1. Community Concept
An assemblage of populations interacting with one another within the same environment
Composition is a listing of various species in the community
Diversity includes both species richness and species diversity

2. Community Structure Competition
When two species compete, the abundance of both species is negatively impacted
Predation (or parasitism)
Expected to increase the abundance of the predator (or parasite)
And reduce the abundance of the prey (or host)

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

4. Feeding niches for Wading Birds

5. Competition Between Populations
Interspecific competition
Members of different species require the same resource
The supply of the resource is limited
Competitive Exclusion Principle
No two species can occupy the same niche at the same time
Resource Partitioning decreases competition

6. Competition Between Two Laboratory Populations of Paramecium

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

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

9. Prey Defenses Prey defenses
Mechanisms that thwart the possibility of being eaten by a predator
Spines
Tough Epidermis
Poisonous Chemicals
Camouflage
Bright Coloration

11. Mimicry
Mimicry
One species resembles another species
Mimicked species possesses an overt antipredator defense
Batesian Mimicry - Mimic lacks defense of the organism it resembles
Müllerian Mimicry - Mimic shares same protective defense

12. Mimicry Among Insects

13. Symbiotic Relationships
Symbiosis
Interactions in which there is a close relationship between members of two species
Parasitism
Parasite derives nourishment from a host, and may use host as habitat and mode of transmission

14. Mutualism Symbiosis, cont. Mutualism
A symbiotic relationship in which both members of the association benefit
Often help each other obtain food or avoid predation
Bacteria in human intestinal tract

16. Commensalism Symbiosis, cont. Commensalism
A symbiotic relationship in which one species benefits and the other is indifferent
Many supposed examples may turn out to be mutualism or parasitism

18. Predation, Competition, and Biodiversity
Predation by a particular species may reduce competition and increases diversity
Such predators are referred to as keystone predators
Exotic species
May lead to unbridled competition
Resultant reduction in biodiversity