1. Biological Communities
Chapter 17

2. How Organisms Interact in Communities
Evolution in Communities lead to special relationships among some species
Examples include:
Predator/Prey
Parasitism
Symbiosis

3. Predators and Prey Predators Prey Population sizes are linked
Consumers that hunt other organisms
Prey
Organisms upon which a predator feeds
Population sizes are linked
Increase in prey  Increase in predator
Decrease in prey  Decrease in predator
Population of prey regulates population of predator
Ex. Lynx and Hare populations

4. Parasitism
One organism feeds on the tissues or body fluids of another (host)
Host – organism on which a parasite feeds
Parasites live on or in organism
Most do not kill their hosts
Parasite populations depend on the host size and populations
Ex. Tapeworms in mammal intestines

5. Symbiosis Relationship where two species live together closely
Parasitism is an example
Commensalism
One species benefits, the other is neither helped nor harmed
Ex. Barnacles and whales
Mutualism
Both species benefit
Ex. Insects and flowers

6. How Competition Shapes Communities
Competition occurs when two species use the same resource.
Examples include: food, nesting sites, living space, light, water, etc
Niche refers to a species role in an ecosystem…where it lives, the “job” or role it plays…
If several species occupy the same niche in an ecosystem competition exists

7. Population Growth Populations grow quickly Exponential Growth
Population growth in which the rate of growth in each generation is a multiple of the previous generation
Ex. 2  4  8  16  32  64 
Is there a limit?

8. Carrying Capacity If population grows, resources become scarce
Individuals compete, death rate rises
Birth rate decreases, if resources are low
When death rate equals birth rate, population stops growing
Carrying Capacity
The number of individuals that can be supported by an ecosystem
Represented by an S-Shaped Curve (graph)

9. Limiting Factors Forces that slow population growth Density-Dependent
Depends on population size
S-Shaped curve
Ex. Food, predation, disease
Density-Independent
Affects same percentage of population regardless of size
Ex. Habitat damage, such as hurricanes and fires
Boom and Bust curve – grows exponentially then collapses

10. Major Biological Communities
Elements of climate (temperature, and moisture) determine ecosystems.
Sometime also called limiting factors
Major biological communities that occur over a large area are called biomes.
Vary depending on latitude or longitude (land biomes) or water type and depth

11. Terrestrial Biomes Tropical Rain Forests Savannas Taiga Tndra Deserts
Temperate Grasslands
Temperate Deciduous Forests
Temperate Evergreen Forests

12. Aquatic Communities Freshwater Estuaries Marine Ponds, Lakes, Rivers
Wetlands
Estuaries
Marine
Shallow Ocean
Surface of Open Sea
Ocean Depths