Road kills of
amphibians in different land use areas from Sharavathi river basin, central
Western Ghats, India
Kadaba Shamanna Seshadri 1, Amit Yadav 2 & Kotambylu
Vasudeva Gururaja 3
1 Asoka Trust for Research in Ecology and the Environment, Royal
Enclave, Sri Rampura, Jakkur P.O., Bengaluru, Karnataka 560064, India
2,3 Centre for Ecological Sciences, Indian Institute of Science,
Bengaluru, Karnataka 560012, India
Email: 1 seshadri@atree.org; 2 amit503sm@gmail.com ; 3 gururaj@ces.iisc.ernet.in (corresponding author)
Date of publication (online): 26
November 2009
Date of publication (print): 26
November 2009
ISSN 0974-7907 (online) |
0974-7893 (print)
Editor: Ranjit Daniels
Manuscript details:
Ms # o2148
Received 21 February 2009
Final received 25 August 2009
Finally accepted 09 November 2009
Citation: Seshadri, K.S.,
A. Yadav & K.V. Gururaja (2009). Road kills of amphibians in different land
use areas from Sharavathi river basin, central Western Ghats, India. Journal
of Threatened Taxa 1(11): 549-552.
Copyright: © Kadaba
Shamanna Seshadri, Amit Yadav & Kotambylu Vasudeva Gururaja 2009. Creative
Commons Attribution 3.0 Unported License. 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.
Author Details:
K.S.
Seshadriis a researcher at ATREE, currently working on epiphytes and canopy ecology at
Kalakad-Mundanthurai Tiger Reserve, Tamil Nadu.
Amit
Yadavis a researcher at CES, currently working on ecological modeling in the
watersheds of western Himalaya.
K.V.
Gururajais a researcher at CES, currently working on the effect of habitat
fragmentation on diversity and distribution of amphibians in the Western Ghats.
Author Contribution: All authors
have contributed equally in conceptualizing, data collection, analysis and
writing of the paper.
Acknowledgements:We
thank Srikant Naik for assisting in vehicular data collection, G. Supriya and
B. Karthick for critical comments on the manuscript and Vijay Mohan Raj, Deputy
Conservator of Forest, Sirsi Division for logistics.
Abstract: A
survey of amphibian mortality on roads was carried out in the Sharavathi river
basin in the central Western Ghats. Road
kills in three different land use areas: agricultural fields, water bodies and
forests were recorded for four days along three 100m stretches in each type of
area. One-hundred-and-forty-four
individuals belonging to two orders, eight families, 11 genera and 13 species
were recorded in the survey. Kills/km
observed were: in forest 55, agricultural fields 38 and water bodies 27, for an
overall average of 40 kills/km. Kill species compositions varied significantly
between land use areas, but not overall kill rates.
Keywords:Amphibians, central Western Ghats, encounter rate, road kills, Sharavathi
river basin, species composition.
For Image &
Table – click here
Introduction
Amphibians are poor dispersers across different
landscapes, on land or water (Marsh et al. 1999). Extinction-recolonization dynamics and
dispersal ability also play a key role in structuring amphibian populations
genetically (Berven & Grudzien 1990; Sjogren 1991), and such poor
dispersers are prone to local extinction and extirpation if their dispersal
corridors/habitats are fragmented (Gururaja 2002). Roads are one of the barriers for dispersal
of amphibians (Gibbs 1998). There are
several studies outside India on the impact of roads and/or road kills on
amphibians and their population density (Fahrig et al. 1995; Jackson 1996;
Gibbs 1998; Carr & Fahrig 2001; Hels & Buchwald 2001; Dodd et al. 2004;
Row et al. 2007; Santos et al. 2007) while in India there is a single study by
Vijayakumar et al. (2001) from a protected area, Indira Gandhi National Park
(southern Western Ghats).
In India the total length of roads and
number of motorized vehicles have increased in the last 50 years (1951-2004)
from 0.4 to 3.4 million kilometre and 0.3 to 30 million respectively (Rao &
Girish 2007). Such an enormous increase
will certainly have detrimental influences on animals that crawl or move across
roads. In this study we have attempted to quantify the road kills of amphibians
across different land use areas along a 3.6km stretch of national highway in
the Sharavathi region of central of central Western Ghats with the following
objectives: 1) to enumerate species composition and encounter rate of
amphibians killed on the road due to vehicular movements, and 2) to assess the influence of different
land uses on observed road kills.
Study Area
We selected a stretch of about 25km from
Talaguppa to Kathalekan (between 14.20N & 74.90E and 14.30N & 74.70E,
altitude 470-630m) on NH 206. This
section of the road traverses through the terrains of central Western Ghats in
Sharavathi river catchment. The major
land use area types observed in the region are evergreen forest, semi-evergreen
forest, moist-deciduous forest, agriculture, monoculture plantation, water
bodies, cultivable land, waste land and built-up area (Sreekantha et al.
2007). We considered three land-uses
namely, agriculture, water bodies and forest for the present study. Image 1 depicts the different segments of the
road considered in the present study based on land-uses. The road segment in Talaguppa is predominated
on either side with agriculture fields (paddy), near Manmane it is with water
body, whereas near Kathalekan it is predominated with evergreen and semi-evergreen
forest.
Methods
The road passing through three land-uses
was sampled for killed amphibians on four consecutive days starting from 24
June 2008 till 27 June 2008. In each
land-use, three 100m segments were sampled with 100m space in between. Total length of road sampled was 3.6km
(3x100m in three land-uses for four days). Sampling was carried out between 0630-0830 hr, so as to record the
accumulated road kills overnight (since majority of the amphibians are active
during the night hours) and to minimize carcass loss due to scavenging by birds
or other animals and by traffic during day hours. The roads were thoroughly searched for the
presence of any killed amphibian. On
sighting a road killed amphibian, it was identified up to species level
(wherever possible) and the other organisms were also listed but not included
in the analysis. Number of kills per kilometre is expressed as encounter rate.
The remains were removed from the road to avoid redundancy. We have not
collected or preserved any dead individuals/materials from this study.
The region receives maximum amount of
rainfall (100-2000 mm) for the year during June to September (Sreekantha et al.
2007). We preferred to carry out
sampling during rainy season as rainfall seems to be the primary extrinsic
factor controlling the timing of reproductive activity of amphibians (Duellman
& Trueb 1994).
The vehicular density on the road was
monitored for two hours each in the early mornings (0630-0830 hr) and late
evenings on three days (1830-2030 hr). Overall vehicular density was 29.69/hr, considering all three days. On further dividing, heavy motor vehicle was
12.54/hr, followed by light motor vehicle 9.15/hr and two wheeler 8/hr. The study area has a major tourist spot, the
world famous Jog Falls, which is located within 10km from all our sampling
sites, attracts large number of tourists during weekends and more precisely
during monsoon period. Hence a detailed
study on vehicular movement during weekends and holidays are essential for better
understanding of traffic in the region. Due to various constraints, intensive vehicular monitoring was not
possible and the counts in this study are just representative of the trends.
One
way Analysis of Variance (ANOVA) was tested on species composition and
encounter rates in three land-uses (k=3, n=12) to know the variation in them.
Results
Amphibians belonging to two orders,
eight families, 11 genera and 13 species were recorded in the survey. Table 1 shows conservation status and encounter
rate of road killed amphibians (individuals/1.2km). A total of 144 individuals over 3.6km were
recorded during the study, of which 32% was in agriculture section, 22% was in
water body section and 46% in the forest section. Seven amphibian species were recorded from
the forest section, followed by six in the paddy section and three from the
water body section.
The road kill encounter rate was highest
in forest with 55 kills/km, followed by the agriculture with 38.33 kills/km and
water body being the least with 26.66 kills/km. Species composition between land-uses were significantly different
(F=5.44, P=0.04), however, overall kill between land-uses (F=1.36, P=0.3) as
well as different days (F=0.23; P=0.87) did not show statistically significant difference. This shows that, irrespective of the
different land-uses, the numbers of road kills were similar, though the species
composition differed.
Among amphibians, Duttaphrynus
melanostictus had maximum kills (n=17) in the forest section followed by Ichthyophis
beddomei a limbless amphibian (n=5) and stream dwelling Nyctibatrachus sp.
(n=3). In agriculture, Fejervaryasp. (n=22) had maximum kills, while it was Microhyla ornata (n=9) in
water body. No species had similar road kill encounter rates in all land-uses.
In case of Fejervarya sp. and
unidentified frogs (n=74), there is a possibility of more than one species
being present, as majority of them provided mere clues like limbs, hands,
mandibles to recognize as frogs due to maceration by repeated movement of
vehicles.
We compared our study with Vijayakumar
et al. (2001), which was carried out for about 171km in the Indira Gandhi
National Park. Although our sampling
length was 3.6km, which is just about 2% of 171km, nonetheless comparison was
made as it was the only other available study on amphibian road kills in
India. Our study showed higher road kill
encounters of amphibians of 40/km compared to 2/km. On comparing the species composition,
Vijayakumar et al. (2001) enlisted five families and three species with 311
kills, whereas our study enlisted 13 species belonging to eight families with
144 kills. In their study, Duttaphrynus melanostictus had highest road kills (145) followed by members of
Ranidae family, while Fejervarya sp. and Duttaphrynus melanostictus had
22 and 17 road kills respectively from our study.
The other organisms observed as road
kills belonged to the following groups viz; invertebrates (crab,
butterfly, insect, earthworm, centipede and snail), reptiles (Malabar Pit Viper
(Trimeresurus malabaricus), Bamboo Pit Viper (T. gramenius),
unidentified keelback (Xenochrophis sp.) and unidentified calotes (Calotessp.) and mammals (rat).
Discussion
According to the study there is a high
incidence of road killed amphibians and marked differences in the species
composition of road kills among different land use areas of forest, agriculture
and water bodies. The difference in the
species composition in land-uses is indicative of habitat specificity of
species. Fejervarya sp. are semi-aquatic, open canopy dwellers,
generally prefer agriculture fields and stagnant water bodies, hence their road
kill encounters were maximum at agriculture fields. Similarly, encounter rate of Ichthyophis
beddomei and Nyctibatrachus sp. in forest stretches, indicates the
affinity of these species to torrential streams and stream beds in forest.
Interestingly, absence of significant variation among total road kills per
land-use emphasises that irrespective of species composition, almost equal
number of individuals are killed in each land-use on each day.
There is a 90% increase in the road kill
encounter rate in this study compared to Vijayakumar et al. (2001). There are several factors influencing such
disparity between the studies. Vehicular traffic is the major driving factor
influencing the road kills. This was not
mentioned in Vijakumar et al.’s (2001) paper. Apart from that, difference in
sampling effort (171km vs 3.6km), vegetation composition, amphibian species
composition, geography and protection status of the study area (National Park
vs non-protected area) must have influenced these two studies.
Since the habitats inhabited by frogs
outside the protected areas (PA) are very large (Das et al. 2006), such studies
outside the PAs have to be done in order to document the impact of road kills
on amphibians and its contribution to local, regional and global level
amphibian decline. The study would have
given a clear picture about the relationship of road kills and vehicular
density, if the vehicular density was monitored more extensively covering the
whole week as we observed that the vehicle density increased drastically during
the weekends. Nevertheless, this study
gives an impetus for further studies in the Western Ghats where large habitats
favourable to amphibians are cut across by extensive road networks and which
may influence the local extinction and decline in amphibian population.
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