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36 Lecture Ppt

  1. 1. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chapter 36 Population Ecology
  2. 2. Ecology Studies Where and How Organisms Live in the Biosphere
  3. 3. 36.1 Ecology is studied at various levels <ul><li>Ecology - study of the interactions of organisms with other organisms and with the physical environment </li></ul><ul><ul><li>ecological interactions are selection pressures that result in evolutionary change, which in turn affects ecological interactions </li></ul></ul><ul><li>Ecology is wide-ranging </li></ul><ul><ul><li>Habitat - the place where the organism lives </li></ul></ul><ul><ul><li>Population - all the organisms within an area belonging to the same species </li></ul></ul><ul><ul><li>Community - all populations interacting at a locale </li></ul></ul><ul><ul><li>Ecosystem - encompasses a community of populations as well as abiotic environment </li></ul></ul><ul><ul><li>Biosphere - encompasses the zones of the Earth’s land, water, and air where living organisms are found </li></ul></ul>
  4. 4. Figure 36.1 Ecological levels
  5. 5. Populations Are Not Static— They Change Over Time
  6. 6. 36.2 Density and distribution are aspects of population structure <ul><li>Density </li></ul><ul><ul><li>Once population size has been estimated, it is possible to calculate the population density , the number of individuals per unit area </li></ul></ul><ul><li>Distribution </li></ul><ul><ul><li>Population distribution - the pattern of dispersal of individuals across an area </li></ul></ul><ul><ul><li>Availability of resources can affect where populations of a species are found </li></ul></ul><ul><ul><ul><li>Resources are nonliving (abiotic) and living (biotic) components of an environment that support living organisms </li></ul></ul></ul><ul><ul><li>Limiting factors - environmental aspects that particularly determine where an organism lives </li></ul></ul><ul><ul><li>Three descriptions— clumped, random , and uniform —are used to characterize observed patterns of distribution </li></ul></ul><ul><ul><li>Range - portion of the globe where the species can be found </li></ul></ul>
  7. 7. Figure 36.2A Distribution patterns of the creosote bush
  8. 8. Figure 36.2B Nesting colony of Cape gannets off the coast of New Zealand
  9. 9. 36.3 The growth rate results in population size changes <ul><li>A population’s annual growth rate is dependent upon </li></ul><ul><ul><li>Number of individuals born each year </li></ul></ul><ul><ul><li>Number of individuals that die each year </li></ul></ul><ul><ul><li>Annual immigration and emigration </li></ul></ul><ul><li>Biotic potential of a population is the highest possible growth rate and is achieved when resources are unlimited </li></ul><ul><ul><li>Depends primarily on: </li></ul></ul><ul><ul><ul><li>Usual number of offspring per reproduction </li></ul></ul></ul><ul><ul><ul><li>Chances of survival until age of reproduction </li></ul></ul></ul><ul><ul><ul><li>How often each individual reproduces </li></ul></ul></ul><ul><ul><ul><li>Age at which reproduction begins </li></ul></ul></ul>
  10. 10. Figure 36.3 Biotic potential varies
  11. 11. 36.4 Survivorship curves illustrate age-related changes <ul><li>Cohort - term used to describe population members that are same age and have same chances of surviving </li></ul><ul><ul><li>Survivorship - probability of cohort members surviving to particular ages </li></ul></ul><ul><ul><ul><li>If we plot the number surviving at each age, a survivorship curve is produced </li></ul></ul></ul><ul><li>Three types of survivorship curves </li></ul><ul><ul><li>Type I Survivorship: Large mammals </li></ul></ul><ul><ul><ul><li>They survive well past the midpoint of the life span, and death does not come until near the end of the life span </li></ul></ul></ul><ul><ul><li>Type II Survivorship: Hydras, songbirds, and small mammals </li></ul></ul><ul><ul><ul><li>Survivorship decreases at a constant rate throughout the life span </li></ul></ul></ul><ul><ul><li>Type III Survivorship: Many invertebrates and fishes </li></ul></ul><ul><ul><ul><li>Most individuals will probably die very young </li></ul></ul></ul>
  12. 12. Figure 36.4A A life table for Dall sheep
  13. 13. <ul><li>Figure 36.4B Three typical survivorship curves </li></ul>
  14. 14. 36.5 Age structure diagrams divide a population into age groupings <ul><li>From the perspective of population growth, a population contains three age groups </li></ul><ul><ul><li>Prereproductive </li></ul></ul><ul><ul><ul><li>When the prereproductive group is the largest of the groups, the birthrate is higher than the death rate, and a p yramid-shaped diagram is expected </li></ul></ul></ul><ul><ul><ul><li>Under such conditions, even if the growth for that year were matched by the deaths for that year, the population would continue to grow in the following years </li></ul></ul></ul><ul><ul><li>Reproductive </li></ul></ul><ul><ul><ul><li>As the size of the reproductive group equals the size of the prereproductive group, a bell-shaped diagram results </li></ul></ul></ul><ul><ul><li>Postreproductive </li></ul></ul><ul><ul><ul><li>If the birthrate falls below the death rate, the prereproductive group becomes smaller than the reproductive group </li></ul></ul></ul><ul><ul><ul><li>The age structure diagram is then urn-shaped , because the postreproductive group is the largest </li></ul></ul></ul>
  15. 15. Figure 36.5 Age structure diagrams
  16. 16. 36.6 Patterns of population growth can be described graphically <ul><li>Particular pattern of a population’s growth is dependent on </li></ul><ul><ul><li>Biotic potential of population along with other factors, such as age structure </li></ul></ul><ul><ul><li>Availability of resources as well as other environmental factors </li></ul></ul><ul><li>Exponential Growth - likened to compound interest at the bank: The more your money increases, the more interest you will get </li></ul><ul><ul><li>Lag phase - Growth is slow because the number of individuals in the population is small </li></ul></ul><ul><ul><li>Exponential growth phase - Growth is accelerating due to biotic potential </li></ul></ul><ul><li>Logistic Growth - as resources decrease, population growth levels off </li></ul><ul><ul><li>Lag phase - Growth is slow because the number of individuals in the population is small </li></ul></ul><ul><ul><li>Exponential growth phase - Growth is accelerating due to biotic potential </li></ul></ul><ul><ul><li>Deceleration phase - The rate of population growth slows because of increased competition among individuals for available resources </li></ul></ul><ul><ul><li>Stable equilibrium phase - Although fluctuations can occur, little if any growth takes place because births and deaths are about equal </li></ul></ul><ul><li>Carrying capacity - total number of individuals the resources of the environment can support for an extended period of time </li></ul>
  17. 17. Figure 36.6A Exponential growth
  18. 18. Figure 36.6B Logistic growth
  19. 19. Application of Population Growth <ul><li>The model predicts that exponential growth will occur only when population size is much lower than the carrying capacity </li></ul><ul><ul><li>Example: Humans are using a fish population as a continuous food source </li></ul></ul><ul><ul><ul><li>It would be best to maintain that population size in the exponential phase of growth when biotic potential is having its full effect and the birthrate is the highest </li></ul></ul></ul><ul><ul><ul><li>If people overfish, the fish population will sink into the lag phase, and it may be years before exponential growth recurs </li></ul></ul></ul>
  20. 20. Environmental Interactions Influence Population Size
  21. 21. 36.7 Density-independent factors affect population size <ul><li>Ecologists have long recognized that environmental interactions play an important role in population size </li></ul><ul><ul><li>An abiotic factor is usually a density-independent factor </li></ul></ul><ul><ul><ul><li>Percentage of individuals killed remains the same regardless of the population size </li></ul></ul></ul><ul><ul><li>Example: A drought on the Galápagos Islands </li></ul></ul><ul><ul><ul><li>Caused the population size of one of Darwin’s finches ( Geospiza fortis ) to decline from 1,400 to 200 individuals </li></ul></ul></ul><ul><ul><ul><li>Caused a reduction in availability of seeds this species ate </li></ul></ul></ul><ul><ul><ul><li>This is a reduction of 86% of the original population size </li></ul></ul></ul>
  22. 22. Figure 36.7A  Percentage that die per density of population
  23. 23. Figure 36.7B Density-independent effect of a flood
  24. 24. Figure 36.7B Density-independent effect of a flood (Cont.)
  25. 25. 36.8 Density-dependent factors affect large populations more <ul><li>Biotic factors tend to be density-dependent factors because percentage of population affected does increase as density of population increases </li></ul><ul><ul><li>Competition - when members of same species attempt to use needed resources (such as light, food, or space) that are in limited supply </li></ul></ul><ul><ul><ul><li>Not all members of population can have access to the resource necessary for survival or reproduction </li></ul></ul></ul><ul><ul><li>Predation - when one living organism, the predator, eats another, the prey </li></ul></ul><ul><ul><ul><li>Effect of predation on a prey population generally increases as the population grows more dense, because prey are easier to find when hiding places are limited </li></ul></ul></ul>
  26. 26. Figure 36.8A Density-dependent effects: competition
  27. 27. Figure 36.8B Density-dependent effects: predation
  28. 28. The Life History Pattern Can Predict Extinction
  29. 29. 36.9 Life history patterns consider several population characteristics <ul><li>Energy is limited and must be distributed between </li></ul><ul><ul><li>Its life span (short versus long) </li></ul></ul><ul><ul><li>Reproduction events (few versus many) </li></ul></ul><ul><ul><li>Care of offspring (little versus much) </li></ul></ul><ul><li>Opportunistic population - live in a fluctuating environment </li></ul><ul><ul><li>Population stays small until conditions promote exponential growth </li></ul></ul><ul><ul><li>Members are small in size, mature early, have a short life span, and provide limited parental care for a great number of offspring </li></ul></ul><ul><ul><li>Density-independent effects dramatically affect population size, which is large enough to survive an event that threatens to annihilate it </li></ul></ul><ul><li>Equilibrium populations - live in relatively stable and predictable environments </li></ul><ul><ul><li>Logistic population growth, and remains close to carrying capacity </li></ul></ul><ul><ul><li>Some, allowing population size to remain fairly stable </li></ul></ul><ul><ul><li>Allocate energy to their growth and survival and that of their few offspring </li></ul></ul><ul><ul><li>They are fairly large, slow to mature, and have a relatively long life span </li></ul></ul>
  30. 30. Figure 36.9A Dandelions are an opportunistic species
  31. 31. Figure 36.9B Mountain gorillas are an equilibrium species
  32. 32. 36.10 Certain species are more apt to become extinct than others <ul><li>Extinction is the total disappearance of a species or higher group </li></ul><ul><ul><li>Three factors can help determine whether an equilibrium species is in danger of extinction </li></ul></ul><ul><ul><ul><li>Size of geographic range </li></ul></ul></ul><ul><ul><ul><li>Degree of habitat tolerance </li></ul></ul></ul><ul><ul><ul><li>Size of local populations </li></ul></ul></ul><ul><li>Results of population studies can assist conservationists and others who are trying to preserve biodiversity </li></ul><ul><ul><li>Metapopulations - local populations connected to one another by individuals moving between them </li></ul></ul>
  33. 33. Figure 36.10 Highlighted factors indicate vulnerability to extinction for an equilibrium species
  34. 34. Human Populations Vary Between Overpopulation and Overconsumption
  35. 35. 36.11 World population growth is exponential <ul><li>World’s population has risen steadily to a present size of about 6.5 billion people </li></ul><ul><ul><li>Potential for future population growth can be appreciated by considering the doubling time , the length of time it takes for the population size to double </li></ul></ul><ul><ul><ul><li>Currently, the doubling time is about 53 years </li></ul></ul></ul><ul><li>More-Developed and Less-Developed Countries </li></ul><ul><ul><li>More-developed countries (MDCs) - countries in North America, Europe, Japan, and Australia </li></ul></ul><ul><ul><ul><li>Population growth is low, and the people enjoy a good standard of living </li></ul></ul></ul><ul><ul><ul><li>The MDCs doubled their populations between 1850 and 1950 due to a decline in the death rate, the development of modern medicine, and improved socioeconomic conditions </li></ul></ul></ul><ul><ul><ul><li>Sequence of events (i.e., decreased death rate followed by decreased birthrate) is termed a demographic transition </li></ul></ul></ul><ul><ul><li>Less-developed countries (LDCs) - countries in Latin America, Africa, and Asia </li></ul></ul><ul><ul><ul><li>Population is growing rapidly, and majority of people live in poverty </li></ul></ul></ul><ul><ul><ul><li>Because of past exponential growth, the population of the LDCs may explode from 7 billion today to 9 billion in 2050 </li></ul></ul></ul>
  36. 36. Figure 36.11 World population growth over time
  37. 37. Figure 36.11 World population growth over time (Cont.)
  38. 38. 36.12 Age distributions in MDCs and LDCs are different <ul><li>Laypeople sometimes think that if each couple has two children, zero population growth (no increase in population size) will occur </li></ul><ul><ul><li>If more women enter reproductive years than there are older women leaving them, replacement reproduction results in population growth </li></ul></ul><ul><ul><li>Many MDCs have a stable age structure, but most LDCs have a youthful profile—a large proportion of the population is younger than 15 </li></ul></ul><ul><li>Population Growth and Environmental Impact </li></ul><ul><ul><li>Population growth is putting extreme pressure on each country’s social organization, the Earth’s resources, and the biosphere </li></ul></ul><ul><ul><li>MDCs consume a larger proportion of the Earth’s resources than LDCs </li></ul></ul><ul><li>Two possible types of overpopulation </li></ul><ul><ul><li>First is due to population growth - more obvious in LDCs </li></ul></ul><ul><ul><li>Second is due to increased resource consumption - more obvious in MDCs where per capita consumption is much higher </li></ul></ul>
  39. 39. Figure 36.12 Age structures in more-developed and less-developed countries
  40. 40. Connecting the Concepts: Chapter 36 <ul><li>An early definition of ecology was “scientific natural history” </li></ul><ul><ul><li>Modern ecology has now grown from a simple descriptive field to an experimental, predictive science </li></ul></ul><ul><li>Much of the success in the development of ecology has come from studies of populations and the creation of models that examine how populations change over time </li></ul><ul><ul><li>Simplest models are based on population growth when resources are unlimited </li></ul></ul><ul><ul><ul><li>Results in exponential population growth, a type only rarely seen in nature </li></ul></ul></ul><ul><ul><li>Because so few natural populations exhibit exponential growth, population ecologists realized they must incorporate resource limitation into their models </li></ul></ul><ul><ul><li>Simplest models to account for limited resources result in logistic growth </li></ul></ul><ul><ul><ul><li>Populations that exhibit logistic growth cease growth when they reach the environmental carrying capacity </li></ul></ul></ul><ul><li>Many modern ecological studies are concerned with identifying the factors that limit population growth and set the environmental carrying capacity </li></ul><ul><ul><li>A combination of careful descriptive studies, experiments done in nature, and sophisticated models has allowed ecologists to accurately predict which factors have the greatest influence on population growth </li></ul></ul>