1. Biodiversity II: patterns of species diversity Bio 415/615

2. Questions 1.What are 2 possible reasons the tropics have more species than temperate and polar regions? 2.What does it mean that biodiversity patterns are ‘scale dependent’? 3.How do we estimate the total number of world’s species? 4.What are two reasons species richness goes up when you sample a larger area?

3. # of Described Species Insecta751,000 Plantae248,428 Other Arthropods 123,151 Mollusks50,000 Fungi46,983 Protozoa30,800 Algae26,900 Fish19,056 Flatworms12,200 Roundworms12,000 Annelida 12,000 Birds9,040 Coelenterata 9,000 Reptiles6,300 Echinoderms 6,100 Sponges5,000 Monera4,760 Amphibians4,184 Mammals4,000

4. How many species are there? How do we know? Take what we do know, project it to include things we don’t Example 1: species-area curves Example 2: body size Example 3: sub-sampling

5. Gross (and Biased) Underestimates Estimates range from 2 to 100 million species (1.4 million described) New species being discovered Strong biases in counts –1980: study of 19 trees in a tropical rainforest 1200 species of beetles 80% previously undescribed Likely 6 to 9 million species of arthropods –1 sq m tropical forest: 200,000 mites, 32 million nematodes, 90 million bacteria # of species? –Oceans: very poorly studied, especially deep sea Estimated 1 million undescribed species from deep sea Hydrothermal vents: 20 new families, 50 genera, 100 species

6. Scale dependence Biodiversity patterns are sensitive to SCALE. Just as what you see through a telescope depends on the magnification and field of view.

7. CVS plot locations, 1988-2000

10. Scale-independence Pine woodlands and savannas

11. Scale-dependence

12. Mechanisms Species pools: Resources and Propagules Size / Density Disturbance

13. Preston 1960, Time and space and the variation of species tropical temperate breeding birds

14. Three phases and coexistence Hubbell 2001 Preston 1960 Shmida and Wilson 1985

15. Three basic reasons species richness increases with area: 1.Habitat diversity goes up (a greater range of environments are sampled, potentially including a greater array of niches) 2.Population sizes increase, leading to a lower extinction rate (from island biogeography) 3.Some species require large areas because they have large ranges or habitat requirements (e.g., large predators)

16. Patters of species richness Broad scale: –Latitude –Climate –Elevation Fine scale: –Productivity –Disturbance

17. Large-scale patterns of species richness Known for well over a century –Joseph Banks, Johann Forester, Alexander von Humboldt, Charles Darwin, Alfred Wallace & others (many more species in the tropics) Not well documented until mid-20 th century Major area of biogeography and ecology today

18. Global plant diversity at large scales

19. 30 35 65 60 55 50 45 40 25 20 15 10 Latitudinal gradients in diversity measure the number of species found within bands of latitude

20. An example of a typical latitudinal gradient Data from Lyons & Willig 1997

21. Another example, Palms of the New World

22. Groups that provide evidence for a latitudinal gradient in diversity: BirdsMarine Gastropods MammalsMarine Bivalves Freshwater FishesMarine Fishes TreesCorals EpiphytesInsects Many have argued that this pattern is universally true for all large taxonomic groups

23. Many small taxonomic groups, e.g. pine trees, don’t show the expected pattern despite the fact that trees overall show the latitudinal gradient Tree species: U.S. and Canada ca. 679 Costa Rica 1400+

24. Other taxonomic groups also don’t show the expected latitudinal gradient in diversity, but in each case the expected pattern is seen at a higher taxonomic level: Penguins (family)vs.Birds (Class) Seals (family)vs. Mammals (Class) Ichneumonidae (family)vs.Insects (Class) Threvidae (family)vs. Insects (Class)

25. Explain the latitudinal gradient There have been over 30 hypotheses What’s yours?

26. Explanations for the latitudinal gradient in diversity: 1. Historical Perturbations – places that have been disturbed (e.g. by glaciation) may have fewer species because of A. Differential rates of extinction B. Inadequate time for species to recolonize 2. Differential rates of evolution – places with more resources or higher temperature may have faster rates of evolution A. Speciation faster then extinction B. More “evolutionary experiments” tried, and more niches filled

27. Others: 3. Climatic Stability – stable climate may promote specialization (and speciation) and reduce extinctions 4. Harshness – harsh conditions may limit species numbers 5. Interspecific interactions – biotic interactions may promote specialization and coexistence and are more intense in the tropics 6. Habitat Heterogeneity – diverse habitat structure may permit finer subdivision of resources and greater specialization 7. Productivity/Energy – greater available energy may allow for greater numbers of species to coexist

31. Species richness and energy Figure 2 Species–energy relationships. a, Mean monthly summer temperature (°C) and richness of breeding birds in Britain (grid cells of 10 km 10 km) 33. b, Mean annual sea surface temperature and richness of eastern Pacific marine gastropods (bands of 1° latitude) 10. c, Potential evapotranspiration (mm yr -1 ) and richness of Epicauta beetles (Meloidae) in North America (grid cells of 2.5° 2.5° south of 50° N, 2.5° 5° north of 50° N) 31.

32. And more… 8. Seasonality versus habitat heterogeneity: or, ‘why mountain passes are higher in the tropics’ 9. Land area greater in the tropics? (no) 10. Mid-domain: must be more range limits at the poles (put ranges on map at random)

33. How do we figure this out? 1.Pose hypotheses based on existing data that can be tested by gathering more data. (cosmologists and geologists do this, too) 2.Reduce hypotheses down to mechanisms that can be experimentally addressed (e.g., rate of evolutionary diversification with microbes)

34. How do we figure this out? 1.Pose hypotheses based on existing data that can be tested by gathering more data. (cosmologists and geologists do this, too) 2.Reduce hypotheses down to mechanisms that can be experimentally addressed (e.g., rate of evolutionary diversification with microbes) Generally speaking, the world has been too complex to give definite answers, and our tools are still too blunt to provide easy resolution.

35. Across scales?

36. Latitudinal patterns can be extended to altitude (elevation) and ocean depth Bird Species in Peru and New Guinea

37. Local richness patterns (fine scales) Local patterns = below a ‘region’, usually a single vegetation plot Local patterns are nested (and thus constrained) within large-scale patterns What varies environmentally at large scales versus small scales? = environmental texture

38. Hump-backed model What is the x-axis?

39. Grime 1979 A model for local diversity

40. Local richness could be set by: 1. Local processes – such as species interactions, or 2. Regional diversity and regional processes – such as dispersal limitation, or 3. Both (metapopulation perspective) Regional richness could be set by: 1.The interaction between alpha and beta diversity 2.By processes that occur at regional scales – such as rates of speciation and extinction Local version regional richness

41. Regional Richness Local Richness boundary proportional sampling ceiling

42. Species in forest habitat of South Africa: mixed evidence From Lawes et al. 2000