1. Community Interactions
Chapter 29

2. Forest of New Guinea
Community includes nine species of pigeons that partition the food supply
Pigeons disperse seeds of the trees that provide their food (fruit)
These are just a few of the many interactions that shape this community

3. Community All the populations that live together in a habitat
Habitat is the type of place where individuals of a species typically live
Type of habitat shapes a community’s structure

4. Factors Shaping Community Structure
Climate and topography
Available foods and resources
Adaptations of species in community
Species interactions
Arrival and disappearance of species
Physical disturbances

5. Niche
Sum of activities and relationships in which a species engages to secure and use resources necessary for survival and reproduction

6. Realized & Fundamental Niches
Theoretical niche occupied in the absence of any competing species
Realized niche
Niche a species actually occupies
Realized niche is some fraction of the fundamental niche

7. Species Interactions
Most interactions are neutral; have no effect on either species
Commensalism helps one species and has no effect on the other
Mutualism helps both species

8. Species Interactions
Interspecific competition has a negative effect on both species
Predation and parasitism both benefit one species at a cost to another

9. Symbiosis Living together for at least some part of the life cycle
Commensalism, mutualism, and parasitism are forms of symbiosis

10. Mutualism Both species benefit Many examples in nature
Some mutualisms are obligatory; partners depend upon each other

11. Yucca and Yucca Moth Example of an obligatory mutualism
Each species of yucca is pollinated only by one species of moth
Moth larvae can grow only in that one species of yucca

12. Mycorrhizae Obligatory mutualism between fungus and plant root
Fungus supplies mineral ions to root
Root supplies sugars to fungus

13. Competition Interspecific - between species
Intraspecific - between members of the same species
Intraspecific competition is most intense

14. Forms of Competition
Competitors may have equal access to a resource; compete to exploit resource more effectively
One competitor may be able to control access to a resource, to exclude others

15. Competitive Exclusion Principle
When two species compete for identical resources, one will be more successful and will eventually eliminate the other

16. Competitive Exclusion Expt
Paramecium caudatum
Paramecium aurelia

17. Keystone Species A species that can dictate community structure
Removal of a keystone species can cause drastic changes in a community; can increase or decrease diversity

18. Lubchenco Experiment
Periwinkles promote or limit diversity in different habitats
Tidepools
Rocks exposed at high tide

19. Resource Partitioning
Apparent competitors may actually have slightly different niches
Species may use resources in a different way or time
Minimizes competition and allows coexistence

20. Predation Predators are animals that feed on other living organisms
Predators are free-living; they do not take up residence on their prey

21. Coevolution
Natural selection promotes traits that help prey escape predation
It also promotes traits that make predators more successful at capturing prey

22. Predator-Prey Cycles
Predator and prey populations may show an apparent correspondence
PREY POPULATION
PREDATOR POPULATION

23. Variation in Cycles
An association in predator and prey abundance does not always indicate a cause and effect relationship
Variations in food supply and additional predators may also influence changes in prey abundance

24. Prey Defenses Camouflage Warning coloration Mimicry
Moment-of-truth defenses

25. Predator Responses
Any adaptation that protects prey may select for predators that can overcome that adaptation
Prey adaptations include stealth, camouflage, and ways to avoid chemical repellents

26. Parasitism
Parasites drain nutrients from their hosts and live on or in their bodies
Natural selection favors parasites that do not kill their host too quickly

27. Types of Parasites Microparasites Macroparasites Social parasites
Parasitoids

28. Change in the composition of species over time
Succession
Change in the composition of species over time

29. Types of Succession Primary succession - new environments
Secondary succession - communities were destroyed or displaced

30. Pioneer Species Species that colonize barren habitats
Lichens, small plants with brief life cycles
Improve conditions for other species who then replace them

31. Climax Community
Stable array of species that persists relatively unchanged over time
Succession does not always move predictably toward a specific climax community; other stable communities may persist

32. Cyclic Changes
Cyclic, nondirectional changes also shape community structure
Tree falls cause local patchiness in tropical forests
Fires periodically destroy underbrush in sequoia forests

33. Restoration Ecology
Natural restoration of a damaged community can take a very long time
Active restoration is an attempt to reestablish biodiversity in an area
Ecologists are actively working to restore reefs, grasslands, and wetlands

34. Community Instability
Disturbances can cause a community to change in ways that persist even if the change is reversed

35. Species Introductions
Introduction of a nonindigenous species can decimate a community
No natural enemies or controls
Can outcompete native species

36. Exotic Species
Species that has left its home range and become established elsewhere
Becomes part of its new community
Can have beneficial, neutral, or harmful effects on a community

37. Endangered Species
A species that is extremely vulnerable to extinction
Close to 70 percent of endangered species have been negatively affected by exotic competitors

38. Nile Perch in East Africa
Nile perch were introduced into Lake Victoria as a food source
This predator ate native cichlids; drove many species to extinction
Now Nile perch species is close to crashing

39. Rabbits in Australia Rabbits were introduced for food and hunting
Without predators, their numbers soared
Attempts at control using fences or viruses have thus far been unsuccessful

40. Kudzu in Georgia Imported for erosion control
No natural herbivores, pathogens, or competitors
Grows over landscapes and cannot be dug up or burned out
May turn out to have some commercial use

41. Diversity by Latitude
Diversity of most groups is greatest in tropics; declines toward poles
Ant diversity

42. Why Are Tropical Species Rich?
Resources are plentiful and reliable
Species diversity is self-reinforcing
Rates of speciation are highest in the tropics

43. Distance Effect
The farther an island is from a mainland, the fewer species
Closer islands receive more immigrants
Species that reach islands far from mainland are adapted for long-distance dispersal and can move on

44. Distance Effect