Biology Chapter 5

Characteristics of Populations Geographic Distribution – the area inhabited by a population Population Density – number of individuals per unit area Growth Rate – an increase or decrease of the number of individuals in a population over time

Population Growth/Decline A population can grow when its birthrate is greater than its death rate Immigration – movement of individuals into an area Populations can increase Animals maybe searching for mates or food Emigration – movement of individuals out of an area Populations can decrease Animals leave to find mates or food

Exponential Growth Under ideal conditions with unlimited resources a population will grow exponentially resulting in a population explosion Exponential growth is characterized by a J-shaped curve

In nature exponential growth does not continue in a population for very long As resources become less available, the growth of a population slows or stops

Copyright Pearson Prentice Hall Exponential Growth Exponential Growth In the presence of unlimited resources and in the absence of predation and disease, a population will grow exponentially. Both hypothetical graphs show the characteristic J-shape of exponential population growth. Copyright Pearson Prentice Hall

Logistic Growth Occurs when a population’s growth slows or stops following a period of exponential growth Logistic growth is characterized by a S-shaped curve

initial carrying capacity new carrying capacity Fig. 46.6, p. 818 Copyright Pearson Prentice Hall

  What prevents the world from being overrun with all kinds of living things? Carrying Capacity – the number of organisms of one species that an environment can support When a population reaches the carrying capacity of its environment, its growth levels off

Limiting Factors Limiting Factor – a factor that causes population growth to decrease Density-Dependent Factors – a limiting factor that depends on population size These factors operate most strongly when a population is large and dense As populations increase so do these factors Example: competition, predation, parasitism, disease Density-Independent Factor – a limiting factor that affects all populations regardless of the population size Example: natural disasters, storms, floods, drought, pollution

Demography – the study of human population growth For most of human existence, the population grew slowly Limiting factors kept population sizes low About 500 years age, the human population began growing more rapidly Life was made easier and safer by advances in agriculture and industry Death rates were dramatically reduced due to improved sanitation, medicine, and healthcare, while birthrates remained high With these advances, the human population experienced exponential growth

Historical Overview Human Population Growth The size of the human population has increased over time. After a long, slow start, the worldwide population grew exponentially following improvements in medicine, sanitation, agriculture, energy use, and technology. Copyright Pearson Prentice Hall

Age Structure Age-Structure Diagrams – show the population of a country broken down by gender and age group Population growth depends, in part, on how many people of different ages make up a given population Demographers can predict future growth using age- structure diagrams

Patterns of Population Growth Slow Growth Rapid Growth Zero Growth Negative Growth Copyright Pearson Prentice Hall

How can you tell if a population is growing? If the birth rate is more than the death rate

Does it make a difference to population growth if the largest proportion of the population is in one age group? If a large percent of the population is teenagers and children there is rapid growth If the percent of people in each category is equal the population is stable