1. The Human Population and Its Impact
Chapter 6
The Human Population and Its Impact

2. Case Study New England Forests Come Full Circle
Describe the temperate forest as seen by the Pilgrims.
What happened to the temperate forest between 1620 and 1800s? Explain why this happened.
What happened to the temperate forest between 1850 and Explain why this happened.
What caused the appearance of the leaf beetle?
What did the “outbreak” of the leaf beetle cause to happen?
Explain the rise and fall of the goldenrod population.
Explain the rise and fall of the other plant species.
What was the first tree species to dominate and why?
What led to the rise of the broadleaf deciduous trees?
What does this process demonstrate?

3. Levels of Complexity

4. Population Ecology Definition:
Knowing the factors that affect a species’ population size helps to implement measures to improve its survival and reproduction.

5. Population Characteristics
Population size
Population density

6. Population Characteristics
Population Distribution
Occupation of a population with respect to one another.
Random
Uniform
Clumped

7. Population Characteristics
Population Sex Ratio
Ratio of males to females.
Number of offspring is primarily:
Population Age Structure
How many individuals are in particular age categories.
Large portion of older individuals …
Large number of young individuals …

8. Factors that Influence Population Size
Density-Dependent factors
Factors that influence the individual’s probability of survival and reproduction that depend on:
Gause’s experiments

9. Limiting Resources Definition Carrying capacity - K
Limiting resource decreases …
Limiting resources for autotrophs …
Limiting resources for heterotrophs …
Carrying capacity - K

10. Density-Independent Factors
Factors that influence the individual’s probability to survive that have nothing to do with the size of the population.
Examples:

11. Growth Models To explain and predict changes in population size.
Exponential Growth Model
Predict the population size at any moment of time.
Growth rate - r
Definition:
Intrinsic growth rate

12. Exponential Growth Model
Nt = N0ert
Nt = population’s future size
N0 = number of individuals currently in population
e is the base of the natural logarithms
r = intrinsic growth rate
t = time passed

13. Do The Math
Consider a population of rabbits that has an initial population size of 10 individuals.
N0 = 10
Let’s assume that the intrinsic rate of growth is 0.5 – 50%, which means that each rabbit produces and net increase of 0.5 rabbits each year.
r = 0.5
With this information, we can predict the size of the rabbit population a year from now.
Nt = N0ert
What about in 10 years?

14. Logistic Growth Model
Populations do not experience exponential growth indefinitely, therefore:
Initial growth is exponential but a slowing of growth as the population reaches the carrying capacity.
S-shaped curve

15. Variations on the Logistic Growth Model
Overshoot
Die-off

16. Predation as a Factor in Limiting Population Growth.

17. Reproductive Strategies
K-selected species
Species with a low growth rate.
Population increases slowly until they reach the carrying capacity.
Number of organisms is determined by the carrying capacity.
Fluctuations in population are small.
Characteristics:

18. r- Selected Species High intrinsic growth rate
Do not typically remain near their carrying capacity.
Rapid population growth
Overshoots
Die-offs
Characteristics:

19. Survivorship Curves Patterns of survival over time Type I Type III

20. Metapopulations
A group of spatially distinct populations that are connected by occasional movement of individuals between them.
Corridors:

21. Species Interactions Factors that determine distributions of species:
Community ecology
Study of interactions of populations within a community.
Competition
Definition:

22. Competitive Exclusion Principle
Resource Partitioning

23. Types of Resource Partitioning
Temporal
Spatial
Morphological

24. Predation Use of one species as a resource by another species.
True predators
Herbivores
Parasites
Pathogens
Parasitoids

25. Prey Defenses
To avoid being eaten or harmed by a predator.

26. Symbiotic Relationships
Relationship of two species that live in close association with each other.
Mutualism
Both interacting species benefit increasing both species chances of survival or reproduction.

27. Commensalism
One species benefits and the other is not harmed or helped.
Cattle egret and cows and sheep.

28. Keystone Species
A species that plays a role in its community that is far more important than its relative abundance might suggest.

29. Predator-mediated Competition

30. Types of Keystone Species
Finding food for the community
Mutualistic interactions
Ecosystem engineers

31. Ecological Succession
Predictable replacement of one group of species by another group of species over time.
Terrestrial communities
Primary succession
Secondary succession

32. Primary Succession
Growth of species on land that has never had growth before – no soil.

33. Primary Succession
The type of community that eventually develops is determined by the temperature and rainfall of the region.
U.S.
Forest in the East
Grasslands in the Midwest
Shrubland in the Southwest
In some areas the number of species increases as succession proceeds.
In some areas there are fewer late successional species than early ones.

34. Secondary Succession
Growth of species in areas that have been disturbed but have not lost their soil.
Pioneer Species

35. Aquatic Succession

36. Factors Influencing Species Richness
The number and types of species present is determined by:
Colonization of the area by new species
Speciation in the area
Loses in the area by extinction
Factors that affect these processes:
Latitude
Time
Size of the habitat
Distance of the habitat from the source of the colonizing species

37. Theory of Island Biogeography
Theory that demonstrates the dual importance of habitat size and distance in determining species richness.
Habitat size
Larger habitats usually contain more species.
Because:
Distance from source of colonizing species
Distance matters because: