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Species Diversity Biogeography November 7-14, 2007.

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Presentation on theme: "Species Diversity Biogeography November 7-14, 2007."— Presentation transcript:

1 Species Diversity Biogeography November 7-14, 2007

2 Geographical Ecology  Ecological Patterns Species diversity Species diversity Species distributions Species distributions Island patterns Island patterns Community distributions Community distributions  Ecological Processes Competition Coexistence Succession disturbance

3 Species Diversity  Measuring Diversity Scales Scales Richness Richness Diversity Diversity Eveness Eveness  Patterns of Diversity Latitudinal gradients Latitudinal gradients Elevational gradients Elevational gradients Precipitation gradients Precipitation gradients Peninsulas Peninsulas Aquatic environments Aquatic environments  Processes Explaining Diversity Gradients Historical Disturbance Hypothesis Equilibrium Theories Productivity Climate stability Heterogeneity Biotic interaction Area/distance Diversity in TRF Equilibrium theory Janzen’s hypothesis Non-Equilibrium theory

4 Species Diversity: A Non- Concept?  What determines the number and kinds of species that occur in a particular place?  Why do number and kinds of species vary from place to place?

5 How many species are there?

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7 Scales of Diversity  Alpha Diversity w/in habitat w/in habitat  Beta Diversity b/w habitat b/w habitat  Gamma Diversity Total diversity Total diversity

8 Species Woodland habitat Hedgerow Habitat Open field habitat Ax Bx Cx Dx Ex Fxx Gxx Hxx Ixx Jxx Kx Lxx Mx Nx Alpha Diversity Beta Diversity Gamma Diversity

9 Species Woodland habitat Hedgerow Habitat Open field habitat Ax Bx Cx Dx Ex Fxx Gxx Hxx Ixx Jxx Kx Lxx Mx Nx Alpha Diversity 1073 Beta Diversity Gamma Diversity

10 Species Woodland habitat Hedgerow Habitat Open field habitat Ax Bx Cx Dx Ex Fxx Gxx Hxx Ixx Jxx Kx Lxx Mx Nx Alpha Diversity 1073 Beta Diversity (W vs. H) = 7 Gamma Diversity

11 Species Woodland habitat Hedgerow Habitat Open field habitat Ax Bx Cx Dx Ex Fxx Gxx Hxx Ixx Jxx Kx Lxx Mx Nx Alpha Diversity 1073 Beta Diversity (W vs. H) = 7 (H vs. F) = 8 Gamma Diversity

12 Species Woodland habitat Hedgerow Habitat Open field habitat Ax Bx Cx Dx Ex Fxx Gxx Hxx Ixx Jxx Kx Lxx Mx Nx Alpha Diversity 1073 Beta Diversity (W vs. H) = 7 (H vs. F) = 8 (F vs. W) = 13 Gamma Diversity

13 Species Woodland habitat Hedgerow Habitat Open field habitat Ax Bx Cx Dx Ex Fxx Gxx Hxx Ixx Jxx Kx Lxx Mx Nx Alpha Diversity 1073 Beta Diversity (W vs. H) = 7 (H vs. F) = 8 (F vs. W) = 13 Gamma Diversity 14

14 Sampling area and species richness Relationship b/w sampling area and bird species richness in North America (Fig MacDonald)

15 Measuring Diversity  Species Richness Total number of species in an area Total number of species in an area can also be measured as biomass, basal area, % cover can also be measured as biomass, basal area, % cover  Species Diversity Considers eveness and richness Considers eveness and richness  Species Eveness Considers how abundance data are distributed among the species Considers how abundance data are distributed among the species 96 humans, 1 dodo, 1 thylacine, 1 honeycreeper, 1 chuckwalla 96 humans, 1 dodo, 1 thylacine, 1 honeycreeper, 1 chuckwalla 20 peccaries, 20 monkeys, 20 leafcutter ants, 20 wasps, 20 lizards 20 peccaries, 20 monkeys, 20 leafcutter ants, 20 wasps, 20 lizards

16 Measuring Species Diversity  Species Richness The number of species in a given area (N0) The number of species in a given area (N0) Sample Size Issue! Sample Size Issue! Margalef Index Mehinick Index Margalef Index Mehinick Index R1 = S-1/ln(n) R2 = S/√n R1 = S-1/ln(n) R2 = S/√n Where S = total number of species in area sampled n = total number of individuals observed n = total number of individuals observedInterpretation: The higher the index the greater the richness Example: S = 6 and n = 50 S = 6 and n = 20 R1 = 1.28 R1 = 1.66

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19 Measuring Species Diversity  Diversity Indices - Simpson’s Index  Diversity Indices - Simpson’s Index = probability that 2 individuals selected = probability that 2 individuals selected at random will belong to the same species at random will belong to the same species =  i (n i (n i -1))/N(N-1) =  i (n i (n i -1))/N(N-1)Where: n i = total number of individuals in each species N = Total number of individuals in all species Interpretation: If probability is high, the diversity of sample is low If probability is high, the diversity of sample is low

20 Measuring Species Diversity  Diversity Indices - Shannon’s Index H’ H’= -  i ((n i /N) ln (n i /N)) H’= -  i ((n i /N) ln (n i /N))Where: n i = total number of individuals in each species N = Total number of individuals in all species Interpretation: 1.5 (low richness/eveness) to 3.5 (high richness and eveness)

21 Hill’s Family of Diversity Numbers  Units are given in numbers of species NO = total number of species in the sample N1 = the number of abundant species N2 = the number of very abundant species N1 = e H’ (H’=Shannon’s index) N2 = 1/ ( =Simpson’s index)

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23 Measuring Species Diversity  Species Eveness How abundance data are distributed among species 96 humans, 1 dodo, 1 thylacine, 1 honeycreeper, 1 chuckwalla 96 humans, 1 dodo, 1 thylacine, 1 honeycreeper, 1 chuckwalla 20 peccaries, 20 monkeys, 20 leafcutter ants, 20 wasps, 20 lizards 20 peccaries, 20 monkeys, 20 leafcutter ants, 20 wasps, 20 lizards Modified Hill’s Ratio E5 = N2-1/N1-1 Where: N1 = e H’ N2 = 1/ Where: N1 = e H’ N2 = 1/ Interpretation: 0 = less even, 1 = more even 0 = less even, 1 = more even

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25 Desert Lizard Diversity Lizard SpeciesNumber of Individuals Cnemidophorus tesselatus 3 Cnemidophorus tigris15 Crotophytus wislizenii 1 Holbrookia maculata 1 Phrynosoma cornutum10 Scleoporus magister 2 TOTAL Individuals32 Number of individuals for each of 6 species of lizards counted in a 1 hectare plot

26 Desert Lizard Diversity N2 = N1 =R2 = H’ =R1 = E5 = = NO = EvenessDiversityRichness

27 Desert Lizard Diversity N2 = 3 N1 = 4R2 = 1.06 H’ = 1.33R1 = 1.44 E5 = 0.80 = 0.31 NO = 6 EvenessDiversityRichness

28 Patterns of Diversity  Latitudinal Gradients  Elevation Gradients  Precipitation Gradients  Peninsulas  Aquatic Environments

29 Mammals Birds

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37 Processes Explaining Diversity Gradients Historical Disturbance Hypothesis Historical Disturbance Hypothesis - landscape reflects historical events, not current environmental conditions (not in equilibrium) environmental conditions (not in equilibrium) Habitats catastrophically disturbed are “undersaturated” in terms of species because there hasn’t been adequate time for adaptation and speciation Problems: evidence from tropics

38 Extent of tropics during last glacial maximum

39  Equilibrium Theories Landscape is a reflection of current environmental conditions (in equilibrium) Landscape is a reflection of current environmental conditions (in equilibrium) ProductivityProductivity Climate stability-Harsh habitatClimate stability-Harsh habitat Habitat heterogeneityHabitat heterogeneity Biotic interactionsBiotic interactions Large AreaLarge Area Processes Explaining Diversity Gradients

40  Productivity What is the link b/w productivity and biodiversity? What is the link b/w productivity and biodiversity? Tropics 2200 g/m2/yrTropics 2200 g/m2/yr Temperate 1200 g/m2/yrTemperate 1200 g/m2/yr Boreal 800 g/m2/yrBoreal 800 g/m2/yr Scale Scale Estuaries, marshes are most productive ecosystems on earth, with lowest diversityEstuaries, marshes are most productive ecosystems on earth, with lowest diversity Processes Explaining Diversity Gradients

41  Climate Stability (Harsh Habitat) Environments with low stability are harsher and are less diverse Environments with low stability are harsher and are less diverse Why? Why? Exceptions Exceptions Areas with stable climate but low diversityAreas with stable climate but low diversity Processes Explaining Diversity Gradients

42  Habitat Diversity (Heterogeneity) What is the link? What is the link? Is it a direct relationship? Is it a direct relationship? Processes Explaining Diversity Gradients

43  Biotic Interactions Is speciation driven by competition in low lats and adaptation to physical stress in high lats? Is speciation driven by competition in low lats and adaptation to physical stress in high lats? Exceptions: trees/plantsExceptions: trees/plants What about predation as a mechanism? What about predation as a mechanism? Circularity Circularity Processes Explaining Diversity Gradients

44  Large Land Area Supports more individs Supports more individs Supports more species Supports more species Tropics? Boreal? Tropics? Boreal? Processes Explaining Diversity Gradients

45 Diversity in TRF and Coral Reefs  Equilibrium Viewpoint Stability is the major characteristic of a community. Following disturbance, it recovers and high diversity is maintained by a variety of mechanisms. Community reflects current conditions. Stability is the major characteristic of a community. Following disturbance, it recovers and high diversity is maintained by a variety of mechanisms. Community reflects current conditions.  Non-Equilibrium Viewpoint Communities rarely reach an equilibrium state and high diversity results from changing environmental conditions. Communities rarely reach an equilibrium state and high diversity results from changing environmental conditions.

46 Diversity in TRF Janzen’s Hypothesis (1970): Biotic interactions Janzen’s Hypothesis (1970): Biotic interactions - host-specific herbivores - seed predation - canopy foliovores Hubbell’s research (1979, 1980) to support Janzen Hubbell’s research (1979, 1980) to support Janzen Non-equilbrium explanation (Connell 1978) Non-equilbrium explanation (Connell 1978) - coral reefs

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49 The Non-Equilibrium Hypothesis (Connell 1978)  Intermediate Disturbance Hypothesis

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51 The Non-Equilibrium Hypothesis (Connell 1978)  Connell’s Conclusions TRF and Coral Reefs demonstrate Non-Equilibrium Hypothesis TRF and Coral Reefs demonstrate Non-Equilibrium Hypothesis Equilibrium and Non-Equilibrium are not mutually exclusive Equilibrium and Non-Equilibrium are not mutually exclusive Bottom line is: Bottom line is: Role of human disturbances Role of human disturbances

52 More Intermediate Disturbance Hypothesis (Denslow 1980)  Intermediate levels of disturbance vary by ecosystem Ecosyste m Historic Rate of Disturbance (years) Prairie2 Chaparral30 Pine50 Oak-HW Spruce-Fir1000


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