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The introduction of brown tree snakes to Guam results in more than a dozen species going extinct.


Brown Tree Serpent

BTS would DEVASTATE Hawaiian Ecosystems


The study of relationships among organisms and the environment


Group of interbreeding organisms of one species in one location


All of the populations in a given area


Community plus nonliving environment

Density and Distribution Patterns Are Static Measures of a Population



Physical location where population members live

Population density

Number of individuals of a species per unit area or unit volume

Population Distribution

Describes how individuals are scattered in the habitat

Isolated Subpopulations May Evolve Into New Species

Overall area occupied by a population is not fixed

Range expansion for invasive species

Brown tree snakes, fire ants, zebra mussels, gypsy moths, European starling, and kudzu

Natural selection may shape a genetically distinct subpopulation


The distribution of humans across the United States is a ___ distribution.


Population dynamics

Study of factors that influence changes in population size


to come to a country of which one is not a native, usually permanent residence.


to leave one country or region to settle in another.

Births Add Individuals to a Population

Survivorship Curves Show the Probability of Dying at a Given Age

Birth rate

Number of new individuals produced per individual in a defined time period

Age structure

Distribution of age classes.
Determines whether a population is growing, stable, or declining.

Death rate

Number of deaths per unit time
Scaled by the population size

Species vary tremendously in their patterns of survivorship

Yellow-eyed penguins

3 survivorship patterns-Type I

mortality rate is highest as individuals approach the maximum life span

Type II

equal probability of dying at any age

Type III

mortality rate highest in young

Yellow-eyed penguins have feature of both type I and type II


Per capita rate of increase, r, is the difference between the birth rate and the death rate

Positive r = growing population
Negative r = population shrinking

Growth Is Exponential When Resources Are Unlimited

G = rN
G = number of individuals added
r = per capita growth rate
N = initial size of population
Exponential growth
J-shaped curve

Exponential growth

Growth pattern in which the individuals in a population reproduce at a constant rate

J-shaped curve

Curve with a shape similar to that of the letter J; can represent prolonged exponential growth.

Population Growth Eventually Slows

Combination of external factors that keep a population from reaching its maximum growth rate. Competition, predation, etc.

Every habitat has a carrying capacity

Maximum number of individuals that the habitat can support indefinitely

Logistic growth model

Early growth of a population may be exponential, but growth slows as the population approaches the habitat's carrying capacity

S-shaped curve

Leveling off of an exponential, J-shaped curve when a rapidly growing population exceeds the carrying capacity of its environment and ceases to grow.

Carrying capacity may or may not be fixed

Rose disease limited by supply of hosts.
Environmental conditions can change.

Some species do not fit neatly into either the exponential or logistic models

Collared lemmings
4-year cycle

Density-dependent conditions

Effects increase as a population grows
Biotic (living)

Density-independent conditions

Effects unrelated to populations size
Abiotic (nonliving)

Life history

Includes all events of an organism's life from conception through death.
Main focus is adaptations that influence reproductive success.

Organisms Balance Reproduction Against Other Requirements

Life history reflects a series of evolutionary trade-offs.
Solutions vary tremendously
Reproduction is extremely costly, Timing also critical

r-selected species

Individuals short-lived
Reproduce at early age
Have many offspring that receive little care
Population's growth rate can be very high
Type III survivorship curve

K-selected species

Individuals long-lived
Produce few offspring that receive extended parental care
Type I or II survivorship curves

Guppies Illustrate the Importance of Natural Selection

Live in rivers and streams on the South American mainland and on the islands of Trinidad and Tobago.
Face different levels of predation.
Predicted predation would effect life history.

Population Dynamics Reflect the Demographic Transition

By early 2010, the world's human population was approaching 6.8 billion

Average population density of 45 people per square kilometer

Distribution not random
China and India account for 1/3 of all humans

Less-developed countries are growing at much faster rates than are more-developed countries

Each country's economic development influences progress along demographic transition
Birth and death rates shift from high to low

Population's age structure helps predict its future birth rate

India - high potential for growth
United States - stable population
China - population declining

Life expectancy has increased throughout history

Today 75 in most-developed countries.
50 in least-developed countries
Substantial differences in mortality rates

The Ecological Footprint Is an Estimate of Resource Use

Measures the amount of land area needed to support a country's overall lifestyle.
World's wealthiest and most populous countries have the largest ecological footprints.
Energy consumption accounts for about half of the ecological footprint.

Firefly Photinus ignitus

Use flashes to deliver precise mating information between sexes


Sperm and amino acids for developing young.
Females should choose males with largest ones.

Males flash duration reliably coded the weight of the spermatophore

Created artificial males to test duration of flashes found attractive by females.
Females preferred long flashes up to a limit
Very long flashes resemble predatory fireflies

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