community ecology ap chapter 54 community ecology ap chapter 54
TRANSCRIPT
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