Populations Ecology Chap 53 1. Ecology is the study of interactions between organisms and their environment. 2. A Hierarchy of interactions: cells tissues organs organism population community ecosystem. Organismal Ecology – evolutionary adaptations; Population Ecology – concerns mainly with population density and growth; Community Ecology – populations of different species, deals with interactions like predation, competition, symbiosis; Ecosystem Ecology – interactions between biotic and abiotic components, concerns with energy flow and chemical cycling. 3. A population is an interaction between individuals of same species at a place. Populations are described by their boundaries and size. 4. A community is an interaction between individuals of different species at a place. A Habitat is the place where the community lives. 5. An ecosystem is an interaction between living = biotic factors = community and nonliving = abiotic factors at a place. 6. Ecology and environmentalism: Rachel Carson’s book ‘Silent Spring’ highlighted the bad role of use of insecticide DDT. It showed decline in populations of Pelicans and Bald eagles was due to DDT. America banned use of DDT and related insecticides and saved the endangered birds. 7. 8. Abiotic factors of the environment include sunlight, Temperature, wind, soil, rock, water (precipitation = rain, snowfall, dew, hailstorm). The local conditions of abiotic factors vary and form patchiness of environment to form Habitat = natural surroundings of a species. Different species can live in same habitat. 9. Disturbances in environment like fires, hurricanes, tornadoes, earthquakes and volcanic eruptions damage the community at a place. Most of the times community can recolonize and can grow to earlier stage. This capacity to resist change is Stability of the community. The disturbance leads to succession of communities called Ecological Succession. 10. Organisms respond to disturbance or change in environment by Physiological response – like long term response Acclimation, for example living at high altitude organism starts producing more blood cells; Anatomical response – by undergoing structural change and behavioral response – some animals can migrate to suitable conditions. 11. Population ecology: 12. Density is the number of individuals per unit area or volume 13. Dispersion is the pattern of spacing among individuals within the boundaries of the population 14. Sampling techniques can be used to estimate densities and total population sizes 15. Population size can be estimated by either extrapolation from small samples, an index of population size (e.g., number of nests), or the mark-recapture method 16. Determining Population Size Using the Mark-recapture method a. Scientists capture, tag, and release a random sample of individuals (s) in a population b. Marked individuals are given time to mix back into the population c. Scientists capture a second sample of individuals (n), and note how many of them are marked (x) d. Population size (N) is estimated by N = sn/x 17. Immigration is the influx of new individuals from other areas 18. Emigration is the movement of individuals out of a population 19. Demography is the study of the vital statistics of a population and how they change over time 20. Death rates and birth rates are of particular interest to demographers. 21. Per Capita Rate of Increase: 22. Change in population size = (Births + Immigrants) – (Deaths + Emigrants) 23. If immigration and emigration are ignored, a population’s growth rate (per capita increase) equals birth rate minus death rate 24. Patterns of dispersion can be clumped, uniform or random. 25. Clumped Dispersion : In a clumped dispersion, individuals aggregate in patches 26. A clumped dispersion may be influenced by resource availability and behavior 27. Uniform Dispersion: A uniform dispersion is one in which individuals are evenly distributed 28. It may be influenced by social interactions such as territoriality, the defense of a bounded space against other individuals 29. Random Dispersion: In a random dispersion, the position of each individual is independent of other individuals 30. It occurs in the absence of strong attractions or repulsions 31. A life table is an age-specific summary of the survival pattern of a population 32. It is best made by following the fate of a cohort, a group of individuals of the same age 33. The life table of Belding’s ground squirrels reveals many things about this population 34. For example, it provides data on the proportions of males and females alive at each age 35. A survivorship curve is a graphic way of representing the data in a life table 36. The survivorship curve for Belding’s ground squirrels shows a relatively constant death rate 37. Survivorship curves can be classified into three general types 38. Type I: Low death rates during early and middle life and an increase in death rates among older age groups, humans 39. Type II: A constant death rate over the organism’s life span, Belding’s ground squirrel 40. Type III: High death rates for the young and a lower death rate for survivors, clams, sea stars 41. Exponential Growth Model – It produces J- shaped growth curve. It grows at constant fast at maximum reproduction rate (r) even beyond carrying capacity. Soon population faces population crash when the resources are exhausted. It is called Boom and Bust population. It is found in Opportunistic Populations. For example in wild flowers. 42. Logistic Growth Model – It produces S-shaped Sigmoid curve. It includes fast growth in the middle part but becomes constant on reaching Carrying Capacity (k) = maximum number of individuals the Habitat at a place can support. It is called Equilibrial Population. For example Polar bears. 43. Life history traits are products of natural selection 44. An organism’s life history comprises the traits that affect its schedule of reproduction and survival 45. Life history traits are evolutionary outcomes reflected in the development, physiology, and behavior of an organism 46. A life history entails three main variables 47. The age at which reproduction begins 48. How often the organism reproduces 49. How many offspring are produced per reproductive episode 50. Species that exhibit semelparity, or big-bang reproduction, reproduce once and die 51. Species that exhibit iteroparity, or repeated reproduction, produce offspring repeatedly 52. Highly variable or unpredictable environments likely favor semelparity, while dependable environments may favor iteroparity 53. Regulation of population growth is done using Density-dependent factors that change birth and death rates; and Density-independent factors that affect same % of individuals in all densities – these populations face boom and bust conditions. 54. Human population Growth – In most of developed world population is either slowly growing (USA) or decreasing (Italy) but increasing very fast in most of the developing world (Afganistan). The age structure figures help us understand population growth. When it is a fast growing population the base is broad and narrows to a point = Pyramid shaped (Afganistan). A steady population has base and middle part equal; and declining population has narrow base than middle. 55. K-selection, or density-dependent selection, selects for life history traits that are sensitive to population density 56. r-selection, or density-independent selection, selects for life history traits that maximize reproduction Opportunistic life history Equilibrial life history Life span short Long climate unpredictable Relatively predictable Growth curve Exponential = J-shaped, boom-bust Logistic = S-shaped, stable at carrying capacity Reproduction High rate Low rate Death rate High, more in early life Low and in late life Body size Small, many wild flowers Big, polar bear 57. Disease 58. Population density can influence the health and survival of organisms 59. In dense populations, pathogens can spread more rapidly 60. Predation 61. As a prey population builds up, predators may feed preferentially on that species 62. Territoriality 63. In many vertebrates and some invertebrates, competition for territory may limit density 64. Intrinsic Factors 65. For some populations, intrinsic (physiological) factors appear to regulate population size 66. Stability and Fluctuation 67. Long-term population studies have challenged the hypothesis that populations of large mammals are relatively stable over time 68. Both weather and predator population can affect population size over time 69. The human population is no longer growing exponentially but is still increasing rapidly 70. No population can grow indefinitely, and humans are no exception 71. The human population increased relatively slowly until about 1650 and then began to grow exponentially 72. Age Structure is the relative number of individuals at each age 73. Infant mortality and life expectancy at birth vary greatly among developed and developing countries but do not capture the wide range of the human condition 74. Global Carrying Capacity 75. How many humans can the biosphere support? 76. Population ecologists predict a global population of 8.1–10.6 billion people in 2050 77. Limits on Human Population Size 78. The ecological footprint concept summarizes the aggregate land and water area needed to sustain the people of a nation 79. It is one measure of how close we are to the carrying capacity of Earth 80. Countries vary greatly in footprint size and available ecological capacity 81. Our carrying capacity could potentially be limited by food, space, nonrenewable resources, or buildup of wastes 82. Unlike other organisms, we can regulate our population growth through social changes .