Chapter 39 – Population growth & regulation World population clock
Chapter 39 – Population Growth & Regulation • What is a population? • What causes population size changes? • How is the human population changes? • What are the environmental effects of population changes?
What is a population? • All members of a species that live within an ecosystem and can potentially interbreed
Population growth A. Factors influencing population growth 1. Birthrate 2. Death rate 3. Migration a. Immigration b. Emigration
Population growth B. Biotic potential—maximal growth rate given ideal conditions • Produces exponential growth if not restrained
Reproduction starts at 4 years Reproduction starts at 6 years
Population growth C. Environmental resistance 1. Decreases birthrate, increases death rate 2. Density-dependent factors a. Predation b. Parasitism • Competition (inter- and intraspecific) • Food & space • Infectious Disease
I. Population growth C. Environmental resistance (cont.) 3. Density-independent factors a. Climate & weather b. Pesticides & pollutants
Human activity can influence population growth • Exotic species
Clark Lewis Human activity can influence population growth
Population effects of introduced species • Brown tree snake
The hypothesis of this research is • Humans are causing the extinction of bird populations in Hawaii • Bird populations on Guam have decreased due to pesticides left over from World War II • Brown tree snakes were introduced to Guam by humans • Brown tree snakes prey on birds on Guam • Native birds are almost extinct on Guam
The data in figure 3 shows • Predation rates were the same at all sites tested • Snake population size increased at all sites over time • Sites with abundant and stable bird populations experienced the highest rates of predation • Predation of snakes on birds in traps was highest in sites where birds were extinct or rare • Bird populations at all sites increased over time as snakes were trapped
Concerning populations in this ecosystem, which of the following statements is/are true? • Snakes act as a form of density dependent environmental resistance on bird populations • There is greater density dependent environmental resistance on snake populations at the NCS and NWF sites than at the NASA and Cocoa Island sites • Inter- and intra-specific competition among native bird populations is greater at the NCS and NWF sites than at the NASA and Cocoa Island sites • All of these • Both 1 and 2 • None of these
Population cycles A boom and bust cycle
Human population Why is it showing exponential growth? How long will it remain exponential? What is the carrying capacity for humans?
Genesis 9:7 As for you, be fruitful and increase in number; multiply on the earth and increase upon it.
D. Our species continues to overcome environmental resistances • 1. Medical advances, agricultural revolution Human population growth – why growing so fast?
Age-structure diagrams (RLF)
Population < 15 (%) Source: Environmental Systems Research Institute Age-structure diagrams online
Infant mortality Source: Environmental Systems Research Institute
Population growth rate (%) Source: Environmental Systems Research Institute
Human population United States population -Growing faster (1.4%) than other developed countries (0.1%) -Immigration = 33% of U.S. growth -Baby boomers at reproductive age U.S. pop. clock
U.S. population growth – is it a problem? U.S. consumption and pollution • U.S. citizen uses 6x more energy than world average • <5% of population, but -consumes 25% of energy -22% of carbon dioxide & CFC emissions • Avg. of 3600 cal/day vs. world avg. of 2700 cal/day
U.S. population growth • By 2050 (Union of Concerned Scientists prediction): • crop/pasture land reduced in half • food prices 3-5x higher • 30-50% of income spent on food (vs. 15%)
How might a Christian respond to human population growth? • Are we abusing God’s creation? • Do other species, as God’s creation, have a right to space and natural resources? • What about birth control? • What about those in need?
1 John 3:17-18 (NIV) • 17 If anyone has material possessions and sees his brother in need but has no pity on him, how can the love of God be in him? • 18 Dear children, let us not love with words or tongue but with actions and in truth.
Which of the following concerning populations is true? • A population consists of all the species that interact within a defined ecosystem • Populations always exhibit exponential growth • A population consists of all members of an interbreeding species in a defined area • Both 1 and 2 • Both 2 and 3
Which of the following serves as a form of density-independent environmental resistance? • Availability of food • Infectious disease • A forest fire • All of these • None of these
Which of the following concerning the human population is true? • The United States has the fastest growing human population in the world • Developing countries have a slower growth rate than developed countries • The human population is growing exponentially • All of these • None of these