1. Population Ecology
Packet #80
Chapter #52

2. Introduction & Review Population Population Ecology
Group consisting of members of the same species that live together in a prescribed area at the same time.
Population Ecology
The study of numbers of individuals of a particular species, at a given time and location, and the interactions of that population with other populations and the environment
Population dynamics
Study of changes in populations

3. Important Features of Populations
Population Ecology
Important Features of Populations

4. Population Density Population Density
This is how population size is expressed
The number of individuals of a species per unit space

5. Dispersion Dispersion
Describes the spacing of individuals and there are three types.

6. Types of Dispersion Uniform Dispersion Clumped (Aggregated) Dispersion
Individuals are evenly distributed
Clumped (Aggregated) Dispersion
Most common type
Individuals are concentrated in specific parts of the habitat
Patchiness
Occurs as a result of distribution of resources or by asexual reproduction
Random dispersion
Occurs when individuals of a population are spaced throughout an area in a manner that is unrelated to the presence of others
Least common; hardest to observe
Results from a lack of interaction between individuals or a homogenous environment

7. Population Ecology
Mathematical Models

8. Equation ∆N/∆t = b – d r = b – d
∆N is the change in numbers in the population
∆t is the change in time
b is the natality (birth) rate
d is the mortality rate
r = b – d
r is the growth rate of the population
If r is 0, the population is stable
If r > 1, the population is increasing in size
If r < 1, the population is declining
These equations can be expressed as dN/dt = rN
N is the population size
Represents arithmetic growth
Population increases by the same amount over each interval of time
Bubble Demonstration

9. Population Ecology
Types of Growth Rates

10. Exponential Growth Exponential Growth
Population growth is at a rapid pace
Reflects the maximum intrinsic rate of growth
Maximum rate of growth under ideal conditions for that population
dN/dt = rmaxN
rmax represents the maximum growth rate
This type of growth may exist for a period of time until limiting factors become important
Humans have exhibited this growth pattern for centuries—but can it last?

11. Exponential Growth & The Human Population I
Thomas Malthus recognized that the human population cannot continue in exponential growth
There has been a large decrease in death rate and the population continues to increase to unknown proportions
No one knows the carrying capacity of humans.
Human growth rate will continue to increase until humans hit carrying capacity
Not all countries have the same growth rate
Growth rate is higher in developing countries
Africa and Southeast Asia countries
Doubling time is the time needed for a population to double in size
Replacement-level fertility is the number of children a couple must have to replace themselves
2.1 developed countries; 2.7 developing countries
Total fertility rate
Average number of children born to a woman during her lifetime
Age structure of country can be used to predict future population growth
Broader base shows growing population
Narrower base shows shrinking population
Environmental degradation is related to population growth and resource consumption
Developed countries require more resources per capita
Cause more environmental problems
People overpopulation, too many people living in certain areas result in people over-utilizing resources

12. Exponential Growth & The Human Population II
Not all countries have the same growth rate
Higher in developing countries
India
South Asia
Africa
Age structure of a country can be used to predict future population growth
Shows the percentages of population at different ages
A broader base to the age structure indicates a growing population while a narrower base indicates a stable or shrinking population.
Human growth rate will continue to increase until humans hit carrying capacity
Not all countries have the same growth rate
Growth rate is higher in developing countries
Africa and Southeast Asia countries
Doubling time is the time needed for a population to double in size
Replacement-level fertility is the number of children a couple must have to replace themselves
2.1 developed countries; 2.7 developing countries
Total fertility rate
Average number of children born to a woman during her lifetime
Age structure of country can be used to predict future population growth
Broader base shows growing population
Narrower base shows shrinking population
Environmental degradation is related to population growth and resource consumption
Developed countries require more resources per capita
Cause more environmental problems
People overpopulation, too many people living in certain areas result in people over-utilizing resources

13. Logistic Growth Logistic Growth
Exponential growth with environmental resistance (carry capacity of the environment = K) incorporated into the equation
dN/dt = rmaxN((K – N) /K)
N = population size
K = carrying capacity
Maximum number of organisms that the environment can sustain indefinitely.
Exhibited by most natural populations.

14. Potential Examination Question Logistic Growth
Populations do not always approach and stabilize at K, but may overshoot K, followed by a population crash.
Why does this occur?
Provide an example.
What reproductive strategies would be advantageous at high population densities (At or close to K)?
What reproductive strategies would be advantageous at low population densities?
High
ability to reproduce with few resources
ability to compete well for limited resources
ability to use resources very efficiently
organisms showing this type of strategy are sometimes called "K-selected", or equilibrial
most likely to be found in stable habitats where population size does not vary much once it has approached K.
Low
early sexual maturity
short generation time
increased fecundity
organisms showing this type of strategy are sometimes called "r-selected", or opportunistic
most likely to be found in unstable habitats where environmental fluctuations result in large die-offs, or in newly colonized habitats where resources are not a limiting factor

15. Factors Influencing Population Size
Population Ecology
Factors Influencing Population Size

16. Dispersal Dispersal Movement of individuals among populations
Immigration
Migration of individuals into the population
Emigration
Migration of individuals out of the population
If incorporated into the growth rate mathematical equation
r = (b – d) + (i – e)

17. Density Dependent Factors
Regulate population size and is difficult to access in nature and are limiting factors that increase in intensity as population size increases

18. Density Dependent Factors II
Predation
Disease
Increases when contact with toxic waste, produced by population itself, increases with population size.
Competition
Intraspecific
Competition between members of the same species
Interspecific
Competition between members of different species

19. Density Independent Factors
Limit population size and are factors that do not increase in intensity as the population size increases.
Most density-independent factors have some relationship to population density.
Many climatic factors are density-independent.

20. Density Independent Factors
Climatic factors
Sunlight
Rainfall
Temperature
All have impacts no matter what the population size
Climatic and seasonal factors, monsoon season for example, can severely decrease populations

21. Life “History” Traits of Populations
Population Ecology
Life “History” Traits of Populations

22. Introduction
Life history traits, products of natural selection, are traits that affect an organism’s schedule of reproduction and survival.
Birth  Reproduction  Death

23. Semelparous vs. Iteroparous Species
Semelparous Species
Expend their energy in a single, immense reproductive effort
Pacific salmon
Agave
Iteroparous Species
Exhibit repeated reproductive cycles
Most vertebrates
Most shrubs
Most trees

24. r Strategists r strategists
Have traits that contribute to a high population growth rate.
High r
Small size
Large numbers of offspring
May live in unpredictable habitats
Weeds
Pests
Roaches

25. K Strategists K strategists
Maximize the chance of surviving in an environment where the number of individuals (N) is near the carrying capacity (K) of the environment.
Population size near K
Larger body size
Long life span
Late reproduction and slow development
Have fewer offspring
May care for their young
African elephants
Humans

26. Survivorship Survivorship is related to r and k selection
Type I Survivorship
Typical of K-selected organisms
High mortality rate later in life
Type II Survivorship
Characterized by constant mortality rate over time
Birds and lizards
Type III Survivorship
r selected organisms.
Characterized by high mortality rate early in life

27. Survivorship Curves

28. Review

29. Review
Students are encouraged to place their own questions and charts on following slides.