Essentials of Biology Sylvia S. Mader Chapter 30 Lecture Outline Prepared by: Dr. Stephen Ebbs Southern Illinois University Carbondale Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

30.1 The Human Population The growth of any population, including humans, is determined by the difference between birth rates and death rates. Until the Industrial Revolution in the 1800s, human population growth was relatively slow. During the Industrial Revolution, a sharp increase in human population growth began.

Present Population Growth

Future Population Growth Rate The number of individuals an environment can maintain over an indefinite period of time is called the carrying capacity. Because of the rapid increase in the human population, there are concerns that the human population may someday reach its carrying capacity.

More-Developed Versus Less-Developed Countries The growth rate of populations in different countries differs. The more-developed countries (MDCs) have modest population growth rates due largely to decreased birthrates. The less-developed countries (LDCs) have higher population growth rates because birthrates remain high.

More-Developed Versus Less-Developed Countries (cont.)

Comparing Age Structures The rate of population growth in a population can be determined from the age structure of a population. The age structure of MDCs is stable because the birthrate of these populations is providing replacement reproduction. The age structure of LDCs has a pyramid shape with a large dependency group, which indicates that population growth will continue to expand.

Comparing Age Structures (cont.)

Comparing Age Structures (cont.)

Environmental Impact When populations grow, they exert a pressure on the Earth’s resources. This pressure can be measured as an environmental impact (EI) Thus there are two causes of overpopulation. Population size Resource consumption

30.2 Characteristics of Population Populations rely on the living (biotic) and non-living (abiotic) resources in an environment. These resources can be distributed in three patterns which affect the population density or range of a population. – Clumped – Random – Uniform

Demographics and Population Growth • Survivorship is also important to an understanding of population growth. The study of survivorship in a population uses life tables and survivorship curves. In Type I curves, there is survival to old age. In Type II curves, death is spread across all age groups. In Type III curves, death occurs at an early age.

Demographics and Population Growth (cont.)

Demographics and Population Growth (cont.)

Demographics and Population Growth (cont.) The influence of the biotic potential on population growth depends upon the reproductive characteristics of the population. The number of offspring per reproduction Chances of survival until reproductive age Frequency of reproduction Age at which reproduction begins

Exponential Growth The pattern of population growth depends upon two primary factors. The biotic potential Resource availability There are two possible patterns of growth. – Exponential growth has a J-shape characteristic of a rapidly growing population. – Logistic growth has an S-shape showing a stabilization of the population size.

Exponential Growth (cont.)

Factors That Regulate Population Growth Several factors affect population growth. – Density-independent factors affect population growth regardless of population size. Examples of density-independent factors include weather and natural disasters.

Factors That Regulate Population Growth (cont.)

Density-Dependent Factors The effect of density-dependent factors are highly dependent on population size. – Competition occurs when more than one population uses the same resource. – Predation occurs when one organism preys upon another organism. • Predator-prey relationships can create specific cycles of population growth.

Density-Dependent Factors (cont.)

Density-Dependent Factors (cont.)

30.3 Life History Patterns and Extinction The life history of a population consists of the variation in population characteristics. – Opportunistic populations show exponential growth and have small organisms that show early maturation, short life span, and limited parental care of offspring. – Equilibrium populations show logistic growth, a population size near carrying capacity, and large animals with long life span.

Extinction • Extinction is the disappearance of a species or higher group. The probability that a species will become extinct depends upon three primary factors. Size of geographic range Degree of habitat tolerance Size of local populations

30.4 The Scope of Ecology • Ecology is the study of the interactions between organisms and with the physical environment. Ecology can be studied at different levels of biological organization. Individual organisms Populations A group of several species (community) A group of several species and the environmental factors that affect those species (ecosystem) The biosphere is a portion of the Earth’s surface where organisms exist.