chapter 53 community ecology. copyright © 2005 pearson education, inc. publishing as benjamin...

Chapter 53Chapter 53

Community EcologyCommunity Ecology

What Is a Biological Community?

• a grouping of populations of various species living close enough for potential interaction

• How big is a community?

– As big as you define it

25000 species of plants1600 birds369 mammals350 reptiles400 amphibians800 fish in Amazon450 in Pacific100,000s of inverts

413 birds17 reptiles12 amphibians56 fish

What’s in a Community?

2,301,000 km2

256,370 km2

How do communities interact? Who eats who?

• interactions include

– competition

– predation

– herbivory

– symbiosis

– disease

Inter-species interactions

Table 53.1

Competition

• Species compete for resource in short supply

• Competitive exclusion principle

– Competing species cannot coexist in the same niche

Ecological Niches

• The ecological niche

– Use of abiotic and biotic resources

– Competitors cannot coexist unless niches change

When Connell removed Balanus from the lower strata, the Chthamalus population spread into that area.

The spread of Chthamalus when Balanus was removed indicates that competitive exclusion makes the realizedniche of Chthamalus much smaller than its fundamental niche.

RESULTS

CONCLUSION

Ecologist Joseph Connell studied two barnacle speciesBalanus balanoides and Chthamalus stellatus that have a stratified distribution on rocks along the coast of Scotland.

EXPERIMENT

In nature, Balanus fails to survive high on the rocks because it isunable to resist desiccation (drying out) during low tides. Its realized niche is therefore similar to its fundamental niche. In contrast, Chthamalus is usually concentrated on the upper strata of rocks. To determine the fundamental of niche of Chthamalus, Connell removed Balanus from the lower strata.

Low tide

High tide

Chthamalusfundamental niche

Chthamalusrealized niche

Low tide

High tideChthamalus

Balanusrealized niche

Balanus

Figure 53.2

Competition

• Fundamental niche (what you want)

• Realized niche (what you can get)

A. insolitususually percheson shady branches.

A. distichus perches on fence posts and

other sunny surfaces.

A. distichus

A. ricordii

A. insolitus

A. christophei

A. cybotes

A. etheridgei

A. alinigar

Figure 53.3

Resource Partitioning

• Resource partitioning allows similar species to coexist in a community

Predation

• Predator kills and eats prey (+/-)

• Includes herbivory and parasitism

Predation

• Feeding adaptations

– Claws, teeth, fangs, stingers, poison

• Defensive adaptations

– Camouflage, mimicking

Plant defenses

Tobacco plant - nicotine

Cinnamon plant

Thorns

Animal Defenses

Cryptic coloration

Chemical defenses

Fleeing

Aposematic coloration

• Warns predators - stay away!

Figure 53.6

Batesian mimicry

• palatable or harmless species mimics an unpalatable or harmful model

(a) Hawkmoth larva

(b) Green parrot snake

Figure 53.7a, b

Parasitism (+/-)

Ectoparasite: a parasite that feeds on the external surface of a host

Endoparasite: a parasite that lives within the host

Parasitism

• Derive nourishment from another organism,

– Host is harmed in the process

– Complex life cycle

– May effect predation

Behavior changes

Symbiosis

Mutualism: interspecific interaction benefits BOTH species

Commensalism: interspecific interaction benefits ONE species, neutral to the other

Symbiosis can include parasitism, mutualism, and commensalism

25000 species of plants1600 birds369 mammals350 reptiles400 amphibians800 fish in Amazon450 in Pacific100,000s of inverts

413 birds17 reptiles12 amphibians56 fish

2,301,000 km2

256,370 km2

SPECIES DIVERSITY

Diversity has 2 components:

• Species richness

– Is the total number of different species in the community

• Relative abundance

– Is the proportion each species represents of the total individuals in the community

2 communities

• Same richness – different abundance

– More diversity where abundance is similar

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

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

Figure 53.11

Trophic Structure

• Feeding relationships between organisms in a community

Food chains

• Link the trophic levels from producers to top carnivores

Quaternary consumers

Tertiary consumers

Secondary consumers

Primary consumers

Primary producers

Carnivore

Herbivore

Carnivore

Zooplankton

Phytoplankton

A terrestrial food chain A marine food chainFigure 53.12

Food Webs

• Branching food chain, complex trophic interactions

Humans

Baleen whales

Crab-eater seals

Birds Fishes Squids

Leopardseals

Elephant seals

Smaller toothed whales

Sperm whales

Carnivorous plankton

Euphausids (krill)

Copepods

Phyto-plankton

Figure 53.13

Limits on Food Chain Length

• Each usually only a few links long

• Energetic hypothesis suggests length limited by inefficiency of energy transfer

– 100kg – 10 kg – 1 kg

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

– Shocks travel up the food chain

Dominant and keystone species

• In general, a small number of species in a community exert strong control on community’s structure

Dominant Species

• Most abundant or have the highest biomass

– Exert control over occurrence and distribution of other species

– Exploit limited resources better or..

– Successfully avoid predators

Keystone species

• Not necessarily abundant

• Control by niche or role

Figure 53.16a,b

(a) The sea star Pisaster ochraceous feeds preferentially on mussels but will consume other invertebrates.

With Pisaster (control)

Without Pisaster (experimental)

1963 ´64 ´65 ´66 ´67 ´68 ´69 ´70 ´71 ´72 ´73

(b) When Pisaster was removed from an intertidal zone, mussels eventually took over the rock face and eliminated most other invertebrates and algae. In a control area from which Pisaster was not removed, there was little change in species diversity.

Brazil nut tree

No longer a keystone

Community organization

• The bottom-up model

– influence from lower to higher trophic levels

– presence or absence of abiotic nutrients

– think “primary producers”

Community organization

• Top-down model:

– Control comes from the trophic level above

– Predators control herbivores

– Herbivores control primary producers

Disturbance

• Influences species diversity and composition

• Equilibrium model – stable unless disturbed by humans

• Non-equilibrium model – constant change due to disturbances

What Is Disturbance?

• A disturbance

– Is an event that changes a community

– Removes organisms from a community

– Alters resource availability

Community Stability

Communities are constantly changing, they are in nonequilibrium – many are in some state of recovery from disturbance

Drought

Fire Clearcut

• Is a significant disturbance in most terrestrial ecosystems

– Is often a necessity in some communities

(a) Before a controlled burn.A prairie that has not burned forseveral years has a high propor-tion of detritus (dead grass).

(b) During the burn. The detritus serves as fuel for fires.

(c) After the burn. Approximately one month after the controlled burn, virtually all of the biomass in this prairie is living.

Figure 53.21a–c

Yellowstone fires, 1988

• Communities can often respond very rapidly to a massive disturbance

Figure 53.22a, b

(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.

Yellowstone wolves

Dying aspen grove

Streamside elk grazing

Hey, what’s that noise?

Yellowstone Ecosystem

Lunch grew back!

• Beaver dams

– Can transform landscapes on a very large scale

Figure 53.18

Succession

• Moraines in Glacier Bay, Alaska

– Follows a predictable pattern of change in vegetation and soil characteristics

(b) Dryas stage

(c) Spruce stage

(d) Nitrogen fixation by Dryas and alder increases the soil nitrogen content.

l nitr

Successional stagePioneer Dryas Alder Spruce

(a) Pioneer stage, with fireweed dominant

- Some species improve

environment for followers

Ecological Succession

chapter 53 community ecology. copyright © 2005 pearson education, inc. publishing as benjamin...

niche slide

pearson education

realized niche of chthamalus

fundamental of niche

community slide

parasitism slide

niche balanus ocean

community ecology slide

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