses, clover, and other small plants that grow above the permafrost

Desert: any region with less than 25 cm (10 in.) of rain/yrHot deserts have different species than cold

deserts

Aquatic systemsAquatic systems have major categories

But are not called biomesAquatic and wetland ecosystems are

determined by depth, salinity, and permanence of waterLakes, marshes, streams, rivers, estuaries,

baysOcean systems

Aquatic systems can be viewed as ecosystemsOr part of landscapesOr as major biome-like features (seas, oceans)

High tideLow tide

Oarweed (to 2 m)Sea star

(to 33 cm)

Intertidalzone

Continental shelf

Brain coral(to 1.8 m)

Sponges (1 cm1 m)

Phytoplankton Zooplankton

Pelagic realm (open water)

Man-of-war(to 50 m

long)

Blue shark (to 2 m)

Sperm whale (1020 m)

Turtle (60180 cm)

Hatchet fish(260 cm)

Gulper eel(to 180 cm)

Angler fish(45 cm2 m)

Rat-tail fish (to 80 cm)

Sea cucumber (to 40 cm)

Tripod fish(to 30 cm)

Octopus(to 10 m)

Sea spider(190 cm)

Glass sponge(to 1.8 m)

Brittle star(to 60 cm)

Benthic realm(seafloor from continentalshelf to deep-sea bottom)

Sea pen(to 45 cm)

200 m

Photiczone

“Twilight”

Aphoticzone1,000 m

No light

6,00010,000 m

Freshwater biomes fall into two broad groups: flowing water biomes (rivers and streams) and standing water biomes (lakes and ponds).

Benthicrealm

Photiczone

Aphoticzone

Ecosystem responses to disturbanceNatural ecosystems operate in dynamic, changing waysDisturbance: a significant change that kills or

displaces many community membersEcological succession: transition from one biotic

community to anotherPioneer species: colonize a newly opened area firstSpecies can create conditions favorable to other species

and less favorable to themClimax is the “final” community but even these

communities experience change if new species are introduced or old ones are removed

Patches of disturbance open space for new growth

Primary succession

Secondary succession

Aquatic successionNatural succession also takes place in lakes

and pondsSoil particles erode from the land and enter the

waterAquatic vegetation provides detritus that also

fills the pond or lakeTerrestrial species advance and aquatic species

move further into the lakeThe climax ecosystem can be a bog or forest

Disturbances (e.g., drought, flood) can send succession back to an earlier stage

Human values and sustainabilityNatural ecosystems are models of sustainability

We depend on them for goods and services (ecosystem capital)

We are threatening their sustainabilityHumans use energy that flows through ecosystems

Converting forests and grasslands into agricultural ecosystems

We appropriate 40% of global net primary productivityFor agriculture, grazing, forestry, houses, roads, etc.Humans are the dominant biological force on Earth

and ecosystems have become degraded or destroyed

Restoration ecologyConsists of developing a model of the desired

ecosystemDesigning and implementing a plan for

restorationStating clear standards to evaluate progressMonitoring the plan Developing strategies for long-term protection

and maintenance of the systemWe should restore ecosystems

For aesthetic reasons, human use, other speciesNature has value separate from humans