Download Population Ecology Chap53

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.
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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)
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d. Population size (N) is estimated by N = sn/x
Immigration is the influx of new individuals from other areas
Emigration is the movement of individuals out of a population
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.
Per Capita Rate of Increase:
Change in population size = (Births + Immigrants) – (Deaths + Emigrants)
If immigration and emigration are ignored, a population’s growth rate (per capita increase) equals birth
rate minus death rate
Patterns of dispersion can be clumped, uniform or random.
Clumped Dispersion : In a clumped dispersion, individuals aggregate in patches
A clumped dispersion may be influenced by resource availability and behavior
Uniform Dispersion: A uniform dispersion is one in which individuals are evenly distributed
It may be influenced by social interactions such as territoriality, the defense of a bounded space against
other individuals
Random Dispersion: In a random dispersion, the position of each individual is independent of other
individuals
It occurs in the absence of strong attractions or repulsions
A life table is an age-specific summary of the survival pattern of a population
It is best made by following the fate of a cohort, a group of individuals of the same age
The life table of Belding’s ground squirrels reveals many things about this population
For example, it provides data on the proportions of males and females alive at each age
A survivorship curve is a graphic way of representing the data in a life table
The survivorship curve for Belding’s ground squirrels shows a relatively constant death rate
Survivorship curves can be classified into three general types
Type I: Low death rates during early and middle life and an increase in death rates among older age
groups, humans
Type II: A constant death rate over the organism’s life span, Belding’s ground squirrel
Type III: High death rates for the young and a lower death rate for survivors, clams, sea stars
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.
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.
Life history traits are products of natural selection
An organism’s life history comprises the traits that affect its schedule of reproduction and survival
Life history traits are evolutionary outcomes reflected in the development, physiology, and behavior of
an organism
A life history entails three main variables
The age at which reproduction begins
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How often the organism reproduces
How many offspring are produced per reproductive episode
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 semelparity, while dependable environments
may favor iteroparity
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.
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.
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
Opportunistic life history
short
unpredictable
Exponential = J-shaped, boom-bust
High rate
High, more in early life
Small, many wild flowers
Equilibrial life history
Long
Relatively predictable
Logistic = S-shaped, stable at carrying capacity
Low rate
Low and in late life
Big, polar bear
Life span
climate
Growth curve
Reproduction
Death rate
Body size
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