The document is a chapter from an environmental science textbook about populations and their characteristics. It discusses topics like population growth curves, limiting factors, carrying capacity, and reproductive strategies. A typical population growth curve shows four phases: a lag phase, exponential growth phase, deceleration phase, and stable equilibrium phase. Limiting factors that control population size can be extrinsic, intrinsic, density-dependent, or density-independent. Carrying capacity is the maximum sustainable population size for a given area. Reproductive strategies also vary, with K-strategists producing fewer offspring and r-strategists producing many offspring.

1. Environmental Science
A Study of Interrelationships
Thirteenth Edition
Enger & Smith
Chapter 7
Populations: Characteristics and Issues
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

2. Populations: Characteristics and Issues

3. 7.1 Population Characteristics
 A population is a group of individuals of the same
species inhabiting the same area.

4. 7.1 Population Characteristics
Effect of birthrate and death rate on population size

5. 7.1 Population Characteristics
Age distribution in human populations

6. Population Density and
Spatial Distribution
 Population density is the number of individuals
per unit area.
• High population density
– injures all individuals within the population
– because they compete for resources

7. 7.2 A Population Growth Curve
 Biotic potential is the inherent reproductive
capacity of a species
• (biological ability to produce offspring).
 biotic potential is much above replacement level.
• natural tendency for increase

8. 7.2 Biotic Potential

9. 7.2 A Population Growth Curve
 Population growth follows a pattern:
•
•
•
•
1st
2nd
3rd
4th
lag phase
exponential growth phase
deceleration phase
stable equilibrium phase

10. 7.2 A Population Growth Curve
A typical population growth curve

11. Population growth curve
 Lag Phase:
 first portion of the curve
 slow population growth
 Few births

12. Population growth curve
 Exponential Growth Phase (Log Phase):
 More organisms reproducing
 causing accelerated growth
 continues if birth rate exceeds death rate

13. 7.2 Population Growth Curve
• Deceleration Phase:
– The population growth rate slows
– death rate and birthrate equal one another

14. 7.2 Population Growth Curve
 Stable Equilibrium Phase:
 The death rate and birth rate become equal
 the population stops growing

15. 7.3 Factors That Limit Population Size
 Limiting Factors--prevent unlimited population
growth
• Extrinsic limiting factors
• Intrinsic limiting factors
• Density-dependent factors
• Density-independent factors

16. 7.3 Factors That Limit Population Size
 Extrinsic limiting factors
 Come from outside the population
•
•
•
•
Predators
Loss of food source
Lack of sunlight
Accidents of nature

17. 7.3 Factors That Limit Population Size
 Intrinsic limiting factors
• factors that originate within the population
• exercise control over it
• Behavioral changes amongst the population cause
lower birthrates and higher death rates.

18. Other limiting factors
 Density-dependent limiting factors
• become more effective as the density of the
population increases.
• Denser population
– Predators more effective

19. Other limiting factors
 Density-independent limiting factors
• population-controlling influences not related to the
density of the population.
• Accidental
• Extrinsic factors

20. Density dependent or independent?
 Mutualism between two species.
 A wolf eating rabbits.
 A large fire burns down many of the trees in a
forest.
 A disease kills all the mice in a local radius and
the foxes have nothing to eat.

21. 7.4 Categories of Limiting Factors
 For most populations, limiting factors recognized
as components of environmental resistance
•
•
•
•
Raw material availability
Energy availability
Accumulation of waste products
Interactions among organisms

23. Discussion
 What will we do?

24. 7.5 Carrying Capacity
 Carrying capacity is the maximum sustainable
population for an area.
 It is not an inflexible number; it can be
influenced by environmental differences

25. 7.5 Carrying Capacity
•
•
•
•
•
Successional changes
Climate variations
Disease epidemics
Forest fires, floods, or natural disasters
Nutrient levels in aquatic ecosystems

26. 7.5 Carrying Capacity

27. 7.6 Reproductive Strategies
and Population Fluctuations
 Species divided into two broad categories based
on their reproductive strategies:
• K-strategists
• r-strategists

28. 7.6 Reproductive Strategies
 K-strategists: Organisms that typically reach a stable
population as the population reaches the carrying
capacity.
 K-strategist characteristics:
 Usually occupy relatively stable environments
• Large organisms
• Long-lived
• Produce few offspring

29. 7.6 Reproductive Strategies
and Population Fluctuations
 K-strategist characteristics:
• Provide substantial parental care
• Reproductive strategy
– invest a great deal of energy in producing a few offspring
that have a good chance of living to reproduce.
 K-strategists
• controlled by density-dependent limiting factors.

30. K-strategist

31. 7.6 Reproductive Strategies
 r-strategist characteristics include:
•
•
•
•
•
Small, short-lived organisms
Produce many offspring
Little if any parental care
Exploit unstable environments
Usually do not reach carrying capacity (boom-bust
cycles)

32. r-strategist
Reproductive strategy
– produce large numbers of offspring to overcome high
mortality.
 r-strategists are controlled by densityindependent limiting factors.

33. r-strategist

35. Summary
 The birthrate (natality) is the number of individuals
entering the population by reproduction during a
certain period.
 The death rate is the number of deaths in a
population in a certain period.
 A typical population growth curve shows a lag
phase followed by an exponential growth phase, a
deceleration phase, and a stable equilibrium
phase at the carrying capacity.

36. Environmental Science
A Study of Interrelationships
Thirteenth Edition
Enger & Smith
Chapter 11
Biodiversity Issues
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

37. 11.3 Invasive Species
 Impact populations (affect population size)
 Some introductions of exotic species are
purposeful, while others are accidental.
 Globalization is responsible for spreading
thousands of invasive alien species around the
world.

38. 11.3 Invasive species
 The IUCN estimates about
• 30% of birds and 15% of plants are threatened
• because they are unable to successfully compete against
invasive exotic species.
 Various insects have had an effect on ecosystem
structure.
• Asian long horned beetle
 Freshwater ecosystems have been greatly affected.
• Zebra mussel

39. 11.3 Threats to Biodiversity
The Asian long horned beetle

40. Overview
 http://www.youtube.com/watch?v=Bu6ouKt9zhs

41. Homework
 4 groups
 Each group answers one question
 Next week (1-29-14), present answers in 5 to 10
minute presentation