1. A community is a group of interacting populations, all living in the same place at the same time –the focus is on the interactions between species or populations including competition, predation, succession, invasion, mutualism, predation, etc. Community Ecology

2. Community Structure and Change COMMUNITY STRUCTURE - a description of the community members (species list) and their relative abundances COMMUNITY DYNAMICS - the changes that occur over time and space in a community. (Even though communities have an underlying structure, the structure may change over time.

3. Emergent Properties Properties not predictable from study of component populations Only apparent at level of community Properties not predictable from study of component populations Only apparent at level of community

4. Why is this important? Appropriate unit of study: - If the community is more than the sum of its parts, then we must study the entire community (holistic approach) - If not then entire picture can be put together from individual pieces (reductionist approach) Appropriate unit of study: - If the community is more than the sum of its parts, then we must study the entire community (holistic approach) - If not then entire picture can be put together from individual pieces (reductionist approach)

5. The Study of Ecological Communities Properties & patterns –Diversity (Number of species) –Species’ relative abundances –Morphology –S uccession Processes –Disturbances –Trophic interactions –Competition –Mutualism –Indirect effects

6. Two Views on Communities Community as a superorganism (equilibrium community, Clements) Species not replaceable Species need one another to survive Community as a group of individual species (non-equilibrium community, Gleason) Species are replaceable Random association of species

7. Community Dynamics: Succession Succession - The change in numbers and kinds of organisms in an area leading to a stable (climax) community. Replacement of communities. Pioneer community - the first community to develop in a successional sequence Seral stage - any successional community between pioneer and climax community

8. 1.Primary – situation where barren substrate is available for habitation (inorganic substrates= lava flows/ spreading centers 2. Secondary – occurs in areas where communities have previously existed (after fires or hurricane; much more rapid) 1.Primary – situation where barren substrate is available for habitation (inorganic substrates= lava flows/ spreading centers 2. Secondary – occurs in areas where communities have previously existed (after fires or hurricane; much more rapid) Types of Succession

9. Succession in community traits  increasing size of organisms  increasing longevity of organisms  shift from predominantly "r-selected" to predominantly "K-selected" species  shift from "individualistic" to predominantly "interactive" organization  increasing biomass  increasing independence of physical/chemical environment

10. Succession in community traits (2)  decreasing rate of change  increasing species diversity  increasing complexity of physical and trophic structures  increasing habitat modification and buffering of environmental extremes  increasing complexity of energy and nutrient flows  increasingly closed systems re-cycling of organic and inorganic materials

11. Opposing Views of Communities Superorganism View (Clements, 1916) - tightly evolved, interacting - functions as a single organism - developmental process (succession) - homeostasis (self maintaining – stable) - underlying “balance of nature” Superorganism View (Clements, 1916) - tightly evolved, interacting - functions as a single organism - developmental process (succession) - homeostasis (self maintaining – stable) - underlying “balance of nature” Individualistic View (Gleason, 1925) - randomly assembled - Similar resource requirements Individualistic View (Gleason, 1925) - randomly assembled - Similar resource requirements

12. F.E. Clements (1916, 1936) idea of succession Succession Sere Climax Ecosystem = superorganism

13. Types of Species Early successional - good colonizers - rapid growth - short lived (r-selected) Early successional - good colonizers - rapid growth - short lived (r-selected) Late Successional -poor colonizers - slow growth - long lived (k-selected) Late Successional -poor colonizers - slow growth - long lived (k-selected) Correlation between life history traits necessary E E L L

14. Succession b b b b A A c c B B c c c c c c C C Early Colonizing Early Colonizing Mid Mixed Mid Mixed Late Climax Late Climax Time

15. Under Equilibrium Models Community returns to same position after disturbance At equilibrium, processes that structure the community produce no net change Community returns to same position after disturbance At equilibrium, processes that structure the community produce no net change

16. Equilibrium Theory Single stable state Multiple stable states Multiple stable states

17. Outcomes of integrated view Equilibrium assumed (not tested) Explained succession Super-organism concept widely accepted Dominated community ecology until the 1950’s and beyond Equilibrium assumed (not tested) Explained succession Super-organism concept widely accepted Dominated community ecology until the 1950’s and beyond

18. Non-equilibrium models Disturbance is the norm rather than the exception Disturbed patches provide opportunities for colonization by dispersive species Patchiness promotes diversity on a larger scale

19. Evidence for each view: Superorganism: remove plants or autotrophs, the community will disappear mutualisms and symbiotic relationships are common example: herbivore gut bacteria Non-equilibrium high-level consumers can be removed without major effects on community disturbances often play a role in determining community structure; these are random

20. Alternative succession models Connell and Slatyer (1977) – outlined 3 models: 1. Facilitation – Clementsian succession 2. Tolerance 3. Inhibition Based on effect of initial spp. on subsequent spp. Connell and Slatyer (1977) – outlined 3 models: 1. Facilitation – Clementsian succession 2. Tolerance 3. Inhibition Based on effect of initial spp. on subsequent spp.

21. Facilitation Model E E L L Recruitment Growth Recruitment E E L L Facilitation Mortality Disturbance E E E E E E E E Early Stand E E E E L L L L L L Mixed Stand L L L L L L L L L L Late Successionals only

22. Tolerance Model E E L L Recruitment Growth Recruitment E E L L Tolerance Mortality Disturbance E E E E L L L L L L Mixed Stand L L L L L L L L L L Late Successionals only E E L L L L L L E E

23. Inhibition Model E E L L Recruitment Growth Recruitment E E L L Inhibition Mortality Disturbance E E E E L L L L L L Mixed Stand L L L L L L L L L L Late Successionals only L L E E L L E E

24. Time 0 Disturbance opens space; slate wiped clean Time 1 Only certain species can establish themselves in open space; Opportunists, Fugitives, Weeds No special requirements for first colonizers Time 2 First colonists modify environment so it becomes less suitable for their further recruitment but more suitable for other species First colonists make environment less suitable for their own further recruitment, but this has little or no effect on other species First colonists make environment less suitable for all subsequent species Time 3 Process continues until residents no longer facilitate recruitment of other species Process continues until no species can invade and grow in presence of residents First colonists continue to hold space and exclude all others (First Come, First Served ) Model FACILITATION TOLERANCE INHIBITION

25. Succession Can occur without invoking the existence of a “Super-organism” Sequential replacement a consequence of individual species properties Can occur without invoking the existence of a “Super-organism” Sequential replacement a consequence of individual species properties

26. Physical disturbance

27. What are the components of disturbance? The frequency of a disturbance The intensity of the disturbance The timing of the disturbance –Influences the availability of larvae to recolonize the disturbed area

28. Disturbance simplified The greater the disturbance the more habitat that will be opened up

29. Intermediate Disturbance Hypothesis ( Connell 1972 ) Disturbance (eg, tree falls, storms) creates patchiness and new space to be colonized Patchwork is created across the landscape with - early and late successional species - inferior and superior competitors This theory is considered a non-equilibrium view of how natural communities are structured because landscape is a patchwork of different stages of succession.

30. Intermediate Disturbance Hypothesis (2) Frequency and intensity of various kinds of abiotic disturbances affect patterns of diversity. Disturbance is critically important in structuring communities because it can prevent competitively dominant species from excluding others. Weak/infrequent disturbances insufficient to prevent competitive exclusion Intense/frequent disturbances exclude species sensitive to disturbance Highest diversity might therefore be expected at intermediate frequency or intensities of disturbance

31. Intermediate Disturbance Hypothesis (Connell)

32. Community structure could be controlled bottom-up by nutrients: herbivores predators nutrients autotrophs numbers of autotrophs are limited by mineral nutrients community structure can be changed by manipulating the lower levels Top-down vs. bottom-up control

33. Community structure could be controlled top-down by predators (trophic cascade model) autotrophs nutrients herbivores predators numbers of herbivores are controlled by predators predicts a series of +/- effects if upper levels are manipulated

34. Reintroduction and protection of otters has reduced urchin barrens Predation by orcas has increased urchin barrens Trophic cascades

36. Species-area relationships species-area curve - the larger the geographic area, the greater the number of speciesspecies-area curve - the larger the geographic area, the greater the number of species fig 53.25 larger areas have more diverse habitatlarger areas have more diverse habitat this can be used to predict how habitat loss may affect key speciesthis can be used to predict how habitat loss may affect key species

37. Species Area Relationships As a rule of thumb for every 10x increase in habitat area you can expect a doubling in species abundance this relationship is best described by the regression formula S=cA z –where: S = the number of species, c= a constant measuring the number of species/unit area, A= habitat area, and z is another constant measuring the shape of the line relating S & A

38. Often linearized ln (S ) and ln (A ) ln (S ) = ln (c ) + z ln (A ) –z is now the slope –ln (c ) is now the intercept ln (S ) ln (A )

43. Island Biogeography ( MacArthur and Wilson, 1960’s) Island Biogeography ( MacArthur and Wilson, 1960’s) fig 53.26a immigration rate decreases with Sp. N since it becomes more likely that immigrants will not be new speciesimmigration rate decreases with Sp. N since it becomes more likely that immigrants will not be new species extinction rate increases with Sp. N because of a greater likelihood of competitive exclusionextinction rate increases with Sp. N because of a greater likelihood of competitive exclusion equilibrium reached when immigration and extinction rates are equalequilibrium reached when immigration and extinction rates are equal equilibrium number is correlated with area and distance from mainlandequilibrium number is correlated with area and distance from mainland The number of species on an island is in a dynamic equilibrium determined by imm. and ext. rates

45. A B Mainland Area effect

46. Area Effect fig 53.26b larger islands are more likely to be found by immigrants which increases immigration ratelarger islands are more likely to be found by immigrants which increases immigration rate organisms are less likely to go extinct on larger islands because there is more available habitatorganisms are less likely to go extinct on larger islands because there is more available habitat equilibrium number is higher on larger islands because of both higher immigration and lower extinctionequilibrium number is higher on larger islands because of both higher immigration and lower extinction Island size influences immigration and extinction rates because……

47. AB Mainland Distance effect

48. Distance Effect fig 53.26c given islands of the same size, immigration will be higher on near islands since they are more likely to be found by immigrantsgiven islands of the same size, immigration will be higher on near islands since they are more likely to be found by immigrants extinction rates the same (same size islands)extinction rates the same (same size islands) equilibrium number is higher on near islands because of higher immigrationequilibrium number is higher on near islands because of higher immigration Distance from the mainland influences immigration and extinction rates

52. Island biogeography is a simple model and we must take into account abiotic disturbance, adaptive changes, and speciation events

53. Latitudinal species richness gradients species richness of many taxa declines from equator to polesspecies richness of many taxa declines from equator to poles Why? NOT KNOWNWhy? NOT KNOWN fig 53.23 Land birds Could be evolutionary or ecological factors, or both?

60. Application of biogeographic principles to the design of nature preserves. In each pair of figures the design on the left is preferred over that on the right, even though both incorporate the same area. The concepts are: A, a continuous reserve is better than a fragmented one; B, the ratio of area to perimeter should be maximized; C, distance between refuges should be minimized; and D, dispersal corridors should be provided between fragments. (from Ecology and Evolution of Communities, ed. M. L. Cody and J. M. Diamond, 1975.

61. What is a Food Web? Describes which kinds of organisms in communities eat other kinds Community food web is a description of feeding habits of a set of organisms based on taxonomy, location or other criteria Webs were derived from natural History approaches to describing community structure

62. Food Webs: trophic assignments Primary Producers –Phytoplankton and some macrophytes Consumers: heterotrophic animals –Primary consumers: herbivores –Secondary and higher-level consumers: carnivores, predators Decomposers: bacteria and fungi

63. Food webs: trophic assignments cont. Trophic level Name 4 Top carnivore 3 Carnivore 2 Herbivore 1 Autotroph

64. What is a Food Web (2)? Food webs portray flows of matter and energy within the community If community is like a city, then Food Web is like a street map of a city Web omits some information about community properties –e.g., minor energy flows, constraints on predation, population dynamics

65. Food Webs: Methods 1.Identify component species 2.Sample to determine who is eating whom 3.Sampling and gut analysis to quantify frequency of encounters 4.Exclosures and removals of species to determine net effects 5.Stable isotopes 6.Mathematical models

66. Descriptive Food Webs

67. Interaction or functional food webs depict the most influential link or dynamic in the community

68. What is a Food Web (cont.): Complexity meets reality Fallacy of linear food chains as a adequate description of natural food webs –Food webs are reticulate –Discrete homogeneous trophic levels an abstraction or an idealism –omnivory is rampant –ontogenetic diet shifts (sometimes called life history omnivory) –environmental diet shifts –spatial & temporal heterogeneity in diet

69. What is a food web (cont.)? Modern Approaches to Food Web Analysis –Connectivity relationships –Importance of predators and interaction strength in altering community composition and dynamics –Identification of trophic pathways via isotope analysis. Weakness of above: no quantitative measure of food web linkages.

70. Trophic Basis of Production Assimilation efficiency varies with resource –10% for vascular plant detritus –30% for diatoms and filamentous algae –50% for fungi –70% for animals –50% for microbes (bacteria and protozoans) –27% for amorphous detritus Net Production Efficiency production/assimilation ~ 40%

71. Energy flow through ecosystems Energy transfer between trophic levels is not 100% efficient, and energy is lost as it passes up a food chain. Herbivores eat a small proportion of total plant biomass They use a small proportion of plant material consumed for their growth. The rest is lost in feces or respiration Less energy is available at the next trophic level.

72. Marine Ecology: Food Webs Ecological efficiency is defined as the energy supply available to trophic level N + 1, divided by the energy consumed by trophic level N. You might think of it as the efficiency of copepods at converting plants into fish food. In general, only about 10% of the energy consumed by one level is available to the next. Difficult to measure so food web scientists focus on measure of transfer efficiency

73. Food Webs A pyramid of biomass represents the amount of energy, fixed in biomass, at different trophic levels for a given point in time The amount of energy available to any trophic level is limited by the amount stored by the level below. Because energy is lost in the transfer from one level to the next, there is successively less total energy as higher trophic levels.

74. Food Webs in the Ocean The oceans can be an exception, because at any time the total amount of biomass in microscopic algae is small. A pyramid of biomass for the oceans can appear inverted However, a pyramid of energy, which shows rates of production rather than biomass, must have the characteristic pyramid shape. Algae can double in days, whereas zooplankton that feed on them might double in months, while fish feeding on zooplankton might only reproduce once a year. Thus, a pyramid of energy takes into account turnover rate, and can never be inverted.