Population Principles
Chapter 7
Population Characteristics
•
Population - Group of individuals of the same species inhabiting the same area simultaneously.
(6.4 Billion – 2004)
–
Natality and Mortality
 Natality ________________________________________________________________
 Birth Rate (Humans Born / 1,000)
–
Mortality - __________________________________
 Death Rate (Humans Died / 1,000)
•
Population Growth Rate - ___________________________________. Often expressed as a
percentage of the total population. (Geometrically – Population)(Arithmetically – Food Supply)
•
Survivorship Curve - Shows proportion of individuals likely to survive to each age.
•
–
High mortality in young.
–
Mortality equitable among age classes.
–
Mortality high only in old age.
Survivorship Curve (Fig.7.2)
•
Sex Ratio - Age Distribution
–
Sex Ratio ___________________________________________________________________.
 Females determine the number of offspring produced in sexually reproducing
populations.
–
Age Distribution ___________________________________________________________________.
 Greatly influences population growth rate.
•
Age Distribution in Human Populations (Fig.7.3)
Population Density and Spatial Distribution
•
Population Density ______________________________________________________________________.
–
High population may lead to increased competition for resources.
 Dispersal - Movement of individuals from densely populated locations to new
areas.
 Emigration - Movement from an area.
 Immigration - Movement into an area.
•
Population Growth Curve
•
Biotic Potential ______________________________________________________________________________
___________________________
–
Generally, biotic potential is much above replacement level.
 Natural tendency for increase.
 All living populations follow an exponential growth curve.
Exponential Growth Curve
•
Lag Phase - ___________________________________.
•
Exponential Growth Phase (Log Phase)______________________________________________________________________________
________________. *Currently*
•
Stable Equilibrium Phase ______________________________________________________________________________
___________________________
•
Biotic Potential (Fig.7.4)
•
Typical Population Growth Curve (Fig.7.5)
Carrying Capacity
•
Carrying Capacity ______________________________________________________________________________
___________________________.
•
Environmental Resistance ______________________________________________________________________________
___________________________.
–
Four main factors:
 Raw Material Availability
 Energy Availability
 Waste Accumulation and Disposal
 Organism Interactions
 Disease, Predation, and Space
•
Carrying Capacity (Fig.7.6)
•
Bacterial Growth Curve (Fig.7.7)
•
Fig. p.138
Reproductive Strategies and Population Fluctuations
•
Not all species reach a stable carrying capacity.
–
Species can be broadly lumped into two categories:
 K-strategists
 r-strategists
K - Strategists
•
Large organisms
•
Long-lived
•
Produce few offspring
•
Provide substantial parental care
•
Populations typically stabilize at a carrying capacity.
•
Usually occupy relatively stable environments.
•
Reproductive strategy is to invest in a few, quality offspring.
•
Controlled by density-dependent limiting factors.
–
Factors that become more severe as the size of the population increases.
 Diseases
•
Deer - Lions – Swans
r - Strategists
•
Small organisms
•
Short-lived
•
Produce many offspring
•
Little if any parental care
•
Usually do not reach carrying capacity (boom-bust cycles).
•
Exploit unstable environments.
•
Reproductive strategy is to produce large numbers of offspring to overcome high mortality.
•
r - Strategists
•
Controlled by density-independent limiting factors.
–
Population size is irrelevant to the limiting factor.
 Weather Conditions
•
Grasshoppers - Gypsy Moths – Mice
•
Population Cycles (Fig.7.8)
Human Population Growth
•
Major reason for increasing human population growth rate
is_____________________________________________________________________________
____________________________
•
Historical Human Population Growth (Fig.7.9)
•
Doubling Time
•
Doubling Time of a Population (years) :
•
70 / Population Growth Rate (%)
( 70 / 2.0% = 35 years )
•
Doubling Time for the Human Population (Fig.7.10)
•
•
Interactions Affecting Carrying Capacity
–
Available Raw Materials
–
Available Energy
–
Waste Disposal
–
Interaction With Other Organisms
Social Factors Influence Human Population
Humans are social animals who have freedom of choice.
–
People make decisions based on history, social situations, ethical and religious beliefs,
and personal desires.
 Biggest obstacles to controlling human population are not biological, but are the
province of philosophers, theologians, politicians, and sociologists.
•
Ultimate Size Limitation
•
If the world continues to grow at current rate, population __________________________.
•
Human population subject to same biological constraints as other species.
–
Human population will ultimately reach a carrying capacity and stabilize.
 Disagreement about exact size and primary limiting factors.