Population Growth Factors that regulate population size Population Growth Patterns • Population Characteristics – Size – Density • number per area – Distribution • Uniform • Random • Clumped Population Distributions Random Uniform Clumped Population Characteristics – Sex ratios – Age structure • Number of individuals in different age classes – Reproductive age – Pre-reproductive age – Post-reproductive age Age Structure Diagrams Population Growth •Growth Rate – Factors that increase population sizes • Birth Rate (BR) • Immigration (Im) – Factors that decrease population sizes • Death Rate (DR) • Emigration (Em) Growth Rate = (BR + ImR) – (DR + EmR) • Exponential growth – A stable rate of growth leads to exponential growth. – As the population size increases, the same percentage increase becomes a larger total increase. Exponential Growth in a population J-curve Occurs when a population starts out small and environmental conditions are ideal. • Factors that limit Growth – Physical, chemical and biological factors (biotic and abiotic) that limit the amount of growth • Space • Nutrients • Predators – All limiting factors together make up the “environmental resistance” and affect the carrying capacity of the environment Environmental Resistance determines Carrying Capacity Logistic Growth Curve (S-curve) Carrying Capacity can change when limiting factors change Limiting Factors • Shelford’s Law of Tolerance (p. 588) – Certain range of environmental conditions that will allow for maximum population growth • Density Independent factors affect a population regardless of its size – Abiotic factors: climate, space Limiting Factors • Density dependent factors – Population size can limit further population growth – Intraspecific competition • Food resources • Mates – Disease – Interspecific Competition – Predation Demography • The study of human populations – Population Size – Population Density and Distribution – Age Structure – Sex Ratios Human Population Growth • Human population growth has been greater than exponential. – Growth rate has increased over time (mostly because of lower death rates). – Global growth rate peaked at 2.1% in the 1960’s. Global Human Population Human Distribution Effect of Age Structure on Population Growth Age Structure Diagrams Age Pyramid for United States Age structures are very different in the developed and developing countries Effect of sex ratios on population growth What is the earth’s carrying capacity? • Carrying capacity is influenced by, but not defined by, environmental impact. • Environmental impact depends on more than population alone. – Technology can increase or decrease the impact. • Cause more consumption – or – • Exploit previously unavailable resources Technological innovations that increased carrying capacity Decline in Global Growth Rate Is growth rate responding to environmental resistance? • What part of the growth rate equation is changing? • Is the change occurring fastest where resources are scarcest? • Is the change resulting in less environmental impact? TFR correlates with social opportunity for women Growth rates are unevenly distributed Population is increasing fastest where the standard of living is lowest Ecological Footprints The amount of resources used per person can be expressed in terms of the amount of land needed to provide those resources What does the future hold?