Transcript Species Abundance & Diversity

AP Environmental Science
Community Interactions, Species Diversity
and Succession
Community Ecology
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Community = an association of interacting
species inhabiting some defined area
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Community structure = includes attributes such
as the number of species and the kinds of
species comprising a community
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Community function = includes attributes such
as energy flow through food webs
Are ecological communities
“real” functional units?
Frederick E. Clements (1874 – 1945)
Holistic community concept (Closed community)
Vegetation Zones
Source: “Biology in the San Juans “ Mountains Studies Institute.. Web 7 November 2011
Closed Communities
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Highly integrated unit
Little interaction with surrounding communities
Distinct observable boundaries called ecotones
Species composition is highly predictable
Species assemblages determined by some
environmental gradient (e.g. temperature, moisture)
Examples:
 Between aquatic and terrestrial areas
 Between distinct soil types
 Between north and south facing slopes
Source: Osbourne, Patrick L. "Chapter 9; Mountains, Zonation, and Community Gradients." Tropical
Ecosystems and Ecological Concepts. Cambridge UP, 2000. 296-97. Print.
Closed Communities
Henry A. Gleason (1882-1975)
Individualistic concept
(Open community)
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The appearance of
communities are simply due to
the individual interactions of
species and don’t reflect any
innate organization above the
species level
Open Communities
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An open community is one in which ‘the populations have
different density peaks and range boundaries and are
distributed more or less randomly.’
Source: Farabee, M. J. "Community and Ecosystem Dynamics." Estrella Mountain Community College. 18 May 2010. Web. 08 Nov. 2011.
<http://www.emc.maricopa.edu/faculty/farabee/biobk/biobookcommecosys.html>.
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Individual species have tolerances for various abiotic
factors
Species exhibit a random distribution based upon these
tolerances.
As ecosystem changes so too will the distribution of
species. If these changes in abiotic factors is abrupt so
too will the changes in species thus the appearance of an
ecotone.
Gradient Analysis of
Vegetation
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Invented by Robert H. Whittaker to analyze
changes in (plant) species abundance along
gradients
Examined the deciduous forests of eastern North America
Gradients are variables that affect plant community structure (i.e
temperature, light & water availability, soil nutrients, etc.)
There were generally two gradients of forest types:
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A north-south gradient based on temperature
An east-west gradient based on moisture
Concluded there were no sharp boundaries between forest types
Source: Whittaker, R. H. "Gradient Analysis of Vegetation." Biological Reviews 42.2 (1967): 207-64. Wiley Online Library.
Web. 8 Nov. 2011. <http://onlinelibrary.wiley.com/doi/10.1111/j.1469-185X.1967.tb01419.x/abstract>.
Open Communities
Factors Affecting Biological
Community Structure
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Species diversity – function of the number of different species that
a community contains (species richness) and the relative
abundance of individuals of each species (species evenness).
Niche structure:
 J.H. Brown (1981) bases this on ‘capacity rules’ (how many
potential ecological niches occur) and ‘allocation rules’ (how
these ecological niches can be divided up among species).
Geographical location
 Consistent climates foster high diversity but ‘specialist species’
 Variable climates foster low diversity but ‘generalist species’
Species Richness
a measure of the
total number of
different species in
a community
Trends?
Species Richness Trends
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Gradual increase in diversity/richness Pole to
Equator
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In a given ecosystem, species richness
increases over time.
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Larger ecosystems tend to have greater
species richness.
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Usually increases with ecological succession.
Why These Trends?
 Productivity?
 Spatial
complexity?
 Spatial
heterogeneity?
 Other
factors?
Species Richness
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Factors that affect species richness
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saturation
rates of colonization and extinction (MacArthur &
Wilson (1967)
• Depend on size of ecosystem and
• Distance from a source of colonists
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disturbance
severity, variability, and predictability (Slobodkin and
Sanders, 1969)
• i.e. rainforests – favorable and constant; therefore
predictable; polluted stream – severe and variable; therefore
unpredictable
Calculating Species Richness
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Generally exclude “accidental species” in the count
Does not take into account abundance patterns
among the various species
Species counts depend on the sample size or
sample area (rarely do you get every one!)
“Equilibrium model of island biogeography”
(MacArthur & Wilson, 1967)
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# of species (species richness) on an “island” is determined
by immigration and emigration of species
Larger islands and islands closer to “mainland” will have
greater species richness.
Equilibrium Model of Island
Biogeography
Species-Area
Curves
• Species-area curve
• S = CAz
• log S = log C + z log A
• An equation for a straight line
where log c = Y intercept and z
= the slope of the line
S
Species
Richness
C
constant
A
Area
z
constant
Species Area Curve
Test Preparation
Which of the following if it occurred in a
particular habitat would most likely lead to
an increase in species richness?
A. Frequent, large scale disturbance
B. Reduction in available niches
C. Removal of a predator
D. Close proximity to another habitat
E. Reduction in the size of the habitat
Diversity Indices
Shannon-Weiner Index
Also known as the “Shannon Index” or
the “Shannon-Weaver Index”
 Based on Information Theory
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Measures the amount of order in a
system in bits of information
 Determines
rarity or commonness of
species
 Combines measure of species
richness with species evenness.
Calculating the
Shannon-Weiner Index
H
= -∑(pi) (ln pi)
H = Shannon-Weiner Diversity Index
 pi = proportion of total sample belonging to
the ith species
 ln pi = the natural log of pi
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An Example
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Community A: 99 individuals in species 1;
1 individual in species 2
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Calculations
“Uneven” community
• H = -[(p1)(ln p1) + (p2)(ln p2)]
• H = -[0.99 (ln 0.99) + 0.01 (ln 0.01)]
• H = -[(-0.0099) + (-0.0461)] = +0.056
Community B: 50 individuals in species 1;
50 individuals in species 2
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“Even” community
• H = -[(0.5) (ln 0.5) + (0.5) (ln 0.5)]
• H = -[(-0.3466) + (-0.3466)] = +0.693
Theory
Comparison of Shannon-Weiner Index Values for Even and
Uneven Communities
3.5000
3.0000
2.5000
H
2.0000
1.5000
1.0000
0.5000
0.0000
0
5
10
15
# of species
H - even community
H- uneven community
20
25
Use of Diversity Indices
Used in applied ecology to measure
differences in diversity between two
or more communities
 Also used to measure changes in
diversity within a community after
some environmental modification or
disturbance
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Robert MacArthur (1930-1972)
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Professor at UPenn &
Princeton
Studied the diversity of
insectivorous warblers in
northeastern forests
Discovered that different
warbler species used
different parts of the
forest canopy
Established the
ecological principle of
resource partitioning
MacArthur’s Warblers
Bird Species Diversity vs.
Foliage Height Diversity
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Also showed that the
greater the Foliage
Height Diversity of
the forest the greater
the Bird Species
Diversity
Ecological Succession
Plant (and animal) communities
develop in often predictable ways
following disturbances, a process
known as succession
 Natural, gradual changes in the types
of species that live in an area
 Classified as primary or secondary
succession
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Indiana Dunes Succcession
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Henry Chandler Cowles
(1869-1939)
American botanist and ecological
pioneer
Ph.D. at University of Chicago
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1898 – published "The ecological
relations of the vegetation of the sand
dunes of Lake Michigan“
Established the idea of succession of
plant species based on distance from
the lake, kind of soil, and geologic time
Primary Succession
General characteristics
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Begins in a place without any soil
 Sides of volcanoes
 Landslides
 Flooding
 Glacial moraine
Starts with the arrival of living things such as
lichens that do not need soil to survive
Lichens (pioneer species) secrete weak acids
which in turn break rocks into soil
Called the Pioneer Stage
Lichens:
Symbiosis of
a fungus &
an alga
Example of a
mutualism
Test Preparation
What organism is most associated with the
pioneer stage of primary succession?
A. lichens
B. grasses
C. trees
D. insects
E. ferns
Primary Succession
General characteristics
Soil starts to form as lichens and the
forces of weather and erosion help break
down rocks into smaller pieces
 When lichens die, they decompose,
adding small amounts of organic matter to
the rock to make soil
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Primary Succession
General characteristics
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Simple plants like mosses and ferns can
grow in the new soil
Primary Succession
General characteristics
The simple plants die, adding more
organic material
 The soil layer thickens, and grasses,
wildflowers, and other plants begin to take
over
 Called Seral Stages
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Primary Succession
General characteristics
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These plants die, and they add more
nutrients to the soil
Shrubs and trees can survive now
Still called Seral Stages
Primary Succession
General characteristics
Insects, small birds,
and mammals have
begun to move in
 What was once bare
rock now supports a
variety of life
 Called a Climax
Community
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Climax Community
A
stable group of plants and animals
that is the end result of the
succession process
 Does not always mean big trees
Grasses in prairies
 Cacti in deserts
 Mosses, sedges and lichens in the tundra
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Test Preparation
What abiotic factor is most responsible for
the climax community in a grassland?
A. temperature
B. precipitation
C. soil pH
D. photoperiod
E. fire
Secondary Succession
 Begins
in a place that already has
soil and was once the home of living
organisms
 Occurs faster and has different
pioneer species than primary
succession
 Example: after forest fires
Intermediate Disturbance
Hypothesis
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J.P. Grime (1973), Henry Horn (1975) and
Joseph Connell (1978)
The Intermediate Disturbance Hypothesis is an
ecological hypothesis which proposes that
biodiversity is highest when disturbance is
neither too rare nor too frequent.
With low disturbance, competitive exclusion by
the dominant species arises.
With high disturbance, only species tolerant of
the stress can persist.
Kinds & qualitative characteristics of
disturbances that impact communities
Disturbance magnitude
Asteroid impact
Volcanism
Glaciation
Landslide
Ice Storm
Hurricane
Fire
Treefall
Disturbance frequency
Role of Disturbance in
Succession