1. Populations
Why they stop growing

2. Population density The number of organisms in a given area
Population growth is limited by several factors:
One set of which depends on population density
Another set does not depend on population density

3. Density Dependent Limiting Factors
Population limiting factors that operate more strongly on larger, denser populations than on small less crowed populations
These are: competition, predation, parasitism and crowding

4. Competition
The more individuals the sooner they use up the available resources
The fewer the individuals the longer resources last
One of the most important factors in determining the carrying capacity of an environment
Can lower birth rates (fewer survivors); increase death rates

5. Predation Most species serve as food for other species
Predators and prey usually coexist for long periods of time
Prey evolved mechanisms (defenses) to avoid predators
Predators evolved mechanisms (counter-defenses) to better capture prey
Predator prey populations always change over time (see graph page 139)

6. Parasitism Organism that take nourishment from a host
Most effective when hosts are present in large numbers
Parasites are host specific
High density means access to more hosts
Successful parasites do not kill their hosts

7. Crowding
Organisms have built in behavioral need for space (hunting, nesting)
Stress from crowding can interfere with hormone and immune systems
Changes in behavior can lead to less offspring being successful (no mating, eating offspring)

8. Density Independent Limiting Factors
These factors limit populations regardless of how large or small the population is
Mostly abiotic (does not involve living things)
Weather is most important (hurricanes, cyclones, rain, drought)
Fires
Physical disruption of the environment (earthquakes, volcanoes, avalanche, rock slides, mudslides, floods)
Human activity (plowing, clear cutting, slash and burn, use of toxins on crops)

9. Review Population density Density dependent limiting factors
Density independent limiting factors