types of growth curves, regulation of ecology, life histories, r and k selection, species

1. Population ecology
= Mansi R. More
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2. Contents
• Introduction of population ecology
• Characteristics of population
• Population growth curve
• Types of population growth curve• Types of population growth curve
• Population regulation
• Life history theories
• r- and k- selected species
• References
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3. Population ecology
• Population ecology is the study of populations
in relation to the environment.
• It includes environmental influences on
population density and distribution, agepopulation density and distribution, age
structure, and variations in population size.
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4. Chracteristics of population
• Population size
• Population density
• Dispersion patterns
• Demographics• Demographics
• Survivorship curves
• Population growth
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5. Population growth curves
• Population growth curve is something that shows the
pattern of the growth of a population over time i.e.,
a growth curve is an empirical model of the evolution
of a quantity over time.
• Population curves are widely used in biology for• Population curves are widely used in biology for
quantities such as population size or biomass,
individual body height or biomass.
• Values for the measured property can be plotted on
a graph as a function of time.
• In theory, any kind of organism could take over the
earth just by reproducing.
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6. Continue…
• But in practical, all living organisms need some
specific resources such as nutrients and
proper environmental conditions to survive
and reproduce.and reproduce.
• The essential resources are not unlimited, and
a population can only reach a size that match
the availability of resources in its local
environment.
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7. Types of population growth curves
• There are mainly 2 types of population growth
curves
1. Exponential growth curve (J- shaped)
2. Sigmoid growth curve (S- shaped)2. Sigmoid growth curve (S- shaped)
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8. Exponential growth curve
• In this type of growth, the population grows
exponentially, and after attaining the peak value the
population may abruptly crash.
• This increase in population is continued till largeThis increase in population is continued till large
amount of food materials exist in the habitat.
• After, due to increase in population size the food
supply in the habitat becomes limited which
ultimately results in decrease in population size.
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9. Continue…
• For eg., many insect populations show explosive
increase in numbers during the rainy season,
followed by their disappearance at the end of the
season.
• The following equation exhibits J-shaped growth:
dN/dt =rN
Where, dN/dt represents rate of change in population
r represents biotic potential
N represents population size
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10. Sigmoid growth curve
• The sigmoid growth curve is also known as Logistics
growth curve which is S-shaped.
• When a few organisms are introduced in an area, the
population increase is very slow in the beginning i.e.,population increase is very slow in the beginning i.e.,
the positive acceleration phase or lag phase.
• In the middle phase the population increase
becomes very rapid which is known as logarithmic
phase.
• Finally, in the last phase the population increase is
showed down i.e., negative acceleration phase.
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11. Continue...
• The level beyond which no major increase can
occur is referred to as saturation level or
carrying capacity is denoted by K.
• In the last phase the new organisms are• In the last phase the new organisms are
almost equal to the number of dying
individuals and thus there is no more increase
in the population size.
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12. Continue…
• The S-shaped (sigmoid) growth form is represented
by the following equation:
dN/dt = rN(K-N/K)
= rN(1-N/K)= rN(1-N/K)
Here, dN/dt is the rate of change in population size.
r= biotic potential
N= population size
(K-N/K) is for environmental resistnce
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13. Types of population growth curve
Exponential or J-shaped curve Sigmoid or S-shaped curve
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14. Population regulation
Population regulation is a density-dependent process, meaning that
population growth rates are regulated by the density of a population.
Density dependent factors
-physiological factors
-competition
Density independent factors
-forest fires
-modification of weather-competition
-territoriality
-unfavourable environment
-disease
-predation
-modification of weather
-Severe storm
-earthquakes and volcanic
eruptions
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15. Life history theories
• Life history strategy is correlated with many aspects
of an organisms reproductive strategy and life
history, as well as with demographic variables such
as generation time, life span, population parameters
such as population density and population dynamics.
• Invoked to predict the relative influence of density• Invoked to predict the relative influence of density
dependant verses density independent influences on
life stages and age classes.
• The most notable example of life history theory is
that of r and k selection (Mac Arthur and Wilson,
1967) based on their work island biogeography.
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16. Life history strategies
r-selected species
• Short life
• Rapid growth
• Early maturity
• Many small offspring
• Little parental care or protection
• Little investment in individual
K-selected species
• Long life
• Slower growth
• Late maturity
• Fewer large offsprings
• High prenatal care
• High investment in individual• Little investment in individual
offspring
• Adapted to unstable
environment
• Pioneers, colonizes
• Niche generalism
• Prey
• Regulated mainly by extrinsic
factors
• Low trophic level
• High investment in individual
offspring
• Adapted to stable environment
• Later stages of succession
• Niche specialists
• Predators
• Regulated mainly by intrinsic
factors
• High trophic level
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17. References
• www.slideshare.net
• Roff, D.A. 1992. the evolution of life histories: theory
and analysis. Chapman and Hall, New York.
• Stearns, S.C.1992. The evolution of life histories:• Stearns, S.C.1992. The evolution of life histories:
theory and analysis. Oxford University Press, Oxford.
• Charlesworth and Michael R. Rose, 1980;
EVOLUTIONARY OF BIOLOGY OF AGING
• Twenberry .(2008). Ecology 1: population ecology.
• Faranany. (2013) population ecology.
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