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Limiting factor = a factor that causes a population growth to decrease. Diagram on page 124 in textbook Density-Dependent limiting factor = a limiting factor that depends on population size. These factors only become limiting when the population reaches a certain size. These factors operate strongly when the population is large & dense. Examples – competition, predation, parasitism, and disease. This illustrates how predation can affect the population growth. The moose population was also affected by changes in food supply, and the wolves were also affected by disease. Density-Independent limiting factors = affect all populations in similar ways, regardless of the population size. Examples – Unusual weather, natural disasters, seasonal cycles, certain human activities, i.e. cutting down forests, and damming rivers. In response to these factors, many species show a crash in population size & then rebuild. Some species are extinguished. The size of the human population tends to increase with time. For most of human existence, the population grew slowly due to lack of food, disease, & death rates were so high. About 500 years ago, the human population began growing more rapidly due to industry, agriculture, improved sanitation, & healthcare. Demography = the scientific study of human population Birthrates, death rates, and age structure of a population help predict why some countries have higher growth rates. Over the past century, population growth has slowed… this is because of a dramatic change in birth & death rates (demographic transistion) Population growth depends on how many people of different ages make up a given population. Demographers can predict future growth by using models called age-structure diagrams or population profiles.