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

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.

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?

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

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

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

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.

Snowshoe Hare and Lynx

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.

The Typical Cyclical Oscillation of the Predator/Prey Relationship

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

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).