Transcript Ch 14: Population Growth + Regulation dN/dt = rN dN/dt = rN(K-N)/K

Fall 2010 IB Workshop Series
sponsored by IB academic advisors
Winning Resumes
for IB Students
Wednesday, Sept. 22
4:00-5:00pm 161 Noyes Lab
Career Center staff will discuss the basics of writing a resume
including format and objectives. Cover letters and special
situations are also addressed.
ASSIGNMENT FOR THURSDAY
1) Complete Problem Set 3: 223-226 in
lab manual
2) Go to:
Course website for Sept. 24
Read article BEFORE class
‘Human Population Explosion’
3) No LO or PPT for Thursday; only ICA.
This lecture Ch 10 + 12:
Population Dynamics and Structure
Read LO Major Concepts
Objectives
• Temporal dynamics: fluctuations through time
•
Density-dependent vs. independent regulation
•
Types and causes of fluctuations
•
Models with time delays
• Population abundance
•
How to estimate?
•
Age and sex structure
• Spatial structures
•
Distribution (range)
•
Density
•
Dispersion
What determines the abundance
and distribution of populations?
Read LO I + II
What controls population size?
density-dependent
K
Chance??
change in
environment
N
density-independent
time
time
time
Logistic equation assumes:
• Instantaneous (d-d) feedback of K onto N
• If time lags in response --> fluctuation of N
around K
• Longer lags---> more fluctuation; may crash.
N
K
time
How well do populations fit the
logistic growth model?
Density-dependent factors drive
populations toward equilibrium
(stable population size),
• BUT
• they also fluctuate around equilibrium due to:
1) changes in environmental conditions
2) chance
3) intrinsic dynamics of population
responses
• Fluctuation is the rule for natural populations.
• Less fluctuation for large animals with
•
long life span because of:
•
greater homeostasis
•
many overlapping generations-->
high intrinsic stability
• Fluctuations greater if small/short lifespan
– little homeostasis
– populations turn over rapidly-->
– low intrinsic stability
Population cycles synchronized among
species in a region. Periodic cycles with
peaks separated by same number of years.
Other species may vary in their response
to changes in the environment -->
asynchronized cycles.
Environmental fluctuations (extrinsic
factors) (and organism responses) tend to
be irregular, not periodic.
But many populations change with
periodic, non-random frequency. *** Is an
extrinsic or intrinsic factor likely to be
responsible? Explain.
Some populations exhibit regular
fluctuations (cycles) in size.
What density-dependent factor causes
grouse populations to cycle? Consider
abiotic and biotic interactions…
What factor causes grouse populations
to cycle? ICA 1
• Hypothesis: Density-dependent infections by a
parasitic roundworm cause the cycles.
• Prediction: Populations treated with antiroundworm drugs will not crash following
treatments, but control populations will.
• Graph the prediction. Label axes.
Control:
no drugs
Control:
No drugs
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
Results
Experimental #
Drug
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
Drug
Control #
What is conclusion?
Is hypothesis proven?
Time
An intrinsic mechanism for population
cycles?
• ‘Momentum’ by high birth rate at low
density --> overshoot K.
• Low survival at high density-->
overcompensate and decrease below K.
• Population cycles result from time delays
in the birth and death rates of populations
in response to their own densities.
Discrete-time models with densitydependence:
• Built-in time delay ---> can’t continually adjust
• Patterns of oscillations depend on value of R
• (per capita growth rate)
>>2 chaos
Population dynamics reflect a complex
interaction of biotic and abiotic
influences, and are rarely stable.
Population: all individuals of a species in an
area
Subpopulations: in different habitat patches
*** What are structures (traits) of populations?
• Size (abundance)
• Age structure
• Sex ratio
• Distribution (range)
• Density (#/unit area)
• Dispersion (spacing)
• Genetic structure
Population size may be estimated by
several methods, e.g. mark-recapture
Aerial censuses
Censusing a population
•
•
•
•
•
•
•
Number of individuals
Sex ratio
Age structure
complex if:
can’t age
size does not = age (plants)
Long-term vs. short-term
Size classes of individuals of same age.
***What’s the ‘take-home message’ = main
conclusion?
Temporal variation in
recruitment of new
individuals affects age
structure --->
long-term implications
on population growth.
Species distributions (ranges): are they
really continuous? Read LO II
What must happen for species
to extend range at periphery?
What prevents it from doing
so?
***What factors limit the (geographic)
distribution (+ range) of organisms?
•
•
•
•
•
•
•
•
Phenology
Dispersal
Behavior (habitat selection)
Biotic factors (other species)
Abiotic factors (chemical / physical)
Human introductions
Chance
History
Geographic distributions are
discontinuous. Within its
range, only suitable habitats
are occupied.
What factor determines
this distribution?
ICA 2
•Transplant 2 species to
range of elevations -->
measure fitness components.
What is the main result :
for lowland species on L?
for highland species on R?
What is the main conclusion?
LOW
HIGH
Geographic range includes all areas occupied
during entire life history; must include migration.
Geographic ranges with migration - know no
political boundaries…adds complexity to protection.
Are ranges stable through time?
Introduced
starlings
Population density declines as body size increases.
ICA 3 Summarize the major result in Fig. 1.
Fig. 1
Summarize major result in Fig. 2
Range
Summarize major result in Fig. 3
Within its range, population density (#/area)
varies with differences in habitat quality.
ICA 4
What accounts for this owl’s distribution?
Owl location
‘Old growth’ forest
Density and reproduction success are
dependent on amount of suitable habitat
for prey.
Number
per km2
Older forest (%)
Contrasting patterns of dispersion
Dispersion = spacing of individuals
with respect to others in a population
(Even)
• Which is most common in plants? animals?
***What factors influence dispersion of
individuals within populations?
•
•
•
•
habitat heterogeneity
dispersal limitation
reproductive mode
social interactions
Dispersal mode of plants affects their spatial
dispersion.
ICA 5
What type of dispersion is shown here?
Hypothesize what causes the pattern.
A
B