Transcript Population Dynamics Notes

POPULATION
DYNAMICS
Population Dynamics
and the Sea Otter
• The population dynamics of the sea otter
have helped us to better understand the
ecological importance of this keystone
species.
• Sea otter – almost extinct in 1900’s, caused
a population explosion of sea urchins because
nothing to keep pop. In check
• Kelp beds lost, decrease in diversity
• When sea otters made a comeback,
deforested kelp areas recovered
Population Dynamics
and the Sea Otter
Population Dynamics
• Population dynamics is the
change in population
structure due to
environmental stress and
changes in environmental
conditions.
Population Dynamics
• Four ways in which population
structure changes:
– Size (# of individuals)
– Density (# of individuals in a
certain space)
– Dispersion (spatial patterns)
– Age distribution
Dispersion – Spatial Patterns
Population Size
• Population change =
• (births + immigration) –
(deaths + emigration)
– Immigration – organisms moving
into a population
– Emigration – organisms leaving
pop.
Population Size
• To determine percent growth
rate:
• =[(CBR-CDR) + (IR-ER)] *100
CBR crude birth rate =
#births/1000
CDR crude death rate =
#deaths/1000
IR Immigration rate =
#immigrating/1000
ER emigration rate =
#emigrating/1000
Population Size
• Biotic Potential – a population’s growth
potential
• Intrinsic Rate of Increase (r) – rate at
which a population would increase with
unlimited resources
– Ex. One single female housefly could give
rise to 5.6 trillion flies in 13 months with no
controls on the pop.
Population Size
• ….but, as we know, in nature
there are always limits to
population growth.
– Environmental resistance are all
the factors that limit population
growth
Population Size
• Together the biotic
potential and
environmental
resistance determine
carrying capacity (K)
Population Size
• Carrying capacity (K) -- # of
individuals of a given species
that can be sustained
indefinitely in a given space
(area or volume)
Population Size
• Exponential Growth – a
population that has few
resource limitations; growth
starts out slowly, but gets
faster and faster (j-shaped
growth curve)
Exponential Growth
Logistic Growth
• Involves exponential growth,
with a steady decrease in
population growth as it
encounters environmental
resistance, approaching
carrying capacity and leveling
off
• Sigmoid growth curve
Logistic Growth
Logistic Growth
• In reality, populations fluctuate slightly
above and below the carrying capacity
Population Size – Doubling
Time
• How long it takes for the
population to double
• = 70/ % growth rate
– Ex. In 2002, world pop. Grew
by 1.28%…..so 70/1.28=54.7 (so
world pop. Should double in
approx. 55 yrs.
What if carrying capacity is
exceeded?
• This happens when a pop. Uses up
its resource base and temporarily
overshoots carrying capacity
• Occurs because of reproductive
time lag: period needed for birth
rate to fall and death rate to rise
• Pop. Would then suffer a crash or
dieback
Example of Overshoot
• 26 Reindeer were introduced to
an island off of Alaska in 1910
• 1935 – pop.= 2,000 (no
predators and plentiful
resources)
• By 1950, the pop. Crashed with
only 8 reindeer remaining
Factors Affecting Carrying
Capacity
• Competition within and between
species
• Immigration and emigration
• Natural and human caused
catastrophes
• Seasonal changes in resource
availability
What About Human Pop.
Carrying Capacity?
• Currently growing at an
exponential rate
• Humans can be affected by
overshooting carrying capacity
– Ex. Potato famine in 1845 (Ireland)
1 million people died and 3 million
emigrated
Population Density
• Density-independent population
controls: affect pop. Size
regardless of density
• Examples: floods, fires,
hurricanes, unseasonable
weather, habitat destruction,
pesticide spraying
Population Density
• Density-dependent population
controls: have a greater affect
as population increases
• Examples:competition,
predation, parasitism, disease
Population Density
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Human Example:
Bubonic Plague
(bacterium usually
found in rodents)
spread like wildfire
through cities of
Europe in 14th
century killing
25 million people
Revisiting Predator-Prey
Relationship
Revisiting Predator-Prey
Relationship
• Top-down control hypothesis:
the predator population keeps
the prey population in check
• …but is this really true?
Revisiting Predator-Prey
Relationship
• Research shows that the snowshoe
hare pop. Has a similar cycle even
when lynx aren’t present
• Bottom-up control hypothesis: the
hare population overshoots its
carrying capacity, and then crashes,
so in reality the hare pop. Controls
the lynx pop.
Revisiting Predator-Prey
Relationship
• It has been found that both
of these hypotheses are not
mutually exclusive, they exist
in different ecosystems
Reproductive Patterns
• Asexual Reproduction: all
offspring are clones or identical
copies
Reproductive Patterns
• Sexual Reproduction: half of
genetic material coming from
each parent; 97% of known
organisms
• Risks: females only ones
producing offspring, chance of
genetic errors, mating may
spread disease, injury
Reproductive Patterns
• If sex is so risky, why do so
many organisms reproduce this
way?
– Greater genetic diversity, so more
likely to survive environmental
change
– Males can help provide for
offspring, increasing chances for
survival
Reproductive Patterns
• Two different patterns:
• r-selected species
• K-selected
• species
Reproductive Patterns
• r-selected species or
opportunists: reproduce early
and put most of their energy
into reproducing
• Called opportunists because can
rapidly colonize a new habitat or
colonize after a disturbance;
usually boom and bust cycles
Characteristics of rselected species
• Little or no parental care
• Early reproductive age
• Many offspring at once
• Short lived
Characteristics of rselected species
• examples
K-selected species or
competitors
• Tend to do well in competitive
conditions when population size is
near carrying capacity (K)
• Thrive best when environmental
conditions are stable
K-selected species or
competitors
• Characteristics:
– Develop inside mothers
– Reproduce late in life
– Mature slowly
– Parental care
– Fewer offspring
– *prone to extinction due to these
char.
K-selected species or
competitors
K-selected species or
competitors
Survivorship Curves
• Shows the # of survivors of
each age group
Survivorship Curves
• Type I: late loss curves
(humans, typical K-selected
species)
– High survivorship (parental care)
until a certain age, then a high
mortality
Survivorship Curves
• Type II – constant loss curve
(songbirds, lizards)
– Fairly constant mortality rate in
all age classes
Survivorship Curves
• Type III: early loss curves (rselected species, fish, insects)
– High juvenile mortality rate
Conservation Biology
• A multidisciplinary science to take action
to preserve species and ecosystems
• 3 principles:
– Biodiversity is necessary to life on earth
– Humans should not cause or hasten
ecological damage including extinction
– Best way to preserve biodiversity is to
protect intact ecosystems
Conservation Biology
Conservation Biology
• How humans have altered natural
ecosystems:
– Fragmenting and degrading habitat
How humans have altered
natural ecosystems:
– Simplifying natural ecosystems
(monocultures)
Conservation Biology
– Using, wasting, or destroying a
percentage of earth’s primary
productivity
Conservation Biology
• Genetic resistance of some pest
and bacteria pops. Due to
overuse of pesticides and
antibiotics
Conservation Biology
• Eliminating some predators
Conservation Biology
• Deliberately or accidentally
introducing nonnative species
Conservation Biology
• Overharvesting renewable
resources
Conservation Biology
• Interfering with the normal
chemical cycling and energy
flows in ecosystems
Conservation Biology
• So… what can we do?
– Learn about processes and
adaptations by which nature
sustains itself
– Mimic lessons from nature