44
Population Ecology
Chapter Outline
Population Ecology
44.1 a honking mess
44.2 Population Demographics
Population Size
Population Density and Distribution
Clumped Distribution
Near-Uniform Distribution
Random Distribution
Age Structure
Effects of Scale and Timing
44.3 Population Size and Exponential Growth
Immigration and Emigration
Zero to Exponential Growth
Biotic Potential
44.4 Limits on Population Growth
Density-Dependent Factors
Logistic Growth
Density-Independent Factors
44.5 Life History Patterns
Quantifying Life History Traits
Environmental Effects on Life History
44.6 effects of predation on life history
A Long-Term Study of Guppies
Overfishing of Atlantic Cod
44.7 Human Population Growth
Early Innovations and Expansions
From the Industrial Revolution Onward
44.8 anticipated growth and consumption
Fertility and Age Structure
A Demographic Transition
Resource Consumption
A honking mess (revisited)
Summary
Self-Quiz
Data Analysis activities
Critical Thinking
Population Ecology
Learning Objectives
44.1 Examine the threats that a growing population of Canada geese pose to humans.
44.2 Examine the different characteristics that are used to describe a population.
44.3 Discuss the factors that determine the size of a population and its growth rate.
44.4 Determine the environmental limits on population growth.
44.5 Discuss how ecologists study life history patterns of different species.
44.6 Discuss how predation affects life history traits.
44.7 Examine the factors responsible for the rapid increase in human population size.
44.8 Determine the factors that will affect future changes in the human population.
Key Terms
Population Ecology
biotic potential
carrying capacity
cohort
demographic
demographic transition model
density-dependent limiting factors
density-independent limiting factors
ecological footprint
ecology
emigration
exponential growth
immigration
intraspecific competition
k-selection
life history pattern
logistic growth
mark-recapture sampling
per capita growth rate
plot sampling
population
population density
population distribution
population size
reproductive base
r-selection
survivorship curve
total fertility rate
zero population growth
Population Ecology
Lecture Outline
44.1 A Honking Mess
A. The Canadian geese population in the U.S. is increasing.
1. These geese are often distasteful to humans because their feces contaminate lakes and
grassy areas.
2. Geese have been known to cause airplane accidents by causing engine failure.
B. Many Canadian geese still migrate to Canada, but non-migratory birds are becoming more
prevalent.
1. The non-migratory birds save energy by not traveling and can devote more energy to
reproduction.
2. Researchers are looking for ways to limit the non-migratory geese populations without harming the migratory birds.
44.2 Population Demographics
A. Population Size
1. Population size is defined by the number of individuals in a population.
2. Since it is difficult to count all individuals in a population, different methods are used.
a. Plot sampling involves dividing an area into a grid, sampling the animals in several
plots on the grid, and multiplying to determine the approximate number in the
population.
b. The mark-recapture method begins by having some representatives of the population
tagged.
1) The portion of marked animals in the second sample is taken to be
representative of those marked in the whole population.
B. Population Density and Distribution
1. Population density is the number of individuals per unit area or volume.
2. Population distribution describes the location of individuals relative to one another.
a. In clumped distribution, the density of the animals is arranged in clumps, possibly
because of patchy resources.
b. In near-uniform distribution, the organisms are fairly evenly placed in the
environment.
c. A random distribution pattern is one in which the individuals have no uniformity in their placement.
C. Age Structure
1. An age structure lists the number of individuals in each age category.
a. Those in the pre-reproductive category are considered the reproductive base.
D. Effects of Scale and Timing
1. Factors such as the scale of the sampling area and the timing of the study may impact the
information concerning a population’s size.
44.3 Population Size and Exponential Growth
A. Immigration and Emigration
1. Members of a population may leave (emigration) or enter a new population
(immigration).
B. Zero to Exponential Growth
1. When zero population growth occurs, it means that the number of individuals born
is equal to the number dying.
2. The per-capita growth rate equals the birth rate minus the death rate.
a. If the per-capita growth rate is more than zero, the population is exhibiting
exponential growth.
b. A J-shaped curve represents a population undergoing exponential growth.
C. The term biotic potential indicates the largest amount of increase that can occur in that particular population.
44.4 Limits on Population Growth
A. Density-Dependent Factors
Density-dependent factors are those that become more critical as the population increases.
a. Examples of density-dependent factors are food, water, and incidence of disease.
B. Logistic Growth
1. The carrying capacity is the largest number of individuals that a certain environment can
support.
a. An S-shaped curve, representing logistic growth, is indicative of how a population
naturally changes.
C. Density-Independent Factors
1. Density-independent factors are those that are not influenced by the size of the population.
a. Examples of density-independent factors are floods, fires, and earthquakes.
44.5 Life History Patterns
A. Quantifying Life History Traits
1. Life tables illustrate the number of individuals that survive in various age categories.
a. This involves the focusing on a cohort, a group of individuals born during the same
interval.
2. A survivorship curve is a visual representation of the age-specific survival of a
population.
a. A type I curve shows that the individuals usually survive until old age.
1) Animals exhibiting a type I curve produce a small amount of offspring that
require much care, e.g., humans.
b. A type II curve illustrates that the survival rate does not relate to age, e.g., squirrels.
c. A type III curve shows that the majority of the individuals do not survive to
maturity.
1) Animals exhibiting a type III curve produce many offspring that do not require
much care, e.g., sea urchins.
B. Environmental Effects on Life History
1. A life history pattern is defined as how an organism allocates its resources between growth, maintenance, and reproduction in its lifetime.
a. An r-selected species is one with many offspring needing little care.
1) These animals tend to be small, have a short lifespan, and may be killed off due to density-independent factors.
b. K-selected species produce few offspring that need much care.
1) These animals are usually larger and populations, controlled by density-
dependent factors, can approach the carrying factor.
44.6 Effects of Predation on Life History
A. A Long-Term Study of Guppies
1. Life history traits can change as a response to an alteration in the types of predators.
a. An example of this was shown by two isolated populations of guppies where there
were different predators.
1) As a result of the studies, it was concluded that differences between guppies
preyed upon by different predators was genetic.
B. Overfishing of Atlantic Cod
1. The life history of the cod population in the North Atlantic changed due to over-fishing.
a. Because of the overfishing, the cod population began to reproduce earlier.
44.7 Human Population Growth
A. The human population’s rate of increase is largely due to migration into new climate zones, new technologies that increased the carrying capacity, and the elimination of some limiting factors.
B. Early Innovations and Expansions
1. This rate of growth is due to the fact that humans can spread easily into new habitat.
a. Man has developed fire and tool-making abilities that are passed on from one generation to the next.
2. Humans have developed new technologies to increase the carrying capacity of the environment.
a. Man learned how to cultivate crops, raise livestock.
C. From the Industrial Revolution Onward
1. Since the 1800s, the human population has increased dramatically.
2. The human population has learned how to overcome some limiting factors.
a. Man learned how to combat many diseases and use fossil fuels for energy production.
b. Fertilizers and pesticides improved agriculture.
c. Improvements in nutrition, sanitation, and medicine also had a large impact.
3. It is estimated that the population on Earth will reach nine billion by 2050.
44.8 Anticipated Growth and Consumption
A. Fertility and Age Structure
1. The average number of children born to each woman of reproductive age is the total
fertility rate.
a. The fertility rate worldwide has decreased from 6.5 to 2.6 in the last 50 years.
b. This decrease still puts the worldwide fertility rate above the number that keeps the population at a constant level.
c. The replacement fertility rate is the average number of children a woman has before she replaces herself with a daughter who reaches reproductive age successfully.
d. Approximately 1.9 billion people are approaching reproductive age.
B. The demographic transition model connects industrial development and changes in population growth rates.
1. In countries where industrialization has not yet occurred, the birth rate is high.
a. Children are needed to perform duties on a farm, e.g., many African countries.
2. In industrialized nations, the birth rate declines, e.g., United States.
a. Industrialized nations use a larger percentage of resources of the world.
3. In post-industrialized nations, the population size may decrease.
C. Resource Consumption
1. The term ecological footprint refers to the amount of the Earth’s surface that is needed to support a level of development and consumption in a sustainable fashion.
a. The U.S.’s ecological footprint is three times higher than other world residents and
nine times higher than a typical Indian citizen.
b. As other less-developed nations progress, we may not have enough land to sustain
the Earth’s population.
44.9 A Honking Mess (Revisited)
A. In 2009, a plane landed successfully on the Hudson River after the engines were damaged by geese.
1. The DNA from the geese remnants obtained from the engines proved that they were from Canada, not New York.
Population Ecology