bioknowledgy c.5 population ecology (ahl)
TRANSCRIPT
C.5 Population ecology (AHL)
Essential idea: Dynamic biological processes impact population density and population growth.
Fish populations, such as the schooling Anchovies (left) being hunted by the Bluefin Trevally (right) are an excellent example of how dynamic populations are. The process affecting population density here is mortality caused by predation.
By Chris Paine
https://bioknowledgy.weebly.com/https://commons.wikimedia.org/wiki/File:Moofushi_Kandu_fish.jpg
Understandings, Applications and Skills
Statement Guidance
C.5.U1 Sampling techniques are used to estimate
population size.
C.5.U2 The exponential growth pattern occurs in an ideal,
unlimited environment.
C.5.U3 Population growth slows as a population reaches
the carrying capacity of the environment.
C.5.U4 The phases shown in the sigmoid curve can be
explained by relative rates of natality, mortality,
immigration and emigration.
C.5.U5 Limiting factors can be top down or bottom up.
C.5.A1 Evaluating the methods used to estimate the size
of commercial stock of marine resources.
C.5.A2 Use of the capture-mark-release-recapture method
to estimate the population size of an animal
species.
C.5.A3 Discussion of the effect of natality, mortality,
immigration and emigration on population size.
C.5.A4 Analysis of the effect of population size, age and
reproductive status on sustainable fishing
practices.
C.5.A5 Bottom-up control of algal blooms by shortage of
nutrients and top-down control by herbivory.
C.5.S1 Modelling the growth curve using a simple
organism such as yeast or species of Lemna.
C.5.U2 The exponential growth pattern occurs in an ideal, unlimited environment.
http://www.biology.arizona.edu/biomath/tutorials/Applications/Population.html
Exponential population growthFor exponential growth to occur it requires an ideal environment:• All individuals survive to reproduce
successfully• Resources are unlimited …
… therefore there is no competition and no limit to the population
J-shaped growth curve
Changes in a population of Paramecium over a six day period
http://www.nature.com/scitable/content/ne0000/ne0000/ne0000/ne0000/13309363/vandermeer_figure1_ksm.jpg
Use the tutorial link to go learn more and attempt problem questions
Conditions needed in nature:• The population is very small• The organism has just colonised a
new environment
C.5.U2 The exponential growth pattern occurs in an ideal, unlimited environment.
Examples of exponential population growth
http://www.nature.com/scitable/knowledge/library/an-introduction-to-population-growth-84225544
Throughout the 1800's, hunters
decimated the American Plains bison populations, and by 1889, only about one thousand bison remained.
The US government, along with private landowners, established protected herds in the late 1800's and early 1900's. The herds started small, but with plentiful resources and few predators, they grew quickly. The bison population in northern Yellowstone National Park increased from 21 bison in 1902 to 250 in only 13 years.
C.5.U2 The exponential growth pattern occurs in an ideal, unlimited environment.
Examples of exponential population growth
http://www.nature.com/scitable/knowledge/library/an-introduction-to-population-growth-84225544
Does it surprise you that
human populationsize is growing exponentially?
This graph shows the explosion of human population over the last 10,000 years along with some relevant historical events.
C.5.U4 The phases shown in the sigmoid curve can be explained by relative rates of natality,
mortality, immigration and emigration.
Limiting factors are environmental factors that controls the maximum rate at which a process, e.g. population growth, can occur.
• build-up of toxic by products of metabolism
• Injury• Senescence (death from age
related illness)
C.5.U4 The phases shown in the sigmoid curve can be explained by relative rates of natality,
mortality, immigration and emigration.
All examples of competition for resources
• Injury• Senescence (death from age
related illness)
• build-up of toxic by products of metabolism
C.5.U4 The phases shown in the sigmoid curve can be explained by relative rates of natality,
mortality, immigration and emigration.
• build-up of toxic by products of metabolism
The effect of these limiting factors increases as the population increases. These factors are described as being density dependent limiting factors.
• Injury• Senescence (death from age
related illness)
C.5.U4 The phases shown in the sigmoid curve can be explained by relative rates of natality,
mortality, immigration and emigration.
• build-up of toxic by products of metabolism
The this limiting factor does not increases as the population increases. This factor is described as being a density independent limiting factor.
• Injury• Senescence (death from age
related illness)
Examples include:• Climate / weather• Availability of light (for plants)• Natural disasters such as volcanic eruptions and fire
C.5.U4 The phases shown in the sigmoid curve can be explained by relative rates of natality,
mortality, immigration and emigration.
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 populations
Population Size = ( Natality + Immigration ) - ( Mortality + Emmigration )
C.5.U4 The phases shown in the sigmoid curve can be explained by relative rates of natality,
mortality, immigration and emigration.
C.5.A3 Discussion of the effect of natality, mortality, immigration and emigration on population size.
Most important factor –without birth the population cannot grow
http://www.slideshare.net/gurustip/populations-2174193
If individuals die before reproducing the population size of the next generation will be reduced / population growth is negatively affected.
density independent limiting factors such environmental change affect the very young, the old and the weak individuals affected the most. Minimal impact on population growth as individuals of reproductive age affected the least.
The more genetically diverse a population is the more likely individuals are to survive (e.g. disease) to reproduce.
The effect of natality, immigration, emigration and mortality on population size:
Increasing population density and the associated competition promotes emigration from a population (and therefore immigration to other populations).
C.5.U4 The phases shown in the sigmoid curve can be explained by relative rates of natality,
mortality, immigration and emigration.
C.5.U3 Population growth slows as a population reaches the carrying capacity of the environment.
• 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)
• 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
• 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 growth)
A summary of population growth described by the sigmoidal curve
C.5.U5 Limiting factors can be top down or bottom up.
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 tropic levels.
A keystone species exerts top-down influence on its community by preventing species at lower trophic levels from monopolizing critical resources, such as competition for space or food sources.
http://commons.wikimedia.org/wiki/File:Tierpark_Sababurg_Wolf.jpg
http://commons.wikimedia.org/wiki/File:Green_Sea_Turtle_grazing_seagrass.jpg
C.5.A5 Bottom-up control of algal blooms by shortage of nutrients and top-down control by
herbivory.
An algal bloom is a rapid increase or accumulation in the population of algae (typically microscopic) in a water system.
Free-living algae blooms can disrupt coral reef communities by blocking sunlight and preventing photosynthesis in the symbiotic zooxanthellae. This can cause coral bleaching (the corals eject the no longer useful zooxanthellae) which leads to the death of the corals.
http://commons.wikimedia.org/wiki/File:Mar%C3%A9_vermelha.JPG
http://commons.wikimedia.org/wiki/File:Algal_bloom_20040615.jpg
C.5.A5 Bottom-up control of algal blooms by shortage of nutrients and top-down control by
herbivory.
http://commons.wikimedia.org/wiki/File:Algal_bloom_20040615.jpg
Nutrients though only needed in small amounts are essential for the synthesis of key proteins and other compounds, e.g. magnesium is needed to make chlorophyll.
With key proteins such as chlorophyll in short supply the rate of photosynthesis and hence algal growth is limited. Nutrients are therefore a bottom-up limiting factor.
The water around coral-reef ecosystems is generally nutrient-poor.
Algae depend on photosynthesis for nutrition.
Nutrient enrichment through human activity (fish farming, fertiliser or sewage outflowsdirectly or from nearby rivers) can cause known as eutrophication – algal populations increase rapidly (blooms) due to the removal of nutrients as a limiting factor.
http://resources3.news.com.au/images/2011/04/28/1226046/589887-raw-sewerage.jpg
C.5.A5 Bottom-up control of algal blooms by shortage of nutrients and top-down control by
herbivory.
Parrotfish are herbivores that graze on free-living algae at a lower trophic
level. This is an example of top-down control of algae.
Fishing practices which remove herbivorous fish from coral reefs can lessen the predation of algae.
If herbivorous fish numbers decline this can lead to algal blooms
http://www.arkive.org/stoplight-parrotfish/sparisoma-viride/image-G84654.html
C.5.S1 Modelling the growth curve using a simple organism such as yeast or species of Lemna.
In the absent of equipment using one or more of the following resources to model population growth:• Yeast Population Growth lab and simulation by i-Biology
(http://www.slideshare.net/gurustip/population-growth-9457952)• Bunny population growth by PhET
(http://phet.colorado.edu/files/activities/3896/04.02 - CW - bunny simulation - 2014-07-30 - vdefinis.docx)
http://commons.wikimedia.org/wiki/File:Lemna_minor_Prague_2012_1.jpg
Duckweed (Lemna sp.) is a good model
organism for measuring sigmoidal population growth
• Place a small number of plants in a container, e.g. a plastic cup• Count the number of fronds (leaves) every day until the surface of
the container is covered, i.e. the population has ceased to increase.• Plot your results – you should obtain a sigmoidal curve• Your investigation can be extended by considering different
independent variables e.g. nutrient availability and the surface area of the container.
C.5.U1 Sampling techniques are used to estimate population size.
A population is a group of organisms of the same species who live in the
same area at the same time.
http://commons.wikimedia.org/wiki/File:Large_number_of_flamingos_at_Lake_Nakuru.jpg
C.5.U1 Sampling techniques are used to estimate population size.
A population is a group of organisms of the same species who live in the
same area at the same time.
It is not practical to count most populations directly. It is only feasible if:• Individuals are large• The area is small
http://commons.wikimedia.org/wiki/File:Large_number_of_flamingos_at_Lake_Nakuru.jpg
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.
n.b. researchers need to remove bias in the selection of areas, e.g. selecting areas might result in a population estimate being too high or low. Therefore the sampled areas are selected randomly.
C.5.A2 Use of the capture-mark-release-recapture method to estimate the population size of an
animal species.
http://www.offwell.free-online.co.uk/lincoln.htm
More information and guidance:
C.5.A2 Use of the capture-mark-release-recapture method to estimate the population size of an
animal species.
C.5.A2 Use of the capture-mark-release-recapture method to estimate the population size of an
animal species.
C.5.A2 Use of the capture-mark-release-recapture method to estimate the population size of an
animal species.
Z
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C.5.A2 Use of the capture-mark-release-recapture method to estimate the population size of an
animal species.
http://www.offwell.free-online.co.uk/lincoln.htm
More information and guidance:
C.5.A1 Evaluating the methods used to estimate the size of commercial stock of marine resources.
http://youtu.be/s3u2ZxKhPoA
http://youtu.be/m2y_M40tmvg http://youtu.be/B2E0QQG4Kk4
C.5.A1 Evaluating the methods used to estimate the size of commercial stock of marine resources.
http://youtu.be/Tf1EgeHDxpA
http://youtu.be/bedirwk95Oc
C.5.A4 Analysis of the effect of population size, age and reproductive status on sustainable fishing
practices.
C.5.A4 Analysis of the effect of population size, age and reproductive status on sustainable fishing
practices.
Population size and sustainable fishing
If the fish population is very small then there will be plenty of resources , e.g. food for all (environmental resistance, e.g. competition is minimal).
The population will growth quickly, it will show exponential growth.
http://www.nature.com/scitable/content/ne0000/ne0000/ne0000/ne0000/50938330/figure1-626_1_2.jpg
C.5.A4 Analysis of the effect of population size, age and reproductive status on sustainable fishing
practices.
Population size and sustainable fishing
If fish are harvested only (down) to this level then fishing can be continued indefinitely and the population will quickly recover.
Steepest part of the slope
highest rate of population growth
=
If greater numbers are taken then the population will decline
http://www.nature.com/scitable/content/ne0000/ne0000/ne0000/ne0000/50938330/figure1-626_1_2.jpg
C.5.A4 Analysis of the effect of population size, age and reproductive status on sustainable fishing
practices.
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.jpg
http://www.bio.gc.ca/otoliths/scientists-scientifiques/images/annuli-2-eng.jpg
Sectioned cod otolith showing annular growth increments (annuli)
C.5.A4 Analysis of the effect of population size, age and reproductive status on sustainable fishing
practices.
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.
http://www.thesundaytimes.co.uk/sto/multimedia/dynamic/00288/SPA_288355k.jpg
C.5.A1 Evaluating the methods used to estimate the size of commercial stock of marine resources.
C.5.A1 Evaluating the methods used to estimate the size of commercial stock of marine resources.
C.5.A1 Evaluating the methods used to estimate the size of commercial stock of marine resources.
Sampling method Situation in which the method is used
Usage and limitations
Random sampling Not used. Ineffective as fish are too mobile.
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:
