1 / 66

Chapter 52

Chapter 52. Population Ecology. Population Ecology. Population ecology is the study of the populations and their interactions with the environment. It also explores how the environment influences these populations in terms of size, age structure, and distribution. Population Ecology.

Download Presentation

Chapter 52

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Chapter 52 Population Ecology travismulthaupt.com

  2. Population Ecology • Population ecology is the study of the populations and their interactions with the environment. • It also explores how the environment influences these populations in terms of size, age structure, and distribution. travismulthaupt.com

  3. Population Ecology • Ecologists usually begin an investigation of a population by defining appropriate parameters such as density and dispersion. travismulthaupt.com

  4. Density • How many individuals live within a given area. • To determine the density of individuals, it is possible to count all of the organisms within a given area, but it is not likely. travismulthaupt.com

  5. Dispersion • Dispersion is the spacing patterns among individuals within the boundaries of a population. travismulthaupt.com

  6. Sampling Techniques • Usually a wide variety of them are used. • Scientists can count all individuals in a given area. • They can do this in a number of different spots. • Then, average all of the numbers together to make educated estimates about the population density. travismulthaupt.com

  7. Sampling Techniques • Scientists also employ the mark and recapture method. • Animals are captured, marked, and released. • The animals can then be tracked or captured at a later date. • Density and distribution can be studied. travismulthaupt.com

  8. Sampling Techniques • These methods are okay, but sometimes the data becomes unreliable because the organisms you are studying behave differently during study. travismulthaupt.com

  9. Population Density • The density is always changing. • Birth, death, immigration, and emigration are ways a population changes. travismulthaupt.com

  10. Dispersal Patterns • There are varying dispersal patterns of organisms within a population’s geographic range. • These variations in local populations are extremely important to ecologists. travismulthaupt.com

  11. Three Common Patterns of Dispersal: • 1. Clumped • 2. Uniform • 3. Random travismulthaupt.com

  12. 1. Clumpled • 1. Organisms are in uniform patches travismulthaupt.com

  13. travismulthaupt.com

  14. 2. Uniform • Organisms are evenly spaced. travismulthaupt.com

  15. travismulthaupt.com

  16. 3. Random • Organisms exhibit unpredictable spacing patterns. They could be grouped together, or there could be an uneven distribution pattern. travismulthaupt.com

  17. travismulthaupt.com

  18. Demography • Demography is the study of the vital characteristics of a population. • For example: • Ecological needs • Spacing of individuals • Interactions of individuals within a population. travismulthaupt.com

  19. Demographers • These are people who study populations. • They develop life tables to determine the survival pattern of a population. • The use a cohort--a group of individuals of the same age that are followed from birth to death. travismulthaupt.com

  20. Life Tables • These are difficult to build and maintain. • It is easier to graphically depict a life table--a survivorship curve. travismulthaupt.com

  21. Survivorship Curves • These typically involve 1000 individuals from a population. • The numbers are obtained by multiplying the surviving population by 1000 each year. • Plotting these numbers vs. age indicates the death rate (or life expectancy). travismulthaupt.com

  22. Survivorship Curves • There are three types of survivorship curves: • 1. Type I • 2. Type II • 3. Type III travismulthaupt.com

  23. 1. Type I • Type I curves start flat indicating a low death rate for early and middle life. • They decline sharply as individuals get older indicating a high death rate. travismulthaupt.com

  24. 2. Type II • Type II curves exhibit relatively constant death rates from birth to death. travismulthaupt.com

  25. 3. Type III • Type III curves see death rates very high in the beginning but as the animals grow and mature the death rates level off. • Example: animals that produce many young and provide little or no care for them. travismulthaupt.com

  26. Life Histories • Life histories are products of natural selection. • The traits that affect an organism’s schedule of reproduction and survival comprise its life history. travismulthaupt.com

  27. Life Histories • There are three basic variables that life histories entail: • 1. When reproduction begins. • 2. How often the organism reproduces. • 3. How many offspring are produced during a reproductive cycle. • For the most part, life histories are the product of evolutionary outcomes because most animals don’t choose when to reproduce. travismulthaupt.com

  28. Reproductive Modes • In general, there are 2 reproductive modes that are followed: • 1. Big bang reproduction--semelparity. • 2. Repeated reproduction--iteroparity. travismulthaupt.com

  29. Reproductive Modes • The evolutionary events that favor these are determined by the environment. travismulthaupt.com

  30. Semelparity • This is a “one and done” scheme for reproduction. • The organism takes a big chance. • Favored when the survival rate of the offspring is low. • Occurs when an organism lives in a highly variable or highly unpredictable environment. • Examples: • Salmon and agave plants. travismulthaupt.com

  31. Iteroparity • This is repeated reproduction. Organisms continually give rise to offspring throughout their lives. • Iteroparity is favored when environments are more stable. travismulthaupt.com

  32. Energy Constraints • Time, energy, and nutrients cannot be used for one thing as well as something else. • This is the tradeoff that prevents producing a large number of offspring very frequently. travismulthaupt.com

  33. Population Growth • Unchecked population growth is considered exponential. • There are mechanisms that prevent exponential population growth. • This can be estimated using mathematical equations to describe the per capita growth rate. travismulthaupt.com

  34. travismulthaupt.com

  35. Population Growth • It essentially boils down to the rate being equal to the number of births minus the number of deaths. • r = b-m • r>0 the population is increasing • r<0 the population is decreasing • r=0 no change travismulthaupt.com

  36. Population Growth • Because resources are limited populations cannot grow exponentially forever. • Ecologists try to identify the carrying capacity of an environment, K. • K is the maximum population size an environment can support. travismulthaupt.com

  37. Population Growth • To account for changes in the environment, scientists have created a logistic growth model to explain how populations vary in size. travismulthaupt.com

  38. Population Growth • The exponential growth model is used as a starting point. • We add information about the environment that acts to reduce the per capita rate of increase. • If K is the maximum, K-N is the number of individuals the environment can accommodate. • N is the population size. travismulthaupt.com

  39. Population Growth • (K-N)/K is the fraction of the carrying capacity available for population growth. • Multiplying by the maximum rate of increase of the population, rmax, allows us to modify the growth rate of the population as its size increases. • rmax N (K-N)/K travismulthaupt.com

  40. Population Growth • When N = K, the population stops growing. • The logistic model will produce an S-shaped (sigmoid) growth curve when population size is plotted over time. travismulthaupt.com

  41. Population Growth • New individuals are added at the highest rate at intermediate population sizes. • This is when the breeding population is of substantial size and space and resources are abundant. • As N approaches K, the population size slows. travismulthaupt.com

  42. travismulthaupt.com

  43. travismulthaupt.com

  44. Population Growth • The logistic model. • This incorporates the idea that every individual added to the population has the same negative effect on population growth. • This is not true. travismulthaupt.com

  45. Population Growth • Certain populations exhibit the Allee effect. • This describes a situation where individuals may have a difficult time surviving and reproducing when the population gets too small. • The logistic model fits few, if any, real populations. • It serves as a good starting point. travismulthaupt.com

  46. Population Growth • There are two general questions that are asked when studying population growth: • 1. What environmental factors stop a population from growing? • 2. Why do some populations show radical size fluctuations while others stay stable? travismulthaupt.com

  47. Population Growth • To understand the answers to these questions, we have to: • Examine the birth and death rates • Immigration and emigration • How these factors affect population density. travismulthaupt.com

  48. Population Growth • If immigration and emigration are equal, then birth and death rates will affect population size. travismulthaupt.com

  49. Population Growth • A birth rate or death rate that does not change with population density is said to be density independent. • A death rate that rises when population density rises is said to be density dependent--an example of negative feedback--it halts population growth. travismulthaupt.com

  50. travismulthaupt.com

More Related