1 / 48

Chapter 53

Chapter 53. Population Ecology. Concept 53.1: Dynamic biological processes influence population density, dispersion, and demographics.

winda
Download Presentation

Chapter 53

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 53 Population Ecology

  2. Concept 53.1: Dynamic biological processes influence population density, dispersion, and demographics. • Population ecology is the study of populations in relation to environment, including environmental influences on density and distribution, age structure, and population size • A population is a group of individuals of a single species living in the same general area

  3. Density and Dispersion • Density is the number of individuals per unit area or volume • Dispersion is the pattern of spacing among individuals within the boundaries of the population

  4. Fig. 53-2 APPLICATION Hector’s dolphins

  5. Fig. 53-3 Births Deaths Births and immigration add individuals to a population. Deaths and emigration remove individuals from a population. Immigration Emigration

  6. Patterns of Dispersion • Environmental and social factors influence spacing of individuals in a population

  7. Demographics • Demography is the study of the vital statistics of a population and how they change over time • Death rates and birth rates are of particular interest to demographers

  8. Table 53-1

  9. Fig. 53-6 1,000 I 100 II Number of survivors (log scale) 10 III 1 0 50 100 Percentage of maximum life span

  10. Concept 53.2: Life history traits are products of natural selection. • An organism’s life history comprises the traits that affect its schedule of reproduction and survival: • The age at which reproduction begins • How often the organism reproduces • How many offspring are produced during each reproductive cycle • Life history traits are evolutionary outcomes reflected in the development, physiology, and behavior of an organism

  11. Evolution and Life History Diversity • Life histories are very diverse • Species that exhibit semelparity, or big-bang reproduction, reproduce once and die • Species that exhibit iteroparity, or repeated reproduction, produce offspring repeatedly • Highly variable or unpredictable environments likely favor big-bang reproduction, while dependable environments may favor repeated reproduction

  12. “Trade-offs” and Life Histories • Natural selection cannot maximize all reproductive variables simultaneously. • Organisms have finite resources, which may lead to trade-offs between survival and reproduction. • Plants and animals whose young are subject to high mortality rates often produce large numbers of relatively small offspring. • In other organisms, extra investment on the part of the parent greatly increases the offspring’s chances of survival.

  13. Fig. 53-9 (a) Dandelion (b) Coconut palm

  14. Fig. 53-8 RESULTS 100 Male Female 80 60 Parents surviving the following winter (%) 40 20 0 Reduced brood size Normal brood size Enlarged brood size

  15. Concept 53.3: The exponential model describes population growth in an idealized, unlimited environment. • It is useful to study population growth in an idealized situation • Idealized situations help us understand the capacity of species to increase and the conditions that may facilitate this growth • If immigration and emigration are ignored, a population’s growth rate (per capita increase) equals birth rate minus death rate

  16. N  rN t Per Capita Rate of Increase • Zero population growth occurs when the birth rate equals the death rate • Most ecologists use differential calculus to express population growth as growth rate at a particular instant in time: where N = population size, t = time, and r = per capita rate of increase = birth – death

  17. dN  rmaxN dt Exponential Growth • Exponential population growth is population increase under idealized conditions • Under these conditions, the rate of reproduction is at its maximum, called the intrinsic rate of increase • Equation of exponential population growth:

  18. Fig. 53-10 2,000 dN 1.0N = dt 1,500 dN 0.5N = dt Population size (N) 1,000 500 0 0 5 10 15 Number of generations

  19. Concept 53.4: The logistic model describes how a population grows more slowly as it nears its carrying capacity. • Exponential growth cannot be sustained for long in any population • A more realistic population model limits growth by incorporating carrying capacity • Carrying capacity (K) is the maximum population size the environment can support

  20. (K  N) dN  rmax N dt K The Logistic Growth Model • In the logistic population growth model, the per capita rate of increase declines as carrying capacity is reached • We construct the logistic model by starting with the exponential model and adding an expression that reduces per capita rate of increase as N approaches K

  21. Table 53-3

  22. Fig. 53-12 Exponential growth 2,000 dN 1.0N = dt 1,500 K = 1,500 Population size (N) Logistic growth 1,000 1,500 – N dN 1.0N = 1,500 dt 500 0 0 5 10 15 Number of generations

  23. Fig. 53-13 180 1,000 150 800 120 Number of Paramecium/mL Number of Daphnia/50 mL 600 90 400 60 200 30 0 0 0 5 10 15 0 20 40 60 80 100 120 140 160 Time (days) Time (days) (a) A Paramecium population in the lab (b) A Daphnia population in the lab

  24. The Logistic Model and Life Histories • Life history traits favored by natural selection may vary with population density and environmental conditions • K-selection, or density-dependent selection, selects for life history traits that are sensitive to population density • r-selection, or density-independent selection, selects for life history traits that maximize reproduction

  25. Concept 53.5: Many factors that regulate population growth are density dependent. • There are two general questions about regulation of population growth: • What environmental factors stop a population from growing indefinitely? • Why do some populations show radical fluctuations in size over time, while others remain stable?

  26. Population Change and Population Density • In density-independent populations, birth rate and death rate do not change with population density • In density-dependent populations, birth rates fall and death rates rise with population density

  27. Fig. 53-15 Density-dependent birth rate Density-dependent birth rate Density- independent death rate Density- dependent death rate Birth or death rate per capita Equilibrium density Equilibrium density Population density Population density (a) Both birth rate and death rate vary. (b) Birth rate varies; death rate is constant. Density-dependent death rate Density- independent birth rate Birth or death rate per capita Equilibrium density Population density (c) Death rate varies; birth rate is constant.

  28. Density-Dependent Population Regulation • Density-dependent birth and death rates are an example of negative feedback that regulates population growth • They are affected by many factors, such as competition for resources, territoriality, disease, predation, toxic wastes, and intrinsic factors

  29. Fig. 53-16 100 80 60 Percentage of juveniles producing lambs 40 20 0 200 300 400 500 600 Population size

  30. Fig. 53-17 (a) Cheetah marking its territory (b) Gannets

  31. Other Density-Dependent Limiting Factors • In dense populations, pathogens can spread more rapidly. • As a prey population builds up, predators may feed preferentially on that species. • Accumulation of toxic wastes can contribute to density-dependent regulation of population size.

  32. Population Dynamics • The study of population dynamics focuses on the complex interactions between biotic and abiotic factors that cause variation in population size • Changes in predation pressure can drive population fluctuations • Mathematical and computer models are used to illustrate and investigate population interactions within and environmental impacts on a community.

  33. Fig. 53-19 2,500 50 Wolves Moose 2,000 40 30 1,500 Number of wolves Number of moose 20 1,000 10 500 0 0 1955 1965 1975 1985 1995 2005 Year

  34. Calculating Lag Time • Use the graph below to calculate lag time in months between the change in the densities of the prey and the predator populations. • To find lag time, calculate the difference in the predator/prey size between peaks or valleys.

  35. Population Cycles: Scientific Inquiry • Some populations undergo regular boom-and-bust cycles • Lynx populations follow the 10 year boom-and-bust cycle of hare populations • Three hypotheses have been proposed to explain the hare’s 10-year interval

  36. Fig. 53-20 Snowshoe hare 160 120 9 Lynx Number of lynx (thousands) Number of hares (thousands) 80 6 40 3 0 0 1850 1875 1900 1925 Year

  37. Variation and Population Dynamics • The level of variation in a population affects population dynamics. • A population’s ability to respond to changes in the environment is affected by genetic diversity. • Species and populations with little genetic diversity are at risk for extinction. • Illustrative Examples: California condors, prairie chickens

  38. Variation and Population Dynamics • Genetic diversity allows individuals in a population to respond differently to the same changes in environmental conditions: • Not all animals in a population stampede • Not all individuals in a population are equally affected in a disease outbreak

  39. Concept 53.6: The human population is no longer growing exponentially but is still increasing rapidly. • No population can grow indefinitely, and humans are no exception • The human population increased relatively slowly until about 1650 and then began to grow exponentially • Though the global population is still growing, the rate of growth began to slow during the 1960s

  40. Fig. 53-22 7 6 5 4 Human population (billions) 3 2 The Plague 1 0 8000 B.C.E. 4000 B.C.E. 3000 B.C.E. 2000 B.C.E. 1000 B.C.E. 0 1000 C.E. 2000 C.E.

  41. Fig. 53-23 2.2 2.0 1.8 1.6 1.4 2005 1.2 Annual percent increase Projected data 1.0 0.8 0.6 0.4 0.2 0 1950 1975 2000 2025 2050 Year

  42. Regional Patterns of Population Change • To maintain population stability, a regional human population can exist in one of two configurations: • Zero population growth = High birth rate – High death rate • Zero population growth =Low birth rate – Low death rate • The demographic transition is the move from the first state toward the second state

  43. Fig. 53-24 50 40 30 Birth or death rate per 1,000 people 20 10 Sweden Mexico Birth rate Birth rate Death rate Death rate 0 1850 1900 1750 1800 1950 2000 2050 Year

  44. Age Structure • One important demographic factor in present and future growth trends is a country’s age structure • Age structure is the relative number of individuals at each age

  45. Fig. 53-25 Rapid growth Slow growth No growth Afghanistan United States Italy Male Female Age Male Female Age Male Female 85+ 85+ 80–84 80–84 75–79 75–79 70–74 70–74 65–69 65–69 60–64 60–64 55–59 55–59 50–54 50–54 45–49 45–49 40–44 40–44 35–39 35–39 30–34 30–34 25–29 25–29 20–24 20–24 15–19 15–19 10–14 10–14 5–9 5–9 0–4 0–4 10  8 6 4 2 0 2 4 6 8 10  8 6 4 2 0 2 4 6 8 8 6 4 2 0 2 4 6 8 Percent of population Percent of population Percent of population

  46. Fig. 53-26 60 80 50 60 40 Life expectancy (years) Infant mortality (deaths per 1,000 births) 30 40 20 20 10 0 0 Less indus- trialized countries Less indus- trialized countries Indus- trialized countries Indus- trialized countries

  47. Global Carrying Capacity • How many humans can the biosphere support? • The carrying capacity of Earth for humans is uncertain • The average estimate is 10–15 billion • Our carrying capacity could potentially be limited by food, space, nonrenewable resources, or buildup of wastes

  48. Fig. 53-27 Log (g carbon/year) 13.4 9.8 5.8 Not analyzed

More Related