Orthopteroids in KazirangaNational Park, Assam, India
N. Senthilkumar
Rain Forest Research Institute, P.O. Box No. 136, A.T. Road
(East), Jorhat, Assam 785 001, India
Present Address: Institute of Forest Genetics and Tree Breeding,
Coimbatore, Tamilnadu, India
Email: senthilnk@icfre.org
Date of publication (online): 26 September 2010
Date of
publication (print): 26 September 2010
ISSN
0974-7907 (online) | 0974-7893 (print)
Editor: Nitin Kulkarni
Manuscript details:
Ms # o2437
Received 07 April 2010
Final received 16 August 2010
Finally accepted 23 August 2010
Citation: Senthilkumar,
N. (2010). Orthopteroids in Kaziranga National Park, Assam,
India. Journal of Threatened Taxa 2(10): 1227-1231.
Copyright: © N. Senthilkumar2010. Creative Commons Attribution 3.0 UnportedLicense. JoTT allows unrestricted use of this article
in any medium for non-profit purposes, reproduction and distribution by
providing adequate credit to the authors and the source of publication.
Acknowledgements: Author is grateful to the Ministry of Environment and Forests,
Govt. of India for the financial support through the project No.
14/25/2005-ESR/RE dt.25.08.2006, the Director, RFRI, Jorhatfor facilities and the Forest Department, Assam State for permission to work in
the Sanctuary.
Abstract: Thirty-six species of orthopteroids belonging to 30 genera, and four families were
recorded in different habitats viz., forestlands, savannahs and grasslands of
the Kaziranga National Park (KNP) at Assam. The observations were recorded during the
period of three years from January 2007 to December 2009, by periodical monthly
visits to Kohora range (central range), Baguri range (western range) and Agoratolirange (eastern range) based on the habitat types selected. The family Acrididaehad the largest species representation (19 species) followed by Tettigoniidae (nine species)
and Mantidae (five species) while Gryllidae was represented by three
species only. None of the species found
in the study area are known to be threatened under any category of IUCN, 2010.
Key words: Acrididae,
Biodiversity, Gryllidae, Mantidae,Orthoptera, Tettigoniidae.
For figures & table -- click here
The KazirangaNational Park (KNP), over an area of 430km2 and bounded by the Mikir Hills on the south and the BrahmputraRiver on the north lies between 26030’-26045’N & 93008’-93036’E
within two districts - Nagaon and Golaghat,
in the Indian state of Assam. The KNP is
approximately 40km from east to west, and 13km from north to south with
elevation ranging from 40 to 80 m above sea level. Average temperature
ranges from 5 to 37 0C and average humidity ranges
between 65% and 95%. Rainy season is May
to October, and the annual rainfall is about 2500mm.
The four main types of vegetation,
alluvial inundated grasslands, alluvial savanna woodlands, tropical moist mixed
deciduous forests, and tropical semi-evergreen forests exist in the park. There is a decline in altitude from the east
to west. The western reaches are dominated by grasslands. Tall elephant grass is found on higher
ground, while short grasses cover the lower grounds. Common tall grasses are spear grass, elephant
grass, and the common reed. Numerous
forbs are present along with the grasses. Amidst the grasses, providing cover
and shade are scattered trees-dominant species including Kumbhi,
Indian Gooseberry, The Cotton Tree (in savanna woodlands), and Elephant Apple
(in inundated grasslands). Thick
evergreen forests have trees of Aphanamixis polystachya, Talauma hodgsonii, Dillenia indica, Garcinia tinctoria, Ficus rumphii, Cinnamomum bejolghota, and species of Syzygium. Tropical semi-evergreen forests have Albizia procera, Duabanga grandiflora,
Lagerstroemia speciosa, Crateva unilocularis, Sterculia urens, Grewia serrulata,Mallotus philippensis, Bridelia retusa, Aphania rubra, Leea indica, and Leea umbraculifera. An invasive species, Mimosa invisa, which is toxic to herbivores is found in the park (UNEP-WCMC, 2009).
The KNP, home to the world’s
largest population of the Great Indian One-Horned Rhinoceros, Wild Asiatic
Water Buffalo and Eastern Swamp Deer has significant breeding populations of 35
mammalian species, of which 15 are threatened as per IUCN Red List. It also has the highest density of tigers in
the world (1 per 5 km²), with a population of 86, as per the latest
census. Nine of the 14 primates of
India, and the only ape, the Hoolock Gibbon
(UNEP-WCMC 2009) occur in the park. Most
of the forest areas (51.14km2) have eroded due to perennial rains
and flooding in the Brahmaputra with loss of biodiversity. There is no authentic record on the insect
fauna of The Kaziranga National Park, and hence this
initial step, on inventorying the Orthoptera fauna of
the park.
Methods
Diverse habitats in KNP, were surveyed monthly, for assessing the distribution
and diversity of Orthoptera, from January 2007 to
December 2009. Three habitat types
representing forestlands, savannahs and grasslands were chosen at Kohora range (central range), Bagurirange (western range) and Agoratoli range (eastern
range) respectively.
Inventorying protocol: Representative habitat types were
selected and survey plots were laid. Each survey plot was divided into
quadrates measuring 10 x 10 m each and five such were chosen for random
sampling. The ground level vegetation
was searched, by hand picking the insects from the vegetation, sweep nets were
deployed for collecting samples. This exercise
was carried out from 0600 to 0800 hr. and repeated from 1800 to 2000 hr. to
enumerate the nocturnal species. The
evening sampling was supplemented with a light trap i.e., a portable light trap
following Sanjayan (1994) for Orthoptera. Collected specimens were narcotized with
menthol (Naphthalene) crystals and brought into the laboratory, air-dried for
preservation as per standard procedures and identification. Specimens collected were identified followingRentz (1979), Naskrecki(1994, 1996 a,b, 2000), Ingrisch & Shishodia (1997,
1998, 2000), Shishodia (2000a, b), and Senthilkumar et al. (2001, 2002).
Data analysis: Shannon’s diversity index (H’) was
calculated since it is well accepted that all species at a site, within and
across systematic groups contribute equally to its biodiversity (Ganeshaiah et al. 1997). In addition, Simpson’s diversity index (λ) as per Ludwig &
Reynolds (1988) and coverage estimators were also calculated using the EstimateS software of Colwell (2004).
Results and Discussion
A total of 36 species of orthopteroids belonging to 30 genera, and four families was
recorded from different habitats viz., forestlands, savannahs and grasslands ofKaziranga National Park during the survey period
(Table 1). The Family Acrididae had the largest species representation (19 species) followed by Tettigoniidae (nine species) and Mantidae(five species) while Gryllidae was represented by three species only (Fig.
1). Short-horned Grasshoppers were
recorded with greater diversity in all the habitats. Grasslands harbouredgreater number of Orthoptera species (21 species)
followed by savannahs (20 species) and forestlands (19 species) (Fig. 2). Four Orthopteranspecies namely Xenocatantops humilis (Serv.),Phlaeoba infumata Brun., Catantops ferruginuous (Walk.)
and Conocephalus maculatus (LeGuilou) were commonly observed in almost all the
habitats. Seventeen species were
encountered in both savannahs and grasslands followed by seven species in both
forestlands and savannahs and six species in both forestlands and
grasslands. Spathosternum prasiniferum (Walk.), Phlaeoba antennataBrunner von Wattenwyl, Trilophidia annulata (Thunb.), Caryanda sp., Tagasta indica Bolívar, Conocephalus (Xiphidion) melaenus (De Haan), Letana rubescens (Stål), Khaoyaiana sp., Hexacentrusmajor Redtenb.,Gryllinae sp.,Creobroter sp.and Mantodea sp. were recorded only in forests, while Hierodula sp. and Phlaeoba sp. were encountered in savannahs
alone. A greater diversity of
short-horned grasshoppers was recorded in all the habitats viz., grasslands,
savannahs and forestlands in KNP. This
conforms to the host plant distribution hypothesis (Cornell & Lawton 1992). Orthopteradiversity is related to the ecosystem, the grassland and savannah habitats
facilitating greater species inhabitation (Senthilkumaret al. 2009). Grasshoppers capable of
feeding on grasses in spite of high silica content (Chand& Muralirangan 2006) take refuge in the
grasslands. Heterogeneous conditions
form the basis of a stable and well-balanced environment in which populations
of orthopterans oscillate within certain limits (Senthilkumar et al. 2006). This observation is in consonance with the study of acrididdiversity in Tamilnadu (Senthilkumaret al. 2009). The finding of uniqueness
of certain species in particular habitats suggested that most of the
grasshoppers are highly selective to host plants or habitats as Mulkern (1967) reported. Oxya hyla hyla (Serv.), Oxya nitidula (Walk.) and Statilia sp. were represented only in the grasslands.
As a measure of diversity within a
habitat, Fisher’s alpha, and Shannon’s diversity indices were calculated. Fisher’s α index indicates richness of
the Orthopteran species in descending order from the
forests, the grasslands, and lastly the savannahs. The diversity indices H’, and λ appear
useful as they incorporate both species richness and evenness into a single
value. Shannon’s (H’) diversity index appears to have more value (2.28 to 2.4)
(Table 2). The present study indicates
that orthopteran species are more diverse in KNP.
Distribution of orthopteran species confirmed the log
series distribution pattern (Fig. 3) thereby giving creditability to the
Fisher’s α values. Simpson’s diversity index,
‘λ’, gives high value for grasslands (8.4), followed by savannah (7.56)
and the forestland (7.19).
Since a complete inventorying is
impractical, extrapolation techniques are widely employed for estimation of
diversity with more intensive sampling. In the present investigation the species
accumulation curve did not attain asymptote even after 36 sampling units with
monthly intervals. Sanjayanet al. (2002) found that even after 24 sampling efforts (months), the species
accumulation curve did not reach asymptote for orthoptera. It is also reflected in the values of the ACE (Abundance based coverage estimator)
(46.54%) and ICE (Incidence based
coverage estimator) (35.13%). This also
indicates the possibility for encountering more species in KNP as against what
the mean species accumulation curve depicted (Fig. 4). This study indicates that distribution,
diversity and richness of orthopterans in different
habitat types of KNP are related to the availability of host plants, subject to
the prevailing ecological conditions. It
is also important to note that a few species are endemic to Assam, in the
eastern sub Himalayas, one of the mega biodiversity hot spots of the
world. Therefore Orthopteranfaunal diversity of Assam, especially the KNP has to be protected.
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