This document summarizes key concepts in population ecology: - Populations initially grow exponentially as birth rates exceed death rates, but growth slows as resources diminish and competition increases, leveling off at the environment's carrying capacity. - Population size is determined by the relative rates of birth, death, immigration and emigration. - Limiting factors like resources and predation can regulate populations from the bottom-up or top-down. - Estimating wild populations relies on sampling techniques since directly counting is impractical, such as capture-mark-recapture of fish.

1. C5: Population Ecology

2. Understandings Applications/Skills
 Sampling techniques are
used to estimate
population size.
 The exponential growth
pattern occurs in an ideal,
unlimited environment.
 Population growth slows
as a population reaches
the carrying capacity of
the environment.
 The phases shown in the
sigmoid curve can be
explained by relative rates
of natality, mortality,
immigration, and
emigration.
 Limiting factors can be top
 A: Evaluating the methods
used to estimate the size of
commercial stock of marine
resources.
 A: Use of the capture-mark-
release-recapture method to
estimate the population size of
an animal species.
 A: Discussion of the effect of
natality, mortality, immigration,
and emigration on population
size.
 A: Analysis of the effect of
population size, age, and
reproduction status on
sustainable fishing practices.
 A: Bottom up control of algal
bloom by shortage of nutrients
and top down control by
herbivory.

3. Increases to
population size
through
reproduction
(i.e. births)
http://www.slideshare.net/gurustip/populations-2174193
Increases to
population size from
external populations
Decreases to
population size
as a result of
death (e.g.
predation,
senescence)Decreases to
population size as a
result of loss to
external populationsPopulation Size = ( Natality + Immigration ) - ( Mortality + Emmi

6. • There is a rapid increase in population size / growth as the
natality rate exceeds the mortality rate
• This is because there is abundant resources (e.g. food,
shelter and water) and limited environmental resistance
A summary of population growth described by the sigmoidal curve

7. • As the population continues to grow, eventually competition
increases as availability of resources are reduced. Natality
starts to fall and mortality starts to rise, leading to a slower
rate of population increase
A summary of population growth described by the sigmoidal curve

8. • Eventually the increasing
mortality rate equals the
natality rate and
population size becomes
constant. The population
has reached the carrying
capacity (K) of the
environment
• Limited resources,
predation and disease all
contribute to keeping the
population size balanced
• While the population size
at this point may not be
static, it will oscillate
around the carrying
capacity to remain
A summary of population growth described by the sigmoidal curve

10. A limiting factor is an environmental selection pressure that limits
population growth. There are two categories of limiting factor:
Top-down factors are
pressures applied by other
organisms at higher trophic
levels.
Bottom-up factors are those
that involve resources or lower
trophic levels.
http://commons.wikimedia.org/wiki/File:Tierpark_Sababurg_Wolf.
http://commons.wikimedia.org/wiki/File:Green_Sea_Turtle_grazing_seagrass.jpg

11. http://commons.wikimedia.org/wiki/File:Large_number_of_flamingos_at_Lake_Nakuru.jpg
How many flamingoes can you
count?
It is not practical
to count most
populations
directly. It is only
feasible if:
• Individuals are
large
• The area is
small
This is rarely the case
therefore researchers
need to use sampling
techniques to
estimate the
population by
measuring population
density in small parts
of the study area.

16. Destructive Trawling Video

17. http://youtu.be/Tf1EgeHDxpA
http://youtu.be/bedirwk95Oc

20. http://youtu.be/Tf1EgeHDxpA
http://youtu.be/bedirwk95Oc
- Increase in pest species

21. Restrictions to ensure fish can
breed before being caught:
• Regulations or international
agreements often restrict the
net mesh size allowing younger
fish to escape.
• Closed seasons are often
declared to allow undisturbed
breeding and exclusion zones
are agreed upon in which all
fishing is banned.
Reproductive status and sustainable fishing
Quotas are agreed upon for
species with low stocks and
moratoria declared on the
fishing of all endangered
species.
Increase the
number of younger
fish to encourage a
growing population.
If young fish are removed the population
enters decline as the fish need to live
long enough to reproduce successfully. If
not enough fish are reproducing the next
generation will be smaller.

22. Age and sustainable fishing
The otolith (ear bone) contains rings, similar to the
rings of a tree, that can be used to determine the age
of the fish.
If a population is in decline, then the
proportion of older fish will be higher (older
fish have a higher mortality and are
unlikely to be as productive in breeding).
If a population is growing, then the relative
number of younger fish will be higher (there are
many potential breeding fish for the future).
http://oceanexplorer.noaa.gov/explorations/04etta/background/barrelfish/media/barrelfish_otolith_600.jp
http://www.bio.gc.ca/otoliths/scientists-scientifiques/images/annuli-2-eng.jpg
Sectioned cod otolith showing
annular growth increments
(annuli)

23. Sampling
method
Situation in which
the method is used
Usage and limitations
Capture-mark-
release-recapture
Fish are temporarily
stunned with electric
shocks and then
counted
Used in lakes and rivers, but
recapture numbers are too small
to be useful in open waters such
as oceans.
Echo sounders Can be used to
estimate the size of
fish shoals
Only useful for schooling fish
species
Fish catches Age structure of
landed fish can be
used to estimate
population size.
Violators of fishing regulations
designed to control the age of fish
landed often do not report what
they land or they dump the
restricted fish causing a bias in
the estimates.
Summary of the sampling methods used for marine
resources:
http://runningatdisney.com/wp-content/uploads/2013/02/Nemo.jpg

24. Homework
Vocab Other
 Natality, mortality,
immigration, emmigration,
exponential growth phase,
transitional phase,
plateau/stationary phase,
carrying capacity, limiting
factors, top-down control,
bottom-up control,
density-dependent factor,
density-independent
factor, trawling, remote
sensing hydroacoustic
method, maximum
sustainable yield,
 Pg 669- Challenge
yourself 33-36
 Pg 706- Challenge
yourself 37-41;
exercises 13-15
 Read C6- Nitrogen
and Phosphorous
cycles