Community EcologyCommunity EcologyChapter 21

I. Species InteractionsSpecies Interactions• Review:

–A Population is a group of individuals of the same species

–A Community is a group of interacting populations of many species

5 ways species interact:• Predation• Competition

• Parasitism• Mutualism• Commensalism

(Symbiotic relationships -next 3)

Categories are based on whether each species causes benefit or harm to the other in the relationship

1. Predation1. PredationWhen one organism kills & eats another.

• Predator- the one that does eating.

• Prey –the eaten• Examples:

Lions –eat zebras Birds - insects

Cougars –eat deer Blue whale- krill

Snakes – eat mice Fox- rabbits

Starfish- clams Eagle- prairie dog

Predator-Prey

http://www.bcseakayak.com/i/destinations2-pic.jpeg

http://www.pbs.org/edens/etosha/images/fm_fc2.jpg

Predator-Prey

http://www.des.ucdavis.edu/faculty/holyoak/Colpidium.jpg

The predator, Didinium nasutum, a medium sized predatory  ciliated protist (length c. 0.1mm) is preying on the larger ciliated protist.

Predator-Prey

• Adaptations - improve hunting in predators or escaping in prey

– Examples of Predator Adaptations: • Rattle snakes have good smell & heat

sensing • Spiders make webs• Tiger striped coat = camouflage

– Examples of Prey Adaptations:• Mantis coloration• Mimicry

Mimicry• Defense mechanism for prey• Deception - A harmless

species LOOKS like a harmful, poisonous or bad tasting species.

• A predator will avoid BOTH species

Predator- Prey Adaptations

• Monarch and viceroy butterflies are an example of mimicry • Similar in appearance & are distasteful to predators. • A strong black line traversing the middle of the hindwing distinguishes

the monarch (right) from the viceroy (left). http://images.google.com/images?svnum=10&hl=en&q=viceroy+butterfly+mimicry&spell=1

2. Competition2. Competition*The relationship between species in

which they attempt to use the same limited resource.

*To fit into a niche, an organism must compete.

*Competition occurs when fundamental niches overlap

Competitive Exclusion- When 2 species of paramecium are grown in same media- note

that 1 species wins, other eliminated.

Character Displacement & Resource Partitioning

• Evolution of niche differences or anatomical differences to lessen competition

• Occurs because– Competition may eliminate species from the

community.– Species may change under the pressure of

natural selection– Example- Darwin’s finches have different

shaped beaks & eat different foods

Competition Interactions:

Competition Interactions:

Organisms can compete even if they never come into contact with each other.

Examples:**One species can feed on a certain plant at night

while another eats the same plant in the daytime.

**2 Flowers compete for pollinators

What happens when competition for the same niche is unnaturally changed?

• Example- the Red Fire Ant- originally from South America-competes for the same niche as the native Black Ant

• Why is the Fire ant dominating?

Red Imported Fire Ant• Introduced from western Brazil- quickly

becomes the number 1 ant pest wherever it occurs. 

• The main reason -its natural enemies from its native habitat were left behind in South America

• Queen ants can live 7 years or more, while worker ants generally live about 5 weeks, although they can survive much longer.

• The venom burns like a hot match and causes tiny blisters or white pustules that persist for days if left untreated or for weeks if scratched or infected and may leave permanent scars.

SymbiosisSymbiosis• Is a close, long-term relationship

between 2 organisms.

• 3 categories:

–Parasitism

–Mutualism

–Commensalism

3. Parasitism3. ParasitismOrganism that lives on or in

another organism and feeds on it without immediately killing it.

Parasites HURT the host

Host-Host- organism that provides nourishment

ParasiteParasite- Organism that does the feeding

Most populations are negatively affected- weakened, sickened, shorten lifespan

Parasitic micro-organisms

(roundworm, protozoan, bacterium,

fungus, yeast)

Parasite examples

4. Mutualism4. Mutualism

Cooperative partnership of 2 speciesExamples:

** Bacteria in your intestines- help you digest food,make vitamin K & fight off other bacteria. You give them a warm, moist habitat to live in. (Lactobacillus sp. & Bifidobacteria sp.

**Central Africa-Ants and Acacia Trees- Trees provide nectar for ant food, ants defend tree against herbivores like grasshoppers and beetles

5. Commensalism5. Commensalism• A relationship in which 1 species benefits

and the other is neither helped or harmed

• Example:Remoras are fish that attach

themselves to sharks. The

remoras get food but the sharks

do not appear to get anything back.

                                               

         remoras on tiger shark

II. Properties of CommunitiesII. Properties of Communities

• Species Richness- number of species it contains.

• (greater number of organisms= increased species richness)

• Species diversity- how common each species is in the community (takes into account the population size - are some species rare or are their lots of most populations?)

Patterns of Species RichnessPatterns of Species Richness

• Species- Area Effect- larger areas contain more species than smaller areas.

• Predators may promote richness by preventing competitive exclusion in their prey.

• Community Stability- resistance to change & disturbances.

III. SuccessionIII. Succession• A regular pattern of change over

time in the types of species in a community.

• Begins when an area is made partially or completely devoid of vegetation because of a disturbance.

• 2 types- primary & secondary

http://www.geo.arizona.edu/Antevs/nats104/00lect20sucn1.gif

http://www.physicalgeography.net/fundamentals/images/succession.gif

http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/B/Bog.gif

Primary Succession• Development of a community in an area

that has not previously supported life.

• Bare rock

• Sand dune

• New volcanic island

• Areas exposed after a glacier retreats

Secondary Succession• Is the sequential replacement of

species after a disruption of an existing ecosystem.

• Fires• Hurricanes• Burned, flattened forest after

volcanic eruption• Abandoned farmland• New pond formed

• Primary succession is slower than secondary succession because it begins where there is no soil.

• It takes several hundred years to produce fertile soil naturally.

• Secondary succession can occur in less than a hundred years

Pioneer Species• First organisms into the area.

• Small, fast growing, fast reproducing

• Examples- primary succession

–LICHENS- colonizing bare rock–“WEEDS” – colonizing cement parking

lots.

–MOSS on old roof.

Example of a Pioneer Species

• Lichens- a mutualistic association between fungi & a photosynthetic organism- either a cyanobacteria or an algae.

• Lichens , along with weathering, break up barren rock in primary succession.

• Decaying dead lichens accumulates and is the first step in creating soil.

Secondary succession• Occurs when an existing

community disrupted.

• Pioneer species usually=grasses.

EX-After agricultural clearing in Temperate Deciduous Forest• Early stages- pioneer species like annual grasses &

dandelions• Later perennial grasses & shrubs.• Next Dogwoods, Pine• Last, large Maple, Oaks, Forest trees

Climax Community• Plant community that no longer

undergoes changes in species composition due to succession.

• Considered the “stable end point”.

• Doesn’t “really “ exist- because communities continue to change-

• Regularly “reset” due to disturbances.