C5: Population Ecology

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

down or bottom up.

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.

S: Modeling the growth curve

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 + Emmigration

• 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

(disease and predation uncommon)

A summary of population growth described by the sigmoidal curve

• 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

• 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

relatively even (no net

A summary of population growth described by the sigmoidal curve

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.

jpg

http://commons.wikimedia.org/wiki/File:Green_Sea_Turtle_grazing_seagrass.jpg

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

smallThis 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.

Destructive Trawling Video

http://youtu.be/Tf1EgeHDxpA

http://youtu.be/bedirwk95Oc

http://youtu.be/Tf1EgeHDxpA

http://youtu.be/bedirwk95Oc

- Increase in pest species

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.

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

g

http://www.bio.gc.ca/otoliths/scientists-scientifiques/images/annuli-2-eng.jpg

Sectioned cod otolith showing

annular growth increments

(annuli)

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

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 hydroacousticmethod, maximum sustainable yield,

Pg 669- Challenge

yourself 33-36

Pg 706- Challenge

yourself 37-41;

exercises 13-15

Read C6- Nitrogen

and Phosphorous

cycles