EnvironmentalScienceChapter 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 (figure 1) –

Ecologist

Section 1 Levels of ecological organization 1. Individuals

What ecologists study:

2. Populations

What ecologists study:

Section 1 Species

3. 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 distribution:

Uniform 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 organisms:

The 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 growthOr

(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.