1	Community Structure The species living at a place are called a community or species assemblage. The species typically share adaptation to the physical environment. They may have strong interactions with other species as well.
2	READING ASSIGNMENT The Community Structure section is 53.2, p1229 – 1240 including the ‘Let it burn’ essay. Pay special attention to Box 53.1
3	Distribution of abundances Not all species living in a place are equally frequent (or of equal size). Some are abundant Some are rare, maybe seen only once Others are intermediate The most abundant (by biomass) species are often referred to as DOMINANTS.
4	Will communities collapse if species are lost? An individuals is tightly integrated, i.e., our functioning is dependent on all parts being present….. Will species loses change the community? If one is sensitive to change, the answer will be YES, if one takes a broad view (community = forest) then the answer may be NO. Life will occupy the area.
5	Gleason Henry Gleason was a UIUC professor. Gleason studied the sand prairies of Illinois. Gleason’s interpretation that communities are loose assemblages of species (adapted to the environment) is closer to correct, than the notion that species in communities are so mutually dependent that the community will collapse if species are lost.
6	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 climate. After the analogy of a ‘community’ being as integrated as an individual was rejected, the words ‘species assemblage’ has come into vogue.
7	Species Specialists There are species that are specialized to utilize only one or a few other species. Such specialists are tightly connected with their host. Most of the specialists are insects. Tight linkages of two species are called mutualism.
8	Relationships with humans Farm animals and plants have much greater populations than they would have without humans. Human populations are also larger. Weeds have adapted to agriculture practice. Some species favored by humans have not lost their ability to grow in the wild.
9	Events impact communities Flooding, drought, fire and temperature extremes are part of the natural world. The frequency and intensity of these events are called the ‘disturbance regime’. The plants and animals are often adapted to different parts of such regimes, i.e., increase considerably in response to a significant event.
10	Agricultural impacts The clear cutting of a forest and plowing the land for agriculture is a ‘disturbance’ that eliminates most species of a native community. Abandonment of agricultural use results in a pattern of change in which grasses and forbs are replaced by shrubs and later by trees. Succession is the word chosen for the sequence.
11	Succession Substantial amounts of land in the eastern USA that was in agriculture is now in ‘forest’. For tree species, the new forest is often similar to the original forests. For herbaceous plants, the new forest is quite different from the original forest.
12	Succession at the Dunes Dr. Cowles, a UC professor, described succession at the Indiana Dunes. Species that can occupy bare sand are called pioneers. Cottonwood, Populus deltoides, is the local pioneering tree.
13	Measuring BIODIVERSITY For me, the best description of biodiversity is the experience of encountering new species as I wander thru the environment. My experience is dependent on encountering individuals and on my ability to categorize individuals into species.
14	Quantitative Diversity Species Richness (SR) is the number of species detected in a community. Usually the SR number is for a particular group such as plants or birds, not all taxa. Species richness is based on a list of species. In plants, this list is known as the Flora.
15	Species Lists Because natural areas are designed to protect native communities, the Native Species Richness (NSR) is more important information than SR. Conservation value can be associated with the species on lists. Endangered or Threatened Species (E&T). Assigning numerical values to species.
16	Abundance and Biodiversity 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. Descriptions of the plants that include a measure(s) of abundance are called vegetation studies. Vegetation contains quantitative information.
17	Quadrats An area within which the species are inventoried. As the size of the area studied increases the number of species on the list increases. As a ‘rule of thumb’, if one increases the area by a factor of 10, one doubles the species richness.
18	Species Diversity quantitatively measures Biodiversity The species diversity of an area is based on the abundances of the species detected. We will look at two quantitative measures of species diversity, the Simpson Index and the Shannon-Weaver Index. Both are based on the proportional abundance, p_i, of the i^th species. p_i = n_i/N
19	Simpson’s Diversity Index, D D = 1 – Σ p_i² Species diversity equals one minus the sum of the squared individual species frequencies If only one species is detected D = 0, if the most common species has a low p, then D approaches the value 1.
20	Shannon-Weaver Index, H H = -Σp_i•ln(p_i) Species diversity equals minus the sum of proportion of the i^th species times the natural log of that proportion. If only one species is detected H = 0 (ln1 = 0). There is no upper bound to H.
21	DATA for communities X, Y & Z
22	Community X calculations
23	Community Diversity Comparisons Community Simpson’s Shannon- SR Index Weaver X 6 0.69 1.4 Y 4 0.74 1.37 Z 5 0.79 1.58 It is not easy to decide which community is most diverse.
24	Problem Calculate SR, D and H from the following information on the abundances of bird species House sparrow 120 Starling 60 Robin 40 Cardinal 10 Blue jay 10
25	Vocabulary Biodiversity Species diversity, D & H Assemblage Native species richness Abundance Disturbance regime Dominant Quadrat Succession Vegetation Flora