2. Community Concept
Community - An assemblage of populations interacting with one another within the same environment
Composition - a listing of various species in the community.
Diversity - includes list of species as well as abundance of each species.

3. Composition - a listing of various species in the community.
Community Structure
Composition - a listing of various species in the community.

4. Community Structure
Diversity - includes list of species as well as abundance of each species. More diversity = more species

5. Diversity and Composition Models
Gleason - Individualistic Model
Each population is there because its abiotic requirements are met

6. Species Richness of Communities
Species may occupy an area because their tolerance range overlaps
Species range is based on tolerance for certain ABIOTIC factors.
There is an optimum range

7. Diversity and Composition Models
Clements - Interactive Model
Community is the highest level of organization
Dependent on biotic interactions

8. Model of Island Biogeography
MacArthur and Wilson
Developed a general model of island biogeography
Explains and predicts how the community diversity of an island is affected by
Distance from mainland
Size of the island

9. Habitat and Ecological Niche
The area an organism lives & reproduces in
Ecological niche
The role a species plays in its community
Includes its habitat
Its interactions with other organisms

10. Feeding niches for Wading Birds

11. Habitat and Ecological Niche
Fundamental niche - All conditions under which the organism can survive.
Realized niche - Set of conditions under which it exists in nature.

12. Habitat and Ecological Niche
Organisms can occupy their fundamental niche, if little competition pressure.
Competition forces an organism to occupy is realized niche.
Realized niche < Fundamental niche

13. Habitat and Ecological Niche
Generalist Species – Have a broad range of niches.
Bears, racoons, humans
Can tolerate a wide range of environments & has a varied diet.
Advantage in changing environment

14. Habitat and Ecological Niche
Specialist Species – Have a narrow range of niches.
Pandas, Koalas, freshwater dolphins
Lives in specific habitats & on a limited diet.
Advantage in stable environment

15. Community Structure Competition
When two species compete, the abundance of both species is negatively impacted

16. Competition Between Populations
Interspecific competition
Members of different species require the same resource
The supply of the resource is limited

17. Species Interactions

18. Competition Between Two Lab Populations of Paramecium
Competitive Exclusion Principle
No two species can occupy the same niche at the same time

19. Character Displacement in Finches on the Galápagos Islands
Competitive Exclusion Principle
Resource Partitioning decreases competition & promote niche specialization.
Can lead to character displacement

20. Niche Specialization Among Five Species of Coexisting Warblers
Competition
Niche Specialization Among Five Species of Coexisting Warblers

21. Competition Between Two Species of Barnacles

22. Community Structure Predation (or parasitism)
Expected to increase the abundance of the predator (or parasite)
And reduce the abundance of the prey (or host)

23. Species Interactions

24. Predator-Prey Interactions
Predation
One living organism, the predator, feeds on another, the prey
Predator is larger
Predator has lower reproductive rate
Prey usually entirely consumed
Presence of predators can decrease prey densities, and vice-versa

25. Predator-prey Interaction Between Paramecium & Didinium

26. Predator-prey Interaction Between a Lynx and a Snowshoe Hare

27. Prey Defenses
Mechanisms that thwart the possibility of being eaten by a predator:
Spines
Tough Epidermis
Poisonous Chemicals
Camouflage
Bright Coloration
Flocking Behavior

28. Camouflage in the Anglerfish
Cryptic Coloration

29. Cryptic Coloration (Camouflage)

30. Anti-predator Defenses
Aposematic (Warning) Coloration

31. Mimicry
Mimicry
One species resembles another species that possesses an overt antipredator defense

32. Mimicry Batesian Mimicry
Mimic lacks defense of the organism it resembles

33. Mimicry
Müllerian Mimicry
Mimic shares same protective defense

34. Symbiotic Relationships
Symbiosis
Interactions in which there is a close relationship between members of two species

35. Species Interactions

36. Symbiotic Relationships
Parasitism
Parasite derives nourishment from a host, and may use host as habitat and mode of transmission
Endoparasites
Ectoparasites

37. The Life Cycle of a Deer Tick

38. Commensalism Commensalism
A symbiotic relationship in which one species benefits and the other is indifferent
Remoras and Sharks
Many supposed examples may turn out to be mutualism or parasitism
Inferred amount of harm or benefit two species do to one another is subject to investigator bias

39. Clownfish Among Sea Anemone’s Tentacles

40. Mutualism
Mutualism
A symbiotic relationship in which both members of the association benefit
Need not be equally beneficial to both species
Cleaning Symbiosis
Often help each other obtain food or avoid predation
Bacteria in human intestinal tract

41. Mutualism Between the Bullhorn Acacia Tree and Ants

42. Cleaning Symbiosis

43. Coevolution Coevolution
When 2 species adapt in response to selective pressures imposed by the other.
Some Examples:
Pollinators and Flowers
Cheetah & Gazelle

44. Community Development
Ecological Succession
A predictable pattern of change in species replacements following a disturbance
Primary Succession
Secondary Succession

45. Ecological Succession
Primary Succession - occurs in areas where there is no soil formation

46. Large-scale Disturbance: Eruption of Mount St. Helens

47. Ecological Succession
Secondary Succession - begins in areas where soil is present
Pioneer Species

48. Moss, a Characteristic
Pioneer Species
Sporophytes
Gametophytes

49. These are classic pioneer
Lichens
Moss
These are classic pioneer
species.

50. Secondary Succession

51. Secondary Succession in a Forest
Climax Community - remains essentially the same over long periods of time.
It is the final stage of ecological succession.

52. Community Diversity Community stability can be recognized in 3 ways:
Persistence through time
Resistance to change
Recovery once a disturbance has occurred

53. Intermediate Disturbance Hypothesis
Widespread Disturbances occur frequently - diversity will be limited (low)

54. Intermediate Disturbance Hypothesis
Moderate Disturbances occur with moderate frequency -diversity is high

55. Effect of a Keystone Species
Keystone Species has an unusually large role in maintaining function & diversity of an ecosystem.
Pisaster (Sea Star)
Sea Otter (in a kelp forest)
Beavers (create dams & make wetlands)

56. Exotic Species (Alien, Introduced, Invasive, Non-native)
Also call Alien, Introduced, Invasive, Non-native
May lead to unbridled competition
Resultant reduction in biodiversity
Examples:
Kudzu vine
Cane toad
African bees (killer bees)

57. Kudzu Vine