Community Ecology

1. Community Ecology Chapter 53

2. Community– the populations that co-occur in a given place at a given time Important static properties of a community: Species richness= the number of species Relative abundance = relative commonness vs. rarity of species Fig. 53.11

3. Community– the populations that co-occur in a given place at a given time Important static properties of a community: Species diversity= an integrated measurement of species richness plus relative abundance Fig. 53.11

4. CommunityEcologists study communities by asking: What ecological and evolutionary processes organize and structure communities(e.g., what types of species are present and what types of interactions exist among species)? Why do communities vary in species composition, species diversity, and other aspects of community organization and structure?

5. Individualistic vs. Interactive Structure A debate raged in the early 20th century between Gleason’s “individualistic”hypothesis vs. Clements’ “integrated”hypothesis Individualistic hypothesis Integrated hypothesis Fig. 53.29

6. Individualistic vs. Interactive Structure Gleason’s “individualistic”hypothesis Species occur in a givenarea because they share similar abiotic (e.g., habitat) requirements Individualistic hypothesis Integrated hypothesis Fig. 53.29

7. Individualistic vs. Interactive Structure Clements’ “integrated”hypothesis Species are locked into communities through mandatory biotic interactions Individualistic hypothesis Communities viewed as “superorganisms” Integrated hypothesis Fig. 53.29

8. Individualistic vs. Interactive Structure Gleason’s “individualistic” hypothesis for community organization has received the most support from field-based studies Individualistic hypothesis Nevertheless, species interactions are important components of community dynamics Integrated hypothesis Fig. 53.29 Trees in the Santa Catalina Mountains

9. + - 0 A B A B A B - - - Antagonism (Predation/Parasitism) Amensalism Competition - + 0 A B A B A B 0 0 0 Neutralism (No interaction) Amensalism Commensalism - + 0 A B A B A B + + + Antagonism (Predation/Parasitism) Mutualism Commensalism Interspecific Interactions Influence of species A - (negative) 0 (neutral/null) + (positive) - Influence of Species B 0 +

10. Mutualism (+/+)E.g., ant-acacias and acacia-ants

11. Mutualism (+/+)Traits of species often evolve as a result of interspecific interactions

12. Mutualism (+/+)One species may evolve traits that benefit that species in its interactions with another species

13. Mutualism (+/+)Coevolution occurs when two species reciprocally evolve in response to one another

14. Pollination (+/+)(Usually a type of mutualism)

15. Frugivory & Seed Dispersal (+/+)(Usually a type of mutualism)

16. Predation (+/-) Striking adaptations often characterize predators and their prey

17. Crypsis Predators may evolve cryptic morphology

18. Crypsis Prey may evolve cryptic morphology

19. Aposematism Prey may evolve aposematic (warning) morphology

20. Mimicry Organisms may evolve to look like other organisms Batesian mimicry – innocuous mimicevolves to look like harmful model Viceroy Monarch

21. Mimicry Organisms may evolve to look like other organisms Mullerian mimicry – two harmful mimics evolve convergentlytoward a common morphology Cuckoo bee Yellow jacket

22. Herbivory (+/-) Feeding (sometimes predation) by animals on plants

23. Parasitism (+/-) Parasites derive nourishment from their hosts, whether they live inside their hosts (endoparasites) or feed from the external surfaces of their hosts (ectoparasites) Tapeworm Tick

24. Parasitoidism (+/-) Parasitoids lay eggs on living hosts and their larvae eventually kill the host

25. Commensalism (+/0) E.g., mites hitching a ride on a beetle

26. Amensalism (-/0)Common, but not considered an important process structuring communities; e.g., elephant stepping on ants

27. Neutralism (0/0)Common, but not considered an important process structuring communities; e.g., hummingbirds and earthworms (they never interact with one another)

28. Competition (-/-) Organisms often compete for limiting resources

29. Competition (-/-) E.g., smaller plants are shaded by larger plants

30. Competition (-/-) E.g., barnacles compete for space on rocky intertidal shores Fig. 53.2

31. Competition (-/-) Fundamental niche – an organism’s “address” (habitat) and “occupation” in the absence of biotic enemies Fig. 53.2

32. Competition (-/-) Realized niche – an organism’s “address” (habitat) and “occupation” in the presence of biotic enemies Fig. 53.2

33. Competitive Exclusion Principle Two species cannot coexist if they occupy the same niche Fig. 53.2

34. Competitive Exclusion Principle “complete competitors cannot coexist”; e.g., the barnacles do not coexist where their fundamental niches overlap Fig. 53.2

35. Competitive Exclusion Principle Competition between two species with identical niches results either in competitive exclusion Fig. 53.2

36. Competitive Exclusion Principle Competition between two species with identical niches results either in competitive exclusion or the evolution of resource partitioning Fig. 53.2

37. Competition (-/-) Resource partitioning may result from character displacement Fig. 53.4

38. Competition (-/-) Resource partitioning may result from character displacement Fig. 53.3

39. Food Chains Species interact through trophic (food) chains "So, the naturalists observe, the flea, Hath smaller fleas that on him prey; And these have smaller still to bite 'em; And so proceed, ad infinitum" Jonathan Swift (1667-1745) "Great fleas have little fleas Upon their backs to bite 'em And little fleas have lesser fleas, And so ad infinitum" DeMorgan (1915) Fig. 53.12

40. Food Chains The length of food chains is rarely > 4 or 5 trophic levels long The main reason follows from the Laws of Thermodynamics: Energy transfer between trophic levels is only ~10% efficient Fig. 53.12

41. Food Chains The length of food chains is rarely > 4 or 5 trophic levels long The main reason follows from the Laws of Thermodynamics: Energy transfer between trophic levels is only ~10% efficient Fig. 53.15

42. Food Webs Food chains combine into food webs: Who eats whom in a community? Fig. 53.13

43. Relative Abundance, Dominance, and Keystone Species Relative abundance = relative commonness vs. rarity Dominance = relative contribution to the biomass of a community Fig. 53.11

44. Relative Abundance, Dominance, and Keystone Species Relative abundance = relative commonness vs. rarity Dominance = relative contribution to the biomass of a community Fig. 53.13

45. Relative Abundance, Dominance, and Keystone Species Sometimes exotic species become deleteriously dominant

46. Relative Abundance, Dominance, and Keystone Species Keystone species influence community composition more than expected by their relative abundance or biomass

47. Keystone Species

48. Keystone Species Removing a keystone species has a much greater effect on community structure than expected by its relative abundance or biomass Fig. 53.16

49. Top-Down vs. Bottom-Up Control Debates continue regarding the relative importance of top-down vs. bottom-up control on community organization Both are important influences in most communities Fig. 53.12

50. Disturbance A discrete event that damages or kills resident organisms e.g., non-catastrophic treefall gap