Population GrowthPopulation Growth

Chapter 35Chapter 35Sections 2 and 3Sections 2 and 3

How to Calculate Growth How to Calculate Growth RateRate

Growth RateGrowth Rate is the change in population size is the change in population size over time elapsed.over time elapsed.

Ex: A population of sea lions decreased from Ex: A population of sea lions decreased from 10,000 to 8,500 from 1995 to 2005. What 10,000 to 8,500 from 1995 to 2005. What is the growth rate?is the growth rate?

GR = GR = 8500-100008500-10000 = = -1500-1500 = -150 sea = -150 sea lions/yearlions/year

2005-19952005-1995 1010

Population Growth can be Population Growth can be Positive, Negative, or ZeroPositive, Negative, or Zero

Positive Growth RatesPositive 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 RatesNegative 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 GrowthZero Population Growth No change in population sizeNo change in population size

Types of GrowthTypes of Growth

EXPONENTIALEXPONENTIAL Population grows Population grows

at a constant rateat a constant rate Represented with a Represented with a

J-curveJ-curve

LOGISTICLOGISTIC Population may Population may

grow exponentially grow exponentially at first, but at first, but eventually one or eventually one or more factors will more factors will limit its growthlimit its growth

Represented with Represented with an S-curvean S-curve

Exponential GrowthExponential Growth

Doubling Time: Doubling Time:

The time it takes The time it takes for a population to for a population to double in sizedouble in size

The larger the The larger the population gets, population gets, the faster it the faster it grows!!grows!!

Logistic GrowthLogistic Growth

A A limiting factorlimiting factor is a condition that restricts a is a condition that restricts a populations growth. Ex: food, space, disease, etc.populations growth. Ex: food, space, disease, etc.

The The carrying capacitycarrying capacity is the number of individuals an is the number of individuals an environment can support for a period of time with no environment can support for a period of time with no net increase or decrease. (Zero Population Growth)net increase or decrease. (Zero Population Growth)

Types of Limiting FactorsTypes of Limiting Factors

DENSITY-DEPENDENTDENSITY-DEPENDENT Limits the population Limits the population

more as density more as density increasesincreases

Typically Typically BIOTICBIOTIC factors (predators, factors (predators, competitors, competitors, parasites) except for parasites) except for spacespace which is which is abioticabiotic

DENSITY-INDEPENDENTDENSITY-INDEPENDENT Limits growth, but is Limits growth, but is

unrelated to densityunrelated to density Typically Typically ABIOTICABIOTIC

factors (rain, wildfires, factors (rain, wildfires, temperature, ice, etc.) temperature, ice, etc.) except for except for human human disturbancesdisturbances which which are biotic (ex: are biotic (ex: pesticides) pesticides)

Population Growth CyclesPopulation Growth Cycles

Populations of Populations of predators and prey predators and prey “boom & bust” in a “boom & bust” in a staggering fashion staggering fashion to keep numbers in to keep numbers in checkcheck

Some populations Some populations do this on their own do this on their own (possibly controlled (possibly controlled by hormones)by hormones)

Human Population GrowthHuman Population Growth

For most of human history, the population has For most of human history, the population has grown very slowly or not at all…WHY?grown very slowly or not at all…WHY?

High Birth Rates and High Death RatesHigh Birth Rates and High Death Rates In the last few centuries, the human population In the last few centuries, the human population

has grown exponentially…WHY?has grown exponentially…WHY?

Improved technology Improved technology makes resources makes resources more accessiblemore accessible

Major medical Major medical advances extend advances extend liveslives

Death Rate Death Rate Decreases and Birth Decreases and Birth Rate Remains High Rate Remains High

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

Age-Structure DiagramsAge-Structure DiagramsDemographers Demographers can look at the can look at the age structure of a age structure of a population to population to predict future predict future growth in various growth in various countriescountries

Most of our Most of our current growth is current growth is occurring in less occurring in less developed developed countriescountries

What is Earth’s Carrying What is Earth’s Carrying Capacity for Humans??Capacity for Humans??

The United Nations predicts that our The United Nations predicts that our population will reach 7.5 to 10.3 Billion population will reach 7.5 to 10.3 Billion by the year 2050by the year 2050

Currently, we already are straining the Currently, we already are straining the planet’s natural resources (water use has planet’s natural resources (water use has increased 600% in the past 70 years)increased 600% in the past 70 years)

What level of resource use by humans What level of resource use by humans can the Earth support? How might new can the Earth support? How might new technologies provide a solution?technologies provide a solution?