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Environmental
Science
Chapter 4
Section 1
 Objectives:
 1.
Describe the different levels of
organization studied by ecologists
 2.
Explain the difference between biotic
and abiotic factors.
 3.
Discuss how an organism’s habitat
relates to its survial.
Section 1
 The
Central Case
 How
do changes in population size relate
to environmental conditions?
Section 1
 Scientists
study life at many levels, from
individual organisms to the entire
biosphere.
 Lets
begin by taking a look at those
different levels……………
Section 1
 Ecology
 Ecologist
(figure 1) –
Section 1
 Levels
of ecological organization
 1. Individuals
What ecologists study:
2. Populations
What ecologists study:
Section 1

 3.
Species
Communities
What ecologists study:
Section 1
 4.
Ecosystems –
What ecologists study
 5.
The Biosphere
Section 1
 Ecosystems
include both biotic and
abiotic factors.
 Biotic
factors
 Abiotic
factors
Section 1
 The
specific environment in which an
organism lives is its ____________________.
It consists of both ________________ and
____________________ factors.
 Anything
an organism needs, including
nutrition, shelter, breeding sites, and
mates is a _________________________.
Section 2
 Objectives:
 1.
Explain the usefulness of tracking
population size.
 2. Describe population density.
 3. Describe the 3 ways populations can
be distributed.
 4. Explain what age structure diagrams tell
you about a population.
Section 2
 The
overall health of a population can
often be monitored by tracking how its
size changes, population density
changes, and distribution changes.
 The
number of individual organisms
present in a given population at a given
time is called the _______________________.
Section 2
 If
a population size increases or remains
the same it is a sign of a
_______________________________________.
 If a population size decreases it can lead
to __________________________________.
 The
Passenger Pigeon
Section 2
 Determining
population size

Do you think Alexander Wilson actually
counted 2 billion passenger pigeons???
NO!!!!

He took a SAMPLE

Section 2
 They
take a reasonable area, count the
number of individuals, and estimate the
number of individuals of a much larger
area.
 Scientists
also look for EVIDENCE that the
organisms exist.

Animal droppings or tracks
Section 2
 The
number of individuals within a
population per unit area describes the
____________________ ___________________.
 High
population densities
Pros:
Cons:
Section 2
 The
number of individuals within a
population per unit area describes the
____________________ ___________________.
 High
population densities
Pros:
Cons:
Section 2
 Low

population densities
Pros:

Cons:
Section 2
 How
the organisms are arranged within
an area is called __________________
___________________________.
 Populations can be arranged
________________, ___________________, or
in ____________________.
Section 2
 Random
 Uniform
distribution:
distribution:
 Clumped
distribution:
Section 2
 Age
structure and sex ratios
 This describes the relative numbers of
organisms of each age within a
population: ___________ ________________.
 ______
____________________ ____________
are visual tools to show the age structure
of populations.
Section 2
 Pre-reproductive
organisms:
 Post-reproductive
 The
organisms:
proportion of males to females in a
population describes _____________
__________.
Section 3
 Objectives:
 1.
Describe the factors that influence a
population’s growth rate.
 2. Explain exponential growth and logistic
growth.
 Explain how limiting factors and biotic
potential affect population growth.
Section 3
A
population’s growth rate is determined
by births, deaths, immigration, and
emigration.
 The
rate at which individuals are born is
called _________________________.
 The rate at which individuals die is called
___________________________.
Section 3
 To
show how the likelihood of death varies
with age, population ecologists use
graphs called _______________ ___________.
 There are 3 types of survivorship curves:
 I:
 II:
 III:
Section 3
 Population
size can also be affected by
people moving in or out of a population.
 ____________ is the arrival of individuals
from outside a given area.
 _____________ is the departure of
individuals from a given area.
 _________________ is the seasonal
movement into and out of an area.
Section 3
 Calculating
Population Growth
 (individuals added)-(individuals
subtracted) = population growth
Or
(birthrate + immigration rate)-(death rate +
emigration rate) = population growth
Example:
Section 3





How populations grow
Growth rates change depending on
resources available to the organisms in the
population
2 ways for populations to grow:
1.
2.

1. _______________________ occurs when a
population increases by a fixed percentage
each year

Produces a J-shaped curve on a graph
Section 3
 1.
_______________________ occurs when a
population increases by a fixed
percentage each year
 Produces

a J-shaped curve on a graph
Exponential growth occurs when:
 1.
 2.
 Examples:


1. Mold growing on bread
2. bacteria growing on dead organisms
Section 3
 2.
___________________ describes how a
population’s initial exponential increase is
slowed and finally stopped by limiting
factors.



Produces an S-curve on a graph
____________ are characteristics of the
environment that limit population.
_____________ is the largest population size a
given environment can sustainably support.
Section 3
 Limiting
Factors and Biotic Potential
 _______________________ is a limiting factor
whose influence changes with population
density

Ex: competition, predation, disease
 __________________
is a limiting factor
whose influence is not affected by
population density

Ex: catastrophic events
Section 3
 _________________
is the growth rate of a
population under ideal conditions

Factors that affect the biotic potential:
 1.
 2.