Populations
- Define
- How de we describe populations?
- Different life strategies….
- How do we know how many there are?
Refer to chapter 44 in text.
Population; an interacting group of one species – same time, same place.
www.thebeehunter.com/idbee.htm
www.homosassausa.com
www.garymbarton.com/2006_photos6.htm
embryology.med.unsw.edu.au/Defect/bacteria.htm
Populations:
N.B. We are NOT using this word to mean the number of humans
in a given area!
It is important to have this straight,
because we will be talking about “population size”.
e.g. a population of coyotes...
the size of a population of coyotes...
the change in the size of a population of coyotes...
NOT “the population of Jacksonville”
If we are describing a human population let’s try to identify it as such.
Describing populations
range - where an organism lives: its distribution.
Why is a species, or a population of a species, where it is?
Within its range, an organism occupies a specific habitat,
or physical environment,
and fulfils a given niche within that habitat,
(a role; interactions and use of resources).
dispersal:
range change
See also http://www.epa.gov/climatechange/
impacts-adaptation/forests.html
Nature on its own is in
dynamic equilibrium.
These examples are man-caused,
(one conjectural), and can cause
imbalance. What factors from the
previous graphic changed?
a pattern of dispersion is the pattern of population density
within an organism’s range:
clumped: e.g. schools, prides,
clustering due to local habitat…
←
uniform:
territoriality,
chemical
inhibition,
resource
distribution…
→
(These are
very close: Contrast
with, say, mountain lions.)
↑
random: like windblown
seeds, but pretty rare.
There are usually reasons
to NOT be random.
What factors affect the size of a population?
What is the affect?
What affects the size of a population?
What is the affect?
natality (birth rate)
mortality (death rate)
immigration (members moving in)
emigration (members moving out)
How would each affect the size of a local population?
How might each be a result of circumstances?
How might each be a reflection of the species?
(Note this is not inclusive without your responses.)
Population growth can be described by a sigmoid (S-shaped) curve,
also called logistic growth.
transition phase:
resources limiting growth rate.
natality +/or immigration dropping, or
mortality +/or emigration rising.
plateau phase: (carrying capacity, K)
population and resources in equilibrium
natality + immigration = mortality + emigration
exponential phase: “J curve”
resources are not limiting:
(adequate food, housing, space, etc.)
natality + immigration > mortality + emigration
N.B. The actual data isn’t so smooth, is it? Why not?
Life strategies: adaptations to optimize population success
K-selected: Few offspring with high expectation of survival
- Good in constant ecosystems (think rain forest)
- Much parental investment (protection, nurturing…)
- Generally slow-maturing and long-lived
- Generally reproducing cyclically
- Relatively large organisms
e.g. large mammals
travel.mongabay.com/uganda/tour/ug5_5241.html
r-selected: Lots of offspring with little expectation of survival
- Good for variable ecosystems (ex. rain in the desert)
- Little parental investment after procreation
- Generally fast-maturing and short-lived
- Often reproducing only once in a lifetime
- relatively small organisms
e.g. insects, many fish
Frequent environmental disruption of “stable” environments
favors these organisms, including weedy plants
and pathogens like bacteria and protists.
www.mar.dfo-mpo.gc.ca/.../eggphoto.html
www.fao.org/DOCREP/003/T0019E/T0019E04.htm
Life strategies: adaptations to optimize population success (cont.)
Survivorship Curves
Type I, typical of
K-selected species,
most living to adulthood
and dying in old age.
Type III, typical of
r-selection,
most dying early,
low percentage
reproducing.
http://www.bioedonline.org/slides/slide01.cfm?tk=9&tr=
Type II, in between,
and most organisms
are not at extremes.
How do we know how many there are?
1. Direct count: aerial surveys, bird counts,
direct counting of sedentary organisms in defined habitats.
advantages: may get actual numbers
disadvantages: not practical for large, mobile, or skittish populations
Case in point: share photo of north Atlantic right whales
2. Sampling: generalizations from sampled plots.
advantages: applicable to larger test areas
disadvantages: subject to sampling errors
quadrats: standard frames
for randomly selected areas
to be sampled.
→
www.mms.gov/omm/pacific/kids/Tidepool_Math/ph...
←
transects: lines or paths
through the subject area.
Sample counts are
taken, along with
distance from line.
www.osl.gc.ca/sl_monitore/en/stations.html
www.science.org.au/nova/053/053print.htm www.coastalplanning.net/.../to_palm_beach.html
How do we know how many there are? (cont.)
How do we know how many there are? (cont.)
3. Capture-mark-release-recapture: for animals. The name says it all.
advantages: good for organisms you may not normally see at all
disadvantages: sampling errors, selecting proper parameters
(ex. open vs. closed populations), and a lot of effort.
the Lincoln index is used to interpret results:
pop. size = n1 x n2
n3
n1 = number initially caught, marked, released.
n2 = total number caught in second run.
n3 = number of marked individuals caught 2nd time.
http://web.stclair.k12.il.us/splashd/caprecap.htm
www.blackwellpublishing.com/southwood/chapter...
An application of monitoring population densities:
WILD FISH STOCKS
Fish are a potentially renewable resource, if managed properly.
In order to be sustainable,
you can’t harvest more fish than can be replenished.
As fish are caught, their resources become more available,
and natality generally goes up accordingly,
but Allott book has example of over-harvested fish
having their spawning rate fall.
In order to set limits on
how much can be caught,
one has to establish
how much is out there,
and get people to buy into the limits.
How do they monitor fisheries?
1. Capture-tag-release-recapture
e.g. used to monitor sea bass around the U.K.
(Best for lakes or local, near-coast populations.)
←capture-tag-release…
…recapture→
http://www.cefas.co.uk/data/fisheries-information/commercial-species/bass/bass-tagging.aspx
monitor fisheries? (cont.)
2. Echolocation:
Sonar is used to detect large shoals of fish.
Problem – some need to be caught to identify the species.
(Usable in open seas, but not for fish swimming at great depth.)
www.simrad.com/www/01/NOKBG0240.nsf/AllWeb/13...
www.whoi.edu/page.do?pid=10897&i=2041&x=131
monitor fisheries? (cont.)
Acronym
Scientific Name
Native or Not
Sacramento
splittail
SPT
Pogonichthys
macrolepidotus
Native
Delta smelt
(larval)
DS
Hypomesus
transpacificus
Native
Yellowfin goby
YFG
Perca flavescens
Native
Striped bass
SB
Morone saxatilis
Introduced
Inland
silverside
ISS
Menidia beryllina
Introduced
Common Name
3. Direct catch data
e.g. impact of flood-control
project in California.
(Again, best for narrowlydistributed fisheries.)
Species
#Capture
d
Mean Fork
Length(mm
)
Min
Max
B
ISS
72
70.00
57
96
8/14/2001
B
LJM
3
76.00
73
81
8/14/2001
B
SFG
1
53.00
53
53
9/11/2001
B
ISS
60
71.00
45
86
9/11/2001
B
SFG
1
50.00
50
50
10/11/2001
B
ISS
384
69.00
0
95
10/11/2001
B
MSQ
6
39.00
28
50
11/9/2001
B
ISS
690
79.00
50
109
11/9/2001
B
MSQ
1
30.00
30
30
12/10/2001
B
CRP
1
455.00
455
455
Sample
Date
Gear
Type
8/14/2001
Note that, once again,
the most plentiful
species is not native.
monitor fisheries? (cont.)
4. Reports of commercial catch:
features.csmonitor.com/.../
- Actual commercial boats file reports on types, ages, sizes
of fish caught, and method used.
- Population profiles are constructed,
including spawn rates and survivorship curves.
- This data is used to project the likely largest
maximum sustainable catch for the coming year,
and countries set their goals accordingly.
At least in theory.
Efforts to protect wild fish stocks
- Research conducted to validate estimates.
- Regulate types of fish caught:
restrict take of fish in low densities,
ban taking of endangered species
- Fishing methods monitored:
e.g. catch-all drift nets vs. more selective long-lines
size of net mesh to allow small one to escape
- Preserves with no fishing
e.g. near New Zealand: Catch in surrounds seas up.
- Non-fishing periods, as during breeding seasons.
- International agencies
don’t generally carry punitive authority.
- Public pressure and publicity
e.g. dolphin netting, Greenpeace
Buy-in is the toughest part.
How do you convince people that it is in their best interest
to protect a resource for use by all?
“Tragedy of the Commons”
Describe and compare
(and contrast!)
r-selected vs. K-selected
populations.
What is a population?
Describe three methods
for estimating population density.
Advantages and disadvantages?
Draw and annotate
a growth curve.
What is the population of Jacksonville?
What are the practical and
ethical issues involved in
marine fisheries management?
Come up with a question you could answer
using a quadrat sampling method, design the
experiment, and do it for the next IB lab.
population
immigration
survivorship curve
species
emigration
type I
range
population growth
type II
habitat
sigmoid curve
type III
niche
logistic growth
direct count
dispersal
transition phase
sampling
dynamic equilibrium
plateau phase
quadrat
pattern of dispersion
carrying capacity
transect
clumped
K
capture-mark-release-recapture
uniform
exponential phase
Lincoln index
random
K-selected
sustainable
natality
r-selected
echolocation
mortality