The hierarchy of life
Jan 05, 2016
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