Patterns in Species Diversity Lecture 10

1. Patterns in Species DiversityLecture 10 Principles of Ecology College of Forestry, Guangxi University EbenGoodale

2. Let’s discuss Terborgh et al. 2001

3. No class Saturday… change syllabus again!

4. Review • We defined a community as a group of species living in the same area. • We said a community has 3 characteristics: • 1) # species • 2) species have different relative abundances • 1 and 2 can be measured together by species diversity. • Today we ask the question, Why? • Why so many species?

5. Today • Species diversity varies over big spaces: • Species diversity is higher in the tropics. • Species diversity on islands of different sizes. • Species diversity within a region: • Heterogenous community theory • Intermediate disturbance hypothesis • Does species diversity matter?

6. The Science of Biogeography（生物地理学） • Alfred Wallace (1823-1913) • Actually co-discover of natural selection, but Darwin is given most credit. • Wallace better remembered for his contributions to Biogeography. • Biogeography is the study of the variation in species composition and diversity among geographic locations, • Like Darwin, Wallace traveled widely, collecting animals as he went.

7. The Science of Biogeography • “Wallace’s Line”: • A line that runs through Indonesia • Wallace discovered that the faunas on the two sides of this line very different. • In fact fauna of Philippines closer to Africa (5500 km) than to New Guinea (750 km). Just like Darwin discovered natural selection But didn’t understand genetics, Wallace discovered this line, but didn’t understand the mechanism. What was it?

8. Plate tectonics（板块构造论） Movie of changes in continents

9. Plate tectonics（板块构造论）

10. Plate tectonics: responsible for difference in large regions of globe • Explains Wallace’s line. • Explains why different lineages of plants, animals in 6 regions of the world proposed by Wallace. • Explains divergence like that seen in flightless birds.

11. Species diversity: a latitudinal pattern（随纬度变化） Why are the tropics so diverse? Plants From Willig et al. 2003 Birds

12. Species diversity: a latitudinal pattern Why are the tropics so diverse? They are more productive（生产的） They’ve been around for longer. They are better fitted to organisms’ biology And more stable In their climate They are bigger… But this isn’t all: Roede (1997) lists 28 different hypotheses! Bigger populations, less extinction.

13. Species diversity: a latitudinal pattern From Colwell and Lee 2000 The mid-domain effect … for anything that affects organisms’ ranges, more organisms will be found in the middle of the gradient… And the equator is at the middle of the world. Robert Colwell, UConn Essentially we’re coming down to explaining these broad trends by geometry（几何学）.

14. Exceptions（例外） to species area curves（种-面积曲线） 3 temperate forest zones about the same size … But Asia has 6 X tree species of Europe and 3 X NAmerica. Why?

15. Exceptions to species area curves Alps blocked the range movements of European trees! In a way too this is a geometric solution…. Shows that length of time Important.

16. Exceptions to species-area curves • Another exception is seabirds, which are more at high latitudes. • Indeed oceans are more productive at high latitudes. • Some evidence that productivity matters. • Overall summary of tropical diversity: many theories that are not-exclusive, and good evidence for many of them.

17. Species diversity: other scales • Global diversity: all species • Regional diversity: plate tectonics. • Regional diversity: latitude • Regional diversity called γ • It includes two components: • α Diversity: the # of species in any one community. • Β Diversity: the change in what species you encounter as you move from community to community in the region.

18. Species-area curves General rule in ecology: the larger area you sample, the more species you will find. Adding β diversity.

19. Species-area curve is different on continents（大陆）vs. islands Is Z higher or lower for islands? Z is higher because dispersal Is limited to islands.

20. What are islands? Lakes in a terrestrial matrix Islands in an aquatic matrix（基质）. Mountains in an arid matrix like Arizona

21. And what appears to be an islandchanges based on organism Dispersal ability varies widely among organisms Spores / seeds of some organisms everywhere Very occasionally a lizard might raft（木筏） across ocean

22. Theory of island biogeography . Originally, a theoretical model, but has been used for applications for how to build reserves – islands – within areas of human disturbance. Robert MacArthur 1967 E.O. Wilson

23. Immigration very high when no species on island. Krakatau Immigration rate hits 0 when all of the mainland species have already arrived How do new species get to islands? • They immigrate（迁入）. Immigration Rate (Species Per year) Number of species on island Important note: this theory doesn’t include speciation on the islands.

24. What factors effect immigration? Distance to (or isolation of) island Size of island Say this immigration line is for a close island… what would the immigration line be for a far island? LARGE Immigration Rate Farther island, fewer immigrants Say this immigration line is for a small island… what would the immigration line be for a large island? (Species Per year) FAR Larger island, bigger target Number of species on island

25. What factors effect immigration? One more question: Should this be a straight line (linear（线性的）)? Species have different dispersal abilities, so ones that disperse easily will come quickly. Immigration Rate (Species Per year) Number of species on island

26. Because the more species there are, the bigger the pool of species to go extinct. Nothing can go extinct because there are no species! How do species disappear from islands? • Extinction（消失） What does this graph look like? Extinction Rate (Species Per year) Number of species

27. What factors effect extinction? Size of island The larger the island, the bigger population a species has. The bigger population a species has, the less chance it will go extinct. Hence, bigger islands have lower extinction rates. Extinction Rate (Species Per year) LARGE OK, so let’s say that this graph is for a small island. What would the graph for a large island look like? Number of species

28. What factors effect extinction? • Distance of island How about the distance of an island? If it’s close, more immigrants will come and there will be fewer extinctions. FAR Extinction Rate (Species Per year) So if we plot a farther island on this plot it goes where? Number of species

29. What factors effect extinction? • Extinction Now is this graph linear? As there are more and more species, interspecific competition will increase, so curve will look like… Extinction Rate (Species Per year) Number of species

30. Level above X axis Represents turnover（物种的数量）in species Theory of Island Biogeography • Postulates（假设） that for every island, there will be some number of species where immigration will be balanced by extinction. Equilibrium Point（平衡点） Important point: equilibrium does not mean that the same organisms will be there year after year… identity of species will change, but number stay the same extinction (Species Per year) immigration Species on island

31. New larger (more species) equilibrium Note that the turnover rate may change as well Theory of Island Biogeography (Species Per year) Species on island Say this is the graph for a small island What’s the graph for a large island? Same result for a close island

32. Exercise • The curves in blue shows a • island that is ______ than the • curves in black. • Farther or smaller • Farther or larger • Closer or smaller • Closer or larger Extinction Immigration (Species Per year) Species on island

33. Theory of Island Biogeography Go through this figure yourself, and make sure you understand it…

34. Testing the theory:observation Plant species on Galapagos Islands

35. Teting the theory: experimentation • Many observational studies show that island area and isolation are major factors influencing species number. • But correlation does not prove causation. • Best to do an experiment.

36. Experimental islands Simberloff and Wilson (1969) fumigate（烟熏） islands and wipe out all insects on them, then watch the number of insects that return…

37. Experimental islands Close island Far island

38. Experimental islands # of species goes down The Simberloff (1976) took some islands and made them smaller…

39. Island-biogeography theory applied to fragmentation and conservation • Fragmentation（破碎化） is a process of making islands. • People have used island biogeography to develop sets of reserves. • Also used it to predict how many species might go extinct given a certain amount of fragmentation.

40. A really large scale experiment • Biological Dynamics of Forest Fragments Project (BDFFP). • Started in 1979 by Thomas Lovejoy. • Made experimental fragments in Amazonian Brazil.

41. As expected, size of island a big factor • Smaller fragments much more hit by extinction. • Also interesting findings show that different kinds of animals and plants have very different kinds of responses. From Stouffer et al. 2011

42. Today • Species diversity varies over big spaces: • Species diversity is higher in the tropics. • Species diversity on islands of different sizes. • Species diversity within a region: • Heterogenous community theory • Intermediate disturbance hypothesis • Does species diversity matter?

43. OK, so communities differ in species diversity … but why? • “Heterogeneous environmental theory（环境异质化理论）”. • First developed by Robert MacArthur • Came out of the idea of niches, and the competitive exclusion theory • MacArthur generally worked with birds Robert MacArthur Student of Hutchinson Died at age of 42 in 1972

44. Heterogeneous Environments: Opportunities for Specialization Remember that each species has a niche – Its occupation. In these birds that MacArthur studied each species uses different part of the tree. And no two species can have the same niche “competitive exclusion principle” (Gause’s experiments) We talked about this when talking about competition.

45. So it makes sense that the higher the canopy of forests, the more species there will be. This was MacArthur’s first result (1958)

46. Further experiments demonstrate that vertical heterogeneity increases species diversity MacArthur hung a rope vertically from the top of the canopy and measured how many times vegetation hit the rope. From this he calculated vertical profiles of different forests, and compared them in their diversity (# of different layers and evenness of layers). MacArthur and MacArthur 1961

47. Further experiments demonstrate that vertical heterogeneity increases species diversity He found that the more diverse the vertical vegetation the more species of birds were present MacArthur and MacArthur 1961 Basically the idea is that the More diverse an area is in vegetation, The more niches can be fit into it = The more species.

48. Heterogeneous environment theory: plants vs. animals • For animals, the environment that’s important is usually structure of vegetation. • What about for plants? • Different plants may use different types of soil nutrients. • And we know that soil resources can be variable in space, suggesting they can help explain plant diversity. Here one species of phytoplankton dominants at high Si:P rations, and one at low

49. Variable（变异的）conditions can also retain diversity • Under unvarying conditions, competitive exclusion occurs. • But disruptive（破坏性） processes such as predation and disturbance can alter the course of competition. • Remember a sea star kept a dominant competitor from getting too abundant.

50. Variable conditions can also retain diversity • Or a sea palm on a rocky tidal short that was a poor competitor, but could colonize areas of high disturbance. • Hence, variable environments can maintain species co-existence