1. Population Ecology
Population ecology is the study of populations in relation to environment
Including environmental influences on population density and distribution, age structure, and variations in population size

2. Levels of Organization
Organism
Population
Community
Ecosystem
Biome

3. Describing populations

4. Size: total # of individuals in a pop (N) Density: # / unit area
Describing populations
Size: total # of individuals in a pop (N)
Density: # / unit area

5. Estimation of Population Size
Describing populations
Estimation of Population Size
Sampling technique
Mark and recapture

6. Mark and Recapture Orgs are captured, tagged, and then released.
Describing populations
Mark and Recapture
Orgs are captured, tagged, and then released.
Some time later, the same process is repeated and the following is used:

7. Describing populations
Ex:
Suppose that 50 zebra mussels are captured, marked, and released. One week later, 100 zebra mussels are captured and 10 are found to have markings already. The estimated population would then be
N= (50·100) / (10) = 5000/10 = 500
N=500

8. Dispersion Clumped Uniform Random
Describing populations
Describes how individuals in a population are distributed
Clumped
Uniform
Random

9. Fish travel in schools – safety in numbers
Clumped dispersion (most common)
Individuals aggregate in patches
May be influenced by resource availability & behavior
Describing populations
Example:
For many animals, such as these wolves, living in groups
increases the effectiveness of hunting.
spreads the work of protecting and caring for young.
helps exclude other individuals from their territory.
Fish travel in schools – safety in numbers

10. Some plants secrete toxins that keep others away
Uniform dispersion
-Individuals are evenly distributed
-May be influenced by social interactions such as territoriality
Describing populations
Birds nesting on small islands, such as these king penguins on South Georgia Island in the South Atlantic Ocean, often exhibit uniform spacing, maintained by aggressive interactions between neighbors.
Some plants secrete toxins that keep others away

11. Random dispersion
The position of each individual is independent of other individuals
Describing populations
Dandelions grow from windblown seeds that land at random and later germinate.

12. Changes in Population Size
Describing populations
Changes in Population Size
Biotic potential of a population=
max rate at which a population could increase under ideal conditions
Influenced by several factors:
Age at which reproduction begins
Life span during which the organisms are capable of reproducing
Number of reproductive periods in the lifetime
Number of offspring the organism is capable of having

13. Age Structure
Describing populations
Description of the abundance of individuals of each age in a population.

14. Age Structure Diagrams
Describing populations

16. 2004
China
India
United States

17. Zero population growth

18. Describing populations
1954
Animation

19. Describing populations

20. Survivorship Curves
Describing populations
Describes how the mortality of individuals in a species varies during their lifetime
1000
100 10 1
Number of survivors (log scale) 2 4 6 8
Age (years)
Males
Females
The survivorship curve for Belding’s ground squirrels
Shows that the death rate is relatively constant

21. A species in which most survive to middle age
Survivorship curves can be classified into three general types: Type I, Type II, and Type III I II
III 50
100 1 10
1,000
Percentage of maximum life span
Number of survivors (log scale)
Type I
A species in which most survive to middle age
Parenting
Type II
Length of survivorship is random. Death rate is constant.

22. Animation Most individuals die young. Few reach reproductive maturity.
Type III
Most individuals die young.
Few reach reproductive maturity.
Fish release 1000s of eggs.
No parenting I II
III 50
100 1 10
1,000
Percentage of maximum life span
Number of survivors (log scale)
Animation

23. Factors Affecting Population

24. Factors Affecting Population
Limiting Factors
Factors Affecting Population
Things that prevent a population from attaining its biotic potential
2 categories
Density-dependent
Density-independent
Density Dependent
Density Independent

25. Factors Affecting Population
Density Dependent
Factors Affecting Population
Populations regulated by density-dependent factors are affected by the number of organisms present.
Predation
Parasitism
Disease
Competition
-the more organisms crowd together, the more damaging are food shortages, parasites, and predators.
Intraspecific Competition = the struggle between members of a population for scarce resources

26. Factors Affecting Population
Density Independent
Factors Affecting Population
The number of organisms present does not affect the influence of the factor.
Fire, earthquakes, storms, floods
Density-independent factors show no correlation with the size of the population.

27. Describing Population Growth
Population ecologists describe two general patterns of populations growth:
Exponential
Logistic

28. Types of Population Growth
The growth of a population can be described by the following equation:
r= reproductive rate (or growth rate)
N= population size at the beginning of the interval for which the births and deaths are counted.
r = .
Types of Population Growth
Net increase of individuals
births-deaths N
Can r be negative? Zero?

29. Types of Population Growth
births-deaths N
Ex:
A population of 1000 had 60 births and 10 deaths over a one year period. What is the growth rate?
0.05 per year

30. Types of Population Growth
Exponential growth
r>0
Types of Population Growth
In a population showing exponential growth the individuals are not limited by food, disease, predation or competition.
If the rate of reproduction per individual remains constant through time, then the rate at which the population increases is a multiple of the number of individuals in the population.

31. Types of Population Growth
Exponential population growth
Results in a J-shaped curve
Usually short lived in nature- not sustainable
r>0
Types of Population Growth 5 10 15
500
1,000
1,500
2,000
Number of generations
Population size (N) dN dt 
1.0N
0.5N
Population size (N)

32. Types of Population Growth
the real world
Carrying Capacity (K)
Types of Population Growth
Populations usually reach a carrying capacity.
Upper limit to the number of individuals the environment can support.

33. Types of Population Growth
Logistic growth dN dt 
rmaxN
Types of Population Growth
In most real populations both food and disease become important as conditions become crowded.
A population can grow exponentially only for short periods of time, because it would very quickly deplete all the resources necessary for its survival.
Over long periods of time, populations tend to attain an equilibrium population size which is determined by the available resources.
Animation

34. Types of Population Growth
Zero population growth
Occurs when the birth rate equals the death rate
The population growth equation can be expressed as dN dt  rN

35. Life-history strategies
Logistic and exponential growth are associated with 2 kinds of life-history strategies
R-selected species (strategists)
organisms are opportunistic; they reproduce rapidly when the environment is uncrowned and resources are vast
K-selected species (strategists)
operate at a density near K

36. Life-history strategies
R-selected species
Life-history strategies
a. Opportunistic species, which tend to be colonizers.
b. Grasses, many insects
-Usually quickly invade, reproduce many offspring and die
-Offspring mature quickly and require very little parental care
c. Strategies for continued existence is based on individuals having the following traits:                 1) small size                 2) short life span                 3) mature fast                 4) produce many offspring                 5) engage in little care of offspring

37. Life-history strategies
K-selected species
Life-history strategies
sensitive to population density
Such populations are equilibrium species, tend to be specialists rather than colonizers, and may become extinct when their evolved way of life is disrupted (e.g., the grizzly bear, Florida panther, etc.).
Overall strategy for continued existence is based on having the following traits:                 1) large size                 2) long life span                 3) slow to mature                 4) produce few offspring                 5) expend considerable energy in care

39. Human Population Growth
The following made exponential growth possible
Increases food supply
Reduction in disease
Reduction in human waste
Expansion of habitat
As of 28 April 2010, the human population of the world is estimated by the United States Census Bureau to be 6,817,500,000.

41. Source: U.S. Census Bureau, International Data Base.
Countries Ranked by Population: 2010
Source: U.S. Census Bureau, International Data Base.
6,817,500,000

42. Map of countries by population for the year 2007