The Human Population and the Environment Chapter 4 The Human Population and the Environment Botkin & Keller Environmental Science 5/e

Basic Concepts of Population Dynamics A group of individuals of the same species living in the same area of interbreeding and sharing genetic information. Species: All individuals that are capable of interbreeding. Made up of populations Population dynamics The general study of population changes. Botkin & Keller Environmental Science 5/e

Environmental Science 5/e Age Structure Population age structure: The proportion of the population in each age class Affects current and future birth rates, death rates and growth rates Has an impact on the environment Has complications for current and future social and economic status. Botkin & Keller Environmental Science 5/e

Forecasting Population Change Formula to represent population change: P2 = P1 + (B – D) + (I – E) Botkin & Keller Environmental Science 5/e

Environmental Science 5/e Fig 4.3 Botkin & Keller Environmental Science 5/e © 2005 John Wiley and Sons Publishers

A Brief History of Human Population Growth Hunters and gatherers The world’s population was probably less than a few million Early, pre-industrial agriculture Allowed a much greater density of people The first major increase in human population Machine age Industrial revolution led to rapid increase in human population The Modern era Rate of population has slowed in wealthy nations but continues to increase rapidly in poorer, less developed nations. Botkin & Keller Environmental Science 5/e

Environmental Science 5/e Fig 4.4a Botkin & Keller Environmental Science 5/e © 2005 John Wiley and Sons Publishers

Environmental Science 5/e Fig 4.4b Human population from 1000 A.D. to 2000 A.D. Botkin & Keller Environmental Science 5/e © 2005 John Wiley and Sons Publishers

Environmental Science 5/e Fig 4.4c Past and forecasted human population growth rate by geographic region and major nations Botkin & Keller Environmental Science 5/e © 2005 John Wiley and Sons Publishers

Environmental Science 5/e Fig 4.5 Logistic growth curve. World population as total numbers and growth per decade and by development status 1750-2100 Botkin & Keller Environmental Science 5/e © 2005 John Wiley and Sons Publishers

Environmental Science 5/e Fig 4.6 United States population 1790-2000. Growth rate of the US population appears to be slowing. Botkin & Keller Environmental Science 5/e © 2005 John Wiley and Sons Publishers

Projecting Future Population Growth Exponential growth and doubling time The logistic growth curve “S” shaped curve that is generated by the logistic growth equation. A small population grows rapidly But the growth rate slows down The population eventually reaches a constant size. Logistic carrying capacity The population size at which births equal deaths and there is no net change in population Botkin & Keller Environmental Science 5/e

Environmental Science 5/e Fig 4.7 Botkin & Keller Environmental Science 5/e © 2005 John Wiley and Sons Publishers

Environmental Science 5/e Fig 4.8 Botkin & Keller Environmental Science 5/e © 2005 John Wiley and Sons Publishers

The Demographic Transition Three-stage pattern of change in birth rates and death rates. Occurred during the process of industrial and economic development of Western nations. Leads to a decline in population growth. Stage I: Decline in death rate Stage II: High growth rate Stage III: Birth rate drops toward the death rate, leading to low or zero growth rate. Botkin & Keller Environmental Science 5/e

Environmental Science 5/e Fig 4.9 Botkin & Keller Environmental Science 5/e © 2005 John Wiley and Sons Publishers

Population and Technology The total impact of the human population on the environment is: the average impact of an individual multiplied by the total number of individuals T = P x I Botkin & Keller Environmental Science 5/e

Environmental Science 5/e The Human Population, the Quality of Life, and the Human Carrying Capacity Human carrying capacity The number of people that can live on Earth at the same time? To determine: Extrapolate from past growth The “Packing Problem” approach Considers how many people might be packed onto Earth, not taking into sufficient account the need for lands and oceans to provide food, water, energy, construction materials, and scenic beauty and the need to maintain biological diversity Botkin & Keller Environmental Science 5/e

Human Death Rates and the Rise of Industrial Societies Acute or epidemic disease Appears rapidly in the population, Affects a comparatively large percentage of it, Declines then almost disappears, only to reappear later Chronic disease Is always present in a population Typically occurs in a relatively small but relatively constant presentation of the population Examples include heart disease, cancer, and stroke Botkin & Keller Environmental Science 5/e

Environmental Science 5/e Fig 4.10 Botkin & Keller Environmental Science 5/e © 2005 John Wiley and Sons Publishers

Longevity and its Effect on Population Growth Maximum lifetime: The genetically determined maximum possible age to which an individual of a species can live Life expectancy: The average number of years an individual can expect to live given the individual’s present age Botkin & Keller Environmental Science 5/e

Limiting Factors Short-term factors Intermediate-term factors Those that affect a population during the year in which they become limiting Intermediate-term factors Those whose effects are apparent after one year but before ten years Long-term factors Those whose effects are not apparent for ten years Some factors fit into more than one category Botkin & Keller Environmental Science 5/e

Environmental Science 5/e Fig 4.11 Life expectancy in ancient Rome and 20th century England Approximate survivorship curve for Rome for the first four centuries A.D. Botkin & Keller Environmental Science 5/e © 2005 John Wiley and Sons Publishers

How Can We Achieve Zero Population Growth? Delay the age of first childbearing by women Birth control Biological and Social Breast-feeding, which can delay resumption of ovulation Abstinence Induction of sterility with natural agents Contraceptive devices National Programs to Reduce Birth Rates Formal family planning programs to explain the problems arising from rapid population growth Describe the benefits to individuals of reduced population growth. Botkin & Keller Environmental Science 5/e