Populations have characteristics like population size, density, age distribution, and dispersion that can change over time. A population's growth is determined by births and immigration minus deaths and emigration. Exponential growth occurs when births exceed deaths, but resources are ultimately limited by the environment's carrying capacity. Populations may exhibit r-selected or K-selected reproductive strategies depending on environmental pressures and resource availability.

1. Population Dynamics Populations.ppt

2. Vocabulary Population Biotic Potential Carrying Capacity r-Selection K-Selection Survivorship Curve Populations.ppt

3. Population number of individuals of a species in a defined place and time. Populations.ppt Dynamic characteristics of populations

4. Dynamic characteristics of populations Population size, number of individuals (N) Density (N/ area) Dispersion Random Uniform Clumped Populations.ppt

5. Dynamic characteristics of populations Age distribution, proportions of young, middle-aged, old Differs in growing, stable, decreasing populations Populations.ppt

6. Changes in populations Growth Expansion of species’ populations may lead to evolution of new species Decline Shrinking species’ populations may lead to extinction Small populations Narrowly specialized species Populations.ppt

7. Changes in populations Δ N = +B +I –D –E +B = births (birth rate) +I = immigrants (immigration rate) – D = deaths (death rate) – E = emigrants (emigration rate) (For many [most] natural populations I and E are minimal.) Populations.ppt

8. Population growth B > D Exponential growth, dN/dt = rN N = number, pop.size r = biotic potential (maximum reproductive capacity of an organism if resources are unlimited) Populations.ppt

9. Population growth Exponential growth unlimited dN/dt = rN Unrealistic

10. Carrying Capacity The population size that the environment can sustain for a long period of time. Determined by Renewable resources (water, light, etc) Nonrenewable resources (land)

11. Population growth Logistic growth, dN/dt = rN (1 - N/K) N = number, population size r = biotic potential K = carrying capacity Better represents real populations

12. Population growth Logistic growth, dN/dt = rN (1 - N/K) N = number, population size r = biotic potential, “intrinsic rate of increase.” K = carrying capacity Better represents real populations

13. Logistic model Logistic model works, to a point. Real organisms have time lags for growth, time to develop eggs, flowers, etc. Real populations may exceed carrying capacity. Kaibab Deer Populations.ppt

14. Various species have various strategies for coping with a variable world. Populations.ppt

15. Two general types of Reproductive Strategies

17. Survivorship Curves • Plots surviving individuals at different age groups r-strategists have Type III K-strategists have Type I Populations.ppt

18. Survivorship Curves Populations.ppt Type I survivorship curves are characterized by high survival in early and middle life, followed a rapid decline in survivorship in later life. Humans are one species that show this pattern of survivorship. Type II curves are an intermediate between Type I and III, where roughly constant mortality rate is experienced regardless of age. Some birds follow this pattern of survival. In Type III curves, the greatest mortality is experienced early on in life, with relatively low rates of death for those surviving this bottleneck. This type of curve is characteristic of species that produce a large number of offspring. One example of a species that follows this type of survivorship curve is the cockroach.