Populations Chapter 19

Understanding Populations Section 19.1

Definition:  A group of organisms of the same species living in the same place at one time

Thomas Malthus ( )  Essay on the Principal of Population  In nature, plants and animals produce far more offspring than can survive  Man, too, is capable of overproducing if left unchecked  Famine and poverty are natural outcomes of overpopulation

3 Characteristics: 1. Size 2. Density 3. Dispersion

Population Size  # of individuals in a given area  Difficult to measure  Estimates often taken

Population Density  How crowded a population is  # of individuals per unit area  E.g.: 30 people/classroom

Population Dispersion  Spatial distribution of individuals 1. Clumped 2. Even 3. Random

Population Dynamics  Populations change over time due to:  Birth rates  Death (Mortality) rates  Life expectancy rates  Age Structure  Patterns of Mortality

Age Structure  Distribution of individuals among different ages in a population

Survivorship Curve Type I Type II Type III

Patterns of Mortality  Survivorship Curves  Type I – death at old age  Type II – death at any age  Type III – death at young age

Measuring Populations Section 19.2

Population Growth Rate  # by which a population’s size changes over time  Depends upon:  1. birth rate  2. death rate  3. emigration  4. immigration

Calculations  ADDS to population = birth & immigration  SUBTRACTS from population = death & emigration  ASSUME immigration = emigration  THEREFORE: birth rate – death rate = growth rate

2 Models of Growth 1. Exponential Model (J curve) 2. Logistic Model (S curve)

Exponential Model  The larger the population gets, the faster it grows!  Birth & Death rates remain constant  Limitation: only exists under rare conditions –Doesn’t account for limiting factors that occur in nature

Logistic Model  The exponential model accounting for the influence of limiting factors  Limiting Factor: condition that restricts growth of a population  Carrying capacity (K): # of individuals the environment can support of a long period of time –Fluctuates slightly

Carrying Capacity

2 types of limiting factors  1. Density-independent factors –Abiotic factors –Reduction of population by same proportion no matter what size it is –Ex) floods or extreme temp. extreme temp.

 2. Density-dependent factors –Biotic factors –The larger the population, the larger the proportion of reduction. –Ex) disease or starvation

Human Population Growth, 19.3

History Lesson  Hunter-gatherer lifestyle: slow human growth because of high mortality rate  Agricultural revolution: human population growth because of an increase in the food supply  Industrial revolution: rapid human population growth because of decline in death rates

Today’s Growth  Developed Countries: 20% of world’s population, low growth rates –Ex) USA, Japan, Germany, France, etc.  Developing Countries: 80% of world’s population, high growth rate –Ex) Central America, South America, Asia, Africa