1. Species Interactions
21-1

2. Symbiosis Communities contain interacting populations of many species.
Symbiosis is the relationships that exist between species.

3. Predation +/- Predator- hunter Prey- hunted
Predators help to regulate and maintain population size.

4. Predation
Natural selection favors adaptations that better enable predators to hunt.

5. Predation
Prey species have adaptations that allow them to avoid, escape or ward off predators.

6. Predation
Mimicry
Camouflage
Bright colors

7. Herbivory
Herbivores consume plants and this is considered a form of predation.
Plants have adaptations to defend themselves as well.

8. Herbivory
Plants may have physical defenses: sharp spines, sticky hairs or tough leaves.

9. Herbivory
Or may produce secondary compounds that are poisonous, irritating or bad tasting.

10. Parasitism +/- Parasites feed on their host without immediate death.
Endoparasites
Ectoparasites

11. Parasitism
Parasites can affect the health and reproduction of the host.
Potential hosts have several lines of defense: skin, chemicals (saliva, mucus), and the immune system.

12. Competition +/- Occurs when there is a fundamental niche overlap.
Prevents others from living
Using resources
more efficiently

13. Competition
Competitive exclusion is when one species is eliminated from competition.
Natural selection favors differences between potential competitors.

14. Competition
Character displacement decreases competition.

15. Competition Resource partitioning occurs when similar species coexist;
each species
uses only
part of an available resource.

16. Mutualism +/+
A cooperative relationship where both species derive some benefit.

17. Mutualism
Pollination- a flower is a lure for pollinators. Insects are attracted to color, shape, pattern and scent.

18. Commensalism +/0
One species benefits and the other is unaffected.

19. Properties of Communities
21-2

20. Community properties and interactions:
Affect the structure of a community
Determine species richness and abundance

21. Species richness The number of species in an area
Independent of pop. size
Varies with latitude

26. Species richness & Latitude
Temperate habitats are younger
Further from 0o were affected by last ice age
Tropics remained unaffected

27. Species richness & Latitude
Stable climate in the tropics allows for greater species specialization
Photosynthesis is constant  more available energy at base

28. Species richness & Latitude
Equatorial rainforests are biologically the richest habitats on Earth.
(Yet make up only ~6% of land area)

29. Species diversity The number of species in relative abundance
Population size of all species in the community

32. Species-Area Effect
Larger areas usually contain more species than smaller areas.

33. Species-Area Effect
Larger areas tend to contain a greater diversity of habitats and thus can support more species.

35. Species-Area Effect
Therefore decreasing the size of habitat reduces the number of species it can support.

37. Species-Area Effect
Habitat destruction from a growing human population leads to species extinction.
2% of the world’s tropical rainforest is destroyed each year.

40. Interactions among species sometimes promotes species richness

41. A superior predator can maintain species diversity by preventing a lessor predator from taking over.
Pisaster
Mytilus

42. Stability of a community indicates its resistance to change
Stability of a community indicates its resistance to change. Species richness improves a community’s stability.

45. Communities with many species have more links, interactions
Communities with many species have more links, interactions. This would disperse the effects of the disturbance and prevent disruption of the community.

48. Succession
21-3

49. Disturbances trigger a sequence of changes in the composition of a community.
Certain species flourish immediately after the disturbance, then are replaced by other species, then still others.

50. Over time, the composition of the community changes.
The gradual, sequential regrowth of a species in an area is called succession.

51. The development of a community in an area that has not supported life previously.
Primary Succession

53. Proceeds slowly since there is no material for plant growth.
Primary Succession

60. Margerie Glacier

62. The sequential replacement of species that follows the disruption of an existing community.
Secondary Succession

65. The organisms in each stage alter the physical environment in ways that make it less favorable for their own survival but more favorable for the organisms that eventually succeed them.

66. Ecologists agree that the idea of a single successional pathway ending in a stable climax community is too simple to describe what actually occurs in nature.