Population Growth Chapter 35 Sections 2 and 3

How to Calculate Growth Rate Growth Rate is the change in population size over time elapsed. Ex: A population of sea lions decreased from 10,000 to 8,500 from 1995 to What is the growth rate? GR = = = -150 sea lions/year

Population Growth can be Positive, Negative, or Zero Positive Growth Rates Birth Rate (number of births per year) Birth Rate (number of births per year) Immigration (number moving IN per year) Immigration (number moving IN per year) Negative Growth Rates Mortality or Death Rate (deaths per year) Mortality or Death Rate (deaths per year) Emigration (number moving OUT per year) Emigration (number moving OUT per year) Zero Population Growth No change in population size No change in population size

Types of Growth EXPONENTIAL Population grows at a constant rate Population grows at a constant rate Represented with a Represented with aJ-curve LOGISTIC LOGISTIC Population may grow exponentially at first, but eventually one or more factors will limit its growth Population may grow exponentially at first, but eventually one or more factors will limit its growth Represented with an S-curve Represented with an S-curve

Exponential Growth Doubling Time: The time it takes for a population to double in size The larger the population gets, the faster it grows!!

Logistic Growth A limiting factor is a condition that restricts a populations growth. Ex: food, space, disease, etc. The carrying capacity is the number of individuals an environment can support for a period of time with no net increase or decrease. (Zero Population Growth)

Types of Limiting Factors DENSITY-DEPENDENT Limits the population more as density increases Limits the population more as density increases Typically BIOTIC factors (predators, competitors, parasites) except for space which is abiotic Typically BIOTIC factors (predators, competitors, parasites) except for space which is abioticDENSITY-INDEPENDENT Limits growth, but is unrelated to density Limits growth, but is unrelated to density Typically ABIOTIC factors (rain, wildfires, temperature, ice, etc.) except for human disturbances which are biotic (ex: pesticides) Typically ABIOTIC factors (rain, wildfires, temperature, ice, etc.) except for human disturbances which are biotic (ex: pesticides)

Population Growth Cycles Populations of predators and prey “boom & bust” in a staggering fashion to keep numbers in check Populations of predators and prey “boom & bust” in a staggering fashion to keep numbers in check Some populations do this on their own (possibly controlled by hormones) Some populations do this on their own (possibly controlled by hormones)

Human Population Growth For most of human history, the population has grown very slowly or not at all…WHY? For most of human history, the population has grown very slowly or not at all…WHY? High Birth Rates and High Death Rates In the last few centuries, the human population has grown exponentially…WHY? In the last few centuries, the human population has grown exponentially…WHY?

Improved technology makes resources more accessible Major medical advances extend lives Death Rate Decreases and Birth Rate Remains High

Predicting The Future Eventually, the demographic transition model predicts that the growth will slow down as birth rate drops and stabilize with a Low Birth Rate and Low Death Rate

Age-Structure Diagrams Demographers can look at the age structure of a population to predict future growth in various countries Most of our current growth is occurring in less developed countries

What is Earth’s Carrying Capacity for Humans?? The United Nations predicts that our population will reach 7.5 to 10.3 Billion by the year 2050 The United Nations predicts that our population will reach 7.5 to 10.3 Billion by the year 2050 Currently, we already are straining the planet’s natural resources (water use has increased 600% in the past 70 years) Currently, we already are straining the planet’s natural resources (water use has increased 600% in the past 70 years) What level of resource use by humans can the Earth support? How might new technologies provide a solution? What level of resource use by humans can the Earth support? How might new technologies provide a solution?