1. Species Diversity

2. What do we mean by diversity? 1.Species Richness Count Species/area Species/number 2. Heterogeneity = Richness + evenness 3. Scales of diversity Alpha Beta Gamma

5. Measures of diversity sensitive to both richness and evenness Simpson’s Index D = 1/Σ p i 2 Shannon Index H’ = - Σ( p i log p i ) or exp(H’)

6. What do we mean by diversity? 1.Species Richness Count Species/area Species/number 2. Heterogeneity = Richness + evenness 3. Scales of diversity Alpha Beta Gamma

8. β=γ/αβ=γ/α γ = α + β Additive Partitioning of Diversity: (Wagner et al. 2003) α1α1 α2α2 α3α3 α4α4 β 3 β 2 β 1 γ

9. Global Patterns of diversity 1. Islands 2. Climate 3. Latitude Dependence of these patterns on grain size?

11. Number of species of reptiles on Caribbean islands

12. Species – Area Relationship S = c A z z ~ 0.3 Galapagos – Land Plants.325 West Indies – Reptiles. & Amph..301 Bahamas – Orchids.31 West Indies – Carabids.34 East Indies – Ants.30 East Indies – Birds.28

13. MacArthur and Wilson 1967 Assumptions: 1.The immigration rate decreases as the number of species on the island increases. This is expected because competition increases and the number of available niches decreases. 2.The extinction rate increases with increasing species number. This is expected because more species implies greater competition. Equilibrium theory

15. Assumptions: 1. The immigration rate decreases as the number of species on the island increases. This is expected because competition increases and the number of available niches decreases. 2.The extinction rate increases with increasing species number. This is expected because more species implies greater competition. 3.For a given number of species, immigration decreases with increasing distance from the mainland. That is, the farther the island is from the mainland, the less frequent Long-distance dispersal events will be.

17. Assumptions: 1. The immigration rate decreases as the number of species on the island increases. This is expected because competition increases and the number of available niches decreases. 2.The extinction rate increases with increasing species number. This is expected because more species implies greater competition. 3.For a given number of species, immigration decreases with increasing distance from the mainland. That is, the farther the island is from the mainland, the less frequent Long-distance dispersal events will be. 4. For a given number of species, the extinction rate increases with decreasing island size. That is, populations on smaller islands have a greater risk of extinction because their population sizes are lower.

18. Equilibrium theory has led to a large body of theory and observation to which we will return in the next lecture.

19. Climate as a determinant of diversity

21. Latitudinal gradient Breeding bird diversity Greenland56(840,000 mi 2 ) New York105 N Am. North of Mexico650 Guatemala469(42,000 mi 2 ) Columbia1395+ (440,000 =1/16 N. Am area)

22. Ant species Arctic Alaska 3 (66-72) Alaska 7 (55-72) Iowa 73 (41-43) Cuba 101 (20-23 N) Trinidad>134 San Paulo, Brazil>222 (20-25 S) Tucuman, Argentina 139 (26-28) Buenos Aires, Argentina 103 (33-39) Humid western Patagonia 19 (40-52) Tierra del Fuego 2 (43-55)

23. Latitude and grain size Snakes per political unit (large grain) Canada 22 US 126 Mexico 293 Trees per 1000 m 2 (small grain) Canadian boreal forest ~2 N. US Deciduous forest ~8 North Carolina Piedmont ~15 (to 30) Panama & Columbia~100 Pluvial Columbia>260

24. Willig et al. 2003. Annual Reviews E&S

31. Exceptions? Often narrow specialist taxonomic groups –Ichneumonid wasps –Saxifrages Buffered environments –endo and ecotoparasites of vertebrates –aquatic plants –secondary marine vertebrates Willig et al. 2003. Annual Reviews E&S

33. Global Mechanisms 1.Area, Heterogeneity & Geometry 2.Time (Age, Time, History, Stability?) 3. Climate/Environment - Favorableness of climate or environment -Constancy, stability or predictability of climate or environment - Energy-diversity or Species-energy Theory - Productivity 4. Biotic interactions or Coevolution - Competition - Predation

34. Area & Heterogeneity More connected (contiguous) area permits greater population size, lower extinction. Premise: More contiguous area of uniform environment in tropics then in temperate to arctic latitudes; tropical area in one block Question: Corrected for area, does diversity reach similar levels across latitudes?

35. Mid-domain effect Random placement of species ranges within a bounded domain Null models all produce latitudinal gradients, but with different specific attributes. –Unconstrained –Constrained by range midpoints –Constrained by the distribution of range sizes Species wholly contained in any geographic domain should exhibit a mid-domain peak. Colwell & Hurtt 1994

36. Time (Age, Time, History, stability?) Evolutionary time: –More time for evolution to produce species; –fewer extinctions in stable environments. Ecological time: –More time for species to colonize appropriate habitat. Premise: the tropics have sustained less drastic change in environmental conditions over time Question: Does species richness increase without limit?

37. Favorableness of climate or environment Fewer species can tolerate climatic extremes. Premise: ideal conditions for life are found in the tropics Questions: What is the limit to evolutionary rate as a function of latitude?

40. Constancy, stability or predictability of climate or environment Fewer species can tolerate varying environments; those that do tolerate great ranges of environment have broad niches Premise: seasons less pronounced in tropical latitudes Problem: some species-rich environments do occur in seasonal environments; some stable environments are poor in species. Questions: Do fluctuating environments select for broad tolerance, broad niches, and low specialization?

41. Variant – speed of speciation

42. Rapoport-Rescue Hypothesis Range size varies inversely with latitude Because seasonality increases with latitude, species with broad tolerance are found at higher latitudes Northern hemisphere fits better than soutehrn hemisphere

43. Energy & Productivity Without production, no diversity More primary production allows more energy and thus more species The Paradox of Enrichment (diversity increases and then decreases with productivity) Problem: many species poor habitats are highly productive, and some unproductive habitats are highly diverse Question: Why do competitive dominants evolve in some ecosystems

45. Biotic interactions or Coevolution Species diversity begets possible interactions, leading to more species Premise: tropics, being more diverse, have more specialized coevolutionary relationships Questions: –Does this argument require that there already be a diversity gradient for this effect to be more pronounced in the tropics? –Does the latitudinal gradient reflect a gradient from selection by biotic interaction to selection by physical factors

46. Competition Competitive exclusion limits richness. Competition promotes specialization, divergence, and niche partitioning. Premise: tropics have higher competition, more niche divergence. Question: competitive pressure to specialize would not occur without diversity—which came first?

47. Predation Predation prevents competitive exclusion. Janzen-Connell hypothesis on tree regeneration vs. density Premise: tropics, being more diverse, have more predators, pests, and diseases, so competitive exclusion less likely. Question: Does a latitudinal gradient in predators, pests, and diseases exist and how did this come about?

49. Global Mechanisms 1.Area, Heterogeneity & Geometry 2.Time (Age, Time, History, Stability?) 3. Climate/Environment - Favorableness of climate or environment -Constancy, stability or predictability of climate or environment - Energy-diversity or Species-energy Theory - Productivity 4. Biotic interactions or Coevolution - Competition - Predation

52. Species pools

53. Zobel 1997

57. Regional patterns & mechanisms - Moisture & Elevation - Substrate - Production - Succession

60. Succession in a neotropical rain forest (0.5ha) Years3-5 30-50 100-150 >300 Birds2149127236 Primates02-66-88-12 Trees 203364112

72. River Floodplain River Bedrock Scour Bar Scoured Island

73. Native Exotic Upland (1090 plots) Riparian (121 plots) 31.12 0.20 268 plots with exotics 55.66 7.98 110 plots with exotics Mean Species Richness

74. After Brown & Peet 2003

75. Not discussed in lecture

78. Community patterns and mechanisms - Environmental tolerance - Competition – the paradox of enrichment - Slow dynamics - Suppression of dominance - Immediate disturbance hypothesis - Spatial mass effects – Propagule pressure - Temporal mass effects - Asymmetry of competition - Ecological equivalency

80. Willig et al. 2003. Annual Reviews E&S

81. Does diversity matter? - Stability ? - Productivity ? - Invasibility ?