Download Notes Chapter 20 Communities

Community Ecology
Chapter 21
I. Species 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
(Symbiotic relationships -next 3)
• Parasitism
• Mutualism
• Commensalism
Categories are based on whether each species causes
benefit or harm to the other in the relationship
1. Predation
When one organism kills & eats another.
• Predator- the one that does eating.
• Prey –the eaten
•
Examples:
Lions –eat zebras
Cougars –eat deer
Snakes – eat mice
Starfish- clams
Birds - insects
Blue whale- krill
Fox- rabbits
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
The predator, Didinium nasutum, a medium sized predatory ciliated protist
(length c. 0.1mm) is preying on the larger ciliated protist.
http://www.des.ucdavis.edu/faculty/holyoak/Colpidium.jpg
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
Predator- Prey Adaptations
Mimicry
• Defense mechanism for prey
• Deception - A harmless
species LOOKS like a harmful,
poisonous or bad tasting
species.
• A predator will avoid BOTH
species
• 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&s
pell=1
2. 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.
Competition Interactions:
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:
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.
Symbiosis
• Is a close, long-term relationship
between 2 organisms.
• 3 categories:
–Parasitism
–Mutualism
–Commensalism
3. Parasitism
Organism that lives on or
in another organism
and feeds on it without
immediately killing it.
Parasites HURT the host
Host- organism that provides
nourishment
Parasite- Organism that
does the feeding
Most populations are negatively
affected- weakened, sickened,
shorten lifespan
Parasitic microorganisms
(roundworm, protozoan,
bacterium,
fungus, yeast)
Parasite examples
4. Mutualism
Cooperative partnership of 2 species
Examples:
** 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. 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 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 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. 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.