Population Ecology

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

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

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

6. 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 Ecosystem ecology

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 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. 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. Population growth models

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!!!