1. Environmental Science
Chapter 4

2. 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.

3. Section 1 The Central Case
How do changes in population size relate to environmental conditions?

4. 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……………

5. Section 1
Ecology (figure 1) –
Ecologist

6. Section 1 Levels of ecological organization 1. Individuals
What ecologists study:
2. Populations

7. Section 1
Species
3. Communities
What ecologists study:

8. Section 1
4. Ecosystems –
What ecologists study
5. The Biosphere

9. Section 1 Ecosystems include both biotic and abiotic factors.

10. 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 _________________________.

11. 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.

12. 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 _______________________.

13. 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

14. Section 2 Determining population size
Do you think Alexander Wilson actually counted 2 billion passenger pigeons???
NO!!!!
He took a SAMPLE

15. 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

16. Section 2
The number of individuals within a population per unit area describes the ____________________ ___________________.
High population densities
Pros:
Cons:

17. Section 2
The number of individuals within a population per unit area describes the ____________________ ___________________.
High population densities
Pros:
Cons:

18. Section 2
Low population densities
Pros:
Cons:

19. Section 2
How the organisms are arranged within an area is called __________________ ___________________________.
Populations can be arranged ________________, ___________________, or in ____________________.

20. Section 2 Random distribution: Uniform distribution:
Clumped distribution:

21. 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.

22. Section 2 Pre-reproductive organisms: Post-reproductive organisms:
The proportion of males to females in a population describes _____________ __________.

23. 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.

24. 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 ___________________________.

25. 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:

26. 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.

27. Section 3 Calculating Population Growth
(individuals added)-(individuals subtracted) = population growth Or
(birthrate + immigration rate)-(death rate + emigration rate) = population growth
Example:

28. 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

29. 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

30. 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.

31. 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

32. Section 3
_________________ is the growth rate of a population under ideal conditions
Factors that affect the biotic potential: 1. 2.