Population dynamics is the study of changes in population sizes over time. Key aspects include population size, density, distribution, and growth trends. Population size is the number of individuals in an area, while density is the number per unit area. Mark-recapture sampling estimates population size by capturing, marking, and recapturing individuals. Demography analyzes population changes through birth rates, death rates, immigration, and emigration to determine growth rates. Populations can exhibit exponential or logistic growth patterns, with the latter limited by environmental carrying capacity. Many factors like resources, competition, and species interactions influence population growth.
2. Introduction
• What is population dynamics?
• The changes in the populations of organisms over time
• Population ecology is the study of populations. Their
size, density, distribution and changes over time
• By doing this ecologists are able to gather data that can
help them predict growth trends, health, manage sizes
3. Population Size & Population
Density
To study populations, scientists measure population size
(the number of individuals of a specific species occupying
a given area/volume at a given time) and population
density (the number of individuals of the same species
that occur per unit area or volume)
• Knowing the population size and density provides more
information about the population’s relationship to
resources it uses
D=N/S
N=Total number of individuals in the population
S=Space occupied by the population
4. Example
The population density of 480 moose living in a 600
hectare (ha) region of Algonquin Park:
D= N
S
D= 480 moose
600 ha
D= 0.8 moose/ha
6. Clumped Dispersion Pattern
A pattern in which individuals
in a population are more
concentrated in certain parts of
the habitat. It occurs in these
3 situations:
1) When suitable living
conditions are distributed in
patches
2) Mates are easier to locate in
groups
3) Limited seed dispersal or
asexual reproduction
7. Random Dispersion
Occurs when environmental
conditions do not vary
greatly within a habitat and
when individuals are neither
attracted to nor repelled by
others of their species.
Organisms are distributed
unpredictably.
9. Mark-Recapture Sampling
A sampling technique used to estimate the
population size of a species.
• A specific number of animals in the natural
population is captured, marked or tagged in
some way and then released back into the
population
• After a period of time when the marked
animals have mixed in with the unmarked
animals, another sample is captured
• Biologists use the proportion of marked to
unmarked animals in the second sample to
estimate the size of the entire population
10. Accuracy is based on 5 assumptions
• the chances for each individual in the population to be caught
are equal and constant for the initial capture and the
recapture
• No new individuals can enter the population through birth or
immigration and no individuals can leave through death or
emigration
• Enough time is given between the release and recapture so
individuals can disperse
• The animals are not affected by their markings
• The marked animals do not lose their markings
The estimated population size can be calculated as
follows:
Total number marked (M) = number of recaptures (m)
Total population (N) size of second sample (n)
OR
N= Mn
m
11. Mark-Recapture Sampling Activity
1) Pick a species
2) Randomly pick out 20 marshmallows from your
paper bag
3) Mark each captured marshmallows with your
marker and return them all to the bag. Shake
and stir the bag to mix the marshmallows up.
4) Without looking in the bag, capture a similar
amount of marshmallows from the bag
5)Calculate the estimate of the total population size
N= Mn
m
6)Compare with other groups
12. Demography
Depending on the species and the environmental
conditions, population numbers can undergo
hourly, daily, seasonal and annual changes.
Demography is the study of these changes. Ecologists
use demographic analysis to predict the growth of a
population
Birth rate, death rate, immigration and emigration can be
used to determine the growth rate of the population in a
given period of time. This data can also be used to
develop plans to protect endangered species
13. Survivorship Curves
Data about survival can be depicted graphically in a
survivorship curve. This displays the survival of
individuals over the lifespan of the species. Most
organisms exhibit survivorship patterns that fall
somewhere between these general patterns:
Low death rate in Constant rate of High death rate in early
early/middle years, death mortality in all age years, declines for the
rate increases in older age groups few individuals that
groups survive
14. Fecundity
The reproductive capacity of an individual or population.
A horseshoe crab can lay An elephant produces a
up to 90 000 eggs in a average of only 4 offspring
single spawning season during a lifetime
15. An animal that has high fecundity normally does little to care for
them.
An animal that has only 1 or 2 offspring per year tend to be
very protective of them. This is called extensive parental care.
16. Population Growth Models
Population growth rate: the change in a population over a unit time
period.
Population (births + immigration) – (deaths + emigration)
= initial population X100
growth rate
• A positive growth rate indicates that the population is increasing
• A negative growth rate indicates that the population is
decreasing
• A growth rate of zero indicates there was no difference between
birth rates and death rates
• Some species reproduce continuously so the sizes of these
populations have the potential to increase exponentially by a
contrast ratio per unit of time. Ex, bacteria, virus
17. Exponential Growth
Model
Associated with the name of Thomas Robert Malthus
(1766-1834) who first realized that any species can
potentially increase in numbers according to a geometric
series.
18. • Populations that grow
exponentially increase in numbers
rapidly, resulting in a J-shaped
growth curve. As the population
gets larger, it grows faster and
becomes steeper.
• We can determine the change in
population size over time by using
the equation
dN = B – D
dt
dN
dt = the change in population size
over time.
B=Birth rate
D=death rate
• This equation can be used for ANY
population if we know the exact
number of births and deaths
19. Limitations
• Environmental limitations prevent
populations from experiencing continuous
growth
• Per capita birth rate decrease and the per
capita death rate increases as competition
for resources such as food and shelter
occurs
• Large sudden birth rates in Canada due to
breeding periods (frogs reproduce in fixes
intervals) not continuously
20. Logistic Model
• Environmental limitations create this model. It describes limited
population growth, often due to limited resources or predation.
• An environment only provides enough resources to sustain only a
limited amount of any species.
• The maximum number of individuals that an environment can support
indefinitely is its carrying capacity.
N=population size
K=carrying capacity
• If a population is very small then plenty of resources are available and
therefore the value of (K-N)/K is close to 1.
• Vice versa, if the population is large, few resources are available and
the value of (K-N)/K is small and the per capita growth rate is very
low.
• Lastly, if the size of the population exceeds the carrying capacity of the
habitat then the population would decrease from lack of food and other
resources. If this is graphed it produces an S shape curve.
21. Sigmoid Curve
Logistic growth can be seen in a population of fur seals on St. Paul Island, Alaska. In
1911, fur seal hunting was banned on St. Paul Island, since the population had
become extremely low. Because their numbers were so severely depressed, the seals
had many unused resources to support the recovering population. The population
began to grow rapidly until it stabilized around its carrying capacity.
22. Activity
A white-tailed deer population in a small forest ecosystem
exhibits logistic growth. The carrying capacity is 300 deer
and rmax =0.23.
a) Determine the population growth rates of 100, 200 and
300 deer.
Equation: dN=rmax N(K-N)
dt K
23. Limitations
• The logistic growth model assumes that all individuals
reproduce, die and use resources at an identical rate.
• It assumes that the carrying capacity remains constant
and there are no environmental variations that might
cause the carrying capacity to fluctuate.
• Assumption that there is no migration and that
populations do not interact with each other.
24. Factors that Affect Population
Growth
Individuals within a population do not live in isolation. They interact with members
of their own species and members of other species. Coevolution occurs when one
species evolves in response to the evolution of another species.
Relationships between pairs of organisms:
Herbivory: the interaction between herbivorous animals
and plants they eat. Ex: White–tailed deer and foliage
Mutualism: an interaction in which both partners benefit.
Ex: honey bee and flowering plant
Parasitism: awhile the tree is unaffected interaction in which one
species benefits and the other is harmed. Ex: mistletoe, which
attaches to a tree and takes water and nutrients from its host;
usually stunts growth but can kill the tree with heavy infestation
Commensalism: an interaction in which one species benefits and
the other is unaffected. Ex: moss, which grows on a tree, getting
light and nutrient it needs
25. Defense Mechanisms
Organisms have evolved mechanisms to avoid being
caught and eaten.
Camouflage Chemical Defense Mimicry
Behavioural defense Spines and armour