CommunitCommunity Ecologyy Ecology

Concerned with community Concerned with community structure and population structure and population

interactionsinteractions

Interactions

Five categoriesFive categories

1.1. CompetitionCompetition

2.2. PredationPredation

3.3. MutualismMutualism

4.4. CommensalisCommensalismm

5.5. ParasitismParasitism

CompetitionCompetition

Competition• Interspecific competition

– The competition between two or more species for some limiting resource

– food or nutrients, space, mates, nesting sites

• Resolutions Resolutions – Competitive exclusion principle (Gause’s

principle)– Resource partitioning– Character displacement– Realized niche

Competitive interactions between organisms can have a great deal of influence on species evolution

The Competitive Exclusion Principle

• G.F. Gause-worked with 2 strains of Paramecium

-States that two species competing for the same limiting resources cannot coexist in the same place• When two species compete, one is

likely to be more successful.– Cannot coexist if they share the

same niche.

• One species could become extinct or evolve to exploit different resources resource partitioning)

• Divergence in adaptation is called character displacement.

Animation

Ecological NichesEcological Niches

• The ecological niche– Is the total of an organism’s use of the biotic

and abiotic resources in its environment

• The niche concept allows restatement of the competitive exclusion principle– Two species cannot coexist in a community

if their niches are identical

Clip

A. insolitus usually perches on shady

branches.

A. distichus perches on

fence posts and other sunny

surfaces.

A. distichus

A. ricordii

A. insolitus

A. christophei

A. cybotesA. etheridgei

A. alinigar

• Resource partitioning is the differentiation of nichesdifferentiation of niches

Resource Partitioning

–That enables similar species to coexist in a community

Minimizes competition & maximizes success

Resource PartitioningResource partitioning is a way in which different species can use the same resource, such as food, without occupying the same physical location at the same point in time. In this example, the different warblers eat the same caterpillar, but they occupy different positions in the tree. Two primarily occupy the area near the trunk, with the others share the edges of the branches, but at different heights. The result is the warblers do not overtly compete for food in the same space.

G. fortis

Beak depth (mm)

G. fuliginosa

Beak depth

Los Hermanos

Daphne

Santa María, San Cristóbal

Sympatric populations

G. fuliginosa, allopatric

G. fortis, allopatricP

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8 10 12 14 16

Character Displacement (niche shift)

There is a tendency There is a tendency for characteristics to for characteristics to be more divergent be more divergent in sympatric in sympatric populations of two populations of two species than in species than in allopatric allopatric populations of the populations of the same two speciessame two species

Speciation:Allopatric-geographic barriersSympatric- no geo barrier

–As a result of resource partitioning.–-Divergence in adaptation

Realized NicheNiche theory distinguishes between fundamental

& realized niches:

– fundamental = all possible conditions under which population reproduces itself

– realized niche = the actual niche exhibited in particular time & place

• True predator• Parasite• Parasitoid• Herbivore

Snowshoe Hare and Canadian Lynx

PredationPredation

Camouflage

Cryptic colorationCryptic coloration– Fur of snowshoe hare is

white in winter and brown in summer

– The larvae of some moths are colored like bird droppings

– Marking on animals to blend in to background.

-passive defense

Lizard

• Aposematic coloration (warning coloration)– Coloration that warns predators– Predators learn to associate color with bad

taste or harmful chemical

• Mimicry– Two types

• Mϋllerian• Batesian

Müllerian mimicry– Two or more unpalatable species resemble each

other

(a) Cuckoo bee

(b) Yellow jacket

Batesian mimicry– A palatable or harmless species mimics an

unpalatable or harmful model

(a) Hawkmoth larva

(b) Green parrot snake

passive defense

•Spins, thorns, poisons

•Hiding, fleeing

Community Interactions

•SymbiosisSymbiosis•Predatory-Predatory-PreyPrey

•CompetitionCompetition

Symbiosis• Mutualism (+/+)• Commensalisms (+/o)• Parasitism (+/-)

Mutualism(+/+)

CommensalismOne species benefits and the other is not affectedIt is difficult to determine true commensalism because it is difficult to ensure host is not harmed.             Ex: Barnacles that attach themselves to the backs of whales

(+/o)

Parasitism (+/-)• Relationship in which one species benefits;

while harming the other • Tomato hornworm covered with cocoons

of pupating wasps

Review of Community Interactions

Ecological Successio

n

Ecological Succession

• Primary succession– Occurs where no soil exists when succession

begins– Starts with pioneer species (lichens & mosses)

Ecological Succession

Ecological Succession• Secondary succession

– Begins in an area where soil remains after a disturbance– takes place where a community has been removed, e.g.,

in a plowed field or a clear cut forest

(a) Soon after fire. As this photo taken soon after the fire shows, the burn left a patchy landscape. Note the unburned trees in the distance.

(b) One year after fire. This photo of the same general area taken the following year indicates how rapidly the community began to recover. A variety of herbaceous plants, different from those in the former forest, cover the ground.