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AnnouncementsAnnouncements
• Midterm Exam: Wednesday, Nov 3Midterm Exam: Wednesday, Nov 3rdrd
• Review this week in section:Review this week in section:• Bring questions to sectionBring questions to section
Summary from FridaySummary from Friday• Building a model to show population Building a model to show population
interactionsinteractions• Age structure affects populationAge structure affects population• Life tablesLife tables
• static vs. cohort-basedstatic vs. cohort-based• Life strategiesLife strategies
• opportunists vs. competitorsopportunists vs. competitors• seasonal variation in life strategy within seasonal variation in life strategy within
a speciesa species• NicheNiche
What is a What is a nicheniche??
• A A nicheniche is the total of all biotic and is the total of all biotic and abiotic factors that determine how an abiotic factors that determine how an organism fits into its environment.organism fits into its environment.
• Where and how does an organism Where and how does an organism live and function?live and function?• habitathabitat• role in communityrole in community
Environmental variable (Temperature, for example)
Succ
ess
optimum
potential survival,
but stressed
potential survival,
but stressed
intolerant intolerant
Niche in n-variable hyperspace
Fundamental vs. Realized Niche
Fundamental niche: where a species could live
Realized niche: with competition from other species, where a species does live
Niche Partitioning in Animals
• Species divide up an apparent niche
annual grassesperennial grasses
Convergent EvolutionConvergent Evolution
• Organisms adapt to fill open nichesOrganisms adapt to fill open niches• Organisms in two different Organisms in two different
environments that are not closely environments that are not closely related may have the same “job” and related may have the same “job” and similar anatomysimilar anatomy
Selection minimizes competition
Two species living separately.
Two species living together.
Species interactionsSpecies interactions
• CompetitionCompetition• Mutualism Mutualism
• both species benefitboth species benefit
• Commensalism Commensalism • one benefits, other is unaffectedone benefits, other is unaffected
• Parasitism Parasitism • one benefits, one losesone benefits, one loses
• Predator-PreyPredator-Prey
ParasitismParasitism
• microparasites vs. macroparasitesmicroparasites vs. macroparasites• BiotropicBiotropic
• thrive on live hosts onlythrive on live hosts only
• NecrotropicNecrotropic• can benefit even if host diescan benefit even if host dies
• ParasitoidsParasitoids• always kill their hostalways kill their host
Predator-Prey RelationshipsPredator-Prey Relationships
• Prey defensesPrey defenses• coevolutioncoevolution
• as predator evolves, prey evolves to evade itas predator evolves, prey evolves to evade it
Predator-Prey RelationshipsPredator-Prey Relationships
• Prey defensesPrey defenses• coevolutioncoevolution
• as predator evolves, prey evolves to evade itas predator evolves, prey evolves to evade it
• warning coloration and mimicrywarning coloration and mimicry• aposematic “away signal” = bright red and aposematic “away signal” = bright red and
yellowyellow• some mimics very toxic, others harmlesssome mimics very toxic, others harmless
Predator-Prey RelationshipsPredator-Prey Relationships
• Prey defensesPrey defenses• coevolutioncoevolution
• as predator evolves, prey evolves to evade itas predator evolves, prey evolves to evade it
• warning coloration and mimicrywarning coloration and mimicry• aposematic “away signal” = bright red and aposematic “away signal” = bright red and
yellowyellow• some mimics very toxic, others harmlesssome mimics very toxic, others harmless
• camouflagecamouflage• blending inblending in
Predator-Prey RelationshipsPredator-Prey Relationships
• Prey defensesPrey defenses• coevolutioncoevolution
• as predator evolves, prey evolves to evade itas predator evolves, prey evolves to evade it
• warning coloration and mimicrywarning coloration and mimicry• aposematic “away signal” = bright red and aposematic “away signal” = bright red and
yellowyellow• some mimics very toxic, others harmlesssome mimics very toxic, others harmless
• camouflagecamouflage• blending inblending in
• moment-of-truth defensesmoment-of-truth defenses• large or startling displayslarge or startling displays
Predator-Prey RelationshipsPredator-Prey Relationships
• Optimal Foraging Theory- describes Optimal Foraging Theory- describes how prey are chosenhow prey are chosen• small prey provide little food, but they small prey provide little food, but they
are easy to huntare easy to hunt• large prey provide a lot of food, but they large prey provide a lot of food, but they
are more difficult to huntare more difficult to hunt
• Trophic CascadesTrophic Cascades• Food webs can be complexFood webs can be complex
Prey Selection
Trophic CascadeTrophic Cascade
Eagles
Foxes
Mice
Plants 1st trophic level
2nd trophic level
3rd trophic level
4th trophic level
autotroph/ primary producer
herbivore/ primary
consumer
predator/ secondary consumer
predator/ tertiary consumer
Trophic CascadeTrophic Cascade
Eagles
Foxes
Mice
Plants 1st trophic level
2nd trophic level
3rd trophic level
4th trophic level
if eagles go extinct, what could happen to…
foxes?
mice?
plants?
Trophic CascadeTrophic Cascade
Eagles
Foxes
Mice
Plants 1st trophic level
2nd trophic level
3rd trophic level
4th trophic levelIf a new
predator on mice is introduced, what could happen to…
mice?
foxes?
plants?
eagles?
Trophic CascadeTrophic Cascade
Eagles
Foxes
Mice
Plants 1st trophic level
2nd trophic level
3rd trophic level
4th trophic levelIf drought
caused a dip in plant production, what would happen to…
mice?
foxes?
eagles?
Simplified Temperate Forest Food Simplified Temperate Forest Food WebWeb
To which trophic level do these organisms To which trophic level do these organisms belong?belong?
Oak seedling
Deer
Wolf
Fox
Rabbit
Grasses Herbs
Caterpillars
Shrews
Eagle
Optimal ForagingOptimal Foraging• Predators tend to target dominant Predators tend to target dominant
preyprey• enhancement of diversityenhancement of diversity
• What about herbivores?What about herbivores?• don’t necessarily eat dominant plantsdon’t necessarily eat dominant plants• plants have secondary compounds and plants have secondary compounds and
chemical toxins that taste badchemical toxins that taste bad herbivores may target tasty rare plants
Community EcologyCommunity Ecology
A A communitycommunity is a group of living is a group of living organisms that organisms that occupy a certain areaoccupy a certain area and and interact with one another.interact with one another.
• Niche partitioningNiche partitioning• Species interactionsSpecies interactions• Food web dynamicsFood web dynamics• Environmental variation/disturbanceEnvironmental variation/disturbance
• driver of diversitydriver of diversity
Do communities change?Do communities change?
• What we see now wasn’t always hereWhat we see now wasn’t always here• communities do changecommunities do change
• Spatial scale is importantSpatial scale is important• global vs. local changeglobal vs. local change
• Time scale is importantTime scale is important• long term changelong term change
• measured in 10’s of thousands of years or moremeasured in 10’s of thousands of years or more
• short term changeshort term change• measure on a decadal time scalemeasure on a decadal time scale
AnnouncementsAnnouncements
• Look at course webpage for Look at course webpage for study guidestudy guide• Read Enserink Read Enserink et al.et al. articles “Biological articles “Biological
Invasions Invasions Sweep In…” for section next Sweep In…” for section next week (after week (after midterm)midterm)
• Please let know today if you have special Please let know today if you have special needs needs for the examfor the exam
• Note on syllabus: problem set will be Note on syllabus: problem set will be handed out handed out Nov. 10Nov. 10thth
• Office hours: Monday after classOffice hours: Monday after class
Summary from WednesdaySummary from Wednesday
• Niche partitioning Niche partitioning • Convergent evolutionConvergent evolution• Community ecologyCommunity ecology
• Species interactionsSpecies interactions• Optimal foraging theory and prey Optimal foraging theory and prey
selectionselection• Herbivory and plant selectionHerbivory and plant selection• Trophic cascades and food web dynamicsTrophic cascades and food web dynamics• Change over timeChange over time
How do we detect long-term How do we detect long-term change?change?
• Sediment coresSediment cores• Ice coresIce cores• Pollen recordsPollen records• Fossil recordsFossil records• Packrat middensPackrat middens• Tree ringsTree rings
IsotopesIsotopes• Isotope: Isotope: element where atoms have a different # element where atoms have a different #
of neutronsof neutrons
= proton
= neutron
O18O16
Lighter and common Heavy and rare
IsotopesIsotopes• Isotope: Isotope: element where atoms have a different # element where atoms have a different #
of neutronsof neutrons• Can be used to detect global-scale long-term Can be used to detect global-scale long-term
changechange
IsotopesIsotopes• Isotope: Isotope: element where atoms have a different # element where atoms have a different #
of neutronsof neutrons• Can be used to detect global-scale long-term Can be used to detect global-scale long-term
changechange• Total oxygen pool is composed of: Total oxygen pool is composed of:
• Mix ofMix of OO1616 and and OO1818
• Fractionation during seawater evaporationFractionation during seawater evaporation• OO1616 evaporates easilyevaporates easily
• OO1818 gets left behindgets left behind
Isotopes in Sediment CoresIsotopes in Sediment Cores• Sediment contains foraminiferansSediment contains foraminiferans
• microscopic sea creaturesmicroscopic sea creatures• OO1616//OO1818 in tests reflects that of seawater in tests reflects that of seawater• live on sediment or sink to bottom when deadlive on sediment or sink to bottom when dead
Isotopes in Sediment CoresIsotopes in Sediment Cores• Sediment contains foraminiferansSediment contains foraminiferans
• microscopic sea creaturesmicroscopic sea creatures• OO1616//OO1818 in tests reflects that of seawater in tests reflects that of seawater• live on sediment or sink to bottom when deadlive on sediment or sink to bottom when dead
• If the climate cools…If the climate cools…• ice sheets will expandice sheets will expand• ice comes from rain from evaporated seawaterice comes from rain from evaporated seawater• evaporated seawater is high in Oevaporated seawater is high in O1616
• seawater left behind high in Oseawater left behind high in O1818
• therefore, high Otherefore, high O1818 in ocean = cold conditions in ocean = cold conditions
Variation in Ocean O18
more negative values: less O18 and warmer conditions
less negative values: more O18 and colder conditions
Ice core Ice core measurements:measurements:
• thickness of layersthickness of layers• physical propertiesphysical properties• dust and siltdust and silt• conductivityconductivity• trapped air (COtrapped air (CO22, ,
NONOxx, and O, and O22))
• ions (Kions (K++, Ca, Ca2+2+, NO, NO33--))
• isotopesisotopes
Pollen records can be used to detect long term change on a regional scale.
Trees can migrate 200-300 miles in 1000 years.
J. G. Ogden III, 1966.
Fossil Pollen – Silver Lake, OH
Dendrochronology:Dendrochronology:• exact calendar dating exact calendar dating
using annual growth using annual growth rings in woodrings in wood
Dendroclimatology:Dendroclimatology:• using tree rings to using tree rings to
look at past climatelook at past climate• very old trees can be very old trees can be
used to get the used to get the longest historylongest history
• Bristlecone pine Bristlecone pine (Pinus longaeva)(Pinus longaeva)
White Mountains, CA White Mountains, CA
~5000 years old~5000 years old
Soil Soil developmentdevelopment
• Weathering of Weathering of primary mineralsprimary minerals• nutrients become nutrients become
more availablemore available• in old soils, the in old soils, the
nutrients get nutrients get leached outleached out
• Formation of Formation of claysclays
• Accumulation of Accumulation of organic matterorganic matter
Long-Term ChangeLong-Term Change
Shifts in climateShifts in climate
Change in vegetation
Change in soil development
Change in animal populations
Long-Term ChangeLong-Term Change
Shifts in climateShifts in climate
Change in vegetation
Change in soil development
Change in animal populations
Community change
Short-Term ChangeShort-Term Change
SuccessionSuccessionTextbook definition: Textbook definition:
““a change in species that occupy a given a change in species that occupy a given area, with some species invading and area, with some species invading and becoming more numerous while others becoming more numerous while others decline in population and disappear”decline in population and disappear”
Can be thought of as the Can be thought of as the replacement replacement of one community by anotherof one community by another
Primary vs. Secondary Primary vs. Secondary SuccessionSuccession
• Primary:Primary:• Community gets established on a Community gets established on a new new
surfacesurface• Lava flowLava flow• River sandbarRiver sandbar• Glacial moraineGlacial moraine
• Secondary:Secondary:• Recovery following disturbanceRecovery following disturbance
• FireFire• FloodFlood• Post-agriculturePost-agriculture
• Primary SuccessionPrimary Succession• Can take Can take
hundreds to hundreds to thousands of thousands of yearsyears
• Soil must developSoil must develop• New species New species
must come from must come from somewhere elsesomewhere else
• Secondary Secondary SuccessionSuccession• FasterFaster
• Primary SuccessionPrimary Succession• Can take Can take
hundreds to hundreds to thousands of thousands of yearsyears
• Soil must developSoil must develop• New species New species
must come from must come from somewhere elsesomewhere else
• Secondary Secondary SuccessionSuccession• FasterFaster
EarlyEarly vs.vs. Late Late Succession Succession SpeciesSpecies
EarlyEarly• shade intolerantshade intolerant• nutrient nutrient
demandingdemanding• short-livedshort-lived• poor competitorspoor competitors
LateLate• shade tolerantshade tolerant• adapted to lower adapted to lower
nutrient nutrient conditionsconditions
• long-livedlong-lived• good good
competitorscompetitors
Classic SuccessionClassic Succession
Clements’ idea of “climax community” Clements’ idea of “climax community” • eventually, a given system reaches eventually, a given system reaches
a predictable steady-state a predictable steady-state • independent of the early independent of the early
succession communitysuccession community
Mixed Beech-Maple Forest
Oak-Hickory
Willow shrub
Cattail marsh
Aquatic plants
Swamp
Oak woodland
Sumac-Pine
Broomsedge
Aster-Goldenrod
Annual weeds
Old field
Oak forest
Pine forest
Poplars
Dune grass
Sand dune
Bird succession
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