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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. growth per 1,000 individuals = (# births - # deaths) 1,000 • 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 LessDeveloped 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 LessDeveloped 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) E.I. = population size x resource consumption per capita = pollution per unit of resource used • 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.