1. Community Ecology
Chapter 53

2. Community An assemblage of populations in an area or habitat
Communities differ in
Species richness # they contain
Relative abundance of diff. species

3. Different Views of Communities
An individualistic hypothesis depicts a community as a chance assemblage of species found in the same area because they happen to have similar abiotic requirements.(Gleason.1900s)

4. An interactive hypothesis depicts a community as an assemblage of closely linked species locked in by mandatory biotic interactions. (Clements 1900s)
In most actual cases, the composition of communities does seem to change continuously

5. Rivet Model & Redundancy Model
The rivet model of communities is a reincarnation of the interactive model.
The redundancy model states that most species in a community are not closely associated with one another.
No matter which model is correct, it is important to study species relationships in communities.

6. Interspecific Interactions
Populations may be linked by Competition, Predation, Mutualism and Commensalism

7. Interspecific Interactions

8. A. Interspecific Competition
Resources are in short supply
Potential for competition between any two species that need the same limited resource.

9. Competitive Exclusion Principle
1934, G.F. Gause P. aurelia & P. caudatum, grown separately-did well but tog. P. aurelia drove P. caudatum to extinction
Two species with similar needs for same limiting resources cannot coexist in the same place
The better adapted of the two will replace the other

10. Ecological Niche
All the biotic and abiotic factors needed to maintain the species.
An organism’s niche is its role in the environment.
Hawks and Owls have the same niche but can coexist b/c hawks are diurnal, owls are nocturnal
The competitive exclusion principle can be restated to say that two species cannot coexist in a community if their niches are identical.

11. Resource Partitioning
Differentiation of niches that enables two similar species to coexist in a community

12. Character Displacement
The tendency for characteristics to be more divergent in sympatric populations of two species than in allopatric populations of the same two species.
Hereditary changes evolve that bring about resource partitioning

13. B. Predation (-/+) A predator eats prey.
Herbivory, in which animals eat plants.
In parasitism, predators live on/in a host and depend on the host for nutrition.
Predator adaptations: many important feeding adaptations of predators are both obvious and familiar.
Claws, teeth, fangs, poison, heat-sensing organs, speed, and agility

14. Plant Defenses Chemical compounds that are toxic Thorns
Secondary compounds not part of normal met, ex poisonous berries

15. Animal Defenses b. Mechanical defenses include spines.
Behavioral defenses include fleeing, hiding, self-defense, noises, and mobbing.
a. Camouflage includes cryptic coloration, deceptive markings.
b. Mechanical defenses include spines.
c. Chemical defenses include odors and toxins
Aposematic coloration is indicated by warning colors, and is sometimes associated with other defenses (toxins).

17. Fig. 53.6
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

18. Mimicry- organisms resemble other species
Batesian mimicry is where a harmless species mimics a harmful one
Snake
Hawkmoth larva

19. 2. Müllerian Mimicry
Two or more unpalatable species resemble each other
Both produce a toxin& predators learn quickly to avoid them
Yellow jacket
Cuckoo Bee

20. Batesian mimicry Convergent evolution Monarch male poisonous
Viceroy male
edible

21. Parasites and pathogens as predators
A parasite derives nourishment from a host, which is harmed in the process.
Endoparasites live inside the host and ectoparasites live on the surface of the host.
Parasitoidism is a special type of parasitism where the parasite eventually kills the host.
Pathogens are disease-causing organisms that can be considered predators.

22. C. Mutualism (+) Two species benefit from their interaction
Acacia & ants
Acaciafood & cover
Ants sting any intruder

23. D.Commensalism (+/o)
One species benefits from the interaction, but other is not affected.
An example would be barnacles that attach to a whale
Bird’s nests in trees

24. E. Coevolution
Two species with intertwined life history- the evolution of one affects the other
When one species evolves, it exerts selective pressure on the other to evolve to continue the interaction
Ex humming bird & flower

25. F.Trophic structure Feeding relationships Food chains
food chain usually 4 or 5 links = trophic levels
length of food chain limited by inefficiency of energy transfer

26. Food webs Food chains are hooked together into food webs
Who eats whom?
a species may weave into web at more than 1 trophic level
bears
“there’s always a bigger fish”
What limits the length of a food chain?

27. G. Dominant & Keystone Species
Dominant species most abundant species or highest biomass (total weight) community
If we remove a dominant species from a community, it can change the entire community structure.
Keystone species exert important regulating effect on other species in community

28. Keystone species Influential ecological role
not necessarily dominant or most abundant
keystone species increases diversity of habitat

29. Keystone species Sea otter is keystone predator in North Pacific
What is the impact of the whale?
Structure of a community may be controlled bottom-up by nutrients or top-down by predators

30. II. Disturbances
Most communities are in a state of non-equilibrium due to disturbances
fire, weather, human activities, etc.
not all are negative

31. Disturbances
Disturbances are often necessary for community development & survival

32. Ecological cycle
fire as part of a natural community cycle

33. IIB. Ecological succession
The sequence of community changes after a disturbance
transition in species composition over ecological time
years or decades
Mt. St. Helens

34. Primary succession
Begins with virtually lifeless area without soil, then…
bacteria
lichens & mosses
grasses
shrubs
trees {
make soil

36. Succession
from mosses & lichens
= pioneer species
to shrubs & trees

37. Secondary succession
Existing community cleared, but soil is intact

38. Climax forest
Plant community dominated by trees representing final stage of natural succession for specific location
stable plant community developed through stages
remains essentially unchanged in species composition for as long as site remains undisturbed
birch, beech, maple, hemlock
oak, hickory, pine

39. Climax Forest
The species mix of climax forest is dependent on the abiotic factors of the region
solar energy levels
temperature
rainfall
fertility & depth of soil
birch, beech, maple, hemlock

40. III. Biodiversity of Communities
Two components
Species Richness
Relative abundance
Greater diversity = greater stability
Which is more diverse?

41. Species richness is related to a community’s geographic size
The species-area curve : the larger the geographic area, the greater the number of species

42. Patterns of Biodiversity
Equatorial/Polar gradient: greatest at equator, less &less as move to poles, because
Climate: poles frozen at times,long growing more solar energy & eq
Age: eq comm. Are older, more established

43. Patterns of Biodiversity
Island Biogeography: diff islands have diff # of species b/c of immigration & extinction.
Immigration & extinction determined by the size of the island & distance from the mainland

44. Factors that determine the number of species that eventually inhabit the island
The rate at which new species immigrate to the island.
The rate at which species become extinct.

45. New Island

46. Size of Island

47. Distance from Mainland