1. Population Ecology
Chapter 19

2. Ecology
Study of interactions of organisms with each other and the physical environment
Can be divided into increasingly comprehensive levels:
Organismal ecology
Population ecology
Community ecology
Ecosystem ecology

3. Organismal ecology Concerned with evolutionary adaptations
Enable individual organisms to meet the challenges posed by their abiotic environments

4. Population ecology
Concentrates mainly on factors that affect population density and growth

5. Community ecology
Focuses on how interactions between species affect community structure and organization

6. Ecosystem ecology
All abiotic factors in addition to the community of species in a certain area
Focuses on energy flow and the cycling of chemicals
among the various abiotic and biotic factors

7. What Is Population Ecology?
Study of how members of a population interact with their environment
Focuses on factors that influence a population’s:
Size
Growth rate
Density
Structure

8. Populations Distribution
Pattern of dispersal of individuals across an area
Affected by availability of resources
nonliving (abiotic) and living (biotic) components of an environment that support living organisms
Limiting factors
Environmental aspects that particularly determine where an organism lives
Range
Portion of the globe where the species can be found

9. Populations Density Number of individuals per unit area
How do we measure population density?
impossible to count all individuals in a population
estimated by indirect indicators
number of bird nests

10. Influences on Population
Carrying capacity
Number of individuals of a species that a particular environment can support

11. PATTERNS OF DISPERSION….
way individuals are spaced within the population’s geographic range
Three main models of dispersion:
Clumped
Uniform
Random

12. Patterns of Dispersion
Clumped pattern of dispersion
Individuals aggregate in patches

13. Patterns of Dispersion
Uniform pattern of dispersion
Results from interactions among the individuals of a population

14. Patterns of Dispersion
Random pattern of dispersion
Individuals are spaced in a patternless, unpredictable way

15. Comparison of species
Survivorship
Life history traits

16. 1. survivorship
Chance an individual in a population survives to various ages
Represented graphically in a survivorship curve
Plot of individuals surviving at each age in maximum life span
Uses a percentage scale
Can compare species with various life spans on same graph

17. Survivorship Type I survivorship curve Type II survivorship curve
Most individuals survive until old age
Type II survivorship curve
Decreases consistently over time
Type III survivorship curve
Most individuals die early

18. 2. life history Set of traits that affect the organisms:
Reproduction
Survival
Key feature of a populations pattern of survivorship
Key life history traits are:
Age at first reproduction
Frequency of reproduction
Number of offspring
Amount of parental care provided

19. Types of life histories
Organisms with an opportunistic life history:
Take immediate advantage of favorable conditions
Typically exhibit a Type III survivorship curve
Organisms with an equilibrial life history:
Reach sexual maturity slowly
Produce few, well cared for offspring
typically large-bodied and longer lived
Typically exhibit a Type I survivorship curve
occur in environments where population size is at or near carrying capacity

20. Population growth models
Populations fluctuate
Mathematical models to illustrate changes:
Exponential population growth
Logistic population growth

21. Population growth models
1. J-shaped Curve – Exponential Growth
Lag phase: Growth is small because the population is small
Exponential growth phase: Growth is accelerating, and the population is exhibiting its biotic potential

22. Population growth models
2. S-shaped Curve – Logistic Growth
Lag phase: Growth is small because the population is small
Exponential growth phase: Growth is accelerating, and the population is exhibiting its biotic potential
Deceleration phase: The rate of population growth slows down
Stable equilibrium phase: Little if any growth takes place because births and deaths are about equal.

23. Regulation of Population Growth
1. density-dependent factor
Intraspecific competition
population-limiting factor
effects intensify as the population increases in density
Percentage of population affected does increase as density of population increases
Includes:
Accumulation of toxic wastes
Limited food supply
Limited territory
Competition and predation

24. Regulation of Population Growth
2. Density-independent factors
population-limiting factors
intensity is unrelated to population density
Population of individuals killed remains same regardless of population size
Includes abiotic factors such as:
Fires
Floods
Storms

25. Human Population Growth
Growing almost exponentially for centuries
Based on the same parameters that affect other populations
Birth rates
Death rates

26. Human Population Growth
Approximately 225,000 people are added to the world’s population every day
Approximately 82 million people are added to the world’s population every year
Current doubling time is 56 years
(length of time it takes for population size to double)
More Developed Countries (MDC’s) versus Less Developed Countries (LDC’s)

27. Estimates of population
Age structure of a population
Proportion of individuals in different age groups
Can help predict the future growth of populations in different countries

28. Effects on populations - Invasive species
Non-native species that has spread far beyond the original point of introduction
Causes environmental or economic damage by colonizing and dominating suitable habitats
In United States, invasive species cost about $137 billion a year
Invasive species typically exhibit an opportunistic life history pattern

29. Invasive species Kudzu 1876 invasive Asian vine
Covers about 12,000 square miles of the southeastern United States
Has a range limited by cold winters
Grows 60 feet per season!

30. Invasive species Biological control
intentional release of a natural enemy to attack a pest population
used to manage an invasive species
Does NOT always work!!!