It is possible to call a surface of a pond, the river, a pool and any other reservoir a unique ecological niche safely. The fact is that two absolutely different environments for dwelling of living organisms – water and air are concentrated on a surface of these reservoirs.
It is a little physics
Before opening a secret of water measures, it is necessary to remember some elements of physical properties of water. It is known that air and water environments are divided among themselves by a special film of a superficial tension. On border of two phases of force of an attraction, the waters arising between molecules, are not counterbalanced, i.e. the sum of forces which I act down appears many times more, than the sum of forces operating up. Thanks to it water density on a surface of a reservoir turns out slightly higher, than in the main water layer.
But there is more to come! The molecules aspiring down lead to emergence of a peculiar elastic membrane which is capable to support on a water surface objects by density above it. However there is one condition: these objects have to be dry. If to moisten them, then they will independently attract to themselves water molecules that will break structure of a superficial film.
It is curious that these surprising physical properties of a water film use various live organisms in the purposes. It is worth passing from physics to zoology. It is known that life on border of two habitats differs in very noticeable advantage. The most famous inhabitants of surfaces of reservoirs are, of course, water measures.
Who such water measures?
These are small insects from group of semi-coleoptera. In other words, it is bugs. As well as their relatives, water measures are equipped with the kolyushche-sucking oral device (proboscis) which allows to enter the special substances which are paralyzing and decomposing it fabrics into a body of the production. It is necessary to exhaust ready "broth" from the victim. Water measures are predatory creations. As their main food serve the insects who accidentally fell to a water surface. If future lunch is rather big by the sizes, then several water measures can regale on it at once. Nevertheless, these creations prefer to hunt and be fed alone.
How does the water measure keep on water?
This simple ability of water measures is explained by the above physical properties of water. To all fault so-called force of a superficial tension. If briefly to retell an essence of this "focus", then the following will turn out: in an interface between air and thickness of water there are water molecules which from below (from depth) force, several times big, than from above affects. Because of it on a water surface a certain thinnest membrane is formed. That's it it also holds a water measure which with pleasure conducts the activity.