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Succession Objectives: • Observe different stages of succession • Learn to use the Jaccard’s coefficient, Sorensen’s coefficient and Morisita’s index to quantify community similarity. Introduction Succession is the directional change in species composition and community structure of an area over time. While most people think first of succession in plant communities, associated animal communities also undergo succession. Consider the colonization of bare rock substrates by algae, mollusks, and anemones in marine intertidal zones (e.g., Sousa 1979), or development of invertebrate communities in flash flood stream environments (e.g., Fisher et al. 1982). As plant communities undergo primary or secondary succession, the associated animal communities (e.g., pollinators, seed disperser, herbivores) respond to the changing habitat. Not only do the living organisms undergo a change in structure and composition over time, but the abiotic conditions such as soil chemistry and composition are also transformed (e.g., soil development following glaciation; Chapin et al. 1994). Ecologists have long investigated the process of community and ecosystem change over time, but the long term nature of succession make it particularly difficult to understand. Henry Cowles (1899) and Frederic Clements (1916) set the stage for the current theories of the mechanisms of succession. Connell and Slatyre (1977), Grime (1979), and Tilman (1988) have advanced the investigations of succession into organismal interactions and their effects on the ecosystem. The study of succession requires consideration of both qualitative and quantitative factors. As succession progresses through its seral stages, or different stages, community composition and predominance shift through time and space. The structure of the community usually becomes more complex, which can be difficult to measure quantitatively. Factors more easily compared between seral stages include changes in density, coverage, frequency, biomass, and productivity of the biotic environment (i.e. plants and animals) (Brower et al. 1998). For example, the relative density (RDi) of a species (i) provides an indication of the predominance in numbers for a species: RDi = Di ÷ Σ D Where: Di = density (number of individuals per unit area) for species i ΣD = sum of densities for all species The relative density for a number of common species could be compared across seral stages to determine when major species composition shifts occur. In this case, relative density would be plotted against seral stage on the x – axis. Other measures, such as relative coverage or frequency, may also be plotted in a similar manner. Coverage by individual species is often grouped using Daubenmire’s cover class system (Barbour et al. 1999). Cover Class 1 2 3 4 5 6 Range of Cover (%) 0-­‐5 5-­‐25 25-­‐50 50-­‐75 75-­‐95 95-­‐100 Median Coverage (%) 2.5 15.0 37.5 62.5 85.0 97.5 Note: The total coverage of your plot may exceed 100% due to vertical stratification of canopies. Easily quantified measures may provide a more satisfying comparison of community similarity. For example, coefficients of community similarity focus on the species composition in common between two communities, and thus neglect the abundance of each species. Two such coefficients are the Jaccard (CCJ) and Sørensen (CCS) coefficients (Brower et al. 1998): Jaccard coef. Sørensen coef. CCJ = c ÷ S CCS = 2c ÷ (s1+ s2) Where: c = number o species in common to both communities S = cumulative number of species S1 and s2 = numbers of species in communities 1 and 2, respectively Example: Assume that one forest community contains white oak, red maple, sugar maple, red oak, and American beech, while another forest community contains silver maple, red maple, white oak, and white ash. Community one contains 5 species (s1), community two contains 4 species (s2), the cumulative number of species (S) is 7, and the number of species in common (c) is 2. The Jaccard coefficient would be 2 ÷ 7, or 0.29, and the Sørensen (CCS) coefficient would be 4 ÷ 9, or 0.44. One index of community similarity that takes into account abundance of organism is Morisita’s index. This index is affected little by the sizes and diversities of the samples and uses Simpson’s index of dominance to estimate the probability that individuals randomly drawn from each of the two communities will belong to the same species relative to the probability of randomly selecting a pair of individuals of the same species from one of the communities (Brower et al. 1998). First, Simpson’s index of dominance (l) is calculated for each community, and then Morisita’s index of community similarity (IM) is calculates as follows (Brower et al. 1998). Simpson’s index Morisita’s index l = [Σ (xi)(xi – 10)] ÷ (N)(N – 1) IM = [(2)(Σ (xi)(yi)] ÷ [(l1 + l2)(N1)(N2)] Where: xi = number of individuals in species i in community 1 N = number of individuals in the community yi = number of individuals in species I in community 2 l1 and l2 = Simpson’s index for communities 1 and 2, respectively For our lab activity when comparing sere 1 vs. sere 2, the Morisita’s index is as follows: IM = [(2)(Σ {(goldenrod in sere 1)(goldenrod in sere 2)+(teasel in sere 1)(teasel in sere 2)+(aster in sere 1)(aster in sere 2)+…}] ÷ [(l1 + l2)(N1)(N2)] The Jaccard’s and Sørensen’s Coefficients, as well as the Morisita’s index, range from 0 (no similarity) to 1 (very similar). Simpson’s index also ranges from 0 (every individual belongs to a different species) to (community contains one species). Simpson’s index shows the probability of getting the same species on a random grab of individuals within the community, thus a higher index value implies a lower evenness of distribution of individuals amongst species. Literature Cited Barbour, M.G., J.H. Burk, W.D. Pitts, F.S. Gilliam, and M.W. Schwartz. 1999. Terrestrial Plant Ecology, 3rd Edition. Benjamin/Cummings, Menlo Park, California, USA. Brower, J.E., J.H. Zar, and C.N. von Ende. 1990. Field and Laboratory Methods for General Ecology, 3rd Edition. Wm. C. Brown Publishers, Dubuque, Iowa, USA. Chapin, F.S. III, L.R. Walker, C.L. Fastie, and L.C. Sharman. 1994. Mechanisms of primary succession following deglaciation at Glacier Bay, Alaska. Ecological Monographs 64: 149 – 175. Connell, J. H. and R.O. Slayer. 1977. Mechanisms of succession in natural communities and their role in community stability and organization. American Naturalist 111: 1119 – 1144. Cowles, H.C. 1899. The ecological relations of the vegetaion on the sand dunes of Lake Michigan. The Botanical Gazette 27: 95-­‐117, 167-­‐202, 281-­‐ 308, 361 – 391. Fisher, S.G., L.J. Gray, N.B. Grimm and D.E. Bush. 1982. Temporal succession in a desert stream ecosystem following a flash flood. Ecological Monographs 52; 93 -­‐110. Grime, J.P. 1979. Plant Strategies and Vegetation Processes. Wiley, New York, NY, USA. Sousa, W. P. 1979. Experiment investigations of disturbance and ecological succession in a rocky intertidal algae community. Ecological Monographs 49: 227-­‐254. Tilman, D. 1988. Plant Strategies and the Structure and Dynamics of Plant Communities. Princeton University Press, Princeton, New Jersey, USA. ACTIVITY You will work in groups to try to detect a successional pattern on Hogback Conservation area, which as three stages (or seres), i.e. 3 sections that have been left alone for different lengths of time. You will start in stage 1, the youngest, and find a 5 x 5 meter plot. Once your plot is delimited, identify every species on this plot and count the number of individual plants for each species (do not consider moss or grass). Once you are done with this stage, repeat the same procedure for stage 2 and then for stage 3. Once each group is done, calculate coefficients and indices to compare the three seres. Since you have data for 3 different seres, you have 3 comparisons to make: • Sere 1 vs. Sere 2 • Sere 2 vs. Sere 3 • Sere 1 vs. Sere 3 For each of thse comparisons, you have 4 different valuses to calculate: Jaccard’s and Sorensen’s coefficients, as well as the Simpson’s index of dominance and the Morsita’s index of similarity. Use the sample calculations example on the following page to help you. Once you have obtained all those vales (a total of 12 or 3 x 4), discuss the meaning of those values and what they tell you about the three seres. What can you conclude? Which seres are the most similar/ the most different? Does it correspond to what you would have predicted? Turn in 1 copy of your calculations and a summary of your conclusions at the end of lab. Sample Succession Calculations The following data is from two adjacent plant communities in northern Michigan. What can you say about the diversity and similarity of these two communities? Number in Comm. 1 Number in Comm. 2 Comm. 1 (xi)(xi-­1) Comm. 2 (yi)(yi-­1) Species (xi) (yi) Juneberry 31 930 15 210 White Pine 78 6006 0 0 Scots Pine 0 0 4 12 White Poplar 0 0 7 42 Black Cherry 15 210 0 0 White Oak 35 1190 0 0 Red Oak 177 31152 68 45556 Black Locust 0 0 2 2 SUM = Nx = 336 39488 Ny = 96 4822 Jaccard’s coefficient: CCJ = c/S = 2/8 = 0.125 Sørensen coefficient: CCS = 2c ÷ (s1+ s2) = (2)(2)/(5+5) = 0.4 Simpson’s indices: lx = [Σ (xi)(xi – 10)] ÷ (Nx)(Nx– 1) = (39488) / [(336)(335)] = 0.3508 ly = [Σ (xi)(xi – 10)] ÷ (Ny)(Ny – 1) = (4822) / [(96)(95)] = 0.5287 Morisita’s index: IM = [(2)(Σ (xi)(yi)] ÷ [(lx + ly)(Nx)(Ny)] = [(2)((31)(15)+(78)(0)+(0)(4)+(0)(7)+(15)(0)+(35)(0)+(177)(68)+(0)(2))] / [(0.3508 + 0.5287)(336)(96)] = 0.8813 Comm. 1 and Comm. 2 have equal species richness (5 vs. 5) while Comm. 1 is more divers based on Simpson’s index of dominance (0.3508 vs. 0.5287) than Comm. 2. The Jaccard’s (0.125) and Sørensen’s (0.4) coefficients suggest that the two communities are not very similar. Morisita’s index takes into account species dominance in both communities and shows that the probability of randomly grabbing two individuals from the same species in the two communities relative to the probability of grabbing two individuals from the same species in one of the communities is quite high (0.8813). These indices suggest that the communities share dominant species but not the less common species. Sere 1 (Early Successional Stage) Species (with Description if necessary) # of individuals (xi) (xi)(xi – 1) Total # of Species = _________________(si) Total # of Individuals ____________ (Ni) Total = _________________ Sere 2 (Intermediate Successional Stage) Species (with Description if necessary) # of individuals (xi) (xi)(xi – 1) Total # of Species = _________________(si) Total # of Individuals ____________ (Ni) Total = _________________ Sere 3 (Late Successional Stage) Species (with Description if necessary) # of individuals (xi) (xi)(xi – 1) Total # of Species = _________________(si) Total # of Individuals ____________ (Ni) Total = _________________