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1
Community Structure and Species Diversity (8-1)
Unit Three
AP Environmental
Ch. 8
Mrs. Dow
2
Keystone species
Mutualism & Coevolution
3
Community Structure
Biological community- Biologists use 3 characteristics to describe a
biological community
1. Physical appearance– Sizes, stratification, distribution– Transition occurs around edges
Species are more vulnerable
4
mft
10
50
20
30100
Tropicalrain forest
Coniferousforest
Deciduousforest
Thornforest
Tall-grassprairie
Short-grassprairie
Desertscrub
Thornscrub
Physical appearance: generalized types, size, and stratification of
plants species in various communities
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2. Species DiversityDef: the variety of species in an area
Two subcomponents: species richness
species evenness
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Species Richness vs. EvennessSpecies Richness: measurement of the number of species in a given area
Species Evenness: measurement of how evenly distributed organisms are among species
Community A
Community B
species 1 25 1species 2 0 1species 3 25 1species 4 25 1species 5 25 96
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Richness (number of species)
Relative abundance
How do we describe these differences?
Comparison of Two Communities
8
Determining Species Diversity
Scientists may want to:
* get an estimate of # of species in an
area
* compare species diversity of two communities
To be accurate, need to:
* take both species evenness and species richness into account
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Species Diversity Indices
Shannon-Weiner (Shannon-Weaver) Index
Diversity =
(p spp 1 - ln(p spp 1)) + (p spp 2 - ln(p spp. 2) + …
(p spp N - ln(p spp. N)
Simpson Index
Diversity = 1 (pspp1)2 + (pspp2)2 + … (psppN)2
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Why should we care about measuring
biodiversity(species diversity)?
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Loss of biodiversity caused by:
Introduction of Habitat Destruction Exotic Species
Human-Caused Factors of Biodiversity Loss
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Biodiversity loss caused by:
Overharvesting/ Pollution Overhunting
Human-Caused Factors of Biodiversity Loss
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There have been 5 mass extinction events
during the history of the earth
Extinction
Are we on the verge of a 6th?
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– 3. Niche structure # of ecological niches, how they resemble each other or
differ from each other, and how they interact. Most species-rich environments
• Rain forest, coral reefs, deep sea, large tropical lakes
High species richness low species evenness
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Factors affecting species diversity
Latitude (distance from equator)– Highest in tropics . . . Declines toward poles
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Biogeographical Changes
Richness declines from equator to pole
Due to:– Evolutionary history– Climate
Fig 53.23 Bird species numbers
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Change in species diversity @ different latitudes
Sp
ecie
s D
iver
sity
200
100
0
90ºN 60 30 0 30ºS 60
Latitude(a) Ants
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Factors affecting species diversity
Pollution (in aquatic regions)
Habitat diversity
Habitat disturbance
NPP (Net Primary Productivity)
Time
Unpolluted
stream
Polluted
streamN
um
ber
of
dia
tom
sp
ecie
s
Number of individuals per diatom species
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Theory of Island biogeographyRobert MacArthur and Edward O. Wilson
1960s
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High
Low
Rat
e o
f im
mig
rati
on
or
exti
nct
ion
Equilibrium number
Immigration and extinction rates
Number of species on island
(a)
© 2004 Brooks/Cole – Thomson Learning
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High
Low
Rat
e o
f im
mig
rati
on
or
exti
nct
ion
Small island
Effect of island size
Number of species on island
(b)
Large island
© 2004 Brooks/Cole – Thomson Learning
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High
Low
Rat
e o
f im
mig
rati
on
or
exti
nct
ion
Far island
Effect of distance from mainland
Number of species on island
(c)
Near island
© 2004 Brooks/Cole – Thomson Learning
Immigration(near island)
Immigration(far island)
Extinction
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Click to view animation.
Animation ( watch on CD)
Area and distance effects interaction.
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Island speciesDetermined by . . . how fast a new species arrives
(immigration)– How fast old species becomes extinct– Size of island (larger more diversity)– Distance from mainland ( closer to mainland the
more diversity)
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Types of Species (8-2)
Native– Those whose original home
is in the ecosystem
Nonnative– Evolved in a different
ecosystem and migrated– Also called invasive or
alien species– Example is Wild African
bees
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Nonnative Species
Nonnative plant species are invading the nation's parks at an alarming rate, displacing native vegetation and threatening the wildlife that depend on them
At some, such as Sleeping Bear Dunes National Lakeshore in Michigan, as much as 23 percent of the ground is covered with alien species, and the rate of expansion is increasing dramatically.
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Indicator species
Why amphibians are declining?
– Habitat loss & fragmentation
– Pollution– Increases in UV radiation– Over hunting– Increase of parasitism– Introduction of
nonnative species
– Alert to environmental changes
– Ex. Birds, amphibians, trout and butterflies (high vulnerability)
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Keystone species– Helps determine the types and numbers of various
other organisms in a community
– Help pollinate or regulate populations– Sea otters in a kelp community– Flying foxes in tropical
forest
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•Foundation speciesFoundation species
–Can shape communities by creating Can shape communities by creating and enhancing habitats that benefit and enhancing habitats that benefit other species other species
–Ex. Elephants uprooting trees & Ex. Elephants uprooting trees & creating openings that promote the creating openings that promote the growth of grasses that benefit growth of grasses that benefit grazing animalsgrazing animals
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Species Interactions: Competition and Predation (8-3)
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Interspecific competition– For food, sunlight, water,
soil, space– One species may
migrate or shift feeding habits or face extinction
– Example-native ants and nonnative fire ants
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Resource partitioning– Evolve more specialized traits
Five species of common insect-eating warblers in the Spruce forests of Maine
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Predators– Use pursuit– Ambush– Camouflage– Chemical warfare (venom)
Prey– Swift movement– Shell– Camouflage– Chemical to poison
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PREDATION
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36
37
38
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Span worm Bombardier beetle
Viceroy butterfly mimicsmonarch butterfly
Foul-tasting monarch butterfly
Poison dart frog When touched, the snake caterpillar changes shape to look like the head of a snake
Some ways prey species avoid their prey
Wandering leaf insect
Hind wings of mothresemble eyes of a much larger animal
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43
44
Parasitism, Mutualism, Commensalism (8-4)
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Parasites– Live on or in another
species– Host is harmed
– Ex. Tapeworms, ticks, fleas, mosquitoes, candiru (vampire fish)
46
Parasites and Parasitoids
Parasites: draw resources from host without killing the host (at least in the short term).
Parasitoids: draw resources from the host and kill them swiftly (though not necessarily consuming them).
47
Mutualism (benefits both species)
– Pollination mutualism (between flowering plants and animals)
– Nutritional mutualism– Lichens grow on trees– Birds/rhinos- nutrition and
protection– Clownfish/sea anemones– Inhabitant mutualism– Vast amount of organisms like
bacteria in an animal’s digestive tract
– Termites and bacteria in gut
48
Obligatory Mutualism
Obligatory: An organism can't live without the mutualism--either cannot survive or cannot reproduce. – the common pollinator systems like
bees and flowering plants– protozoans in the guts of termites– the alga in the lichen partnership
49
Yucca’s only pollinator is the yucca moth. Hence entirely dependent on it for dispersal.
Yucca moth caterpillar’s only food is yucca seeds.
Yucca moth lives in yucca and receives shelter from plant.
Yucca and Yucca Moth
50
Facultative Mutualism
Facultative: This is "take it or leave it" for one or both partners
While the organism benefits when the mutualism is present, it can still survive and reproduce without it– ant mutualisms, such as ants
protecting plants from predation – ants tending aphids
51
Figure 8-10Page 155
Oxpeckers and black rhinoceros Clown fish and sea anemone
Mycorrhizae fungi on juniper seedlings in normal soil
Lack of mycorrhizae fungi on juniper seedlings in sterilized soil
Examples of Mutualism
52
Commensalism– Helps one species
but does nothing for the other
Ex. Redwood sorrel grows in shade of redwood
- Humans and Eyelash Mites
53
Ecological succession: Communities in Transition (8-5)
54
Primary Succession
Glacier Retreat
55
Time
Small herbsand shrubs
Heath mat
Jack pine,black spruce,
and aspen
Balsam fir,paper birch, and
white spruceclimax community
Exposedrocks
Lichensand mosses
Primary Succession
56
57
Time
Annualweeds
Perennialweeds and
grasses
ShrubsYoung pine forest
Mature oak-hickory forest
Secondary Succession
58
Succession = change
– 1. Primary succession Gradual establishment of biotic community on lifeless
ground Barren habitat
– Bare rock / retreating glacier– A newly- cooled lava– A newly formed pond
It takes several centuries to several thousands of years for natural processes to produce fertile soil.
Ex. Hawaii Pioneer species (lichens, moss and microbes)
59
– 2. Secondary successionDevelop in places with existing soil or
bottom (aquatic)Ex. Forest fires, deforestation, abandoned
farmland, heavily polluted streams, dammed or flooded land.
60
Succession of an Aquatic Ecosystem
Aquatic ecosystem gradually increasing in sedimentation/inflow of nutrients from surrounding land areas
Slowly filling w/ silt, sand and other particles; shoreline gradually advances toward the center of the pond;
Aquatic vegetation contributing to this filling In a “classic scenario” the pond would eventually
become a wetland, then perhaps a grassland, followed by some type of forest.
61
Climax community (a.k.a. mature community)– Stable stage– Deemed the balance of nature
62
Factors affecting succession
– 1. Facilitation One species makes an area of suitable for another species Ex. Moss build land for grasses
– 2. Inhibition Early species limit later species Ex. Plants may release toxins
– 3. Tolerance Later species are unaffected by earlier species
63
Disturbance
Event that disrupts an ecosystem or community;
• Natural disturbance
•tree falls, fires, hurricanes, tornadoes, droughts, & floods
• Human–caused disturbance
•deforestation, erosion, overgrazing, plowing, pollution,mining
• Disturbance can initiate primary and/or secondary succession
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Ecological Stability, Complexity, and Sustainability (8-6)
65
Ecological StabilityCarrying Capacity – maximum number of individuals
the environment can support
66
Ecological Stability - Stress
1. Drop in Primary Productivity
2. Increased Nutrient Losses
3. Decline or extinction of indicator species
4. Increased populations of insect pests or disease organisms
5. Decline in Species diversity
6. Presence of Contaminants
67
Inertia or persistence (ability of a system to resist being altered)
Constancy (ability of a system to keeps its #’s within resource limits)
Resilience (ability of a living system to repair damage)
Three aspects of sustainability in living systems
68
Precautionary principle
– “better safe than sorry”– When an ecosystem is deemed threatened,
stop negative affects
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“Ecological stability or sustainability by having different species present”