Research Articles

1. Community Composition and Biomonitoring Potential of Hill Stream Insects of the Western Ghats

2. Western Ghats Aquatic Biodiversity.

Community Composition and Biomonitoring Potential of Hill Stream Insects of the Western Ghats
Centre for Ecological Sciences,
Indian Institute of Science, Bangalore-12

Current Address:

National Centre for Biological Sciences,
GKVK Campus, Bangalore-65


Inland waters comprise a small fraction of world’s water resource. Despite this, inland aquatic habitats show far more variety in their physical and chemical characteristics than marine habitats and contain a disproportionately high fraction of the world’s biodiversity. Animal species are far more diverse and numerous in the inland waters than plants. Apart from fishes, invertebrates form an important group. As on land, insects (Phylum: Mandibulata) are the most diverse group of organisms in inland waters (WCMC, 2000).

Aquatic insects of running waters, comprising some well-known groups like mayflies, dragonflies and caddisflies are important group of organisms in the stream ecosystem function. Different functional group of aquatic insects such as shredders, scrapers, filter feeders and predators are important links in nutrient recycling in forest streams. Aquatic insects primarily process wood and leaf litter reaching the stream from the surrounding vegetation. Nutrients processed by aquatic insects of stream are further degraded into absorbable form by fungal and bacterial action. Aquatic insects are also a primary source of food for fishes (Merritt et al., 1984 & Wallace and Jackson, 1996).

In addition to this significant ecosystem function, aquatic insects are very good indicators of human impact on the fresh water ecosystem. Biological monitoring methods using aquatic insects have been developed and reliably tested in both temperate and tropical aquatic systems (Resh 1979, Armitage et al., 1983, Trivedi, 1991,  Sivaramakrishnan et al., 1996a).

The Western Ghats of Peninsular India along with Srilanka is recognized as one of the 25-biodiversity hotspots of the world (Myers et. al, 2000).  The Western Ghats is also well known for its high diversity of angiosperms, amphibians and freshwater fishes.  Invertebrates, especially insects, which form the bulk of the diversity, are poorly known from the region, except for butterflies (Daniels, 2002). Earlier studies on aquatic insects of the region were cursory and restricted to very few localities. The present study conducted across the entire length of the Western Ghats tries to address the distribution and diversity of stream insect communities at different spatial scales.  The study also tries to evaluate and prioritize the riverine ecosystems at various spatial scales for conservation using aquatic insects.


  1. To study the distribution and diversity patterns of stream insect communities at the scale of (1) latitude (2) altitude (3) stream order (4) habitat and (5) microhabitat.
  2. To study the impact of catchment landuse on the composition and community structure of stream insects.
  3. To evolve a biomonitoring methodology using aquatic insects for riverine ecosystems of the Western Ghats.
  4. To identify and prioritize habitats and regions for conserving riverine biodiversity.

The above questions were addressed by looking at the diversity and distribution of aquatic insect communities at two scales in the Western Ghats. To address questions at a regional scale (objectives i, iii and iv), aquatic insect samples collected across 39 localities in the Western Ghats is used. Questions related to local scale (objectives i & ii) are addressed by samples collected from the Swarna and Bhadra drainage basin at Kudremukh National Park (Maps 1&2).


Aquatic insect communities were sampled from hill streams of 39 sites located between 8°N to 20°N of Western Ghats during August 1999 to February 2002.  The community was sampled from three major riverine habitats: runs, riffles and pools (Plate-1). The insects were collected using kicknets, pond nets and by all out search method. Collected specimens were preserved in 70% alcohol in the field and brought back to lab for identification. In addition to biological sampling, 16 environmental variables such as stream depth, width, pH, temperature, substrate type, canopy cover etc. were also collected for each sample. Samples were assigned to family and genus using keys for that particular group. Following keys were used for identification: Ephemeroptera (Dudgeon, 1999; Sivaramakrishan, unpublished); Odonata, Plecoptera, Hemiptera, Megaloptera, Coleoptera, Diptera and Lepidoptera (Fraser, 1933-36;Morse et al., 1994; Dudgeon, 1999); Hemiptera (Thirumalai 1989,1999; Morse et al., 1994), Trichoptera (Wiggins, 1975, 1996). The distribution and diversity of aquatic insects were looked at the spatial scales of: latitude, altitude, stream order, habitat and microhabitat. In addition to this, the impact of riparian landuse on the diversity and distribution of aquatic insects were also investigated. Biomonitoring scores and conservation value for each genus was derived based on the current knowledge on the distribution and diversity of that particular taxon (Dudgeon, 1999).


A total of 15, 260 individuals belonging to 12 order, 59 families and 94 genera were collected in 293 sampling sessions from 39 localities in the Western Ghats. Of these 14,824 individuals were assigned to genus, 406 to families and remaining 30 to orders.  The rarefied generic and family richness decreased significantly with increasing latitude (Fig-1). The aquatic insect family and generic richness decreased significantly with increasing number of dry months (Fig-2) and it had no significant relation with the average annual rainfall. Cluster analysis shows that there are two distinct communities north and south of 15°N (Fig-3). Interestingly this corresponds to two geological formations of the Western Ghats viz. Deccan Trap and Precambrian. At the scale of altitude, the generic, family and functional group richness decreases significantly with increasing altitude (Fig-4). Aquatic insect faunal and functional group composition changes along the stream order and habitat. Highest generic richness was observed in the second order streams and in runs (Fig-5). The family and generic richness was significantly positively correlated with microhabitat richness.

Of the 94 genera, 60 (64%) were restricted to less than four microhabitats and remaining were occupying four or more microhabitats (Fig-6). Maximum generic richness was observed among cobbles for runs and riffles; bedrock harbored maximum richness in pools. Riparian zone with natural vegetation had higher family, generic and guild richness than human modified ones within the same catchment (Fig-7). Family and generic composition changes with riparian landuse and widespread taxa with pollution tolerance dominated streams with human influenced catchments.

(Fig-8). Sites north of 14°N had lowest and sites between 8°N-12°N had intermediate scores and conservation values. The low altitude (1-200m) sites ranked high both in terms of biomonitoring scores and conservation values than the high altitude ones (1000-2400m). At the scale of stream order and habitat, the second order streams and runs had highest biomonitoring scores and conservation values. Biomonitoring scores and conservation values of streams reflected the riparian landuse (Table-1). Streams with natural riparian cover had higher biomonitoring scores and conservation value.


Like other taxa such as angiosperms and butterflies, aquatic insect generic and family richness decreases towards northern latitude and shows a strong decreasing trend with increasing number of dry months in the Western Ghats.  Similar pattern is also observed for other aquatic organisms such as amphibians (Daniels, 1992). Similarly, low diversity of aquatic insects in high altitude streams is also observed (Suren, 1994). However, the high and low altitude streams harbour different sets of species.  The high altitude streams are characterized by Palaearctic genera such as Rhyacophila and Polycentropus.  The typical Oriental genera such as Rheonathus and Stenopsyche are restricted to low altitude streams.  Family and generic composition changes with increasing stream order. The low order streams are dominated by genera such as Glossosoma, Teloganodes, Epeorus and Petersula, which have morphological adaptations to cling to substratum in fast flowing streams.  On the other hand, burrowing families such as Libellulidae and Tabanidae dominate the higher order streams. The generic and family richness is highest in the second order streams. Similar patterns have also been reported from temperate streams (Vannote et al., 1980). This poverty in higher order streams is probably due to decrease in available substrate heterogeneity and canopy opening. The poor substrate richness allows only few species to colonize in wider streams and streams with open canopy or less riparian vegetation receive less organic inputs, which is a major source of nutrition for the aquatic insects. At the scale of habitats, runs, riffles and pools have different set of genera. For example, the aquatic bugs (Hemiptera) and beetles with a mode of life on water surface dominate stream pools.  Genera such as Rhagovelia, Amemboa, Metrocoris, Cylindrostethus and Dineutus represent the fauna of a typical stream pool.

High diversity of family and genera with increasing diversity of microhabitat is very well known in temperate streams (Hynes, 1970; Rabeni and Minshall 1977;Allan, 1995). Similar pattern was also observed for all the three habitats viz. runs, riffles and pools. Within a habitat, the high diversity was restricted to microhabitats, which give maximum seclusion and access to food source. For example, in runs and riffles highest diversity was among cobbles and trapped litter. The influence of catchment landuse on the stream insect communities was hitherto unknown from the tropics. The present study addresses this question, which have important implications for developing a biomonitoring tool. High family and generic richness was clearly confined to less disturbed areas in the upper catchment. Families such as Leptophlebiidae, Heptageniidae, Ephemereliidae, Perlidae, Calopterygidae, Euphidae, Naucoridae, Helicopsychidae and Glossosomatidae dominate the natural stream community.  The streams flowing through human impacted areas such as paddy fields and mines were poor in family and genera. The dominant families of the community are Baetidae, Libellulidae, Psephinidae, Dytiscidae, Hydropsychidae and Simulidae.  These families are tolerant to aquatic pollution. Absence of pollution-sensitive families of aquatic insects and low biomonitoring scores indicate the poor quality of the water flowing through human impacted area.

Composite Conservation Value (CCV) developed for Indian birds were adopted to develop CCV for aquatic insect genera. Using this, riverine ecosystems were assessed for conservation at various spatial scales. It is interesting to note that rivers flowing through the central Western Ghats have (13°N-15°N) highest conservation value. This may be due to the presence of more rivers without impoundment than in northern or southern Western Ghats. However, this pattern needs to be corroborated with other taxa such as freshwater fishes.

Summary and Synthesis

Of the factors examined, the length of the dry season, altitude, stream order, microhabitat richness and the riparian landuse influenced stream insect diversity.  The species richness at a habitat is a result of interplay between factors acting locally and regionally. The biogeographic evolution, historical immigration and climatic factors determine the regional taxon pool. Within a region, the factors such as altitude, microhabitat richness and riparian landuse play an important role in influencing taxa composition and richness. It is evident from the study that, the stream insects are very good indicators of the health of the riverine ecosystem and could be incorporated into the environmental impact assessment protocols.  However, some basic questions need to be immediately addressed to fully understand and appreciate the role of stream insects in the ecosystem functioning. First and the foremost, the taxonomy of the stream insects of the Western Ghats is poorly known. A concentrated effort is required to fill this gap and need to update with the recent international taxonomic revisions. The process oriented experimental studies needs to be given immediate attention to understand the role of the stream insects in the nutrient dynamics.  Moreover, the importance of other macroinvertebrates in the stream ecosystem function is little known from the region that is essential for understanding the nutrient dynamics.  Future investigations should focus on the whole macroinvertebrate communities of the streams and studies should extend to full river stretches. This will create baseline information for identifying and conserving riverine ecosystems of the region.

Subramanian in Field:


This work was carried out during author’s tenure at CES, IISc between 1999-2003. Students and teachers of the Western Ghats Biodiversity Network were the inspiring force behind this study and assisted me in the field. The forest departments of Maharastra, Goa, Karnataka, Kerala and Tamil Nadu were cooperative and helpful. I also thank my friends and former colleagues at CES for valuable suggestions and constant encouragement during the study.


Map-1: The map of the Western Ghats.  The study sites are shown as red spots.


Map-2: Sampling localities at Kudremukh National Park



Fig.1. Rarefied generic richness across latitude

Fig.2. Generic Richness and number of dry months

Fig:3. Dendrogram showing similarity in Ephemeroptera genera composition across latitude


Fig.4. Generic Richness Across altitude at Kudremukh

Fig.5: Generic richness of across stream orders

Fig.6: Frequency distribution of genera across microhabitat

Fig.7: Generic richness across landscape elements types

Fig.8: Composite Conservation Values across latitudes

Table-1: BMWP and BMWP-ASPT across LSE types  


LSE Types




















































Legend: EVG-Evergreen; MDF- Moist Deciduous Forests; SEVG-Semievergreen; HAB- Habitation; ARE-Arecanut garden; SCR-Scrub; FOR-Forestry Plantations; PAD-Paddy; GSL- Grasslands; SHOL-Shola; DDF: Dry deciduous forests;MINE- Mine

BMWP: Biomonitoring working party score system.

ASPT: Average score per taxon


Western Ghats Aquatic Biodiversity
Ahalya N. and Ramachandra T.V.
Energy & Wetlands Research Group, Centre for Ecological Sciences, Indian Institute of Science, Bangalore 560 012

Western Ghats is a mountain chain running north-south and parallel to the west coast of India. The hill chain is 1600 km long and between 5 and 150 km wide, separated from the coast by a low land strip usually 40 - 60 Km wide. The Western Ghats traverse 6 south Indian states viz., Gujarat, Maharashtra, Goa, Karnataka, Tamilnadu and Kerala. The area experiences an average annual rainfall of 2500 mm. Depending upon the geographical location and topography, rainfall is locally much higher crossing 10,000 mm a year. Forests cover nearly one - fourth of the total area in Western Ghats and give rise to east flowing rivers that form the water source for the entire peninsular India. The Western Ghats is the catchment of 3 large, 13 medium and 17 minor rivers of the peninsular India.

The Western Ghats have an ancient history. The past 12,000-5,000 years have seen a lot of changes in terms of the magnitude and distribution of biodiversity due to settled agriculture and extensive transformation of habitats in and around the Western Ghats (Subash Chandran, 1997). What is present today is the testimony to the human interference in the area. It is estimated that 12, 450 km2 of natural forest cover exist in the Western Ghats, which is about 6.8 % of the original forest cover. Irrigation and hydroelectric power projects, timber operations and agriculture expansion are the major reasons for the decline in forest cover.

The once continuous tropical rainforests in the Western Ghats have been modified into heterogeneous mosaic of evergreen, semi-evergreen and moist deciduous formations. Though the Western Ghats have undergone changes, they still harbor an exceptionally high magnitude of biodiversity and provide immense ecosystem services.

The estimated number of species of microorganisms, plants and animals in the Western Ghats is in the range of 10,000-15,000. Roughly 40% of these could be endemic ( The magnitude of diversity coupled with the anthropogenic threats has made Western Ghats one of the biodiversity hotspots.

(Biodiversity is the variety and differences among living organisms from all sources, including terrestrial, marine, and other aquatic ecosystems and the ecological complexes of which they are a part.

India is one of the mega biodiversity centres in the world and has two of the world's 25'biodiversity hotspots' located in the Western Ghats and in the Eastern Himalayas)

Forest clearing and human encroachment remain the biggest threats to this regions natural habitat and biodiversity. Large areas have already been converted into rubber, tea, and coffee plantations. Because of extensive forest fragmentation, it may not be possible to create additional large protected areas without extensive restoration.

The dense human population led to a change in conservation status from endangered to critical. This physical alteration, habitat destruction and creation of new dams and reservoir has caused a decline in the aquatic biodiversity in the Western Ghats. Apart from the decline in invertebrate and fish population in the streams of the Western Ghats, other vertebrates like amphibians, reptiles, birds and mammals are also affected by deterioration of freshwater systems (Subramanian, 2003).

There are around 218 species of primary and secondary freshwater fishes in the Western Ghats. 53% of all fish species (116 species in 51 genera) in the Western Ghats are endemic (Talwar and Jhingran, 1991; Jayaram, 1999; Menon, 1999; Daniels, 2001a.).

Freshwater fishes of the Western Ghats have economic value as food and ornamental fish. Gopalakrishnan and Ponnaiah have listed at least 100 species, many of which are endemic, as having potential economic value. Such species belong to the genera Tor, Neolissochilus, Gonoproktopterus, Hypselobarbus, Labeo, Barbodes, Osteocheilus, Horabagrus, Mystus, Ompok, Silurus, Wallago, Clarias, Channa, all of which are considered as food and sport fishes and in the genera Puntius, Danio, Rasbora, Barilius, Chela, Bhavania, Homaloptera, Travancoria, Balitora, Nemacheilus, Garra, Glyptothorax, Pristolepis, Aplocheilus, Tetradon, Macropodus, Etroplus, etc., are of potential ornamental value (Daniels and Ouseph, unpublished; Gopalkrishnan and Ponniah, unpublished).(

One hundred and twenty one species of amphibians are known from the Western Ghats (Daniels, 1992). Of these, 94 species are endemic (Daniels, 1992, 1993 & 1997c; Dutta 1997). Few studies have specifically focused on habitat use by amphibians. In the early 1990s, Daniels (1991) highlighted the role of habitat destruction in the loss of amphibians in the Western Ghats. At very local scales it has been observed that amphibian species richness is determined by the proximity to water - most species tending to aggregate closer to a source of water (Vasudevan et al, 2001). 157 species of reptiles including a species of crocodile Crocodylus palustris is known from the Western Ghats, majority being snakes. 97 species, representing 36 genera (2 genera of turtles/tortoises, 14 lizard genera and 20 genera of snakes) of all reptiles in the Western Ghats are endemic (Table 1). Endemism is highest amongst snakes, especially with the family Uropeltidae alone contributing 33 species. Amongst lizards, dwarf geckoes (Cnemaspis spp) and skinks (Ristella, Lygosoma, Mabuya and Scincella) have the maximum number of endemic species.

Table 1: Taxonomic breakup of reptilian diversity in the Western Ghats


No. of species

Endemic species
















Source: Whitaker (1978); Das (1985 & 1997); Murthy (1985 & 1990).

With regard to freshwater invertebrates in the Western Ghats, the species level inventories have been lacking.  But an exception to this is Odonata (Dragonflies and Damselflies). Out of the 176 species of Odonates in Western Ghats, 67 i.e., 38% are endemic (Subramanian K.A). Stream insects belonging to 13 orders, 53 families and 80 genera have been collected. Families such as isonychidae (Ephemeoptera: Mayflies) and blephariceridae (Diptera: Netwinged midges) known to be present in the cold streams of the Himalayas were collected for the first time in the Western Ghats. A preliminary study by Madhyastha has suggested that Silent Valley and many other well preserved parts of the Western Ghats may well support over a 100 species of molluscs locally (

The principal causes for the loss in biodiversity is anthropogenic. The direct impacts are due to collection, harvest and poaching and indirectly through habitat destruction. The loss of aquatic biodiversity would be attributed to change of flow, depth and turbidity in aquatic habitats, opening of canopy (often due to selective logging) in the catchment area, overuse of pesticides ands fertilisers, etc.


Subramanian K.A, (2003). Strean Insect Communities of Western Ghats and their Bioindicator Potential. (Thesis submitted to Madurai Kmaraj University)