1. Population Equilibrium
A dynamic balance between births and deaths.
Births = Deaths

2. Biotic Potential and Environmental Resistance

3. Population Growth Curves
Reproductive strategies:
Many offspring with low parental care
Example  fish
J-shaped growth curve
Few offspring with high parental care
Example  mammals
S-shaped growth curve

4. Population Growth Curves

5. Density Dependence and Critical Numbers
Factors of environmental resistance are either:
density-independent: effect does not vary with population density; e.g., adverse weather
density-dependent: effect varies with population density; e.g., infectious disease
Critical number: the lowest population level for survival and recovery

6. Mechanisms of Population Equilibrium
Predator–prey dynamics
Competition
Interspecific
Intraspecific
Introduced species

7. Predator–Prey Balance: Wolves and Moose

8. Predator–Prey Balance
Absence of natural enemies allows a herbivore population to exceed carrying capacity, which results in overgrazing of the habitat.
The herbivore population subsequently crashes.
The size of the herbivore population is maintained so that overgrazing or other overuse does not occur.

9. Keystone Species
A single species that maintains biotic structure of the ecosystem
Example:
Pisaster ochraceus: a starfish that feeds on mussels (Mytilus californianus) , keeping them from blanketing the rocks
Pacific coast intertidal zone

10. Competition: Intraspecific
Territoriality: defense of a resource against individuals of the same species
Examples of wolves and songbirds
Results in priority access and use of resources

11. Competition: Interspecific
Grasslands contain plants with both fibrous roots and taproots
Coexist by accessing resources from different soil levels

12. Introduced Species Examples (Long Island): Mute swans Starling
House Sparrows
Gypsy Moths
Japanese Beetles
Pheasants
Phragmites
Eurasian fresh water clam
And LOTS MORE!!!

13. European Green Crab – Native Species

14. Asian Shore Crab – Introduced Competitor
Introduced to New Jersey in 1988
Spread up to Maine
Native Species are diminishing
Asian Shore Crab
European Green Crab

15. Mechanisms of Species Adaptation
Change through natural selection
Selective pressure determines which organisms survive and reproduce and which are eliminated.

16. The Limits of Change
Adapt
Move (migrate)
Die (extinction)

17. Vulnerability of different organisms to
environmental changes

18. Prerequisites for Speciation
Original population must separate into smaller populations that do not interbreed with one another.
Separated populations must be exposed to different selective pressures.

19. Speciation: Foxes

20. Speciation: Galápagos Finches