Ecology Biological Communities NO species exists independently of other species

EcologyEcology

Biological CommunitiesBiological CommunitiesNO species exists independently of other speciesNO species exists independently of other species

The CommunityThe Community• A group of populations of different species A group of populations of different species

living close enough to interactliving close enough to interact

Interspecific interactions between populations of different species within a community

Community structureCommunity structure• CommunityCommunity~ an assemblage of ~ an assemblage of

populations living close enough together for populations living close enough together for potential interactionpotential interaction

• Richness Richness abundance and distribution of abundance and distribution of numbers of different speciesnumbers of different species

• Species diversity Species diversity number of different number of different speciesspecies

• Hypotheses:Hypotheses:– IndividualisticIndividualistic chance assemblage chance assemblage

with similar abiotic requirementwith similar abiotic requirement– InteractiveInteractive~ ~ assemblage locked into assemblage locked into

association by mandatory biotic association by mandatory biotic interactionsinteractions

Interaction in CommunitiesInteraction in Communities• Community Community

interactions are interactions are classified by whether classified by whether they help, harm, or they help, harm, or have no effect on the have no effect on the species involved.species involved.

Co-evolution is a result of this history of interactionCo-evolution is a result of this history of interaction

When two species use the same resource, When two species use the same resource, they participate in a biological interaction they participate in a biological interaction called called competitioncompetition

How Competition Shapes Communities How Competition Shapes Communities

How Competition Shapes Communities How Competition Shapes Communities

IntraIntraspecificspecific – between individuals – between individuals of the of the SAMESAME species species

InterInterspecificspecific – between individuals – between individuals of of DIFFERENTDIFFERENT species species

Interspecific CompetitionInterspecific Competition

• Competition occurs Competition occurs when resources are when resources are in short supplyin short supply

• Competition is -/- Competition is -/- interaction between interaction between the species involvedthe species involved

Competition evidenceCompetition evidence• Resource partitioningResource partitioning~ ~

sympatric species consume slightly sympatric species consume slightly different foods or use other resources different foods or use other resources in slightly different waysin slightly different ways

• Character displacementCharacter displacement~ ~ sympatric species tend to diverge in sympatric species tend to diverge in those characteristics that overlapthose characteristics that overlap

Ex: Anolis lizard sp. perching sites in the Dominican Republic

Ex: Darwin’s finch beak size on the Galapagos Islands

Central to Competition and Central to Competition and CommunityCommunity

• The Ecological NicheThe Ecological Niche• Law of Competitive Law of Competitive ExclusionExclusion

• No two species will occupy the No two species will occupy the same niche and compete for same niche and compete for exactly the same resources for exactly the same resources for an extended period of time.an extended period of time.

• One will either migrate, become One will either migrate, become extinct, or partition the resource extinct, or partition the resource and utilize a sub-set of the same and utilize a sub-set of the same resource.resource.

• Given resource can only be Given resource can only be partitioned a finite number of partitioned a finite number of times.times.

Interaction By PredationInteraction By Predation• The act of one organism killing another for foodThe act of one organism killing another for food• +/- interaction+/- interaction• Often involves keystone speciesOften involves keystone species

Types of predatorsTypes of predators• CarnivoresCarnivores – kill the prey – kill the prey

during attackduring attack

• HerbivoresHerbivores –– remove remove parts of many prey, rarely parts of many prey, rarely lethal.lethal.

• ParasitesParasites – consume – consume parts of one or few prey, parts of one or few prey, rarely lethal.rarely lethal.

• ParasitoidsParasitoids – – kill one prey kill one prey during prolonged attack.during prolonged attack.

Striking adaptations often characterize Striking adaptations often characterize predators and their preypredators and their prey

Cryptic ColorationCryptic Coloration

Predators may evolve Predators may evolve cryptic morphology cryptic morphology (camouflage)(camouflage)

Cryptic ColorationCryptic Coloration

Prey may evolve to blend in Prey may evolve to blend in too!too! CamouflageCamouflage

AposematismAposematismPrey may evolve warning morphologyPrey may evolve warning morphology

Aposematic colors = warning

MimicryMimicryOrganisms may evolve to look like other organismsOrganisms may evolve to look like other organisms

Batesian mimicry Batesian mimicry • harmless mimic evolves to look like harmful modelharmless mimic evolves to look like harmful model• looks like something that is dangerous or tastes badlooks like something that is dangerous or tastes bad

ViceroyViceroy

MonarchMonarchMilk SnakeMilk Snake Coral SnakeCoral Snake

MimicryMimicry

Mullarian mimicryMullarian mimicry

Bracoria MillipedessBracoria Millipedess NudibranchsNudibranchs

Two bad tasting organisms resemble each other, Two bad tasting organisms resemble each other, ostensibly so that predators will learn to avoid them ostensibly so that predators will learn to avoid them equally.equally.

Predation defense reviewPredation defense review

• Cryptic Cryptic (camouflage)(camouflage) coloration coloration• Aposematic Aposematic (warning)(warning) coloration coloration• MimicryMimicry~ superficial resemblance to another ~ superficial resemblance to another

speciesspecies √ √ BatesianBatesian~ palatable/ harmless species mimics an ~ palatable/ harmless species mimics an

unpalatable/ harmful modelunpalatable/ harmful model √ √ MullerianMullerian~ 2 or more unpalatable, aposematically ~ 2 or more unpalatable, aposematically colored species resemble each othercolored species resemble each other

Interaction By SymbiosisInteraction By Symbiosis• Where two organisms live Where two organisms live

together in close association. together in close association. • Can be mutually beneficial or Can be mutually beneficial or

benefit one organism and benefit one organism and leave the other unharmedleave the other unharmed

HerbivoryHerbivory

• +/- interaction in which an +/- interaction in which an herbivore eats part of a plant.herbivore eats part of a plant.

• It is advantageous for an It is advantageous for an animal to be able to animal to be able to distinguish toxic from distinguish toxic from nontoxic plants.nontoxic plants.

• A plant’s main protective A plant’s main protective devices are chemical toxins, devices are chemical toxins, spines, and thorns.spines, and thorns.

Commensalism Commensalism One member benefits while other is neither benefited nor harmedOne member benefits while other is neither benefited nor harmed

mites hitching a ride on a beetle

A symbiotic relationship in which both species benefit A symbiotic relationship in which both species benefit +/++/+

MutualismMutualism

Tick

Tapeworm

ParasitismParasitism

• Parasites derive nourishment from their Parasites derive nourishment from their hostshosts +/- interaction+/- interaction

• endoparasitesendoparasites

• ectoparasitesectoparasites

Often described in terms of how the organism affects energy Often described in terms of how the organism affects energy flow within the ecosystem, it is a flow within the ecosystem, it is a pattern of livingpattern of livingTo understand how competition influences the makeup of To understand how competition influences the makeup of communities, you must look at the communities, you must look at the functional role of the species:functional role of the species:

Ecological NicheEcological Niche

• NicheNiche• Habitat & microhabitat (Space utilization)Habitat & microhabitat (Space utilization)• Food “spectrum,” essential nutrients Food “spectrum,” essential nutrients • Reproductive requirementsReproductive requirements

– Nutrition, nest/den sitesNutrition, nest/den sites

• Seasonality: When are resources required, used.Seasonality: When are resources required, used.

NOT TO BE CONFUSED WITH:NOT TO BE CONFUSED WITH: • Habitat - location where a particular organism livesHabitat - location where a particular organism lives

What is the niche?What is the niche?

set of conditionsset of conditions within which an organismwithin which an organism can maintain a viablecan maintain a viable populationpopulation

multi-dimensionalmulti-dimensional with as manywith as many dimensions as theirdimensions as their are limiting conditionsare limiting conditions

temperature

light intensity

okaysalinity

ecologicalniche

Size of the NicheSize of the Niche

• Fundamental nicheFundamental niche– The entire range of opportunityThe entire range of opportunity– The organism’s potential (the role it could play) in the The organism’s potential (the role it could play) in the

absence of biotic enemies absence of biotic enemies – depends on physical (abiotic) conditions.depends on physical (abiotic) conditions.

• Realized nicheRealized niche– The actual range of the organism (the role it does play The actual range of the organism (the role it does play

in the community) – in the presence of biotic enemiesin the community) – in the presence of biotic enemies– depends on biotic as well as abiotic conditionsdepends on biotic as well as abiotic conditions

Competition and Limitation of ResourcesCompetition and Limitation of ResourcesBarnacles compete for space on rocky intertidal shoresBarnacles compete for space on rocky intertidal shores

What is the What is the realized nicherealized niche of each barnacle? of each barnacle?What is the What is the fundamental nichefundamental niche of each? of each?

Competition and Limitation of ResourcesCompetition and Limitation of Resources

growthgrowthraterate

Location in intertidal zoneLocation in intertidal zonelowlow highhighmiddlemiddle

Chthamalus Chthamalus alonealone

Balanus Balanus alonealone

How can we determine the How can we determine the fundamental nichefundamental niche of each barnacle? of each barnacle?

Removal experiments –Removal experiments –remove each species and see remove each species and see where the other growswhere the other grows

BalanusBalanusfundamental fundamental

nicheniche

Chthamalus Chthamalus fundamental fundamental nicheniche

growthgrowthraterate

Location in intertidal zoneLocation in intertidal zonelowlow highhighmiddlemiddle

How can we determine the How can we determine the realized nicherealized niche of each barnacle? of each barnacle?

Where do they grow when allowed to compete?Where do they grow when allowed to compete?

BalanusBalanusrealized realized

nicheniche Chthamalus Chthamalus realized realized

nicheniche

BalanusBalanus

ChthamalusChthamalus

Competition and Limitation of ResourcesCompetition and Limitation of Resources

Two species cannot coexist if they occupy the same nicheTwo species cannot coexist if they occupy the same niche((the barnacles did not coexist where their fundamental niches overlapped)the barnacles did not coexist where their fundamental niches overlapped)

Competitive Exclusion PrincipleCompetitive Exclusion Principle

• Competition between two species with Competition between two species with identical niches results either in identical niches results either in competitive exclusioncompetitive exclusion or the evolution of or the evolution of resource partitioningresource partitioning

• Stable coexistence requires Stable coexistence requires niche niche differentiationdifferentiation,,– members of each species compete members of each species compete

more strongly among themselves more strongly among themselves than with members of the other than with members of the other speciesspecies

– (intraspecific > interspecific)(intraspecific > interspecific)

Avoiding CompetitionAvoiding Competition• Resource partitioningResource partitioning

sympatric species consume sympatric species consume slightly different foods or use slightly different foods or use other resources in slightly other resources in slightly different waysdifferent ways

• Character displacementCharacter displacement sympatric species tend to sympatric species tend to diverge in those characteristics diverge in those characteristics that overlap that overlap

Ex: Anolis lizard sp. perching sites in the Dominican Republic

Ex: Darwin’s finch beak size on the Galapagos Islands

Resource PartitioningResource Partitioning

Competition: a closer lookCompetition: a closer look

• InterferenceInterference~ actual fighting ~ actual fighting over resourcesover resources

• ExploitativeExploitative~ consumption or ~ consumption or use of similar resourcesuse of similar resources

• Competitive Exclusion Competitive Exclusion Principle Principle – (Lotka / Volterra)~ 2 species (Lotka / Volterra)~ 2 species

with similar needs for the with similar needs for the same limiting resources same limiting resources cannot coexist in the same cannot coexist in the same placeplace

predict the outcome ofpredict the outcome ofinterspecific competitioninterspecific competition

Gause ExperimentGause Experiment

two species of two species of ParameciumParamecium

P. caudataP. caudata

P. aureliaP. aurelia

•Competitive exclusionCompetitive exclusion–When forced to compete, one species eliminates otherWhen forced to compete, one species eliminates other

Species DiversitySpecies Diversity• Measures the Measures the numbernumber of different species in the community of different species in the community

(species richness) and the (species richness) and the relative abundancerelative abundance of each species. of each species.• Community with even species abundance is more diverse than Community with even species abundance is more diverse than

one in which one or two species are abundant and the one in which one or two species are abundant and the remainder are rare.remainder are rare.

Keystone SpeciesKeystone Species• Exerts strong control on the community structureExerts strong control on the community structure• The affect on its community or ecosystem is much larger The affect on its community or ecosystem is much larger

and more influential than would be expected from mere and more influential than would be expected from mere abundance.abundance.– Often large predatorsOften large predators– Critical food organisms (bamboo and pandas)Critical food organisms (bamboo and pandas)– Often, many species are intricately interconnected so that it is Often, many species are intricately interconnected so that it is

difficult to tell which is the essential component.difficult to tell which is the essential component.– Picky predators can promote coexistence among competing prey Picky predators can promote coexistence among competing prey

species.species.– Competitive exclusion is prevented when the dominant competitor Competitive exclusion is prevented when the dominant competitor

is the preferred prey.is the preferred prey.

Barnacles Barnacles Mussels MusselsBalanusBalanus MytilusMytilus

StarfishStarfishPisasterPisaster

Starfish are Starfish are pickypicky – they prefer to eat mussels (dominant competitor), – they prefer to eat mussels (dominant competitor), allowing barnacles (weaker competitor) to coexist.allowing barnacles (weaker competitor) to coexist.

HowHow do starfish promote coexistence? do starfish promote coexistence?

How Keystone Species Affect Community StructureHow Keystone Species Affect Community Structure

preditorpreditor

competitorscompetitors

Removal experimentRemoval experiment

timetime

starfishstarfishremovedremoved

%%ofof

inter-inter-tidaltidalzonezone

musselsmussels

- mussels are the dominant competitor- mussels are the dominant competitor- competitive exclusion of barnacles- competitive exclusion of barnacles

barnaclesbarnacles

GENERALIST VS SPECIALIST

•Animals are generally Animals are generally selective and efficient in selective and efficient in their food choicestheir food choices

–Some animals, such as Some animals, such as gulls, are feeding gulls, are feeding “generalists” “generalists” –Other animals, such as Other animals, such as koalas, are feeding koalas, are feeding “specialists”“specialists”

GENERALIST VS SPECIALIST

specialist consumes only one prey typespecialist consumes only one prey type

generalist consumes many prey typesgeneralist consumes many prey types

broad diet

narrow diet

GENERALIST VS SPECIALIST

Generalists - Broad nicheGeneralists - Broad niche

Specialists - Narrow nicheSpecialists - Narrow niche

When generalists and specialists When generalists and specialists collide, generalists usually wincollide, generalists usually win

Invasive SpeciesInvasive Species• Invasive species Invasive species

competitively exclude competitively exclude native speciesnative species– Imported fire antImported fire ant– KudzuKudzu– Purple loosestrifePurple loosestrife– Zebra musselZebra mussel– SquirrelsSquirrels

•SuccessionSuccession - orderly, natural changes that take - orderly, natural changes that take place in communities of an ecosystem over time.place in communities of an ecosystem over time.

Ecosystem Change: SuccessionEcosystem Change: Succession

Pioneer speciesPioneer species: first organisms to live in a new habitat. : first organisms to live in a new habitat.

Tend to be small, fast growing plants, lichens, fungus. Increase Tend to be small, fast growing plants, lichens, fungus. Increase soil and make the ground more hospitable for other species.soil and make the ground more hospitable for other species.

Ecosystem ChangeEcosystem Change• Constant state of changeConstant state of change

– Disturbance influences species diversity Disturbance influences species diversity and compositionand composition

– Storm, fire, flood, human activity Storm, fire, flood, human activity changes a community by removing changes a community by removing organisms or changing resource organisms or changing resource availabilityavailability

– Not necessarily badNot necessarily bad

Ecosystem ChangeEcosystem Change• Intermediate disturbance Intermediate disturbance

hypothesishypothesis– Moderate levels of disturbance Moderate levels of disturbance

create conditions that foster create conditions that foster greater species diversity than greater species diversity than low or high levels of disturbancelow or high levels of disturbance

Primary SuccessionPrimary Succession• Primary succession is Primary succession is

colonization by communities colonization by communities of organisms where life has of organisms where life has not existed before.not existed before.

Terrestrial Primary SuccessionTerrestrial Primary Succession

Secondary SuccessionSecondary Succession• Secondary succession is the sequence of community Secondary succession is the sequence of community

changes that occur when a community is disrupted by changes that occur when a community is disrupted by natural disasters or human actions.natural disasters or human actions.

Climax CommunityClimax Community• The final stable plant community is called a climax The final stable plant community is called a climax

community. This community may reach a point of community. This community may reach a point of stability that can last for hundreds or thousands of years.stability that can last for hundreds or thousands of years.

Ecosystem StabilityEcosystem Stability• The interrelationships and The interrelationships and

interdependencies of interdependencies of organisms affect the organisms affect the development of development of stable stable ecosystemsecosystems – in other words – in other words the the homeostasishomeostasis of of ecosystems.ecosystems.

Tolerance Tolerance • Tolerance Tolerance is the ability to is the ability to

withstand fluctuations in withstand fluctuations in biotic and abiotic biotic and abiotic environmental factors.environmental factors.

• BiodiversityBiodiversity gives an gives an ecosystem more ecosystem more tolerancetolerance..

• The greater the The greater the biodiversity, the healthier biodiversity, the healthier the ecosystemthe ecosystem..

Island BiogeographyIsland Biogeography

• Because of their isolation Because of their isolation and limited size, islands are and limited size, islands are natural laboratories for natural laboratories for studying bio-geographical studying bio-geographical factorsfactors

• Also applies to islands of Also applies to islands of land such as national parks land such as national parks or preserves.or preserves.

Island BiogeographyIsland Biogeography• Two factorsTwo factors

– Rates of immigration and Rates of immigration and extinction are influenced extinction are influenced primarily by the size of the primarily by the size of the island and the distance of the island and the distance of the island from the mainland.island from the mainland.

• The greater the size of the The greater the size of the island, the higher the island, the higher the immigration rates and lower the immigration rates and lower the rates of extinction.rates of extinction.

• As the distance from the As the distance from the mainland increases, the rate of mainland increases, the rate of immigration falls, whereas immigration falls, whereas extinction rates increaseextinction rates increase