Chapter 53

Community Ecology

• Community- a group of populations of various species living close enough for potential interaction

How many interactions between species are occurring in this scene?

Competition

• Competitive exclusion- strong competition can lead to the elimination of a competing species

• Competitive exclusion principle- two species competing for the same limiting resources cannot coexist in the same place

Ecological Niches

• Ecological niche- the total of a species’ use of biotic and abiotic resources

• Resource partitioning- differentiation of ecological niches, enabling similar species to coexist in a community

A. ricordii

A. insolitus usually percheson shady branches.

A. distichus perches on fenceposts and other sunny surfaces.

A. alinigerA. distichus

A. insolitus

A. christophei

A. cybotesA. etheridgei

Resource partitioning among Dominican Republic lizards

Predation

• Cryptic coloration (camouflage)- makes prey difficult to spot

Canyon tree frog

Crypticcoloration

• Aposematic coloration- animals with effective chemical defense often exhibit bright warning coloration

Poison dart frog

(b)

• Batesian mimicry- a harmless species mimics an unpalatable or harmful model

Hawkmothlarva

Green parrot snake

• Müllerian mimicry- two or more unpalatable species resemble each other

Cuckoo bee

Yellow jacket

Symbiosis

• Parasitism- the parasite derives nourishment from a host which is harmed in the process

• Mutualism- an interaction that benefits both species

• Commensalism - one species benefits and the other is apparently unaffected

Species Diversity

• Species Diversity of a community is the variety of organisms that make up the community

• Species richness- the total number of different species in the community

• Relative abundance- the proportion each species represents of the total individuals in the community

Community 1A: 25% B: 25% C: 25% D: 25%

Community 2A: 80% B: 5% C: 5% D: 10%

A B C D

Trophic Structure

Trophic Structure- the feeding relationships between organisms in a community

• Food chains link trophic levels from producers to top carnivores

• Food web- a branching food chain with complex trophic interactions

Carnivore

Carnivore

Carnivore

Herbivore

Plant

A terrestrial food chain

Quaternaryconsumers

Tertiaryconsumers

Secondaryconsumers

Primaryconsumers

Primaryproducers

A marine food chainPhytoplankton

Zooplankton

Carnivore

Carnivore

Carnivore

Humans

Smallertoothedwhales

Baleenwhales

Spermwhales

Elephantseals

Leopardseals

Crab-eaterseals

Birds Fishes Squids

Carnivorousplankton

CopepodsEuphausids(krill)

Phyto-plankton

Each food chain in a food web is usually only a few links long

• Energetic hypothesis- length is limited by inefficient energy transfer

• Dynamic stability hypothesis- long food chains are less stable than short ones

Species with a Large Impact

• Dominant species- those that are most abundant or have the highest biomass

• Invasive species -introduced to a new environment, often lack predators or disease

• Keystone species- exert strong control on a community by their ecological roles, or niches

Foundation Species (Ecosystem “Engineers”)

• Foundation Species (Ecosystem “Engineers”)- cause physical changes in the environment that affect community structure

Ecological Succession

Ecological succession-the sequence of community and ecosystem changes after a disturbance

• Primary succession occurs where no soil exists when succession begins

• Secondary succession begins in an area where soil remains after a disturbance

Pioneer stage, withfireweed dominant

1

19411907

1860

1760

Alaska

GlacierBay

Kilometers5 10 150

Dryas stage2

Alder stage3Spruce stage4

Glacial retreat and primary succession at Glacier Bay, Alaska

Fig. 54-22a

Pioneer stage, with fireweed dominant1

Dryas stage2

Alder stage3

Spruce stage4

Successional stagePioneer Dryas Alder Spruce

Soil

nitr

ogen

(g/m

2 )

0

10

20

30

40

50

60

Area Effects

• Species-area curve- all other factors being equal, a larger geographic area has more species

Area (hectares)

Num

ber o

f spe

cies

1,000

100

10

10.1 1 10 100 103 104 105 106 107 108 109 1010

Species-area curve for North American breeding birds