EcosystemsEcosystems

Structure and DynamicsStructure and Dynamics

Community Ecology Community Ecology The scientific study of interactions among organisms and The scientific study of interactions among organisms and between organisms and their environments. between organisms and their environments.

Ecosystems: Everything Is ConnectedEcosystems: Everything Is Connected

Everything in an Everything in an ecosystem is ecosystem is connected.connected.What affects one What affects one part of an part of an ecosystem often ecosystem often affects many other affects many other parts of the parts of the ecosystem as wellecosystem as well..

Organisms and SpeciesOrganisms and Species

• An An organismorganism is a single is a single living thing.living thing.

• A A speciesspecies is a group of is a group of organisms that can organisms that can produce fertile produce fertile offspring with the offspring with the same characteristics.same characteristics.

PopulationsPopulations

• A A populationpopulation is a group of organisms is a group of organisms from the same species living in the same from the same species living in the same place.place.

• There may be thousands of populations There may be thousands of populations for any particular speciesfor any particular species..

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

species living close enough to interactspecies living close enough to interact

Interspecific interactions = all the species in a Interspecific interactions = all the species in a given area. given area.

Some habitatsForest

• TreeLake or pondCity parkCaveFen or swamp or marshlandReef

HabitatHabitatAny place within the Any place within the ecosystem ecosystem where a population or where a population or community livescommunity lives  

SpeciesSpecies

PopulationPopulation

CommunityCommunity

EcosystemEcosystem

BiomeBiome

BiosphereBiosphere

Levels of OrganizationLevels of Organization

Biome

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

Competition Shapes Communities Competition Shapes Communities

How Competition Shapes Communities How Competition Shapes Communities

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

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

How Species Interact With Each OtherHow Species Interact With Each Other

• Ecosystems work best Ecosystems work best when every when every niche in it in it is filled.is filled.

• Species interact with Species interact with each other in many each other in many ways. The most ways. The most common common relationships are:relationships are:1.1. PredationPredation2.2. CompetitionCompetition3.3. ParasitismParasitism4.4. MutualismMutualism5.5. CommensalismCommensalism

Central to Competition Central to Competition and Communityand Community

• Habitat & microhabitat Habitat & microhabitat (Space utilization)(Space utilization)

• Food “spectrum,” essential Food “spectrum,” essential nutrients nutrients

• Reproductive requirementsReproductive requirements

• Nutrition, nest/den sitesNutrition, nest/den sites

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

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

The Ecological NicheThe Ecological Niche

PredationPredation• In predation, one organism In predation, one organism

eats another.eats another.• The animal that kills and eats The animal that kills and eats

is the is the predatorpredator..• The animal that is eaten is the The animal that is eaten is the

prey.prey.• PredatorsPredators typically kill the typically kill the

young and weak/sick young and weak/sick members of their prey. members of their prey. Consequently they help limit Consequently they help limit the size of the the size of the prey prey population.population.

• As the As the preyprey die off, the die off, the predators predators either switch their either switch their prey or die off also.prey or die off also.

• This creates a specific cyclical This creates a specific cyclical relationship between relationship between predators predators andand prey.prey.

PredationPredation

Hare cycles may be caused by increasing food shortages during winter caused by overgrazing Or they may be due to predator-prey interactionsCycles could be affected by a combination of food resource limitation and excessive predationPredators reproduce more slowly than their prey so they always lag behind prey in population growth.

HerbivoryHerbivory

• +/- interaction in which +/- interaction in which an herbivore eats part of an herbivore eats part of a plant.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 devices are chemical toxins, spines, and thorns.toxins, spines, and thorns.

Interaction By SymbiosisInteraction By Symbiosis

• Two organisms living Two organisms living together in close together in close association. association.

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

MutualismMutualism

Tick

Tapeworm

Parasitism Parasitism • Parasitism is a relationship Parasitism is a relationship between two organisms in between two organisms in which one feeds off another. which one feeds off another.

• The organism that feeds off The organism that feeds off the other is the the other is the parasiteparasite..

• The organism that contains The organism that contains the parasite is the the parasite is the hosthost..

• The main difference The main difference between parasitism and between parasitism and predation is that in predation is that in parasitism, the parasitism, the parasite does parasite does not usually kill the host not usually kill the host quickly.quickly.

CommensalismCommensalism One member benefits while other is neither benefited nor One member benefits while other is neither benefited nor harmedharmed

mites hitching a ride on a beetle

Population NichePopulation 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))

Law of Competitive ExclusionLaw of Competitive Exclusion

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

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

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

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 diverge sympatric species tend to diverge in those characteristics that in those characteristics that overlap overlap

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

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

BiodiversityBiodiversity• Measures the Measures the numbernumber of different species in the of different species in the

community (species richness) and the community (species richness) and the relative relative abundanceabundance of each species. of each species.

• Community with even species abundance is more Community with even species abundance is more diverse than one in which one or two species are diverse than one in which one or two species are abundant and the remainder are rare.abundant and the 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 The affect on its community or ecosystem is much larger and more influential than would be larger and more influential than would be expected from mere abundance.expected from mere 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 Often, many species are intricately interconnected so

that it is difficult to tell which is the essential that it is difficult to tell which is the essential component.component.

– Picky predators can promote coexistence among Picky predators can promote coexistence among competing prey species.competing prey species.

– Competitive exclusion is prevented when the dominant Competitive exclusion is prevented when the dominant competitor is the preferred prey.competitor is the preferred prey.

Barnacles Barnacles Mussels MusselsBalanusBalanus MytilusMytilus

StarfishStarfishPisasterPisaster

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

coexist.coexist.

HowHow do starfish promote coexistence? do starfish promote coexistence?

How Keystone Species Affect Community StructureHow Keystone Species Affect Community Structure

preditorpreditor

competitocompetitorsrs

Removal experimentRemoval experiment

timetime

starfishstarfishremovedremoved

%%ofof

inter-inter-tidaltidalzonezone

musselsmussels