Too Much of a Good Thing!

Too much of a good thing!

Too much of a good thing?

The red lionfish (Pterois volitans) is a beautiful-looking fish with venomous spines. The fish can be found in the Indian Ocean and the Pacific, but more recently also in the Caribbean Sea and the Atlantic. These lionfish are most likely the offspring of six fish that escaped from an aquarium in Miami that was destroyed during hurricane Andrew in 1992. The lionfish then quickly spread along the east coast of the United States, before heading for the Bahamas and Bermuda. They have now reached the Caribbean and not everyone is happy to see them.

Take a look at this video clip:

BBC – Oceans venomous Lionfish -

Fallow deer (Dama dama) are larger than roe deer but smaller than red deer. Fallow deer were once native to the Netherlands, but disappeared from the country during the last ice age. The Romans brought the species with them on their travels and the animal was reintroduced throughout the Roman Empire.

Although fallow deer are on the "Red List" of endangered species, they are nevertheless seen in large numbers in certain areas.

This has a large impact on the environment.

Red List

List specifying the endangered species of plants and animals in each country.

Take a look at this video clip:

The Netherlands – Fallow deer -

What are the similarities between red lionfish and fallow deer?

Both animals certainly cause problems. How are they a nuisance?

Should humans intervene in order to reduce the populations of lionfish and fallow deer?

Which control measures are available and are they effective?

At the end of this module you will have answered these questions and have formed your own opinion about the issue.

For starters

Refresher test

1 The tropical cloud forest on Saba has a rich biodiversity that includes mahogany trees, epiphytes, orchids and tree frogs.
Mahogany trees (Swietenia mahagoni) are well known for their high quality wood. Epiphytes are plants that grow on other plants without extracting food from their host (unlike parasites).
a. Are these organisms all part of the same population?
yes
no
b. Are these organisms all part of the same community?
 yes
 no
c. Are the epiphytes all part of the same population?
 yes
 no
d. Could the mahogany trees on Saba all belong to the same population?
 yes
 no
2 Write the following words in the correct order from small to large.
Population – ecosystem – individual – community
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3 Write down the following situations in a logical sequence.
Due to a shortage of prey, many foxes emigrate from the area.The fox population collapses. - The numbers of foxes increase, the fox population grows. –
The population of rabbits grows again. - The numbers of rabbits decrease, the rabbit population declines.
1. The population of rabbits in the dunes grows due to sufficient food.
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4 Which term is used to describe the maximum number of organisms of a species that can live in a certain area?
 density
 equilibrium
 dynamic
 carrying capacity
5 In which of the following situations will the carrying capacity of an ecosystem most likely be exceeded?
 When too many plants and animals in an ecosystem die.
 When the population density is high.
 When animals eat too much food.
 After a successful year during which a species produces a high number of offspring.
6 Biologists want to determine the size of the bream population in a lake. They first catch 250 bream and mark them. The fish are then released. After some time they catch 800 bream, of which 50 are marked. What is the size of the bream population in the lake?
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7 Take a look at the graph. In which of the following situations will the population growth most likely have this S shape?
 A field left fallow is taken over by pioneer plants.
 The natural increase in a population of songbirds in springtime.
 A dead animal is colonised by a population of bacteria.
 An animal with no natural enemies settles in an area where it has not lived before.

Final product - Assessment

Final product

At the end of this module you will give your own opinion about human intervention to reduce the population of red lionfish. You will choose both the type of final product (poster, presentation or article) and the target group. In your final product you are expected to provide answers to the questions named above.

Assessment

Your teacher will assess the final product according to the following criteria:

Content based on knowledge of ecology
Your poster, presentation or article is in fitting with the target group
For an article: 350-650 words plus suitable image
For a poster: images supported by clear captions
For a presentation: concise text and images that support the oral presentation
Your sources of information are clearly stated

Goals - Concepts

Learning goals

determining population size and population density;
describing dynamics and equilibrium in an ecosystem;
explaining the role of competition between populations in the dynamics of an ecosystem;
explaining the role of biotic factors in the dynamics of an ecosystem;
explaining how measures taken by humans can affect self-regulation in ecosystems.

Subconcepts

Birth rate, death rate, migration, introduced species, predation, limiting factor, biological equilibrium, competition, carrying capacity, species composition, Red List, area of distribution.

Skills

A2 Communicating

A5 Investigating

A8 Scientific instrumentarium

A9 Appraising and judging

A10 Perceiving and experiencing

A12 Reasoning in terms of ecology

Method

Format

Work through steps 1 to 3 individually or in groups of 2 using the theory provided in the module.

More information can be found in your textbook or other sources. The experiment in step 1 is performed outside in groups of 2. For the final product you will work in groups of 2 or 3.

Materials required

Worksheet Vegetation sampling -
Worksheet Limited and unlimited population growth -
White beans and brown beans

Time required

For this module you will need about 8 hours.

GET TO WORK!

Step 1

Studying populations

All ecosystems have different communities, each with a different species composition.

Information on the current status of the different populations can be obtained by investigating various different aspects, such as:

population size
population density
species composition
population growth over time

Population size

1. Counting

In order to determine the population size in a certain area, you can simply count the number of individuals.

Although this is practical for a limited area and a large species, in most cases it will not be suitable.

Other methods are available:

2. Sampling (quadrat method)

The quadrat method is suitable for studying plant populations.

The size of the quadrat and the number of quadrats will depend on the area to be studied and the type of vegetation. In a sparsely covered area of shrubland you will need a quadrat that is tens of m2 in size, while for a tree covered in beard lichen you will need one that is only several dm2 in size.

For each quadrat you first identify whether or not the species lives there and then count the number of individuals in the quadrat.

A more reliable result can be obtained by repeating this at a number of different sites in the ecosystem.

Population size = (mean) number of individuals in quadrat x total area

A variation on this method is to walk through the quadrat following a fixed route, counting how many individuals of a species you see along the way.

3. Mark and recapture

The population size of more mobile species can be estimated by catching the animals, marking them and releasing them again. When you recapture the animals for the 2nd time, some of them will be marked.

1. A number of animals are caught and marked.

y = number of animals caught and marked the 1st time.

2. The marked animals are released.

3. A number of animals are recaptured.

r = number of individuals caught the 2nd time. Some of them are marked.

m = number of marked individuals upon recapture.

The size of the population (x) can be calculated using the following equation:

Population density

The population density = the number of individuals per unit of area

(on land) or per unit of volume (in water).

Assignment 1

For each of the three methods described above, find at least one suitable plant or animal on Caribbean that could be counted using that method.

Exchange your findings with a classmate.

Assignment 2

Take a population of 150 white beans. Without looking, 'catch' 15 white beans and 'mark' them by replacing them with brown beans. Mix the brown and white beans and 'recapture' 15. Do this 10x.

Calculate the population size after each recapture.

Present your results in a table.

What conclusion can be drawn about the reliability of the method and the number of recaptures?

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Questions

1 When studying a population of sea bream, a biologist catches 1000 individuals, marks their fins and releases them again. Sometime later he catches 3000 sea bream, of which 60 have the same mark in their fin.
What is the size of the population?
 3000
 30000
 50000
 180000
 300000
2 You want to determine the size of a population of guinea pigs.
You first catch 50 guinea pigs and mark them. You then let them go again.
After some time you catch 200 guinea pigs, of which 4 are marked.
What is the size of the population?
 200
 2500
 4000
40000
3 It turns out that guinea pigs that have been caught before are more difficult to catch the second time around. What can you now say about the true number of animals in the population, compared with your answer to question 2? The true population size is...
 lower
 similar
 higher

Experiment

In groups of 2.

Choose a plant occurring in open vegetation (e.g. shrubland). Determine the population size using the quadrat method and calculate the population density. You will need to download the worksheet:

Step 2

Growth of a population

The population size in a certain area (ecosystem) will depend on the following factors:

birth rate (N) = number of offspring born each year;
death rate (M) = number of animals that die each year;
emigration (E) = number of animals that move away and never come back;
immigration (I) = number of animals that move into the area from elsewhere and settle permanently.

Population size P = (N + I) - (M + E)

In turn, these figures will depend on the following:

predation, disease, competition and availability of food.

immigration + emigration =migration

Predation

Killing animals for use as food.

Competition

Process of rivalry, whereby individuals negatively affect one another's survival due to a common limiting factor (e.g. food). Competition can take place both within a species and between different species.

The maximum size of a population that an ecosystem can tolerate is known as the carrying capacity. When you collect data over a longer period, you often see that the population density fluctuates around

a certain level.This is called a stable population.

Limited and unlimited growth

When conditions are ideal, a population will double in size over a period of time. During such exponential growth the birth rate is much higher than the death rate. This increase in population size over time can be plotted in what is known as a J-shaped curve or J-curve.

The abiotic and biotic factors In an ecosystem are changing continuously. This is why population sizes are not constant. Eventually a new balance is established that is more in line with the carrying capacity of the ecosystem. Once a balance has been reached, the population size no longer increases. This can be plotted in what is known as an S-shaped curve or S-curve.

Once an ecosystem has been in existence for some time, and the abiotic and biotic factors remain more or less the same, it reaches what is known as a biological equilibrium. The population size of each population in the ecosystem fluctuates around a certain level.

Assignment

Print the worksheet:

Cut out the words and place them on a large piece of paper(A3 format) to create a mind map.

Connect the words that arerelated to one another (e.g. cause and effect).Use the mind map to explain the S-curve and the J-curve toa classmate.

Questions

1 Which biotic and abiotic factors can cause a population to grow?
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2 Explain the shape of the lines in this graph.
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The Graylag goose

Over the past 25 years, the numbers of Greylag geese in the Netherlands have increased from about 3500 to 60,000 birds. These large numbers can also be seen as a plague. Land managers want to intervene in order to limit the population of Greylag geese, by either removing eggs or pricking and draining them.

The problem is caused by those Greylag geese that have decided to stay during the summer months.

They have chosen the Netherlands as their permanent settlement and do not migrate elsewhere to breed. Not only can they can find sufficient protein-rich grasses and grains in the Netherlands, there are now also increasing numbers of wetlands where geese can sleep safe from foxes.

3 The Greylag goose has become a plague in the Netherlands.

Plague

Uncontrolled multiplication of a certain species.

This has been caused by...
 an excess of food.
 the low numbers of predators in the area.
 their short stay in the Netherlands.

4 In a certain Dutch nature reserve, 15,000 geese were known to spend the summer. There were no foxes living in this area. In 2005, 20 foxes were released into the area (♂ and ♀). The intention was to reduce the size of the population of geese so that it remained stable at about 4500 birds.

You can assume that after a number of years the population of geese went down to this number and the population remained stable.

On the worksheet provided you will find a graph showing the size of the goose population since 2005.

Print the worksheet with the graph and add a line that shows how the number of foxes changed over time.

Step 3

Fallow deer in the Dutch dunes

Dunes are sand hills interspersed with lower areas known as interdunal valleys. They are formed by the wind and are sometimes stabilised by plants. Coastal dunes, seen along the entire Dutch coastline, start where the beach ends. One such area of dunes is the Amsterdamse Waterleiding Duinen or Amsterdam Water Board Dunes, a nature reserve that supplies drinking water to the city of Amsterdam. It has the largest population of fallow deer in the Netherlands.

Assignment 1

Where in the Netherlands are the Amsterdam Water Board Dunes?

Find out using

Although fallow deer were native to the Netherlands before the last ice age, they are still considered to be an introduced species. Introduced species are non-native plants or animals that have been introduced into a country by human activity. They are also known as exotic or alien species.

The introduction of such species may take place on purpose or by accident, when a plant or animal escapes into the wild. In the absence of natural enemies, the introduced species can multiply undisturbed, which can have various consequences. Such invasive species pose a strong threat to the native flora and fauna.

Assignment 2

1 Which animals on Saba can be classified as introduced or invasive species?
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2 Introduced species also include plants. Which introduced plants do you know of that displace the natural vegetation on Saba?
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3 Choose one introduced species on Saba and take a photograph of its negative effects.

Now back to the fallow deer. In 1990, regular deer counts carried out since the 1960s revealed

a small population of fallow deer. The population appeared to be stable and low in number, but in fact the population grew exponentially.

Source:

Assignment 3

The total area of the Amsterdam Water Board Dunes is 3400 hectares.

1 Calculate the population density per hectare each year. Present your results in a graph.

In contrast to roe deer, fallow deer eat many different types of plants.

Roe deer are what is known as 'browsers' or 'pruners' − they feed selectively on the buds and young shoots of woody plants.

Fallow deer have far more sources of food than roe deer. When food is scarce, fallow deer and roe deer must compete for food.

2 Given this information, what do you predict will happen to the size of the roe deer population in the Amsterdam Water Board Dunes?
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Harmful impact on the dunes

The large population of fallow deer has an impact on the vegetation in the dunes. This is known as over-grazing. They strip off and eat tree bark, particularly in the winter when there is little other food (e.g. leaves) available. Some plants cannot flower, which also has consequences for various insects. This disrupts the stability of the ecosystem.

Step 4