Download Model of lake ecosystem

A. Verner
Description
Assembling
Modelling
Food chain
Light is the main source of energy for life on the Earth. All other living
organisms depend on the capability of the green plants to produce feeding materials.
Transfer of energy from the green plants to animals takes place in the food chain. Part
of the energy is lost at each level of the food chain, as it gets dispersed in the
environment in the form of heat.
The food chain is an abstract concept that may not be directly seen in the
nature, but it may be imagined. Sometimes only one or two stages of the food chain
may be seen when carrying out observations in nature. Most of animals do not depend
exclusively on one type of food, therefore the food chain may be extended to a food
network. It provides a more comprehensive representation as regards to how the
organisms living in the same environment subsist on each other.
Degrading or reducing agents play a very important role in the food chain.
They feed themselves by degrading the destroyed organic matters. Bacteria, fungi and
other organisms are important reducing agents.
The model represents the food chain up to the highest level of carnivorous
animals.
Food chain model
Components
1. Light green
Pictures of algae and small aquatic plants
2. Light yellow
Pictures of plant eating fish
3. Dark yellow
Pictures of perches
4. Orange
Picture of a pike
5. Red
Picture of an osprey
Assembling
All five parts of the model must be folded along the dashed line to form the
shape of a caret so that the pictures of species are on the outside, but the explanatory
text is inside of the model.
Parts of the model must be stored in a box.
Demonstration
When carrying out the demonstration, parts of the model must be placed sequentially
above each other, starting with the first one, so that a a pyramid is formed, with the
pictures facing the audience. Characterization of organisms on each level and
assembling must be performed simultaneously.
The following food chain is obtained: green aquatic plants, plant-eating fish,
predatory fish, large predatory fish, fish-eating birds.
The pattern of the pyramid demonstrates the relations of the number of
organisms at each level of the food chain.
At the upper, fifth level, other species are possible as well. The grey heron,
cormorant, otter or a human. It is advisable to note the species, characteristic for the
particular surroundings.
The person performing the demonstration may invite the audience to come up
with their proposals regarding other species for each level of the food chain. The
modelling may be accompanied by active discussions on feeding relations in the
environment.
The cannibalism phenomenon is demonstrated by utilising the following parts
of the model: the green aquatic plants – perch. Perches may live in lakes where there
are no other plant-eating fish species, since the adult perch can eat the young perch
which in turn feed on the green aquatic plants at the initial stage of its development.
Lake ecosystem
Lake as a freshwater ecosystem
Let’s look at a lake as a whole, especially at the coastal part where plant
associations and animal habitats are located. Considerable activity of factors affecting
abiotic, biotic and anthropogenic ecosystem are present at the costal part of a lake.
Autotrophic green plants synthesize organic matters from the non-organic
substances obtained in the environment by utilising the solar energy. These green
plants are the producers, providing the lake ecosystem with the energy, necessary for
vital processes. The green algae, which are the main phytoplankton organisms, form a
considerable biomass of a lake. Surface plant associations (“hard” plants) – reeds,
rush, reedmaces, water horsetails are widespread at the coastal part. In some places
water soldiers may be found which form dense stands, raising off the lake bed when
the weather is warm.
The coastal area of the lake is a transition area – ecotone between two
ecosystems. This is where the most of biological diversity and the highest population
density can be observed in comparison with each of the bordering ecosystems
separately. Diverse habitats can be found here. Often there are several ecotones at the
coastal area, for instance, aquatorium of the lake and reedbeds, reedbeds and coastal
marsh, marsh and osier-beds, osier-beds and grey alder forest stands.
Ecological succession. Allogenic succession can be seen in the overgrowing
parts of a lake where gradual forming of a marsh occurs. The coast is turning into a
marsh. Further towards the coast bushes appear and gradually an undergrowth
develops. This is where melting pieces of ice are brought by winds in spring. This ice,
when moving, breaks reeds and forms reed piles which decay during the entire warm
period, creating large stocks of detritus. Formation of detritus can be easily observed
in a reedbed where reeds, water horsetails and rush grow on sandbanks in the depth
from 0.2 up to 1.6 meters. Lots of fish live here and several hundreds of water birds
nest.
In many lakes up to 16 fish species can be found. Fish is the main group of
animals in the lake which can be utilised by humans. The local inhabitants are
engaged in angling and recently also in commercial fishing, one of the best types of
active recreation at the lake. The composition of the fish species, their distribution and
density in various parts of a lake, development, reproduction and feeding depends on
various factors. All species of fish at a particular age need their own specific basis for
feeding which enables them reproduce and grow qualitatively. They also need
particular conditions, which may differ quite significantly by the range of their
impact. The capability to adapt to changing conditions is one of the most important
qualities of the living organisms.
The amount of zoobenthos and especially zooplankton increases by increasing
the eutrophication level of water, but the number of species will decrease in such case.
The zooplankton biomass in the lake is mainly formed of water fleas (Cladocera)
which are common in the open part of the lake in the depth up to 5 meters. The
organisms of zoobenthos – mainly larvae of true midges (Chironomidae) are found in
the muddy soil.
The impact of the lake bed. The fish that bury themselves in the soft soil resp.
clay and sand fields can be found at the lake bed. Fish adapt to certain conditions.
Depending on the colour of the soil, the colour of the fish changes. It has a masking
purpose, helping the fish to hide from carnivores. The feeding objects living in the
soil form the habitat of the fish and determine distribution of species in the lake.
The clarity of water depends on the amount of suspended substances and
phyto- and zooplankton organisms. The impact of clarity can be particularly seen in
shallow waters, coastal areas and on sandbanks. The suspended substances reduce
lighting and affect fish also mechanically by hindering the water flow through gills,
which inhibits the respiration process and oxygen exchange. The light in the water in
turn affects the daily rhythm, metabolism and functioning of the reproductive glands
of fish.
The young fish usually obtain their food in the top layers of water because it is
warmer there and more light is available.
Water temperature plays an important role. It affects the metabolic processes,
respiratory intensity, digestion, functioning of the reproductive glands (by
determining the beginning of the spawning period), moving of fish in the lake,
growing speed of the fish and beginning of hibernation. Like all other cold-blooded
animals, life of fish greatly depend on water temperature. Water temperature affects
the minimum oxygen content in the water, which in turn has an impact on the gas
exchange. In this way water temperature influences effect of various toxic substances
upon fish as well as disposition of fish in a lake in various seasons.
Some fish in the lake require significant oxygen content in water. Freshwater
cods live in small numbers in medium-deep places in the vicinity of rocky sandbanks,
where the swell of water enriches it with oxygen and where there are no large stocks
of detritus which can decrease the oxygen content due to decay processes. Most
common fish species of the lake live in waters with a comparatively low oxygen
content. These are breams, perches, ruffs, roaches, moderlieschens, pikes and other
species. Such species are more common in sludgy places and in the vicinity of
reedbeds. Breams are the species with the highest number of individuals in the lake,
leading to overpopulation. In case of insufficient amount of food the slow-growing
breams develop, when older fish are smaller in size and their length increases
insignificantly within a year. Here we face the concept of the environmental capacity.
It would be necessary to increase the catch of bream, which is an anthropogenic
factor, influencing the fish population and dynamics.
Populations. Depressed river mussel, great pond snail, great ramshorn snail
form the largest mollusc populations in a lake. Molluscs function in the lake as bioaccumulators, accumulating polluting substances. Occassionally numbers of dead
molluscs can be found in the vicinity of a sewage inlet in a lake.
The largest density of the fish population occurs in the coastal areas, near
sandbanks and in holes, reaching the depth of up to 10 meters.
The colony (micropopulation), consisting of at least 300 pairs of the blackheaded gulls (Larus ridibundus) nested in the reedbeds at the eastern coast of the lake
in the High Reeds. The birds made their nests of reed stalks and leaves; the nests were
floating in the water, fixed on the reed piles or in shallow places on a solid surface.
There are certain similarities between the structure of the colony, its processes or
internal life and the structure and dynamics of the population. We can use it
successfully to develop understanding of the structures, dynamics, processes and
interactions of populations.
The black-headed gulls feed in the aquatorium and coastal part of the lake, on
fields, city landfills and in the adjacent ponds. The conditions for nesting in the
reedbeds of the lake were not favourable since changes of the water level, impact of
the leading winds and waves are common here. The spring ice regularly changed
reedbeds and moved the alluvion. Also the disturbance factor was significant, since
there are good fishing places surrounding the reedbeds and the use of boats in the lake
is permitted starting from 1 May, soon after the ice melts and seagulls start nesting.
Thus we have answered the question: why did the black-headed gulls leave nesting
places in the lake and moved to the adjacent pond? As soon as a separately grouped
dense stand of reedmace was formed in the pond and conditions appropriate for
nesting were in place, part of the black-headed gulls started nesting in the pond in the
vicinity of the lake. Gradually the following was observed: the density of the new
colony increased, stable nesting areas of the old and young birds were established, the
density of nests in the middle part of the colony increased compared to the margins,
the so-called ‘club of seagulls’ was established in the coastal area of the pond where
rutting games, mating and communication of birds took place.
The effects of human activity caused significant changes in the lake
ecosystem, especially due to pollution with waste water. Fishing, angling, disturbance
factor – motor boats, recreational activities. Changing the water level of the lake.
Many of the changes now affect lives of the people living in the vicinity of the lake. It
is not advisable to swim in the lake, in summer the blue-green algae cause intense
discharge of toxins into the bay of the lake close to the city. An improvement of the
lake water quality occured only after the wastewater discharge was stopped. Microorganisms and plankton organisms play the main role in the self-purification of water.
The artificial propagation of fish in the lake and introduction of new species. The
measures mentioned above have changed the density of the fish population as well as
the interaction of interspecies and internal species. Entering pike-perches into the lake
significantly reduced the number of European whitefish, namely, it affected the
population of this species negatively. Now, when assessing the data of occurrence of
the European whitefish in the lake, we can conclude that the population is
overexploited. The population of pike-perches in the lake was developing rapidly and
now there are cases reported where the pike-perches attack and bite even big fish.
Biotic relationship in the lake ecosystem. They are mutually substantiated and
closely related to the abiotic environment.
Interaction among species. Competition, allelopathy, interaction among adult
and young, female and male individuals of fish. One of the most important forms of
relationship is forming of flocks, which has as a safety function, feeding function and
hibernation function. There are various forms of grouping of the same species – flocks
of various ages, clusters.
European perch (Perca fluviatilis) eats its own young fish – cannibalism. It
provides an opportunity for the European perch to live in a water body where there
are no other fish species, and, by eating the young ones, the big European perch
actually is living on the plankton which is food of the young ones and which the
adults can not use. This creates a food chain: plankton – European perch (young) –
European perch (adults). Normally the sequence would have been as follows:
plankton – moderlieschen – European perch, or different food chains: algae –
zooplankton – roaches – European perch – pike – human, or: algae – copepod –
moderlieschen – European perch – pike – osprey.
Interspecies interaction. Predation, parasitism, competition.
Fish – bacteria and viruses whach are fish food and agents causing fish
diseases.
Fish – plants. Plants create favourable living environment, food resources
(especially plankton plants, also plant detritus), produce oxygen, reduce carbon
dioxide content in the water, form spawning substratum and hideaways. Functioning
of plants in water under shade, in the darkness is negative, because under such
circumstances they produce more carbon dioxide which is harmful to fish. Growing of
the solid aquatic plants in parts of the lake worsens conditions in the water body.
Quite often intensive water blooming or development of the blue-green
plankton aquatic plants occurs (mainly due to polluting substances). They produce
toxins which are harmful to other water organisms.
Fish – prothea, which are fish food, fish parasites and agents causing fish
diseases.
Fish – worms. Worms as fish food, fish parasites, as, for instance, fish
tapeworm in breams. Often breams infected with tapeworms can be found in the lake.
Fish – molluscs. Molluscs as fish food, benthos organisms, parasitism and
commensalism are present.
Crustaceans as fish food, especially plankton crayfish which serves as a food
mainly for young fish. Crustaceans live on fish roe and on young fish. They often
hinder the development of fish.
Insects are one of the most important lake organisms. Larvae and adult
specimens of many insects are irreplaceable food source for fish, birds and other
organisms. Bloodworms, larvae of caddisflies and day-flies are particularly important.
There are also insects – carnivores which eat other insects, their larvae, thus affecting
the basis of fish food. Water stick insect and beetles attack fish, their young.
Amphibia. Frogs and tritons are food for pikes. Frogs eat insects related to
water. Lake frogs eating young fish.
Birds – fish. Birds as fish food. It has been established that pikes eat young
water birds. Birds, especially duck species, carry fish roe to another water body. Birds
fill water with fertiliser, especially where nesting colonies are located (great crested
grebe, black-headed gull, etc.). It causes proliferation of phytoplankton and water
invertebrates as well as introduces changes in the fish food basis. This fertiliser also
determines the prevalence of fish in the lake and habitats for the young as well as the
prevalence of the predatory fish.
Birds eat fish. The techniques birds use for catching fish differ. They affect the
species of most consumed fish. Here we come across the ecological niche concept.
For example, black-headed gulls do not dive and catch the small fish from the top
layer of the water. The common terns are small birds, they dive but not too deep and
they feed on small fish from the top layers of water in a wider lake aquatorium, both
in the coastal areas and on sandbanks where most of the small fish species and the
young of the big fish can be found. The grey heron catches fish by paddling in the
shallow waters of the coastal area in the depth of up to 0.5 m. The great crested grebe
is a typical diver and catches fish both in medium deep and top layers. Loons which
rarely stay at lakes, catch fish by diving deep and eat bigger fish. The osprey which
flies to the lake from a distant nesting place in a marsh in order to get food, catches
medium and big fish (most often those are breams) within the coastal area. Birds also
carry fish parasites.
Fish – mammals. Pikes frequently devour water voles. There are fish eating
mammals in the lake – otters, minks. A fox can catchs fish at the coast, it also preys
on water voles and birds. These mammalians act as carnivorous animals.
Populations of all species in the lake have a system of regulating mechanisms
which ensures changes in the number of the populations and in the biomass depending
on the changes in the living conditions. Populations function only in a particular
amplitude scope of conditions which differ from species to species.
Model of lake ecosystem
Components
Folding basic layers
1.
2.
3.
4.
5.
6.
7.
Dark brown the soil
Dark blue deepwater 8 m
Blue – depth 6 m. Two cut out pieces with numbers 33 for inserting in order to
cover the depth of up to 8 m.
Lighter shade of blue – depth 4 m. One cut out piece with numbers 44 for
inserting in order to cover the depth of 6m.
Light blue – depth of up to 2 m. Two cut out pieces with numbers 55 for
inserting in order to cover the depth of up to 4 m.
Grass green – caulescent plants. The cut out piece No. 16 caulescent plants of
the lake island.
Multi-coloured the grass green, dark green areas in the forest places, a moss
green area in the middle with 2 cut out pieces with numbers 77 for inserting.
Added components
Dark brown – soil of the island - irregular shape, with numbers 11,
Dark green – forests of the island - irregular shape, with numbers 20,
Dark green – forests – irregular shape, with numbers 21,
Dark green – forests - irregular shape, with numbers 22,
Dark green – forests - irregular shape, with numbers 23,
Moss green – irregular shape- with numbers 40,
Moss green – irregular shape- with numbers 41,
Moss green – irregular shape- with numbers 42.
Species pictures
Species of marsh plants
A4 sheet of cardboard, moss green background
Sphagnum moss, cranberry, marsh tea, sheathed cottonsedge
Lake species
A4 sheet of cardboard, light grass green background
Algae, lesser duckweed, reedmace, common reed, bulrush
A 4 sheet of cardboard, light yellow background
Zooplankton, great pond snail, roach, tench, minnows, silver bream,
coot, beaver.
2 A4 sheets of cardboard, yellow background.
Perch, pike perch, great reed warbler, frog, golden-eye, widgeon,
black headed gull, herring gull, curlew, wood sandpiper
A4 sheet of cardboard, orange background
Pike, common tern, European bittern, great crested grebe, goosander
A4 sheet of cardboard, red background
Fox, otter, grey heron, osprey, goshawk, marsh harrier
Preparation for modelling
Parts of the environmental model are stored folded in the transport box.
Large details of the model
Take all parts of the model out of the box and unbend each coloured layer.
Accurately cut the necessary contours along the cut line by using the oblique
knife. It is advisable to place a plate of condensed paper, plywood or other material
under the cardboard.
The details cut out must be stored in accordance with the description.
Small details
All the small details are cut out of cardboard sheets. They are intended to be
placed on the big layers.
Species pictures
All pictures of plants and animals on the coloured papers are cut out, by
cutting along the interrupted lines. Short cuts must be made also in the base of the
pictures.
Then the parts of the base are folded towards the side of each part along the
interrupted line forming supports. They will hold the species pictures in a vertical
position during the demonstration.
In order for the base part of a model to serve longer it is necessary to maintain
the direction of the initial fold.
Modelling
Modelling the lake structure
Assembling the model must start with the brown cardboard layer No.1.
The blue water layers designated by numbers starting from 2 to 5 are placed
thereon. They depict the depth of up to 8 meters of the lake. Then the green herbage
grasses layer is placed.
Layers of islands of the lake are placed in-between the two depths, beginning
with the brown one. It is followed by the light green symbol of caulescent plants and
the dark green symbol of the forest. If there are only caulescent plants on the island
the layer of forests is not used.
Symbols of the reedbeds are placed in the most appropriate places in coastal
areas.
Three dark green forest layers are placed in the vicinity of the lake.
Arranging lake species
The prepared species cards are placed in the places where the natural presence
of the species is most common. Thus a visual model of the food network of the lake is
obtained.
Species cards may be arranged in different combinations, depending on the
theme to be depicted.
Modelling overgrowing of lakes and formation of marshes
Layers of a corresponding colour are placed in the deep parts of the lake,
ensuring the lake’s depth of up to 2m.
The island model is taken off the lake.
The multicoloured layer which pictures the overgrown coast of the lake and
layers of forests drawn in the relevant places is placed over all parts.
Overgrowing of the lake and its turning into a marsh is modelled by placing in
the multicoloured layer the cut out moss green squares with numbers 77 that cover the
blue picture of the lake.
It is followed by the arrangement of the cards of the plants and animals of the
lake.
Translate by G. Kupča