Transcript Population Dynamics

Population Dynamics
 Population dynamics is the study of the long term
changes in population sizes and the factors that cause
a change.
 The current focus is on human populations (ageing
studies, population booms or declines), but biologists
use population dynamics to study competing species
and predator-prey relationships as well.
Examples
Examples
Population Dynamics
 It has been around for 210
years which was when
Thomas Malthus proposed
the first mathematical
equation to characterize
human population growth.
 This lead to the equations
for both exponential and
logistic growth which we
will examine later in this
unit.
Factors affecting population
growth
 There are four factors affecting population growth:
 1) Births (natality)
 2) Deaths (mortality)
 3) Immigration
 4) Emigration
 They can all be put into a neat little equation…
N1 = N0 + (B – D) + (I – E)
 If you simply want to look at the change in population from one
time interval to the next simply look at:
(B – D) + (I – E)
Population Dispersion
 Population Dispersion is how individuals are arranged in their
habitat.
 There are 3 types of population dispersion:
 1) Uniform Dispersion (usually due to competition between
individuals)
 2) Clumped Dispersion (usually due to uneven distribution of
resources)
 3) Random Dispersion (usually due to an even distribution of
resources)
Population Density
 Population Density is a measure of how many
individuals of a given species are found in a given area.
 Two types of density:
 1) Crude density: total number of individuals divided
by the total area
 2) Ecological density: total number of individuals
divided by the total useable area
 Equation is D = N/S
 (D is density, N is population size and S is area)
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 Density
 It is found differently
depending on whether
the species being studied
is mobile or stationary.
 Quadrat studies are used
for non-mobile
populations like plants.
 Mark-Recapture studies
are used for mobile
populations like animals.
Quadrat Studies
 These are used to study
non-mobile populations.
 A quadrat is simply a small,
known area (usually a
square or rectangle) that is
placed in a larger
ecosystem at random and
all the species in question
that are located in that
quadrat are counted and
recorded.
 More practical than
counting every individual
in a given ecosystem!
Quadrat Studies
 All the quadrats and
their individuals are
added together in the
following equation to
figure the population
density in a given area.
 Estimated Population
Density (EPD) = total
number of sampled
individuals / sample area
 Basically a density
equation.
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 Studies
 For mobile populations we
use mark and recapture
analysis.
 On day one, traps are laid
out in the study area and
any subjects that are
captured are marked and
returned to the
environment.
 On the right is a
Longworth trap… standard
small mammal capturing
material.
Mark-Recapture Studies
 Sometime later in time,
usually no more than a day
or two, the traps are set
again and individuals are
captured.
 This time it is noted how
many individuals were
recaptures and how many
were new captures.
 All this data can be
plugged into an equation
to figure out population
density.
Mark-Recapture Study
 M/N = m/n
 M is the number of individuals marked the first day
 m is the number of marked recaptures on the second
day
 n is the total number of captures on day two
 N is the estimated population size
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.
Transect Studies
 A transect is a straight line (or rectangle) chosen by
researchers along which they will travel counting the
species being monitored.
 Both mobile and stationary species can be counted this way.
 Size of the transect depends on the species monitored.
 Works best when the expected density is low or when the
individuals are very large (i.e. Douglas Fir Trees).