Community
Structure and
Biodiversity
Chapter 46, part 1
Bell Ringer, 9/9
 Come
in and sit down QUIETLY. You can keep
your desks in groups as long as you can do so
quietly.
 What is one question that you wish had been on
the test? Write the question and then answer it.
 What are some ways that organisms interact in the
environment? (‘I don’t know’ is not an acceptable
answer. Brainstorm some ideas!)
Levels of Organization
 Biosphere:
The earth’s surface; where all life
exists
 Ecosystem: The interactions of all living and nonliving things in an area
 Community: The interactions of all living things
in an area
 Population: The members of a species in an area
interacting with one another
 Organism: One individual living thing
Levels of Organization
 Organ
System: Group of organs that interact with
each other
 Organ: Group of tissues interacting with one
another
 Tissue: Group of specialized cells interacting
 Cell: The basic unit of life
Biosphere
Ecosystem
Community
Population
Organism
Organ System
Tissues
Cell
Biosphere
Ecosystem
You are here
Community
Population
Organism
Organ System
Organ
Tissues
Cell
Factors that Shape Community
Structure
 Habitat:
The type of place where a species lives
 Communities have dynamic structures based on:





Climate and topography
Types and amounts of food and other resources
Species’ adaptations
Species’ interactions
Timing and history of disturbances
Bell Ringer, 9/10
 Come
in and find your seat quietly
 Get out your notes
 Answer the following question on your bell ringer:

Pick ONE factor that shapes community structure
and explain how it affects the community.
Factors that Shape Community
Structure
 All
members of a community have the same
“address” but different “professions”
 Niche: A species’ ecological role; includes
conditions, resources, and interactions necessary
for survival and reproduction


Fundamental niche: The niche that an organism can
have
Realized niche: The niche that an organism
ACTUALLY has
Factors that Shape Community
Structure
 Example:
Barnacles
Factors that Shape Community
Structure
 Ex.
Finches
Factors that Shape Community
Structure
 Coevolution:
When two species in close
interaction with one another evolve in response to
one another


Hummingbirds and flowers
Garter snake and rough skinned newt
Factors that Shape Community
Structure

Categories of Species Interactions:





Commensalism: Benefits one species and does not affect
the other (bacteria in your gut; barnacles on a whale)
Mutualism: Benefits both species (ants & acacia tree)
Interspecific competition: Harmful to both species
Predation: Free-living organism kills and eats another
(lion and gazelle)
Parasitism: Live in or on host and usually don’t kill it
(fleas, ticks, mistle toe, tape worms)
Exit Slip, 9/9
 When
will your rewritten notes be checked?
 Compare and contrast predation and parasitism.
Give an example of each.
Bell Ringer, 9/10
your Exit Slips (on 2nd lab table)
 Get your pink paper (on 2nd lab table)
 On your bell ringer paper, answer the following
question:
 Get


Explain the difference between a fundamental niche
and a realized niche. Give an example of each.
Pick ONE factor that shapes community structure
and explain how it affects the community.
Bell Ringer, 9/11
 Get
your FRAYER MODELS from the back and
put them behind your Ch. 47 notes in your binder
 Answer the following questions on your bell
ringer:

A unicorn can survive in warm or cool temperatures.
Their main competition, the magical fairy, thrives in
warm temperatures. Based on this information, what
is the unicorn’s fundamental niche? Realized niche?
Factors that Shape Community
Structure
 Symbiosis:
Species that spend most or all of their
life cycles in close association




Symbiont: A symbiotic species
Endosymbiont: A species that lives inside its partner
Parasitism, mutualism, and commensalism can all be
types of symbiosis
http://www.brainpop.com/science/ecologyandbehavi
or/symbiosis/
Commensalism
 Relationship
in which one species benefits and the
other is not affected



Cattle egrets and livestock
Army ants and birds
Stomach bacteria?
Mutualism
 Interaction
in which both species benefit
 In some mutualisms, neither species can complete
its life cycle without the other

Yucca plants and moths
Mutualism
 Most



mutualistic interactions are not life or death
Plants have more than one pollinator
Nitrogen-fixing bacteria
Lichens
 There

is often some conflict between partners
Lichens: Algae and fungal symbionts
Mutualism
 Some


mutualists defend one another
Clown fish and sea anenomies
Ants and the acica tree
Mutualism
 The



Theory of Endosymbiosis
Mitochondria and chloroplasts were once
independent bacteria engulfed by a bigger cell
Host relied on ATP produced; symbiont relied on
raw materials from the host
Eventually, they became incapable of living
independently
Mutualism
 Evidence




for the Theory of Endosymbiosis
Amoeba experiment by Kwang Jeon (1966)
Resemblance to bacteria in size and structure
Replicates independently of the main cell
Internal membranes resemble those of bacteria
See Ch. 20.4 for more information!
Parasitism
 Parasites
spend all or part of their life living in or
on other organisms


Steal nutrients from the host
Have big impacts on host populations: Disease,
weaken host so it is vulnerable to predation or
unattractive to potential mates, cause sterility, shift
sex ratios of host species, and many more!
Parasitism
 Parasites



usually don’t kill the host right away
Ideally, a host will live long enough to give the
parasite time to reproduce
The longer the host survives, the more offspring are
produced
Host usually only dies from the parasite (not
secondary effects) when:
 It
is overwhelmed with parasites or
 A parasite invades a novel host with no defenses
against it
Parasitism
 Parasites
often lead to secondary effects on the
host

Gradual drain of nutrients leads to the inability to
fight off secondary infections
Parasitism
Roundworms
Mistletoe
Ophiocordyceps unilateralis
Flea
Lymphatic Filariasis
Tapeworm
Bell Ringer, 9/12
 What
evidence have scientists found for the
Theory of Endosymbiosis?
 Why is it beneficial to parasites to keep the host
alive as long as possible?
 Why do some scientists believe that
commensalism does not really exist in nature?
Fish Dating Service
Videos


http://www.youtube.com/watch?v=zTGcS7vJqbs
Mutualism


Ants:



http://www.youtube.com/watch?v=Xm2qdxVVRm4
http://www.youtube.com/watch?v=UozWJTuhbMQ
http://www.youtube.com/watch?v=R3Mt2E1M6dU
Parasites:



http://www.youtube.com/watch?v=i80DvTmLPeE
http://www.youtube.com/watch?v=uvdiYg6ZN-U
http://www.youtube.com/watch?v=xDMzubAvzgg
Bell Ringer, 9/13
 Put
your homework in the tray
 On your bell ringer…


Choose a parasite that you learned about yesterday
and explain its interaction with its host.
List the levels of organization.
Virtual Lab
 http://www.biologycorner.com/worksheets/virtual_
lab_population.html#.UjJ2odJQEud
Bell Ringer, 9/14
 In
Friday’s virtual lab, what happened when the
two paramecium were grown together? Why?
Competitive Interactions
 Competition
among members of the same species
is very intense; leads to evolution by natural
selection


Natural selection: Process of evolution in which
individuals of a population vary in the details of a
heritable trait and reproduce with varying amounts
of success
Evolution: Change in a line of descent
Competitive Interactions
 Interspecific


competition is not usually as intense
Interference competition: One species actively
prevents another from accessing from a resource
Exploitative competition: Species don’t interact
directly; they reduce the amounts of resources
available for the other by using it
Competitive Interactions
Competitive Interactions
 Any
two species differ in their resource
requirements
 Competition is the most fierce when the supply of
a shared resource is the main limiting factor for
both
Competitive Interactions
 G.
Gause (1930) conducted an experiment
involving two species of ciliated protists



Both compete for the same prey (bacteria)
Separately, their growth curves are almost the same
When grown together, one grew slightly faster and
outpaced the other, driving it to extinction
P. caudatum
4
8
12
16
Time (Days)
P. aurelia
Population density
Population density
Competitive Interactions
20
24
4
8
12
16
20
Time (Days)
24
Population density
P. caudatum and P. aurelia
4
8
12
Time (Days)
16
20
24
Competitive Interactions
 This
experiment is the basis of the competitive
exclusion principal


Whenever two species require the same limited
resource to survive or reproduce, the better
competitor will drive the less competitive to
extinction in that habitat
Competitors can only coexist if their resource needs
are not exactly the same
 Example:
Gause’s second protist experiment
Think About It…
 Can
you think of any examples of times this has
occurred in nature?


If yes, describe the situation.
If no, make up a hypothetical situation and explain
it.
Competitive Interactions
 When
two competitor species coexist they
suppress each other’s population growth





Concept shown in experiment by Nelson Hairston
Hairston studied two species of salamanders
In two plots, he removed one of each type of
salamander. In the control plot he left the
populations the same
In plots with one salamander, populations soared
On control plot, populations stayed in check
Competitive Interactions
 When
two species in an ecosystem are similar,
they must find a way to coexist or one will be
driven to extinction
 They do this in two main ways:


Resource partitioning
Character displacement
Competitive Interactions
 Resource



partitioning
Subdividing an essential resource
Reduces the competitions among species that require
it
Ex. Plant roots
Competitive Interactions
 Character


displacement
Over generations a trait of one species diverges to
lower the competition with other species
Natural selection favors individuals that differ most
from the other species
 These
are the individuals that get to survive and
reproduce (the goal of nature)
 These are the traits that are passed on to future
generations
Predator-Prey Interactions
 Predators:
Consumers that get energy and nutrients
from prey
 Prey: Living organisms that predators capture,
kill, and eat
Predator-Prey Interactions
 The
quantity and type of prey species available
affects predator types and vice versa


The extent of this affect depends on how the
predator responds to changes in prey density
Prey density: The population of prey in an area
Predator-Prey Interactions
 There
are three main predator responses to prey
density:




Type I: Depends solely on prey density
Type II: Depends on the predator’s ability to
capture, eat, and digests prey
Type III: Depends on both prey density and the
ability of the predator to capture the prey
Knowing the type of predator response helps
ecologists predict long-term effects of predation on a
prey population
Predatory-Prey Interactions
 Type



I Response
The proportion of prey killed is a constant so the
number killed depends solely on density
Passive and filter-feeding predators
Ex. Spiders, whales, flamingos
Predator-Prey Interactions
 Type




II Response
The number of prey killed depends on the predator’s
ability to capture, eat, and digest it
When prey density increases, kills rise sharply at
first (more prey available)
Eventually kill rate slows (more prey than predator
can handle)
Ex. Wolf and caribou
Predator-Prey Interactions
 Type


III Response
Number of kills increases until prey density exceeds
a certain level, then rises rapidly, then levels off
Common in three situations:
 Predator
switches among prey, concentrating on the
most abundant prey (“prey switching”)
 Predators need to learn how to effectively catch the
prey
 Number of hiding places for the prey is limited
Predator-Prey Interactions
 Sometimes
a predator’s lag in response to changes
in prey density leads to a cyclic change in the
abundance of predators and prey





When prey density is low, predators decline
Prey is safer and density increases
Predators increase
Predation leads to a decrease in prey
The cycle repeats
Predator-Prey Interactions
 Charles
Kreb tracked population densities of the
Canadian lynx and snowshoe hare in Alaska for 10
years



Set up 1 sq. km plots
Used fences to keep predators out of some plots
Put extra food and fertilizers on some plots
Predator-Prey Interactions
 Results



Predator-free plots: Hare density doubled
Plots with extra food: Hare populations doubled
Found that all these precautions delayed the cycle
but did not stop it
 Other
predators flew over the fences
 Some hares starved to death
 These models are WAY more complicated than high
school biology gives them credit for!
Predator-Prey Interactions
 If
a genetic trait helps a species escape predation,
that trait will increase in frequency
 If a genetic trait helps a predator overcome its
prey, that trait will increase in frequency
 Each development requires a counterdevelopment
 This creates a “never ending arms race” for
evolutionary developments (coevolution)
Prey Defense
 There






are a myriad of prey defenses:
Spikes and hard outer parts
Camouflage
Warning coloration
Mimicry
Toxins
Last minute survival tactics
Prey Defense
 Spikes


and hard outer parts
Make the prey much more difficult to eat
Predators abandon prey in pursuit of an easier catch
Prey Defense
 Camouflage


Body shape, color pattern, behavior, or a
combination thereof that makes an individual blend
in with its surroundings
Predators can’t eat prey that they can’t find
Prey Defense
 Warning


coloration
Flashy patterns and colors that predators learn to
recognize as bad tasting or toxic
Predators learn to avoid organisms with that
coloration
Prey Defense
 Mimicry


Evolutionary convergence in body form (species
come to resemble each other)
Batesian mimicry: When one mimic doesn’t have
any undesirable characteristics, but looks like an
organism that does
Prey Defense
 Mimicry

Muellerian: When two species with similar
appearance both have unpalatable characteristics
Prey Defense
 Toxins

Some organisms produce chemicals that make them
unpalatable or toxic if eaten
 Plants

Some organisms use toxins they get from their prey
 Sea
slugs
Prey Defense
 Last




minute survival tactics
When an animal is cornered, there are many “last
minute” defense tactics
Playing dead
“Puffing up”
Spitting venom or unpleasant odors
Adaptive Predator Response
 Predators




must adapt to prey defenses
Stealth
Camouflage
Avoiding repellents
Speed
Adaptive Predator Response
 Stealth

Predator is able to sneak up on prey
Adaptive Predator Response
 Camouflage

Predators blend in with the surroundings and can’t
be seen by prey
Adaptive Predator Response
 Avoiding
 Ability
 Speed
repellants
to “dodge” toxins released by prey