4
factors which are required to defi ne a habitat
could be ordered manually on the axes of
n -dimensional coordinate systems (Hutchinson
1957 ). In brief, the term niche is used in an
abstract and purely intensive sense to designate
the requirements of an organism abstracted from
the specially extended habitat. The habitats of
two species may overlap completely; it is empirically probable that, at equilibrium, their niches
never do.
1.6.6 Strata and Zones
Each lake is regarded as an ecosystem which
could be divided horizontally into strata and
along the bottom into zones . In other words, in
limnology, as it leaves the shore and approaches
the centre of the lake along the bottom, we pass
over a number of zones which represent intersection of strata with the bottom.
1.6.7 The Lacustrine Biocoenosis
A number of detailed attempts had been made to
treat the biota of a lake as composed of an assemblage of species of different life forms within the
biocoenosis. The most ambitious of these is due
to Gams ( 1918 ), who had provided a classifi cation of life forms suitable for all organisms. The
basic distinction in this classifi cation is whether
the organism is adnate or attached to a surface,
rooted in a solid medium or free. The three
assemblages are termed, respectively, as (a) ephaptomenon, (b) rhizomenon and (c) planomenon.
As far as aquatic forms are concerned, the ephaptomenon consists of the plants which Warming
( 1895 ) called ‘nereids’, together with equivalent
sessile animals. The rhizomenon consists of the
ordinary rooted higher vegetation. The planomenon, or the free forms which Gams ( 1918 ) had
distinguished as ‘plankton’, drifting in water,
‘pleuston’ at the surface; ‘edaphon’ in the interstitial water of soils; and ‘tacheion’, actively
moving organism, all are divided into subclasses,
the aquatic tacheion comprising the crawling
organism or ‘herpon’ and the swimming organisms or ‘nekton’.
Warming ( 1923 ) had produced a modifi ed
scheme solely for plants, in which the aquatic
forms are divided into free forms, or ‘planophyton’, which constitutes the ‘plankton’ and ‘pleuston’, and attached forms or ‘benthos’. The
‘benthos’ is further classifi ed into ‘herpobenthos’
(to include BGA and diatoms in the top layer of
soft sediments), ‘rhizobenthos’ (to include the
rooted vegetation), ‘haptobenthos’ (to include the
‘epilithon’ and ‘epiphyton’ attached to the solid
surfaces) and ‘endobenthos’ (to include the
boring algae).
The schemes of both Gams and Warming had
much to recommend them, but they had not been
greatly used by other investigators.
Concomitant to above, Naumann ( 1917 )
emphasised what seemed to be a sounder
approach, namely, to classify the lake biocoenosis into those forms associated solely with the
liquid medium, those forms associated with the
lower, solid–liquid interface and those associated
with the liquid–gas interface.
When in dealing with motile but still small
forms partly controlled in their behaviour by gentle water movements, it is desired to emphasise
this aspect of such organisms, the term ‘nektoplankton’ may be used.
1.6.8 Plankton, Seston and Tripton
Hensen’s ( 1887 ) original defi nition of plankton
included all particulate organogenic material, living or dead, passively drifting in the water. Later
workers had refi ned this concept and had inevitably added to the terms used in describing such as
assemblage of particulate matter. For both technical and theoretical reasons, it is often desirable to
consider together all the particulate material
present in the free water. This collectively is
termed ‘seston’ (Kolkwitz 1912 ). The seston consists of ‘bioseston’ or ‘plankton’ and ‘nekton’,
which the latter is ordinarily quantitatively negligible, and of ‘abioseston’ or ‘tripton’ (Wilhelmi
1917 ). Further, the ‘tripton’ may be of autochthonous or allochthonous origin, termed ‘eutripton’
and ‘pseudotripton’, respectively.
The term ‘nannoplankton’ was originally coined
to include everything not retained by a tow net
1 Introduction
factors which are required to defi ne a habitat
could be ordered manually on the axes of
n -dimensional coordinate systems (Hutchinson
1957 ). In brief, the term niche is used in an
abstract and purely intensive sense to designate
the requirements of an organism abstracted from
the specially extended habitat. The habitats of
two species may overlap completely; it is empirically probable that, at equilibrium, their niches
never do.
1.6.6 Strata and Zones
Each lake is regarded as an ecosystem which
could be divided horizontally into strata and
along the bottom into zones . In other words, in
limnology, as it leaves the shore and approaches
the centre of the lake along the bottom, we pass
over a number of zones which represent intersection of strata with the bottom.
1.6.7 The Lacustrine Biocoenosis
A number of detailed attempts had been made to
treat the biota of a lake as composed of an assemblage of species of different life forms within the
biocoenosis. The most ambitious of these is due
to Gams ( 1918 ), who had provided a classifi cation of life forms suitable for all organisms. The
basic distinction in this classifi cation is whether
the organism is adnate or attached to a surface,
rooted in a solid medium or free. The three
assemblages are termed, respectively, as (a) ephaptomenon, (b) rhizomenon and (c) planomenon.
As far as aquatic forms are concerned, the ephaptomenon consists of the plants which Warming
( 1895 ) called ‘nereids’, together with equivalent
sessile animals. The rhizomenon consists of the
ordinary rooted higher vegetation. The planomenon, or the free forms which Gams ( 1918 ) had
distinguished as ‘plankton’, drifting in water,
‘pleuston’ at the surface; ‘edaphon’ in the interstitial water of soils; and ‘tacheion’, actively
moving organism, all are divided into subclasses,
the aquatic tacheion comprising the crawling
organism or ‘herpon’ and the swimming organisms or ‘nekton’.
Warming ( 1923 ) had produced a modifi ed
scheme solely for plants, in which the aquatic
forms are divided into free forms, or ‘planophyton’, which constitutes the ‘plankton’ and ‘pleuston’, and attached forms or ‘benthos’. The
‘benthos’ is further classifi ed into ‘herpobenthos’
(to include BGA and diatoms in the top layer of
soft sediments), ‘rhizobenthos’ (to include the
rooted vegetation), ‘haptobenthos’ (to include the
‘epilithon’ and ‘epiphyton’ attached to the solid
surfaces) and ‘endobenthos’ (to include the
boring algae).
The schemes of both Gams and Warming had
much to recommend them, but they had not been
greatly used by other investigators.
Concomitant to above, Naumann ( 1917 )
emphasised what seemed to be a sounder
approach, namely, to classify the lake biocoenosis into those forms associated solely with the
liquid medium, those forms associated with the
lower, solid–liquid interface and those associated
with the liquid–gas interface.
When in dealing with motile but still small
forms partly controlled in their behaviour by gentle water movements, it is desired to emphasise
this aspect of such organisms, the term ‘nektoplankton’ may be used.
1.6.8 Plankton, Seston and Tripton
Hensen’s ( 1887 ) original defi nition of plankton
included all particulate organogenic material, living or dead, passively drifting in the water. Later
workers had refi ned this concept and had inevitably added to the terms used in describing such as
assemblage of particulate matter. For both technical and theoretical reasons, it is often desirable to
consider together all the particulate material
present in the free water. This collectively is
termed ‘seston’ (Kolkwitz 1912 ). The seston consists of ‘bioseston’ or ‘plankton’ and ‘nekton’,
which the latter is ordinarily quantitatively negligible, and of ‘abioseston’ or ‘tripton’ (Wilhelmi
1917 ). Further, the ‘tripton’ may be of autochthonous or allochthonous origin, termed ‘eutripton’
and ‘pseudotripton’, respectively.
The term ‘nannoplankton’ was originally coined
to include everything not retained by a tow net
1 Introduction