32
forest, while the scrappers (Elmidae, Dryopidae) and predators
(Rhyacophilidae, Agrionidae) the pine–oak forest. Trichoptera is abundant
in the forest as well as forest–agriculture land use. They functioned as
shredders, collectors and gatherers in the former, whereas collectors, gatherers, fi lterers in the forest–agriculture land use. Scrapers (mainly
Ephemeroptera) occurred in very low percentage in the forest–agriculture
land use. Slope is observed to be an important environmental variable
infl uencing taxonomic composition and distribution of caddisfl y with case
(Limnephilidae, Leptoceridae, Philopotamidae) along with mayfl y
(Leptophlebiidae, Baetidae) and stonefl y (Perlodidae). As slope is a
manifestation of altitude, it indirectly indicates the role of altitude and
hence the forest.
Keywords
Forest type • Himalaya • Ordination techniques • Slope • Trichoptera
Introduction
Odum ( 1996 ) classifi ed organisms in water
according to their life form or life habit based on
their mode of life into the following:
1. Periphyton or Aufwuchs, the organisms (both
plant and animals) attached or clinging to
streams and leaves of rooted plants or other
surface projecting above the bottom.
2. Plankton, the free-fl oating microscopic organisms of plant or animal origin, which remain
at the mercy of the current and associated with
water–water interface.
3. Benthos, the fl oral or faunal components that
dwell on the bottom or in the bottom sediments of the stream and are associated with
solid–water interface.
4. Neuston, the organisms associated with air–
water interface and resting or swimming on
the surface of water.
5. Nekton, the fauna associated with water–
water interface capable of performing active
locomotion as they have powerful locomotory
organs (e.g. fi shes).
The rivers are characterised by their unidirectional fl ow and thoroughly mixed waters (Patrick
1948 ). Cooper et al. ( 1998 ) state that streams are
characterised by a unidirectional fl ow, and solutes, detritus, sediments and organisms are constantly delivered from upstream to downstream
areas. Odum ( 1996 ) is of the view that current
velocity is the major limiting factor in the lotic
environment. Thus streams generally exhibit two
major communities, rapids and pools; within
these broad categories the type of bottom whether
sand, pebbles, clay and bedrock determines the
nature of the communities and the population
density of community dominants. The biota of a
river channel resembles that of the rapids, except
the population distribution is highly “clumped”
owing to the frequent absence of fi rm substrates.
The feeding relationships and other interactions form a complex whole often referred to as
the biological community. Community is usually
applied to a group of populations that occur
together, but there ends any similarity among
defi nitions. Ecologists also defi ne communities
on the basis of interactions among associated
populations. This is a functional rather than
descriptive use of the term. Community itself is
a wide term with various meanings, but essentially it is used to denote a collection of species,
living together, and usually linked to a particular
habitat. Kendeigh ( 1980 ) considered community
or biocenose as an aggregate of organisms,
which form a distinct ecological unit. Association
P. Nautiyal et al.
forest, while the scrappers (Elmidae, Dryopidae) and predators
(Rhyacophilidae, Agrionidae) the pine–oak forest. Trichoptera is abundant
in the forest as well as forest–agriculture land use. They functioned as
shredders, collectors and gatherers in the former, whereas collectors, gatherers, fi lterers in the forest–agriculture land use. Scrapers (mainly
Ephemeroptera) occurred in very low percentage in the forest–agriculture
land use. Slope is observed to be an important environmental variable
infl uencing taxonomic composition and distribution of caddisfl y with case
(Limnephilidae, Leptoceridae, Philopotamidae) along with mayfl y
(Leptophlebiidae, Baetidae) and stonefl y (Perlodidae). As slope is a
manifestation of altitude, it indirectly indicates the role of altitude and
hence the forest.
Keywords
Forest type • Himalaya • Ordination techniques • Slope • Trichoptera
Introduction
Odum ( 1996 ) classifi ed organisms in water
according to their life form or life habit based on
their mode of life into the following:
1. Periphyton or Aufwuchs, the organisms (both
plant and animals) attached or clinging to
streams and leaves of rooted plants or other
surface projecting above the bottom.
2. Plankton, the free-fl oating microscopic organisms of plant or animal origin, which remain
at the mercy of the current and associated with
water–water interface.
3. Benthos, the fl oral or faunal components that
dwell on the bottom or in the bottom sediments of the stream and are associated with
solid–water interface.
4. Neuston, the organisms associated with air–
water interface and resting or swimming on
the surface of water.
5. Nekton, the fauna associated with water–
water interface capable of performing active
locomotion as they have powerful locomotory
organs (e.g. fi shes).
The rivers are characterised by their unidirectional fl ow and thoroughly mixed waters (Patrick
1948 ). Cooper et al. ( 1998 ) state that streams are
characterised by a unidirectional fl ow, and solutes, detritus, sediments and organisms are constantly delivered from upstream to downstream
areas. Odum ( 1996 ) is of the view that current
velocity is the major limiting factor in the lotic
environment. Thus streams generally exhibit two
major communities, rapids and pools; within
these broad categories the type of bottom whether
sand, pebbles, clay and bedrock determines the
nature of the communities and the population
density of community dominants. The biota of a
river channel resembles that of the rapids, except
the population distribution is highly “clumped”
owing to the frequent absence of fi rm substrates.
The feeding relationships and other interactions form a complex whole often referred to as
the biological community. Community is usually
applied to a group of populations that occur
together, but there ends any similarity among
defi nitions. Ecologists also defi ne communities
on the basis of interactions among associated
populations. This is a functional rather than
descriptive use of the term. Community itself is
a wide term with various meanings, but essentially it is used to denote a collection of species,
living together, and usually linked to a particular
habitat. Kendeigh ( 1980 ) considered community
or biocenose as an aggregate of organisms,
which form a distinct ecological unit. Association
P. Nautiyal et al.