Population Dynamics

Populations A population is a group of organisms of the same species that live in a particular place at one time. A population could be a species of plants, animals, bacteria, or people, living in a given area (for example, bass living in an isolated pond).

Population Dynamics: Populations are constantly changing and we need to keep up with the changes. The study of human population is demography. Some measures are: Birth Rate – Number of births in a given time. (U.S. – 4 million per year) Death Rate – Number of deaths in a given time. (U.S. – 2.4 million per year) Life Expectancy – how long the avg. person lives. (U.S. men – 77, women – 80)

Age Structure Diagrams Distribution of people of different ages (shown: histogram) Also Shows Sex Ratio – number of males to females.

Other histograms:

Population Growth Rate Amount by which a pop. changes over a period of time, depends on 4 processes: birth rate, death rate, immigration, and emigration. BR + immigration - DR + emigration = growth Growth of a population is usually exponential, only contained by limiting factors (food, water, space,density…)

Exponential Growth – J-shaped curve. Unlimited growth ex. Humans

Logistic Growth – S-shaped curve Logistic Growth – S-shaped curve. Pop’s growth slows because of a limiting factor (at carrying capacity) ex. Rabbits in the wild

Exponential and Logistical Growth Graph

Density Factors Density-independent – affect all populations in similar ways regardless of size. Fires, deforestation, dams, floods, hurricanes etc… Density-dependent factors – a limiting factor that depends on the size of a population. The more crowded = more competition, predation, parasitism, and disease. CYCLIC