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BIOLOGY
POPULATION ECOLOGY
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Keira Le Roux
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Cards (34)
Population Ecology
The
study
of
populations
in
relationship
to their
environment
and the
social interactions
amongst
each
other
Species
A
group
of
organisms
capable of
interbreeding
, producing
fertile
offspring
Population
A
group
of the
same
species
that
occupies
the same
habitat
at the same
time
Community
Groups
of
different
populations that
interact
with each other within a specific
habitat
Ecosystem
A
community
of
interacting
organisms
and their
physical
environment
Population size
is influenced by both
abiotic
and
biotic
factors factors present in the environment
Natality
Mortality
Immigration
Emigration
Causes of fluctuations in population size
Density
dependant
and
independent
factors
contribute to fluctuations in population size
These factors
increase
environment
resistance
(pressure that suppress the population
size)
Together these factors
limit
population
growth
Environmental resistance
includes
carrying capacity
,
density dependant
and
independant
factors
Carrying capacity
The
number
of
individuals
of a
particular
population
an
environment
can
support
in a
specific
season
Density dependant factors
Factors
that
have a
direct
correlation
to the
size
of the
population
in an
area
Exert a greater
influence
when a population is
large
Examples
Territorial behaviour
Predation and Competition
Accumulation of waste
Food,space, and shelter
Parasitism and disease
Density Independant Factors
Factors that will
exert
an
influence
on a
population
regardless
of its
size
Abnormal
events in
nature
and occur
randomly
Examples
Tsunamis
Landslides
Volcanic eruptions
Veld fires
Floods
Geometric Growth
Lag Phase
Population number increases
slowly
because individuals may still be
acclimitising
to their environment
Need time to
fin
mates
Most of the population is
sexually immature
Geometric phase
Individuals have acclimatised
Many
reproducing
individuals exist and in
favourable
conditions produce many
offspring
Birth rate is
higher
than death rate
Very little
environmental resistance
Extinction
Resources become
limited
Build up of
toxic waste
Mortality rate becomes
greater
than the natality rate
Population decreases
rapidly
Logistic Growth: found in
higher-order
organisms
which typically reproduce
slower
Lag phase
Growth is
slow
Small
number of reproducing individuals
Individuals need time to
settle
in and they become
sexually mature
Population density is
low
-
difficult
to find a
mate
Exponential phase
Population grows
rapidly
More
sexually mature individuals
procreating
Little
or
no
environmental resistance
Higher
natality than mortality
Decelerating growth
Growth rate
slows
down
Environmental
resistance
develops
More
competition
for resources
Natality still
higher
than mortality
Equilibrium
Population
stabilzes
Natality more or less
equal
to mortality
Carrying capacity
for the environmental has been
reached
Death Phase
Sudden
large
drop in
population
size
Conditions have become
unsuitable
/external environmental change
Direct counting techniques
Aerial photography
Census
Indirect counting techniques
Mark and recapture
Ensure validity
Same
method
of
marking
Same
species
Same
area
Same
method
of
catching
Improve reliability
Repeat
investigation
Increase
sample size
Give
sufficient
time
to remix after 1st capture
Make sure organisms do not become
trap shy
/
addicted
Make sure the mark does not affect movement/behaviour
Simple sampling
To ensure reliability
Several
quadrat throws should be made to determine the
average
number
of individuals per quadrant
Quadrat samples must be done
randomly
throughout the total area
The process should be
repeated
should be repeated several times and the average number of organisms per quadrat calculated
Competition:
Interaction
between
individuals
over
scarce
resources
Intraspecific
- When individuals of the
same
species compete
Interspecific
- Individuals of
different
species compete
Competitive exclusion - when
two
species competing for the
same
resources,
one
species will
out-compete
the other
Resource
partitioning - The
storing
of
resources
so that
different
species can
co-exist
in the same area
Temporal
- using the
same
resources
at
different
times
Spatial
- using
different
parts
/areas of the
same
resource
Ecological
- using the
same
resource
in
different
habitats
Examples
Herbivores
grazing
in the
same
area
Taller animals graze on leaves at the top of tress while others graze from the middle and lower branches
Partitioning
of
light
in a
forest
(
stratification
)
Plants grow to a certain height dependant on the light requirements
Plants which require less light grow in the shade of taller plants
Predation: a
predator
is an
organism
that
actively
hunts,
kills
and
consumes
its
prey
to meet its
energy
needs
First the number of prey
increases
The number of
predators
only
rises
after the
prey
numbers have
increased
Prey
numbers start to
decrease
Predator
numbers start to
decrease
one
prey
numbers are
low
Symbiotic relationships: a
close,long-term
biological
relationship
between
individuals
of
2
or
more
species
Parasitism
One species
benefits
while the other species in
harmed
parasites can be either
endoparasites
- those that host
internally-
or
ectoparasites
- those that host
externally
Mutualism
Two-different
species in which
both
species
benefit
Buffalo
and
oxpeckers
Sunbirds
and
Erica’s
Commensalism
One
species
benefits
while the
other
neither
benefits
or is
negatively
affected
Whales
and
barnacles
Short
and
remora
fish