1. Community Interactions

2. Communities Habitat is the environment in which an organism lives.
A population's niche is its role in the community
How it uses the biotic and abiotic resources of its habitat

3. Community interactions
There are five main types of relationships among species within communities
Competition
Predation
Parasitism
Commensalism
Mutualism

4. Community interactions
Interspecific competition occurs between
two populations if they both require the same limited resource
Intraspecific competition occurs between organisms of the same species.
Resources include food, water, nesting sites
Plants compete for sunlight, water, soil nutrients, space

5. The competitive exclusion principle
Populations of two species cannot coexist in a community if their niches are nearly identical
High tide
Chthamalus
Barnacle expt shows two outcomes possible:
Remove blue barnacles, brown ones grow down and cover entire rock.
Ther4, blues outcompeting brown for low space on rock.
Remove brown ones, blue ones do NOT grow up. Ther4, resource (space on rock) has been divided and only brown are adapted to drier upper zones of rock.
Balanus
Ocean
Low tide
Figure 36.2

6. Competition between species with identical niches has two possible outcomes
One population will eventually eliminate the other
Natural selection may lead to resource partitioning (division)

7. Predation Predation is an interaction where one species eats another
consumer = predator
food species = prey
Predation is severe form of natural selection. Leads to many diverse adaptations designed to escape predation and to make more successful predators.
Explains why the most successful parasite is not a fast killer.
Examples: mistletoe on oaks, dodder on phosyn plants, fungal hyphae on nematodes

8. Adaptations are driven by these relationships…COEVOLUTION!
Prey gain protection against predators through a variety of defense mechanisms
1. Mechanical defenses, such as the quills of a porcupine

9. 2. Chemical defenses
Animals are often brightly colored to warn predators
Example: the poison-arrow frog
Many interesting chemicals from amphibs. Antibiotic megainan, anithestic.

10. Physical/Chemical Combat

11. 3. Camouflage
Example: gray tree frog
Figure 36.3C

12. Camouflage

14. 4. Batesian mimicry occurs when a harmless species mimics a harmful one
mimicry can involve behavior
hawkmoth larva puffs up its head to mimic the head of a snake
Figure 36.3D

15. Trickery/Mimicry

16. How does predation affect the community?
Eliminates weaker individuals
keystone predator maintains diversity by reducing numbers of the strongest competitors in a community
- Ex. sea star is a keystone predator
Figure 36.4A

17. Predation by killer whales on sea otters, allowing sea urchins to overgraze on kelp
Sea otters represent the keystone species

18. Parasitism Parasitism is a form of predation Parasite, host
Not immediately lethal
Example: mistletoe on oaks, tapeworm in human intestine

19. Commensalism - one partner benefits and the other is unaffected
Examples
- Algae that grow on the shells of sea turtles
Barnacles that attach to whales
Birds that feed on insects flushed out of the grass by grazing cattle

20. Mutualism: both partners benefit Examples:
- Nitrogen-fixing bacteria and legumes
Acacia trees and the ants of the genus Pseudomyrmex
Figure 36.5B

21. Symbiosis
Any long term biological interaction is known as symbiosis or a symbiotic relationship
Some biologists only characterize mutualism and commensalism as symbiosis
Others include parasitism as well
Endosymbiosis is the theory that several eukaryotic organelles are the result of a symbiotic relationship between specialized prokaryotic cells.

22. Your task… Community Interaction comic
Pick one of the types of interactions we discussed. (competition, predation, parasitism, mutualism, commensalism)
Draw a comic showing the interaction.
Comic must have at least three panels
No words are necessary, but it must clearly show the type of interaction
Do not write the type of interaction on your comic or your name
When it is finished, bring it to me for a number and further directions.