Download What is a population?

Chapter 8
Understanding Populations
8-1: How Populations Change Size
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Describe the three main properties of a
population. (slide 3 & 4)
 Describe exponential population growth.
(slide 6, 7, 11, 12)
 Describe how the reproductive behavior of
individuals can affect the growth rate of their
population. (slide 6 & 7)
 Explain how population sizes in nature are
regulated. (slide 8)
What is a population?
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All the members of the same species living in
the same place at the same time.
“reproductive group” or “gene pool”
Population refers to the group in general and
to the size of the group
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Daisies in Ohio, not in Maryland
Bass in a lake in Iowa
Properties of populations:
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Size
Density
Dispersion
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Size
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Number of individuals in the population
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Density
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Individuals per unit of area or volume
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250,000 people in Kalamazoo County (2010 census)
75 deer per square mile
Dispersion
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Distribution or arrangement
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Even – pine trees in rows in a forest; corn fields
Clumped – zebras in the savanna; deer herds
Random- dandelions in a field; lizards in the desert
Population Growth

Growth rate is calculated using
change in
population size
=
births – deaths
*Also included would be immigrants (in) to the
area and emigrants (out) from the area
*Growth rate can be positive or negative
numbers; with negative numbers equaling a
decrease in population size
Growth Curves

Biotic potential = fastest rate at
which a population can grow.
This is also called fercundity
(max number of offspring that
could be produced vs fertility
which is number actually
produced).
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Reproductive potential = max.
number that a population can
produce.
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Earlier maturity
Larger numbers of eggs
Shorter generation time
Survival rate
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Sea turtle lay >2000 eggs, they
don’t all survive
A pair of elephants could
produce 19 million
descendants in 750 years….but
have one at a time, gestate 20+ months,
nurse 4+ years, 15 when mature, raise 1
at a time; even if live to be 100 – only
have a couple kids

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Bacteria and insects have very
short generation times.
Average generation time for
humans is 20 years
Limits to population growth
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Resources are never unlimited or constant; they are either used
up or they change.
 A limited resource is something the species needs and consumes
at the same rate its produced.
 Leads to competition
Carrying capacity = theoretical limit to populations size in a given
ecosystem.
 Rabbits in Australia
 Islands make good studies because of boundaries
Regulation
 Density dependent – rate of death is worse when
individuals are closely packed (infection in pine trees)
 Density independent – rate of death is not dependent on
numbers of individuals in the area; storms, crops freezing , etc.
8-2: How Species Interact with
Each Other
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Explain the difference between niche and habitat.
(slide 17-19)
Give examples of parts of a niche. (slide 17-19)
Describe the five major types of interactions
between species. (slide 14 & 15)
Explain the difference between parasitism and
predation. (slide 14)
Explain how symbiotic relationships may evolve.
8.2: Population Dynamics
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Population – group of similar individuals that are in
the same place, at the same time and comprise a
gene pool
Species – organisms that are similar enough to
interbreed in nature and produce viable offspring.
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Breed, variety, strain, subspecies, etc.
“dynamic” means in constant motion, always
changing, not static.
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Births increase population
Deaths decrease population
If births = deaths then
population is steady, called
“replacement rate”
If growth is exponential,
then population increases
rapidly…. Parents have 2
kids (4) and they each have
2 kids (8), and they have 2
kids (16)….. The sum of
population would go like this
2,4,8,16,32….
Population Growth patterns
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Logistic – steady (“S”)
Exponential – increasing rapidly (“J”)
In a new situation, populations have the
potential to increase exponentially, but
natural forces like food/resources, predators
and space will eventually create a stable level
when the population reaches “Carrying
Capacity”
Symbiosis
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In addition to enough food, water, oxygen, sun, space,
mates and other resources – individuals have interactions
with other species that impact their survival and
reproductive success.
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Competition (bugs and food)
 Can be direct or indirect
 NOT an example of symbiosis!
Predator – prey (rabbit – lynx)
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NOT an example of symbiosis!
Commensalism (bromeliads like orchids)
Mutualism (acacia/ants, pollinators/flowering plants,
intestinal bacteria)
Parasitism (mosquito, lice, leech, tapeworm)
Resource Partitioning
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In order to decrease competition some
resources are allocated or partitioned to
specific species
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Common examples include birds that specifically
live in the upper branches, lower branches, or
interior of the tree so that one tree can house 3
species in their own separate zones
Niche
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An organism’s unique role within an ecosystem is
it’s NICHE; FUNCTION or job… “grazer”,
“pollinator”, etc
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Realized Niche vs Fundamental Niche
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Physical space +
Environmental factors +
Interactions
Where you actually are vs. anywhere you could be
successful
HABITAT= WHERE you live
Humans
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The human population is also subject to all of the
conditions studied in ecology
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Resource availability (coal, Al, transportation, Rx)
 Material resources, goods and infrastructure including
services
Water, air, food
Space
Waste
Pollution
Disease/ immunity
Genetic impacts
“Creativity”
Carrying capacity is hard to calculate due to the
number of variables.