1. Population Growth
There is a “standard” pattern of growth changes seen when an organism is introduced into a new environment.

2. Growth Phases Lag phase – Organism adjusts to new environment.
Log phase - Reproduction is occurring at an exponential rate (doubling predictably).
Stationary phase - Environmental surroundings and food supply cannot support rapid growth (Rates of birth and death balanced).
Death phase – Toxins build up and nutrients become “locked up” and unavailable. Death rate overtakes reproduction.

3. Human Population Growth
Compare this with the previous slide.
Where is the human population on this typical growth curve now?
Is there any reason to believe that we will not experience the “standard” pattern?
Can we do anything about this?

4. Population Changes
Although most wild populations stay relatively constant, there are highly significant fluctuations in numbers due to several key factors

5. Key Factors Affecting Populations
Birth Rate
Death Rate
Competition
Availability of Food (or Prey)
Predators
Disease
Parasites
Space or Territory
Migration (Emigration and Immigration)

6. Competition Intraspecific
Between members of the same species, who will have very similar needs.
Interspecific
Between members of different species that “overlap” for resources.

7. Predator/Prey Cycles
One of the most significant factors affecting populations.
In some environments the numbers of a particular animal is critically dependent on the availability of it’s prey.
Equally, the presence or absence of significant numbers of predators has a dramatic effect on prey populations.

8. Snowshoe Hare and Lynx

9. Elton and the Hudson Bay Co.
The Scientist Charles Elton used the records of the Hudson Bay Company to track changes in the populations of these two animals over nearly 100 years. Skins traded provided a consistent sample from the two wild populations.

10. The Typical Cyclical Oscillation of the Predator/Prey Relationship

11. The Reason for the Cycle
Few Prey
Few Predators
Predator numbers fall
Prey numbers rise
Many Prey
Few Predators
Few Prey
Many Predators
Many Prey
Many Predators
Prey numbers fall
Predator numbers rise

12. The Typical Result
The predator “tracks” the prey with population peaks later in time than the peaks of the prey.
(Predator numbers will always be fewer than prey).