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Biology - Populations
Transcript of Biology - Populations
Chapter 5 How do populations grow? What limits population growth? How have human populations grown? Charateristics of populations
growth rate area or range where the population lives number of individuals per unit area increase or decrease of the number of individuals in a population over time Factors that affect population size:
the number of births
the number of deaths
the number of individuals that enter or leave immigration individuals move into the area Emigration individuals move out of an area Under ideal conditions with unlimited resources, a population will grow exponentially Exponential growth occurs when the individuals in a population reproduce at a constant rate.
As resources become less available, the growth of a population slows or stops Logistic growth occurs when a population's growth slows or stops following a period of exponential growth Carrying Capacity is the largest number of individuals of a population that a given environment can support limiting factor - anything that can cause the population growth to decrease 2 groups of limiting factors the larger the population in an area the greater the affect of the factor competition
predation affect all populations in similar ways, regardless of the population size unusual weather
human activities Density-Dependent Factors Density-Independent Like the populations of many other living organisms, the size of the human population tends to increase with time. For most of human existence, the population grew slowly.
Limiting factors kept population sizes low Until about 500 years ago Demography
scientific study of human populations
examines the characteristics of human populations
attempts to explain how those populations will change over time Predicts why some countries have high growth rates while other countries grow more slowly
age structure demographic transition - a dramatic change in birth and death rates. Occurs in 3 steps
1. there are high death rates and high birthrates.
2 the death rate drops, while the birthrate remains high. The population increases rapidly.
3 the birthrate decreases, causing population growth to slow Demographers can predict future growth using models called age-structure diagrams