Calculator Policy• A four-function calculator (with square root) is permitted on both the

multiple-choice and free-response sections of the AP Biology Exam since both sections contain questions that require data manipulation. No other types of calculators, including scientific and graphing calculators, are permitted for use on the exam. Four-function calculators have a one line display and a simple layout of numeric keys (e.g., 0–9), arithmetic operation keys (e.g., +, -, ×, and ÷), and a limited number of special-use keys (e.g., %, +/-, C, and AC). Simple memory buttons like MC, M+, M-, and MR may also be included on a four-function calculator. Scientific calculators have a more complicated, multi-row layout that includes various special-use keys, including ones for trigonometric and logarithmic functions such as SIN, COS, TAN, TRIG, LOG, and LN. In contrast to scientific calculators, four-function calculators do not include trigonometric and logarithmic functions, statistical capabilities, or graphing capabilities. Students may bring up to two four-function calculators (with square root) to the exam.

What is a community?

• A biological community is an assemblage of populations of various species living close enough for potential interaction

What are the types of interactions?

• relationships between species in a community interspecific interactions

• Examples are competition, predation, herbivory, and symbiosis (parasitism, mutualism, and commensalism)

• Interspecific interactions can affect the survival and reproduction of each species, and the effects can be summarized as positive (+), negative (–), or no effect (0)

Competition

• Interspecific competition (–/– interaction) occurs when species compete for a resource in short supply

• Strong competition can lead to competitive exclusion, local elimination of a competing species

• The Gause competitive exclusion principle states that two species competing for the same limiting resources cannot coexist in the same place

Ecological Niches

• The total of a species’ use of biotic and abiotic resources is called the species’ ecological niche

• An ecological niche can also be thought of as an organism’s ecological role

• It is the functional position of an organism in its environment, comprising its habitat and the resources it obtains, periods of time it is active, etc.

Adaptations forLocomotionBiorhythmsTolerance

Predator avoidanceReproduction

feeding

Physical conditionsSubstrateHumiditySunlightTemperatureSalinitypHExposureAttitudedepth

Resources offered by the habitatFood

ShelterMating sitesNesting sites

Predator avoidance

Otherorganisms

• Ecologically similar species can coexist in a community if there are one or more significant differences in their niches

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

Fig. 54-2

A. ricordii

A. insolitus usually percheson shady branches.

A. distichus perches on fenceposts and other sunny surfaces.

A. aliniger

A. distichus

A. insolitus

A. christophei

A. cybotes

A. etheridgei

• The full range of environmental conditions under which an organism can exist is its fundamental niche.

• Due to interactions and evironmental pressures, organisms are usually forced to occupy a niche that is narrower than this…their realized niche.

Fig. 54-3

Ocean

Chthamalus

Balanus

EXPERIMENT

RESULTS

High tide

Low tide

Chthamalusrealized niche

Balanusrealized niche

High tide

Chthamalusfundamental niche

Low tideOcean

• Question: Two species of Anolis lizards are often found perched and feeding in the same trees, with species I in the upper and outer branches, and species II occupying the shady inner branches. After removing one or the other species in test trees, an ecologist observes the following results: Species I is found throughout the branches of trees in which it is now the sole occupant. Species II is still found only in the shady interior when it is the sole occupant. What do these results indicate about the niches of these two species?

Species I

Species II

The realized niche of Species I is smaller than its fundamental niche when it is in competition with SpeciesII.

Species II’s fundamental andRealized niche are the same.

Predation

• Predation (+/– interaction) refers to interaction where one species, the predator, kills and eats the other, the prey

• Some feeding adaptations of predators are claws, teeth, fangs, stingers, and poison

• Prey display various defensive adaptations - hiding, fleeing, forming herds or schools, self-defense, coloration patterns, mimicry, and alarm calls

Coloration Patterns and Mimicry

Herbivory

• Herbivory (+/– interaction) refers to an interaction in which an herbivore eats parts of a plant or alga

• It has led to evolution of plant mechanical and chemical defenses and adaptations by herbivores

Fig. 54-6

A manatee is feeding on water hyacinth, an introduced species, in Florida.

Symbiosis

• Symbiosis is a relationship where two or more species live in direct and intimate contact with one another

• parasitism (+/– interaction)• mutualism (+/+ interaction), is an interspecific

interaction that benefits both species A mutualism can be

– Obligate, where one species cannot survive without the other

– Facultative, where both species can survive alone

• commensalism (+/0 interaction)

Fig. 54-7

(a) Acacia tree and ants (genus Pseudomyrmex)

(b) Area cleared by ants at the base of an acacia tree

The tree and the ant are locked into relationship where the survival of both partners depends on the other. The ants provide the Acacia with protection from herbivores and from competing plants, while the tree provides the ants with food and shelter. Facultative mutualism

Clownfish and Sea Anemones

FacultativeMutualism

Fig. 54-8

FacultativeMutualism

Parasitism

Commensalism – epiphytes

protists in termite guts

ObligateMutualism

• In general, a few species in a community exert strong control on that community’s structure

• Two fundamental features of community structure are species diversity and feeding relationships

Species Diversity

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

• It has two components: species richness and relative abundance

• 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

Fig. 54-9

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

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

A B C D

Two communities can have the same species richness but a different relative abundance

Trophic Structure

• Trophic structure is the feeding relationships between organisms in a community

• It is a key factor in community dynamics• Food chains link trophic levels from

producers to top carnivores

Fig. 54-11

Carnivore

Carnivore

Carnivore

Herbivore

Plant

A terrestrial food chain

Quaternaryconsumers

Tertiaryconsumers

Secondaryconsumers

Primaryconsumers

Primaryproducers

A marine food chain

Phytoplankton

Zooplankton

Carnivore

Carnivore

Carnivore

Fig. 54-12

Humans

Smallertoothedwhales

Baleenwhales

Spermwhales

Elephantseals

Leopardseals

Crab-eaterseals

Birds Fishes Squids

Carnivorousplankton

CopepodsEuphausids(krill)

Phyto-plankton

A food web is a

branching food chain

with complex trophic

interactions

Limits on Food Chain Length

• Two hypotheses attempt to explain food chain length:

• The energetic hypothesis suggests that length is limited by inefficient energy transfer

• The dynamic stability hypothesis proposes that long food chains are less stable than short ones

• Most data support the energetic hypothesis

Experimental data from the tree hole communities showed that food chains were longest when food supply (leaf litter) was greatest. Which hypothesis about what ali its food chain length do these results suggest?

energetic

Fig. 54-14

Productivity

Nu

mb

er o

f tr

op

hic

lin

ks

0

1

2

3

4

5

High (control):natural rate of

litter fall

Medium: 1/10

natural rateLow: 1/100

natural rate

Species with a Large Impact

• Certain species have a very large impact on community structure

• Such species are highly abundant or play a pivotal role in community dynamics

• Dominant species are those that are most abundant or have the highest biomass (the total mass of all individuals in a population)

Why are they dominant?

• One hypothesis suggests that dominant species are most competitive in exploiting resources

• Another hypothesis is that they are most successful at avoiding predators

Invasive Species

• Species typically introduced to a new environment by humans, often lack predators or disease

Kudzu • Kudzu is a vine which was brought to North America from

Asia in 1876 to help prevent soil erosion, which has since become an utter nuisance in some areas of the country. It can grow up to 6.5 feet a week and its roots are nearly impossible to eradicate entirely.

Other examples• Dutch Elm Disease – caused by a fungus

and accidentally spread into the United States.

• Potato Blight – caused by a fungus that caused the Great Potato Famine in Ireland in the 1840’s. Spores have been carried all over the world.

• Small Pox – spread of virus from Asia to all over the world. Dutch Elm Disease

• Dutch elm disease (DED) is caused by a member of the sac fungi (Ascomycota) affecting elm trees, and is spread by the elm bark beetle. Although believed to be originally native to Asia, the disease has been accidentally introduced into America and Europe, where it has devastated native populations of elms which had not had the opportunity to evolve resistance to the disease. The name "Dutch elm disease" refers to its identification in 1921 in the Netherlands by Dutch phytopathologists.

Potato Blight caused by a fungus.

Smallpox caused by a virus.

Keystone Species

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

• In contrast to dominant species, they are not necessarily abundant in a community

Fig. 54-15

With Pisaster (control)

Without Pisaster (experimental)

Nu

mb

er

of

sp

ec

ies

pre

se

nt

Year

20

15

10

5

01963 ’64 ’65 ’66 ’67 ’68 ’69 ’70 ’71 ’72 ’73

RESULTS

EXPERIMENT

Field studies of sea stars exhibit their role as a keystone species in intertidal communities

They keep the number of mussels controlled thatoutcompete other species.

Fig. 54-16

(a) Sea otter abundanceO

tte

r n

um

ber

(% m

ax.

co

un

t)

100

80

60

40

20

0

400

300

200

100

0(b) Sea urchin biomass

Gra

ms

per

0.25

m2

1086420

1972

Nu

mb

er p

er0.

25 m

2

1985 1997Year

(c) Total kelp densityFood chain

1989 1993

Observation of sea otter populations and their predation shows how otters affect ocean communities

Keystone species

After orcas entered thefood chain and preyed on the otters, notice thechange in thesea urchins andkelp.

This resulted in a loss of kelp forests.

Ecological Succession

• Ecological succession is 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

Successive species can

• Inhibit growth of new organisms

sphagnum moss making boggy areas

in poorly drained sites

• Promote growth of new organisms

Dryas and Alder trees raising N content

• Tolerate conditions that resulted from former species

Fig. 54-22-4

Pioneer stage, withfireweed dominant

1

1941

1907

1860

1760

Alaska

GlacierBay

Kilometers5 10 150

Dryas stage2

Alder stage3Spruce stage4

Succession on the moraines in Glacier Bay, Alaska, follows a predictable pattern of change in vegetation and soil characteristics

Succession at Mt. St. Helen’s in 1980

• Pioneer stage – first species

• Climax or dominant species – stable, typically most biomass species

Mosses - pioneers Hardwood Forests - dominant

Fig. 54-23

Successional stagePioneer Dryas Alder Spruce

So

il n

itro

gen

(g

/m2 )

0

10

20

30

40

50

60

Succession is the result of changes induced by the vegetation itself.On the glacial moraines, vegetation lowers the soil pH and increases soil nitrogen content.

Dune Succession

Primary Succession

Pond Succession

Secondary succession

Human Disturbance

• Humans have the greatest impact on biological communities worldwide!

• Human disturbance to communities usually reduces species diversity

• Humans also prevent some naturally occurring disturbances, which can be important to community structure

Fig. 54-24

Resultsfrom trawling.

Biogeographic factors affect community biodiversity

• Latitude and area are two key factors that affect a community’s species diversity

- generally declines along an equatorial-polar gradient and is especially great in the tropics

- two key factors are evolutionary history and climate

• The greater age of tropical environments may account for the greater species richness – more growing time so more chance for evolutionary changes

Area Effects

• The species-area curve quantifies the idea that, all other factors being equal, a larger geographic area has more species

• A species-area curve of North American breeding birds supports this idea

Fig. 54-26

Area (hectares)

Nu

mb

er o

f sp

ecie

s1,000

100

10

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

Island Equilibrium Model

• Species richness on islands depends on island size, distance from the mainland, immigration, and extinction

The number of species found on an island can be determined by a balance between the immigration rate (or the movement of species onto the island from other islands) and the extinction rate (or the rate at which species already on the island become nonexistent). 

Immigration and extinction rates are affected by the size of the island and its distance from a non-island source of immigrant species

Effect of Island Size

A larger island has higher species diversity for two reasons: it is a larger target, giving it a greater probability of becoming the home to immigrants, and it has a larger supply of resources necessary to prevent extinctions. 

Effect of Island Distance

• An island's distance from a mainland source of new immigrants, despite its size, is an important factor in species diversity. Even if two islands are the exact same size and all other factors are constant, the island closest to the mainland is more likely to attract a larger number of immigrant species due to its proximity and convenience

Fig. 54-28

Area of island (hectares)(log scale)

Nu

mb

er o

f p

lan

t sp

ecie

s (l

og

sca

le)

10 100 103 104 105 106

10

25

50

100

200

400

5

Studies of species richness on the Galápagos Islands support the prediction that species richness increases with island size

Community ecology is useful for understanding pathogen life cycles and

controlling human disease

• Ecological communities are universally affected by pathogens, which include disease-causing microorganisms, viruses, viroids (viral DNA), and prions (proteins)

Pathogens can alter community structure quickly and extensively

For example, coral reef communities are being decimated by white-band disease

• Human activities are transporting pathogens around the world at unprecedented rates

• Community ecology is needed to help study and combat them

• Zoonotic pathogens have been transferred from other animals to humans

• The transfer of pathogens can be direct or through an intermediate species called a vector

• Many of today’s emerging human diseases are zoonotic SWINE FLU!

Fig. 54-30Avian flu is a highly contagious virus of birdsEcologists are studying the potential spread of the virus from Asia to North America through migrating birds