Species Diversity. What do we mean by diversity? 1.Species Richness Count Species/area...

download Species Diversity. What do we mean by diversity? 1.Species Richness Count Species/area Species/number 2. Heterogeneity = Richness + evenness 3. Scales.

of 87

  • date post

    20-Dec-2015
  • Category

    Documents

  • view

    214
  • download

    0

Embed Size (px)

Transcript of Species Diversity. What do we mean by diversity? 1.Species Richness Count Species/area...

  • Slide 1
  • Species Diversity
  • Slide 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
  • Slide 3
  • Slide 4
  • Slide 5
  • Measures of diversity sensitive to both richness and evenness Simpsons Index D = 1/ p i 2 Shannon Index H = - ( p i log p i ) or exp(H)
  • Slide 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
  • Slide 7
  • Slide 8
  • =/=/ = + Additive Partitioning of Diversity: (Wagner et al. 2003) 11 22 33 44 3 2 1
  • Slide 9
  • Global Patterns of diversity 1. Islands 2. Climate 3. Latitude Dependence of these patterns on grain size?
  • Slide 10
  • Slide 11
  • Number of species of reptiles on Caribbean islands
  • Slide 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
  • Slide 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
  • Slide 14
  • Slide 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.
  • Slide 16
  • Slide 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.
  • Slide 18
  • Equilibrium theory has led to a large body of theory and observation to which we will return in the next lecture.
  • Slide 19
  • Climate as a determinant of diversity
  • Slide 20
  • Slide 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)
  • Slide 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)
  • Slide 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
  • Slide 24
  • Willig et al. 2003. Annual Reviews E&S
  • Slide 25
  • Slide 26
  • Slide 27
  • Slide 28
  • Slide 29
  • Slide 30
  • Slide 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
  • Slide 32
  • Slide 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
  • Slide 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?
  • Slide 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
  • Slide 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?
  • Slide 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?
  • Slide 38
  • Slide 39
  • Slide 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?
  • Slide 41
  • Variant speed of speciation
  • Slide 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
  • Slide 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
  • Slide 44
  • Slide 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
  • Slide 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 diversitywhich came first?
  • Slide 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?
  • Slide 48
  • Slide 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
  • Slide 50
  • Slide 51
  • Slide 52
  • Species pools
  • Slide 53
  • Zobel 1997
  • Slide 54