180
than in the ocean, provides the simplest possible
example of a food chain as developed by
Lindeman ( 1942 ) on the basis of an Eltonian pyramid considered energetically.
The second type of aquatic food chain is found
in rivers and lakes, in which, there is a welldeveloped phytolittoral component. Propagules
form a relatively small part of the total productivity. Some direct grazing of fresh attached vegetation by herbivores may occur, but it seems as
though there is less of such feeding on rooted
macroscopic plants than would be expected. The
curious absence of sucking insects feeding on
higher plants, attributed by Hutchinson ( 1982 ) to
the low energetic cost that would be incurred by
any predator feeding on such insects under water,
is probably only one of the little-studied problems
of edibility raised by the trophic ecology of
inland waters.
9.6.3 Importance of Detritus
The various modes of feeding, namely, herbivory,
carnivory, detritivory and parasitism, are well
known in terrestrial, freshwater and marine environments. However, probably, more consumption
of detritus occurs in shallow FW than in any
other kind of habitat. A large amount of celluloses and lignins are produced on both land and
in shallow FW habitats. These two classes of
components are, probably, the most abundant
organic materials in the biosphere at any time.
However, celluloses are several times more plentiful as compared to lignins.
The changes which take place in any plant
material soaked in water are naturally complicated, depending upon the complexity of the
composition of the organic mixture being decomposed. When leaves die and fall or are blown into
water, an initial loss of material may take place
which might be different, if they had been
recently washed by rain and then dried on the
bank or had been immediately submerged.
Notwithstanding the above, the behaviour of
nitrogen might be attributed to two quite different
processes. One is the more rapid decomposition
of nonnitrogenous compounds relative to certain
very stable organic nitrogen compounds. Odum
et al. ( 1979 ) had suggested that the stable compounds are likely to be amino-sugar polymers,
such as chitin, resistant complexes of proteins
with lignin, chitin and phenols.
9.7
Insects at Play
Insects display plays of different types, like dancing and swarming. Each play is said to be aimed
at different types of purposes indicating distinct
social behaviour.
9.7.1 Mating Games
The reproductive system of aquatic insects is
comparable with and seemingly as elaborate as
those of fi sh. In water surface bugs, precopulatory defence is common. The males of the veliid
water strider ( Halovelia marianarum ) grasp
potential mates and may hold them for several
days before the female is receptive. In sminthurid
Collembola ( Sminthurides aquaticus ), the diminutive male grasps the female with its prehensile
antennae and may be carried about by the female
on the water surface for several days before the
female ready to oviposit (Schaller 1971 ). Among
the belostomatid water bugs, the females lay their
eggs on the backs of males. Combined clutches
of eggs from several females may be present
together on the back of one male (Smith 1980 ).
9.7.2 Surface Activity
The insect cuticle has hydrophobic properties.
This has enabled a number of groups, notably
the Collembola, heteropteran bugs and certain
families of Coleoptera to colonise the water surface. Here, they exploit a rich resource of organic
matter, mainly the insects and spiders which
generally become trapped at the air–water interface. The gyrinid (the wriggling beetles) are perhaps the most conspicuous among the
scavenger–predators. Their rapid circling, sometimes in large aggregations, on quiet waters is
9 Other Organisms in the Lakes
than in the ocean, provides the simplest possible
example of a food chain as developed by
Lindeman ( 1942 ) on the basis of an Eltonian pyramid considered energetically.
The second type of aquatic food chain is found
in rivers and lakes, in which, there is a welldeveloped phytolittoral component. Propagules
form a relatively small part of the total productivity. Some direct grazing of fresh attached vegetation by herbivores may occur, but it seems as
though there is less of such feeding on rooted
macroscopic plants than would be expected. The
curious absence of sucking insects feeding on
higher plants, attributed by Hutchinson ( 1982 ) to
the low energetic cost that would be incurred by
any predator feeding on such insects under water,
is probably only one of the little-studied problems
of edibility raised by the trophic ecology of
inland waters.
9.6.3 Importance of Detritus
The various modes of feeding, namely, herbivory,
carnivory, detritivory and parasitism, are well
known in terrestrial, freshwater and marine environments. However, probably, more consumption
of detritus occurs in shallow FW than in any
other kind of habitat. A large amount of celluloses and lignins are produced on both land and
in shallow FW habitats. These two classes of
components are, probably, the most abundant
organic materials in the biosphere at any time.
However, celluloses are several times more plentiful as compared to lignins.
The changes which take place in any plant
material soaked in water are naturally complicated, depending upon the complexity of the
composition of the organic mixture being decomposed. When leaves die and fall or are blown into
water, an initial loss of material may take place
which might be different, if they had been
recently washed by rain and then dried on the
bank or had been immediately submerged.
Notwithstanding the above, the behaviour of
nitrogen might be attributed to two quite different
processes. One is the more rapid decomposition
of nonnitrogenous compounds relative to certain
very stable organic nitrogen compounds. Odum
et al. ( 1979 ) had suggested that the stable compounds are likely to be amino-sugar polymers,
such as chitin, resistant complexes of proteins
with lignin, chitin and phenols.
9.7
Insects at Play
Insects display plays of different types, like dancing and swarming. Each play is said to be aimed
at different types of purposes indicating distinct
social behaviour.
9.7.1 Mating Games
The reproductive system of aquatic insects is
comparable with and seemingly as elaborate as
those of fi sh. In water surface bugs, precopulatory defence is common. The males of the veliid
water strider ( Halovelia marianarum ) grasp
potential mates and may hold them for several
days before the female is receptive. In sminthurid
Collembola ( Sminthurides aquaticus ), the diminutive male grasps the female with its prehensile
antennae and may be carried about by the female
on the water surface for several days before the
female ready to oviposit (Schaller 1971 ). Among
the belostomatid water bugs, the females lay their
eggs on the backs of males. Combined clutches
of eggs from several females may be present
together on the back of one male (Smith 1980 ).
9.7.2 Surface Activity
The insect cuticle has hydrophobic properties.
This has enabled a number of groups, notably
the Collembola, heteropteran bugs and certain
families of Coleoptera to colonise the water surface. Here, they exploit a rich resource of organic
matter, mainly the insects and spiders which
generally become trapped at the air–water interface. The gyrinid (the wriggling beetles) are perhaps the most conspicuous among the
scavenger–predators. Their rapid circling, sometimes in large aggregations, on quiet waters is
9 Other Organisms in the Lakes