Chapter 19: Community Structure in Space Biodiversity

Transcription

1 Chapter 19: Community Structure in Space Biodiversity

2 Measurement of biodiversity Commonness, rarity and dominance Preston s log normal distribution model a few common species with high abundances many rare species with low abundances Rare many species with low abundance Common few species with high abundance 2

3 Measurement of biodiversity Commonness, rarity and dominance MacArthur s broken stick model stick broken up at random points results in a few large pieces and many small pieces 3

4 Length of stick piece (Number of individuals) Measurement of biodiversity Commonness, rarity and dominance MacArthur s broken stick model arrange the pieces of the stick by size (large to small) log normal distribution Number of pieces (Number of species) represents a few species with large abundances and many species with small abundances 4

5 Measurement of biodiversity Commonness, rarity and dominance Community organization model 1 a few very common species many rare species model 2 a few very common and very rare species most species of intermediate abundance 5

6 Fig. 19.1, p. 379: Relative abundance of Lepidoptera captured in a light trap in England (6814 individuals representing 197 species) (Williams 1964). 6

7 Fig. 19.2, p. 380: Relative abundance of tropical rainforest trees >10cm diameter on a 50-ha plot on Barro Colorado Island, Panama, 2005 (Hubbell et al. 2005). 7

8 Fig. 19.2, p. 380: Relative abundance of tropical rainforest trees >10cm diameter on a 50-ha plot on Barro Colorado Island, Panama, 2005 (Hubbell et al. 2005). 8

9 Fig. 19.3, p. 380: Log-normal distribution of relative abundances in two diverse communities (Williams 1964). Snakes in Panama Birds in Great Britain 9

10 Measurement of biodiversity Biogeography (Chapter 21) Observations of relationships between area and number of species distance from source Island biogeography E.O. Wilson and Robert MacArthur 10

11 Island biogeography Island communities: well-defined, captive Variables size degree of remoteness elevation Simple community structure Increase in area increase in number of species 11

12 Island biogeography Habitats considered as insular because they are isolated from other communities caves mountain tops some peninsulas wildlife or game preserves 12

13 Fig , p. 442: Number of land-plant species on the Galapagos Islands in relation to the area of the island. 13

14 Fig , p. 442: Species-area curve for amphibians and reptiles of the West Indies. 14

15 Island biogeography Relationship between remoteness and number of species increase distance from mainland decrease number of species number of species present is dependent on immigration from mainland rate is a function of the number of species already present on the island number of species present = balance between immigration and extinction 15

16 Fig , p. 442: Equilibrium model for biota on a single island (MacArthur and Wilson 1967). 16

17 Fig , p. 443: MacArthur and Wilson s equilibrium model for biota on several islands of different sizes and remoteness. 17

18 Island biogeography Small species are found on more islands than are large species Number of herbivore species > carnivores Number of generalist herbivore species > specialist herbivores 18

19 Island biogeography MacArthur and Wilson s species:area relationship log : log relationship 10-fold decrease in area 50% decrease in number of species OR 10-fold increase in area doubles the number of species 19

20 Species: area relationship (log:log) species species 10 ~7,000 sq mi ~70 sq mi 20

21 Diversity gradients Abundance and diversity patterns latitude elevation mountainsides peninsulas 21

22 Fig. 19.6, p. 382: Number of tree species in Canada and U.S. 22

23 Number of species of land birds in North and Central America. 23

24 Number of species of calanoid copepods in top 50 m of transect from tropical Pacific to Arctic Ocean. 24

25 Fig. 19.7, p. 383: Bird species richness for the biogeographic regions of the earth. 25

26 Fig. 19.8, p. 383: Species diversity of Alcid seabirds and seals / sealions in relation to latitude (Proches 2001). 26

27 Fig. 19.9, p. 384: Species density contours for mammals in continental North America (number / 150m 2 quadrats). 27

28 Species richness of mammals in North and South America in relation to latitude. 28

29 Latitudinal diversity gradients Tree species Malaysia (4 acres): 227 Michigan (4 acres): <15 Ant species Brazil: 222 Trinidad: 134 Cuba: 101 Utah / Iowa: 63 / 73 Alaska: 7 29

30 Latitudinal diversity gradients Snake species Mexico: 293 U.S.: 126 Canada: 22 Fish species Amazon R: >1000 Central American rivers: 450 Great Lakes:

31 Fig , p. 385: The 34 global hotspots of biodiversity (high endemic plant species richness). 31

32 Table 19.1, p. 386: Characteristics of 25 of the highest ranked biodiversity hotspots. 32

33 33

34 Hypotheses for latitudinal diversity gradients Evolutionary speed (aka History or Time) Geographic area (aka Spatial heterogeneity) Interspecific interactions Competition Predation Ambient energy (aka Environmental stability, Climate) Productivity Intermediate disturbance 34

35 Latitudinal gradient hypotheses Evolutionary speed hypothesis tropical habitats older, more stable support for geological past of temperate less constant than tropics due to glaciation all communities diversify with time argument against as glaciers moved in, species moved south to escape history hypothesis can not be tested 35

36 Fig , p. 387: Evolutionary speed as a factor in biodiversity. Hypothetical increases in diversity in absence of interruptions Actual pattern of change in area influenced by climate change and glaciation 36

37 Fig , p. 388: Pattern of increase in the number of terrestrial plant species over evolutionary time (data from fossils). 37

38 Latitudinal gradient hypotheses Geographic area hypothesis spatial heterogeneity higher diversity in tropics due to increase in number of potential habitats environmental complexity moving away from equator macro level: e.g., topographic features micro level: e.g., particle size, vegetation complexity 38

39 Fig , p. 389: Illustration of biodiversity in a region that includes three different habitats. 39

40 Latitudinal gradient hypotheses Spatial heterogeneity hypothesis Hutchinson s n-dimensional niche specialization types of diversity defined by spatial heterogeneity within-habitat ( diversity) between-habitat ( diversity) 40

41 α-diversity versus β-diversity α-diversity β-diversity 41

42 Diversity defined by spatial heterogeneity Between habitat diversity ( ) Temperate Tropical No. species per habitat No. different habitats Within-habitat diversity ( ) Temperate Tropical No. species per habitat No. different habitats

43 Latitudinal gradient hypotheses Interspecific interactions hypothesis role of competition less competition in temperate and polar environments compared to tropics because these populations are more regulated by extreme environmental conditions than by biological factors populations maintained <K due to weather, etc. and major sources of mortality are abiotic since population sizes small, decreased competition for resources 43

44 Latitudinal gradient hypotheses Interspecific interactions hypothesis role of competition no weather extremes in tropics, populations can increase to densities at which competition for resources is necessary promotes species diversity through specialization resource partitioning and diversity higher in tropics due to organisms being more specialized to habitats 44

45 Fig , p Niche breadth versus niche overlap determined by competition within the community. 45

46 Fig , p Niche breadth versus niche overlap determined by competition within the community. Number of species in the community is determined by niche breadth 46

47 Fig , p Niche breadth versus niche overlap determined by competition within the community. Number of species in the community is determined by amount of niche overlap 47

48 Fig , p. 392: Niche breadth of two Anolis lizard species on Caribbean islands. 48

49 Latitudinal gradient hypotheses Interspecific interactions hypothesis role of predation increased species diversity in tropics is function of increased number of predators that regulate the prey species at low densities decreases competition among prey species allows coexistence of prey species and potential for new additions 49

50 Fig , p Janzen-Connell model for increased diversity of tropical rainforest trees: seed predation versus distance of seed from tree versus seed survival. 50

51 Fig , p. 393: Mortality rate of 843 Ocotea saplings from Barro Colorado Island in relation of distance of each sapling from the nearest adult tree of the same species. 51

52 Latitudinal gradient hypotheses Interspecific interactions hypothesis role of predation there is more selective pressure on prey evolving avoidance mechanisms than in becoming better competitors cropping principle remove predators and prey start competing predation increases diversity by reducing intraspecific competition among prey species 52

53 Latitudinal gradient hypotheses Interspecific interactions hypothesis role of predation cropping principle in lakes top predators (fish) feed on zooplankton if fish are removed community diversity decreases, becomes dominated by a few species of large, grazing zooplankton add fish diversity of small zooplankton and their invertebrate predators increases 53

54 Latitudinal gradient hypotheses Ambient energy hypothesis the energy available generates and maintains the species richness gradients example parameters evapotranspiration temperature solar radiation moisture availability 54

55 Fig , p The ambient energy hypothesis for biodiversity gradients. 55

56 Fig , p Polar to tropics biodiversity gradients for terrestrial animals according to the ambient energy hypothesis. 56

57 Fig., 19.22, p. 395: Biodiversity of corals throughout the world. Best predictors of coral species diversity = ocean temperature and coral biomass. 57

58 Latitudinal gradient hypotheses Ambient energy hypothesis environmental stability high diversity habitats generally found in stable climates low diversity habitats associated with severe and/or unpredictable climates 58

59 Latitudinal gradient hypotheses Productivity hypothesis tropics support a greater number of species because more resources are available, allowing for more specialization in general: production diversity exceptions marshes: high production, relatively low diversity deserts: low production, high diversity 59

60 Latitudinal gradient hypotheses Intermediate disturbance hypothesis if community disturbance frequency is very high local extinction of species species diversity if community disturbance frequency is very low competitive exclusion by dominant species species diversity 60

61 Latitudinal gradient hypotheses Intermediate disturbance hypothesis moderate disturbance maximizes diversity leads to patches at local level intermediate disturbance high species diversity in some communities (not all) 61

62 Fig , p Model for intermediate disturbance hypothesis. 62

63 Fig , p Effect of disturbance in periwinkle grazing on algae diversity. Community dominated by one algal species Predator limits number of possible algal species 63

64 Chapter 20: Community Dynamics I 64

65 Basic concepts related to energy flow and trophic structure Energy moves through community and is lost as heat Nutrients move through the community in cycles and are retained 65

66 Basic concepts related to energy flow and trophic structure Niche sum of all parameters that enable an organism to live in its biotic and abiotic environments competition, food gathering, predator escape, mate location, reproduction, etc. temperature, moisture, nutrients, soil structure, salinity, etc. Hutchinsonian niche: n-dimensional hypervolume 66

67 Basic concepts related to energy flow and trophic structure Food chains and trophic levels (Lindeman 1942) classification of animals according to location in lake lake trophic groups: benthic demersal plankton nekton described food chain with primary producers at base and other trophic levels of animals based on feeding relationships more accurately described as food web, since few organisms other than plants occupy only one feeding level 67

68 Food webs and energy flow Trophic levels ecosystem feeding levels biomass and usable energy as level most systems support only four trophic levels aquatic communities have slightly longer food chains than terrestrial communities ultimate food chain length limited by inefficiency of energy transfer from one trophic level to the next 68

69 Food webs and energy flow Food chains sequence of organisms where each is the food source for the next Food webs represent energy flow through ecosystem 69

70 Trophic levels 70

71 Energy / biomass representation by trophic level Tertiary consumers (top carnivores) Secondary consumers (carnivores) Primary consumers (herbivores) Primary producers (plants) 71

72 Food chain model First Trophic Level Second Trophic Level Third Trophic Level Fourth Trophic Level Producers (plants) Primary consumers (herbivores) Secondary consumers (carnivores) Tertiary consumers (top carnivores) Heat Heat Heat Heat Solar energy Heat Heat Heat Heat Detritivores (decomposers and detritus feeders) Heat 72

73 Fig. 20.5, p. 407: Hypothetical food web model 73

74 Table 20.1, p. 407: Food web terminology 74

75 Distribution of food chain lengths in the Ythan Estuary, NE Scotland. 95 species 5518 food chain lengths were counted 75

76 Food web of a rocky intertidal community, northern Gulf of California (after Paine 1966). Producers Producers Producers Producers 76

77 Rocky intertidal community food web (Paine s 1966 study) (Producer level omitted from original figure) Level 1 herbivorous gastropods and chitons filter feeding bivalves suspension feeding barnacles and brachiopods Levels 2-4: carnivorous gastropods Level 5: top carnivore Heliaster starfish 77

78 Keystone species Usually the top carnivore Presence or absence determines community structure and composition 78

79 Food web of a rocky intertidal community, northern Gulf of California (after Paine 1966). X Top carnivore: Heliaster Producers Producers Producers Producers 79

80 Food web of a rocky intertidal community, northern Gulf of California (after Paine 1966). Top carnivore: Heliaster X X X Space competitor: Mytilus californiensis X X X X X X Producers Producers Producers Producers 80

81 Fig , p. 392: Keystone predator effect in the rocky intertidal zone (Paine 1974). 81

82 Keystone species Paine (1974): Pacific rocky intertidal community dominated by Pisaster starfish remove starfish mussel Mytilus californiensis excludes all other invertebrate species Mytilus becomes numerically dominant Pisaster feeds on Mytilus prevents Mytilus domination of community community diversity 82

83 Figure 20.3, p. 405: Simplified Antarctic marine food web. 83

84 Fig. 20.4, p. 406: Partial food web for moderately exposed rocky shores in the Gulf of Maine. 84

85 Food web of boreal forest of northwest Canada 85

86 Fig , p. 413: Sea otters as keystone species in the Aleutian Islands and changes in apex predator. 86

87 Generalizations about food webs Size of animal increases with increase in trophic level Abundance decreases with increase in trophic level Large animals can not exist on small animals as prey Small carnivores are limited to prey that can fit into their mouths 87

88 Which trophic level is most important? Studies by Charles Elton in two square miles of Wytham Woods Which species could be removed without changing the community? top carnivore, except keystone species lower levels are food source for higher levels importance of top carnivores <<< herbivores 88

89 Which trophic level is most important? Dependent on complexity of community increased number of interconnections in community increased complexity of food web increased stability of community structure alternate food sources should one be removed redundancy model versus rivet model 89

90 Which trophic level is most important? Determining species importance species with highest biomass where nutrients accumulate where energy accumulates 90

91 Dominant versus keystone species Dominant species highest relative abundance or biomass in community achieved by competitive exclusion or predation Keystone species maybe common or rare but never dominant effect on community structure much greater than relative abundance 91

92 Fig , p. 414: Illustration of difference between dominant and keystone species. 92