Transcript Characteristics of Populations Chapter 11.1 McGraw-Hill Ryerson Biology 12 (2011) CHARACTERISTICS of POPULATIONS • Habitat: the place where an organism lives • Species: organisms that.

Characteristics of Populations
Chapter 11.1
McGraw-Hill Ryerson
Biology 12 (2011)
CHARACTERISTICS of POPULATIONS
• Habitat: the place where an organism lives
• Species: organisms that resemble one another
in appearance, behaviour, chemistry and
genetic makeup and that have the ability to
interbreed with each other under natural
conditions (produce viable offspring).
• Population Size (N): the number of individuals
of a species occupying a given area at a given
time (ex. 700 Wood ducks in Elevator Bay).
POPULATION DENSITY
• Population Density (D) is calculated by dividing
the population size or number of individuals (N)
by the space occupied by that population (S).
D= N
S
• Usually smaller organisms have much greater
population densities than larger organisms.
(Ex. 350 field mice per hectare in Algonquin
Park vs. 0.8 moose per hectare)
TYPES of DENSITY
• Crude Density: number of individuals of the
same species per total unit area or volume.
• Ecological Density: number of individuals of the
same species per useable unit area or volume.
D= N
S or useable S
Density Sample Questions
1) A backyard measuring 3.0 m by 4.0 m contains 215
dandelions. Determine the population density of the plants.
2) A small field having an area of 1.5 ha contains a pond with a
surface area of 0.3 ha and is home to 300 field mice.
Calculate their ecological density.
3) Researchers want to relocate some nuisance black bears into
a forest in Northern Quebec that is 750 km2. If each bear
requires 40 km2 of forest to live successfully, how many bears
can be successfully relocated here?
POPULATION DISPERSION
• Population Dispersion is the pattern in which
individuals are dispersed throughout a specific
area. There are 3 general types:
POPULATION DISPERSION
• Clumped Dispersion: organisms are densely
populated in areas of the habitat with
favourable conditions for survival, usually
around resources (most populations exhibit
this...cattails growing at the edges of ponds, fish
swimming in schools...)
POPULATION DISPERSION
continued...
• Uniform Dispersion: individuals are evenly
distributed throughout the habitat. Occurs
when individuals set up territories (ie
Penguins).
POPULATION DISPERSION
continued...
• Random Dispersion: occurs when the habitat is
particularly uniform and interactions with other
members of the same species do not affect
distribution. This is fairly rare in nature, ex.:
some tropical trees.
SAMPLING TECHNIQUES
• It is rare that biologists can
take an exact count of all the
members in a population due
to the size and/or range over
which the population lives.
• Instead biologists count a
sample of the population and
estimate the population size
from this sample.
QUADRAT SAMPLING
• A common sampling technique for stationary
populations is quadrat sampling.
• A quadrat, or sampling frame, is placed in a
region within the habitat and each member of
the population of the species in question that
appears in the frame is counted.
• The more quadrats used the more accurate the
population density and population size
measurements.
Equations
• Average sample density = total number of
individuals counted in sample/ total sample
area
ASD = sample N
sample Area
• Estimated population size = average sample
density X total size of study area.
Estimated Pop size = ASD x total area
Quadrat Study Example
4) Scientists are studying the distribution of
Trilliums in a section of Lemoine Point
covering 100m by 100m. They place four
1.0m X 1.0m quadrats randomly in this area
and count the number of trilliums in each to
be 5, 2, 1 and 3.
• What is the estimated trillium population density?
• What is the estimated trillium population size?
• What is one source of error in this method?
MARK-RECAPTURE SAMPLING
• A common sampling technique for mobile or
dangerous populations is mark-recapture.
• Biologists trap/tranquilize/catch a number of
individuals of a population, mark them and then
release them back into their habitat.
• A short time later they catch a second sample of the
population and use the ratio of the marked
recaptures to the unmarked captures to estimate
the population size.
• The marking must not :
– harm the individual,
– prevent it from going about daily activities or
– make it more easily caught a second time.
Example
MARK-RECAPTURE formula
• Total # marked (M) = # of recaptures (m)
population size (N) 2nd sample size (n)
Solving for
M = m
N
n
• Rearrange to solve for population size
N = Mn
m
• The accuracy of the mark-recapture method
depends on certain assumptions:
– every organism in the population has an equal
chance of being captured,
– during the time between captures the
proportion of marked to unmarked remains
unchanged,
– and, the population size does not increase or
decrease during the sampling study.
Mark-Recapture Example
5) On day one, 20 warblers are captured in mist
nets. The birds are then marked with leg
bands and released. One week later, the nets
are reset and 50 warblers are captured. Of
these 50, 10 of them were banded from the
week before. Estimate the warbler
population size.

Fecundity/Biotic Potential: potential number of
offspring that can be produced.



eg HIGH – starfish, 1 million eggs/year
LOW – hippo, 20 births in 45 years
Fertility: actual number of offspring produced
SURVIVORSHIP CURVES
• General patterns in the survivorship of species
Type I
• Species have a low
mortality rate when young
• These are slow to reach
sexual maturity and
produce small numbers of
offspring.
• Have a longer life
expectancy.
• Ex: Large mammals,
including humans
Type 2
• Intermediate between
types I and III
• Have a uniform risk of
mortality over their
lifetime.
• Certain lizards, perching
birds, rodents.
Type 3
• Very high mortality rate
when young
• Those that reach sexual
maturity have a greatly
reduced mortality rate
• Very low average life
expectancy (ex. Green Sea
Turtle).
ETHICS
• The Canadian Council on Animal Care (CCAC) had
developed ethical guidelines for wildlife research.
They stress the three R's:
• Reduce the use of animals in their study as much as
possible.
• Refine your techniques to minimize discomfort and
stress on the animal
• Replace live-trapping with computer modelling
whenever possible.
www.ccac.ca
Homework
• Pg 508 #2, 3, 5, 6, 8,