COMMUNITY ECOLOGYCOMMUNITY ECOLOGYChapter 54

What is a community?What is a community?Many species living closely

together, so that they interact with each-other.

Population Interactions:Population Interactions:Intraspecific competition - within

a speciesInterspecific interactions -

Individuals of different species compete for a resource that limits their growth and survival

Interspecific competitionInterspecific competition-/- interaction Competition must occur:

◦interference competition - actual fighting occurs

◦exploitation competition - consumption or use of similar resource

Ex: weeds growing in a garden compete with garden plants, lynx and foxes compete for snowshoe hares

Competitive Exclusion Competitive Exclusion PrinciplePrincipleTwo species cannot coexist in a

community if their niches are identical

Ecologically similar species can coexist in a community if there are one or more differences in their niches

Competitive Exclusion PrincipleCompetitive Exclusion Principle

Ecological NicheEcological NicheSum total of a species’ use of the

biotic and abiotic resources in its environment

Habitat=addressNiche=habitat + occupation

Resource partitioning of lizardsResource partitioning of lizards

Fundamental / Realized NichesFundamental / Realized Niches

Character Character displace-displace-mentment

Upon What Do These Animals Prey?

Upon What Do These Animals Prey?

Animals

Upon What Do These Animals Prey?

Animals

Plants

Animal DefensesAnimal Defenses

RunningHidingPhysical or Chemical Defenses

Chemical Defense and Aposematic coloration are seen

here

Aposematic colorationAposematic coloration

Cryptic coloration

is seen here

Cryptic ColorationCryptic Coloration

MimicryMimicryBatesian mimicry - harmless

species resembles harmful or distasteful species

Mullerian mimicry - two or more unpalatable species resemble one another.

Batesian MimicryBatesian Mimicry

Batesian MimicryBatesian Mimicry

Mullerian MimicryMullerian Mimicry

Plant Defenses Against Plant Defenses Against Predators:Predators:

What defense is seen here?

Other defenses:

• Chemicals that cause plant to taste bad

• Poisonous chemicals

In this relationship, the ant hollows out the thorns of the plant for nests, feed on sweet secretions from the four nectaries at the base of each petiole, and protect these trees from invertebrate herbivores.

Heliconius butterflies (Heliconius sp.) lay their eggs on the leaves of the passionflower vine (Passiflora sp.). When the eggs hatch into hungry, leaf-eating Heliconius caterpillars, the passionflower vines protect themselves with an array of defenses.

Fake eggs . . . some passionflower vines grow parts that look like Heliconius caterpillar eggs. This keeps the female Heliconius butterfly from laying eggs on leaves that appear to be occupied by other cannibalistic caterpillars.

Dumpers . . . Some Heliconius butterflies like to lay their eggs on upward-curling tendrils of passionflower vines. Some vines produce fake tendrils that are weak and fall off under the weight of the developing butterfly eggs.

SymbiosisSymbiosisClose association between two

speciesParasitism +/-Commensalism +/0 interactionMutualism +/+ interaction

PredationPredation+/- interactionPredator eats prey

◦Ex. Lion eats an antelope, animal eats a plant

PredatorsPredators

Can reduce relative abundanceCan reduce diversity by

eliminating competitors - keystone predators◦sea star feeds on mussels and other

organisms, remove sea star and mussels take over the region and eliminate species diversity.

Parasites are also +/-Parasites are also +/-Endoparasites-live within the body of

their host◦Ex. tapeworms

Ectoparasites-parasites that feed on the external surface of a host◦Ex. Ticks, lice

Parasitoid insects-lay eggs on the body of the host, the larva then feed on the body of the host, eventually killing it

One parasite example:

MutualismMutualism+/+ interaction

◦Ex. Nitrogen fixation by bacteria in root nodules of legumes

◦Ex. Termites and microorganisms in their gut

Interspecific Interactions:Interspecific Interactions:What is co-evolution?Reciprocal evolutionary changes

between two or more species.Results in a close association

between certain species

CommensalismCommensalism+/0 interaction

◦Ex. Cowbirds and cattle egrets feed on insects flushed out of the grass

Which symbiosis is seen here?

Which symbiosis is seen here?

parasitic

Which symbiosis is seen here?Which symbiosis is seen here?

Which symbiosis is seen here?Which symbiosis is seen here?

Mutualism

Community StructureCommunity StructureFeeding relationshipsRichness - number of different

speciesRelative abundance - number in

individuals in each speciesDiversity - combination of abundance

and richnessCommunities with even distribution

of species are more diverse than communities with greater richness but skewed distributions

Trophic StructureTrophic StructureFeeding relationships-transfer of

food energyPlants to herbivores to carnivores

to decomposers = food chainFood web - interconnected food

chains

Control of community Control of community structurestructureDominant species-species in a community

that have highest abundance or biomass◦ Sugar maples

Keystone species-not abundant but exert strong control on community structure◦ Remove the species to determine if it is a

keystone species◦ Sea otters

Invasive species-no natural predators so their population is not held in check◦ Buckthorn, garlic mustard, purple loosestrife

NonequilibriumNonequilibriumMost communities are not stableDisturbances such as storms,

floods overgrazing etc. can effect stability

Humans bring disturbance

Succession Succession Example of disturbance leading

to changeprimary succession - soil never

formed beforesecondary succession - existing

community was disturbed and returned to original state.

Secondary SuccessionSecondary Succession

BiogeographyBiogeographyStudy of past and present

distribution of individual species and communities

Limitation of species to one region:◦species never dispersed◦pioneers did not survive◦species retracts from once larger

range to smaller boundaries

Island biogeographyIsland biogeography

Review the following slides Review the following slides and identify which community and identify which community interaction you are observinginteraction you are observing

Where is the Moth?

Can you see it now?Can you see it now?

What What coloration is coloration is seen in the seen in the next slides?next slides?What does What does this tell you this tell you about the about the way these way these animals live animals live in their in their communities?communities?

This animal is not a bee, why This animal is not a bee, why does it look like one?does it look like one?

Species Richness and Species Richness and Island SizeIsland Size

Species diversitySpecies diversity

Which forest is more diverse?