populations
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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 (1766-1834). Essay on the Principal of Population - PowerPoint PPT PresentationTRANSCRIPT
PopulationsChapter 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 (1766-1834) 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
Age
% Survival
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 PopulationsSection 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.
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
