Transcript Environmental Science Chapter 8

Environmental Science
Chapter 8
Understanding Populations
8-1: How Populations Change Size
 Describe
the three main properties of a
population.
 Describe exponential population growth.
 Describe how the reproductive behavior of
individuals can affect the growth rate of
their population.
 Explain how population sizes in nature are
regulated.
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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(2010 census)
Density
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Individuals per unit of area or volume
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250,000 people in Kalamazoo County
75 deer per square mile
Dispersion
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Distribution or arrangement
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
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Population Growth
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Growth rate is calculated using
change in
population size
=
births – deaths
Also included would be immigrants to the area
and emigrants from the area
Growth rate can be positive or negative numbers;
with negative numbers equaling a decrease in
population size
Growth Curves
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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.
 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.
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Carrying capacity = theoretical limit to populations size
in a given ecosystem.
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Limiting resource is something the species needs and consumes
at the same rate its produced.
Competition
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.
Give examples of parts of a niche.
Describe the five major types of interactions
between species.
Explain the difference between parasitism and
predation.
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
Exponential – increasing rapidly
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 (rabbit and penguins, bugs and food)
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Can be direct or indirect
Predator – prey (rabbit – lynx)
Commensalism (bromeliads like orchids)
Mutualism (acacia/ants, pollinators, 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
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Humans
The human population is also subject to all of the
conditions studied in ecology
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Resource availability (coal, Al, transportation, Rx)
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Material resources, goods and infrastructure including services
Water, air, food
Space
Waste
Pollution
Genetic impacts
Disease/ immunity
“Creativity”
Carrying capacity is hard to calculate due to the
number of variables.