Transcript Populations Dynamics

Populations Dynamics
Chapter 36
I. Environmental Factors
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Living organisms are influenced by a wide
range of environmental factors. These can
be two types:
Abiotic factors – nonliving environmental
factors (water condition, air quality, salinity,
temperature, soil content, etc.)
Biotic factors – living organisms that interact
with the organism we are studying (prey,
predators, infectious agents etc.)
II. Population ecology
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Population ecology is the study of how and
why populations change. Also studies
population numbers, where you find the
studied population and how many organisms
live in it, how/why it increases/decreases in
numbers.
Population – a group of individuals of the
same species that live in the same general
area (same resources, same environmental
influences, common breeding, social
interactions)
III. Population Growth
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The number of individuals comprising a population
may fluctuate over time. These changes make
populations dynamic.
A population in equilibrium have about the same
individuals from one generation to the next.
Factors that can change the number of individuals in
a population:
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Birth (B)
Death (D)
Immigration (I)
Emigration (E)
IV. Population Structure (density,
dispersion and age structure)
A.
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Population Density – the number of
individuals of a species per unit area or
volume.
Measuring population density:
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By counting
Sampling techniques
(http://www.biologycorner.com/flash/mark_recap.swf )
Patterns of distribution
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Clumped
Uniform
Random (rare, temporary)
B. Age structure is determined by
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Life tables – Determine the average
lifespan to study the dynamics of population
growth.
http://www.ssa.gov/OACT/STATS/table4c6.html
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Suvivorship Curves – they plot the # of
individuals alive in each age
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Type I – produce few offspring, take care of their young,
many survive into maturity
Type III – high death rates for the very young, mature
individuals survive longer, usually involves very large #
of offspring with little or no parent care.
Type II – intermediate, more constant mortality over the
entire lifespan
V. The Patterns of Growth
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The Exponential Growth Model
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The rate of population increases exponentially under
ideal conditions (high birth rate, low death rate).
The population multiplies by a constant factor during
each time interval.
Endless resources
J-shaped curve
Colonizing populations
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http://www.pbs.org/wgbh/nova/earth/global-population-growth.html
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During exponential growth, all members of the
population will have the maximum capacity of
reproduction.
B) Carrying Capacity – Logistic Growth
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Environmental factors limit population growth.
With limiting factors included growth curve resembles a
logistic growth curve (S-shaped curve)
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K : Carrying capacity – the maximum population size
that a particular environment can support. It’s value
depends on the species and environmental resources.
Ultimately, a population would stabilize on the carrying
capacity (K) – birth rate equals death rate.
C) Factors Limiting Population Growth
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Density-dependent factors – factors that have
greater effect when the population density is
higher.
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Competition for food, territory
Health of organisms
Predation
Parasites
Physiological factors (reproduction, growth, hormonal
changes)
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Density-independent factors – Regardless of
population density, these factors affect individuals
to the same extent.
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Weather conditions
Acidity
Salinity
Fires
Catastrophies
Boom-and-bust cycles – the number of individuals
within the population seems to show a cyclic
change.
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Predator/prey relationships
Changing food supply
Figures 36.5C and 36.6 on page 733.
VI. Age Structure Diagrams
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Human population can also be described by
age structure diagrams. These diagrams are
frequently dependent on the economy and
social state of the country that they are
measured in.