Exam 3 #09
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UIC BioS 101 Nyberg
Community Structure
The species living at a place are called a community or species assemblage. All species typically share adaptations to the climate. They may have strong, weak or no interaction with other species.
Speaker Notes:
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Do ecological communities have parallels with human communities?
Exam 3#09
UIC BioS 101 Nyberg
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READING ASSIGNMENT
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The Community Structure section is 53.2, p1209 – 1221.
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Pay special attention to Box 53.1
Speaker Notes:
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Exam 3 #09
UIC BioS 101 Nyberg
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Distribution of abundances
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Not all species living in a place are equally frequent (or of equal size).
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Some are abundant
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Some are rare, maybe seen only once
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Others have intermediate abundances
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The most abundant (by biomass) species are often referred to as community DOMINANTS.
Speaker Notes:
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Typically only a few species add up to over 50% of biomass.
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UIC BioS 101 Nyberg
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Will communities become different, if species composition changes?
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Individuals are integrated, i.e., function pretty much requires all parts being present, but function does not disappear if parts are lost.
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Will species loses change a community? How do you decide if the community is different? Life goes on.
Speaker Notes:
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We can lose limbs and some of our organs and still function so perhaps individuals are not as integrated as commonly thought.
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UIC BioS 101 Nyberg
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Gleason
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Henry Gleason was a UIUC professor.
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Gleason studied the sand prairies of Illinois.
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Gleason’s interpretation that communities are loose assemblages of species (adapted to the environment) is closer to correct, than the notion that all species in communities are so mutually dependent that the community will collapse if species are lost.
Speaker Notes:
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Pairs or even larger sets of species may be tightly connected.
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UIC BioS 101 Nyberg
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If each species has a preferred range of abiotic variables, then we expect to find similar sets of species in places that have a similar abiotic environment. After the analogy of a ‘community’ being as integrated as an individual was rejected, the words ‘species assemblage’ has come into vogue.
Speaker Notes:
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Many plants that have lived in northeastern IL in last 10,000 years are no longer in this area. Nature is always changing.
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UIC BioS 101 Nyberg
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Species Specialists
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There are species that are specialized to utilize only one or a few other species.
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Such specialists are dependent on the success of their host.
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Many of the specialists are insects.
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If the two species are both dependent on each other, their relationship is called mutualism.
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Speaker Notes:
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Exam 3 #09
UIC BioS 101 Nyberg
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Relationships with humans
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Domestic animals and plants have much greater populations than they would have without humans.
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Human populations are also larger.
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Some (most?) domesticated species have lost their ability to grow in the wild.
Speaker Notes:
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Humans and their domestic plants and animals have a mutualistic relationship.
Exam 3 #09
UIC BioS 101 Nyberg
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Events impact communities
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Flooding, drought, fire and temperature extremes are part of the natural world.
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The frequency and intensity of these events are called the ‘disturbance regime’.
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Events and actions of humans harm some species and benefit others.
Speaker Notes:
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Dams on the Colorado river have ‘disturbed’ the normal course of events and made it tough for some species that were adapted to the disturbance.
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UIC BioS 101 Nyberg
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Agricultural impacts
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The plowing the land for agriculture is a ‘disturbance’ that eliminates perennial native species of the community and uses the space for annuals (row crops).
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Abandonment of agricultural use of land results in replacement of annuals by perennial grasses and forbs, followed by trees, if moisture is adequate.
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Succession is the word chosen for the sequence.
Speaker Notes:
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Much of the eastern USA that was original woods that were cleared for agriculture has again become woods.
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UIC BioS 101 Nyberg
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Succession
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Substantial amounts of land in the eastern USA that was in agriculture is now in ‘forest’.
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For tree species, the new ‘forest’ is often similar to the original forests.
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For herbaceous plants, the new ‘forest’ is quite different from the original forest.
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‘Climax’ community is being abandoned.
Speaker Notes:
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Planting of trees is often encouraged by government programs.
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UIC BioS 101 Nyberg
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Succession at the Dunes
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Dr. Cowles, a UC professor, described succession at the .
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Species that can occupy bare sand are called pioneers.
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Cottonwood, Populus deltoides, is the local pioneering tree.
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Melting of glaciers provides an opportunity to study succession.
Speaker Notes:
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Bare sand is often colonized underground.
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UIC BioS 101 Nyberg
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Measuring BIODIVERSITY
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For me, the best description of biodiversity is the experience of encountering new species as I wander thru the environment.
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My experience is dependent on encountering individuals and on my ability to categorize individuals into species.
Speaker Notes:
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Even if you move less than 50 miles you have the potential to encounter new species (enter the range of a species).
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UIC BioS 101 Nyberg
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Quantitative Diversity
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Species Richness (SR) is the number of species detected in a community.
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Usually the SR number is for a particular group such as plants or birds, not all taxa.
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A list of species is the basic data from which species richness is calculated.
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In plants, this list is known as the Flora.
Speaker Notes:
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Go to the Woodworth Website and look at a couple of lists.
Ask the question how do we compare two places.
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UIC BioS 101 Nyberg
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Species Lists
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Because natural areas are designed to protect native communities, the Native Species Richness (NSR) is more important information than SR.
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Conservation value can be associated with specific species on species lists.
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Endangered or Threatened Species (E&T).
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Assigning numerical values to species.
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Speaker Notes:
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Both the Federal government and the state of Illinois have lists of endangered and threatened species.
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UIC BioS 101 Nyberg
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Abundance and Biodiversity
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The flora is a list of plant species encountered in an area. All species regardless of abundance are on the list. Rare ones are more likely to be missed.
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Descriptions of the plants that include a measure(s) of abundance are called vegetation studies.
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Vegetation contains quantitative information.
Speaker Notes:
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Many measures of biodiversity require information on abundance or frequency of occurrence.
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UIC BioS 101 Nyberg
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Quadrats
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An area within which the species are inventoried is called a quadrat (or plot).
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As the size of the area studied increases the number of species on the list increases.
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As a ‘rule of thumb’, if one increases the area by a factor of 10, one doubles SR.
Speaker Notes:
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Curves can be made of the number of species detected versus the area studied.
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UIC BioS 101 Nyberg
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Species Diversity quantitatively measures Biodiversity
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The species diversity of an area is based on the abundances of the species detected.
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We will look at two quantitative measures of species diversity, the Simpson Index and the Shannon-Weaver Index.
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Both are based on the proportional abundance, pi, of the ith species. pi = ni/N
Speaker Notes:
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The pi values range from 0 to 1 and sum to 1. N = sum of all individual abundance, ni
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UIC BioS 101 Nyberg
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Simpson’s Diversity Index, D
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D = 1 – Σ pi2
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Species diversity, D, equals one minus the sum of the squared individual species frequencies.
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If only one species is detected D = 0, if the most common species has a low p, then D approaches the value 1.
Speaker Notes:
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A variant of the Index uses 1/ Σ pi2 as the measure of diversity. This has the advantage of generating large values when there are a lot of evenly distributed species.
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UIC BioS 101 Nyberg
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Shannon-Weaver Index, H
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H = -Σpi•ln(pi)
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Species diversity equals minus the sum of proportion of the ith species times the natural log of that proportion.
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If only one species is detected H = 0 (ln1 = 0). There is no upper bound to H.
Speaker Notes:
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Shannon was an inventor of the computer. Even with a lot of species this index doesn’t get very large.
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UIC BioS 101 Nyberg
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DATA for communities T, Y & Z
SR = 6
N = 20
SR = 4
N = 10
SR = 5
N = 15
T
Y
Z
Speaker Notes:
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Each color/shape represents a species.
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UIC BioS 101 Nyberg
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Community T calculations
Speaker Notes:
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Try these calculations on your own spread sheet.
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UIC BioS 101 Nyberg
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Community Diversity Comparisons
Community Simpson’s Shannon-
SR Index Weaver
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T 6 0.69 1.4
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Y 4 0.74 1.37
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Z 5 0.79 1.58
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It is not easy to decide which community is most diverse.
Speaker Notes:
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Different indexes can yield different orders of the community diversity.
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UIC BioS 101 Nyberg
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Problem
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Calculate SR, D and H from the following information on the abundances of bird species
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House sparrow 120
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Starling 60
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Robin 40
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Cardinal 10
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Blue jay 10
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Speaker Notes:
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UIC BioS 101 Nyberg
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Vocabulary
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Biodiversity
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Species diversity, D & H
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Assemblage
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Native species richness
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Abundance
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Disturbance regime
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Dominant
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Quadrat
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Succession
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Vegetation
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Flora
Speaker Notes:
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