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Ecological Niche
H err Gustav Druer, the Brno wine merchant has a problem and Brother Gregory has been asked to help.

You are to become his research assisitants and help him carry out a research investigation into the properties of microbes.


Brother Gregory has collected a variety of microbes from around Brno. He has taken these back to his monastery to investigate their growth properties and find out the conditions under which they grow best.

In this way he hopes to be able to find out which kinds of microbes can grow in, and spoil, Herr Gustav Druer's wine. He wants you to help him.

In this investigation you will first determine the best growth conditions for microbes, by growing them under a variety of conditions and determining their rate of growth by "direct counts" under a microscope.

Then you will test a selection of microbial species under different conditions of temperature and pH to find out the upper and lower limits for each species for each variable, and the conditions under which each species grows best.

These values for these variables define the "ecological niche" (see below) for each species.

Once you have determined the "niche" for each species of microbe, you can then see which ones could possibly grow in Herr Gustav Druer's wine.

Background -
Ecological Niche

Microbes, like all other creatures, live in a complex world where each individual cell constantly interacts with its environment. High energy molecules (food) are absorbed from the environment and turned into low energy waste, which in turn is excreted back into the environment.

These wastes, and the wastes from many other cells and organisms constantly change the world in which the microbes live. Competition between cells for food, living space, predator avoidance and unhealthy chemicals creates a web of actions and interactions we call the ecology of that world.

Within this world a particular species of microbe will live in its own habitat. This is the "address" of the microbe. Examples of habitats could be ponds, soil, food, or the human intestines.

Living in this habitat, each microbe has a range of needs (food, pH, temperature, etc.), and contributes its wastes and other products back into its habitat. This sum of its interactions with its environment, interactions with other microbes or organisms, and its range of needs is called the niche of the organism or species.

An ecological niche is a very complex description of the way in which a species of microbe lives in its world and habitat. A full description of even the simplest niche is probably too complex to completely understand, but certain parameters or boundaries of a niche can be measured, studied and reported.

For example, a bare skinned human will freeze to death at temperatures approaching 0o C, and die of heat stroke above about 60o C. The range of permissible temperatures for bare skinned humans is therefore quite narrow. Polar bears, on the other hand, can live at temperatures well below freezing, and still live quite well at 37o C. So their range of permissible temperatures is different from ours.

With respect to this one parameter, the polar bear "niche" is different from ours.

Any two variables, such as temperature and pH, which can be measured, and a range established, will define a "space" (or set of values) within which a species can be found; i.e. its ecological niche.

Move outside this "space" and you will no longer find that species. You may find another species, but it's niche will be different. The more variables you are able to measure (e.g. pH range, temperature range, salinity range, etc.) the more multidimensional the "space" or niche becomes. This multidimensional space is sometimes called the fundamental niche of the species.

Niche Diversification
A fundamental principle of ecology is that no two species can occupy exactly the same niche within the environment.

This is called Gause's Principle, or the principle of competitive exclusion.

For example, if two species of microbe compete for a single source of food, the microbe with the more efficient absorption system will acquire most of the food, grow faster, reproduce faster, and eventually displace the microbe that absorbs food slower and thus cannot grow as fast.

Competition between species will be most intense if their needs are the same, they live in the same place, tolerate the same ranges of variables (temperature, pH, etc.) and have similar requirements. Eventually one species will win. The other will die out, and the niche will be occupied by a singe species again.

Under this kind of selection pressure, therefore, evolution tends to operate in such way as to minimize niche overlap. Species specialize in ways that limit their competition with other species. Different habitats are chosen, different tolerances evolve and different requirements mean that there is always something for everyone; peaceful co-existence is achieved.

Tools of the Trade
In this investigation you are going to find the ecological niches occupied by two or more microbes.

For each microbe you must determine the range of pH values at which it will grow (maximum and minimum), and the optimum pH at which it grows best.

Similarly, you must determine the range of temperatures (maximum and minimum) between which the same microbes will grow, and the temperature at which each of them grows the best (optimum temperature).

Using this data, you must then plot your results on a graph. On this graph, one axis is the range of pH values, and on the other axis the range of temperature values. In this way you will position each microbe in its own niche.

Once you have determined the niche values for several microbes, you will be able to determine if they are in competition, or far enough apart to avoid such competition. You will also be able to find out if they have a niche that is compatible with growing in Herr Druer's wine!

Recording Results

print out, and use this
Table of Results
to record your data

The results of each of your investigations should be recorded as a table (Presenting the Results). In this table you should indicate the names of the microbe being studied, the optimum temperature growth (as determined in a separate investigation), and the optimum pH for growth (as determined in a separate investigation).

The results of each investigation should also be presented as a graph.

The horizontal axis of the graph should be the intervals of the different temperatures at which the microbes grow best (optimum temperatures). The vertical axis should represent the pH values at which the various microbes grow best (optimum pH).

This is called a Niche.

The position of each species of microbe on this graph will show both its optimum temperature (where growth proceeds most rapidly), and the pH at which it grows best (optiumu pH). Outside these temperature and pH ranges all growth of the microbe stops. This is the niche of the microbe.

------ Investigate the effect of temperature.


Investigate the effect of pH. -------


Science at a Distance
© 2000, Professor John Blamire