Comparison
of insect biodiversity between organic and conventional plantations in Kodagu, Karnataka, India
Shamika Mone 1,
K.M. Kusha 2, Devcharan Jathanna 3, MusthakAli 4 & Anurag Goel5
1 OFAI - Organic Farming Associationof India, G-8 St. Britto’s Apts,Mapusa, Goa 403507, India
2 120/121 Dharani Nilaya, Manganahalli, Jnanabharathi,
Bengaluru, Karnataka 560056, India
3 Centre for Wildlife
Studies, CWS, Bengaluru, Karnataka, India
4 UAS - University
of Agricultural Sciences, GKVK Campus, Bengaluru, Karnataka 560065, India
5 WAPRED - Worldwide
Association for Preservation and Restoration of Ecological Diversity,
P.O. Box-101, Madikeri, Kodagu, Karnataka
571201, India
1 shamikamone@gmail.com,2 kusha.km.85@gmail.com, 3 devcharan@gmail.com, 4 ali.musthak@gmail.com,5 annugoel@gmail.com (corresponding author)
Abstract: We undertook a
comparative analysis of ground insects and fruit eating butterflies on 29
different plantations in Kodagu District of Karnataka which is one of the rich biodiversity zones of the
Western Ghats. These included organic and conventional coffee and cardamom
plantations using different levels of chemical fertilizers and pesticides. A
total number of 457 ground insect species were collected using pit-fall traps which included 92 species of ants and 123 species of
beetles, among other insect taxa that we measured. Similarly, 25 species of
butterflies belonging to the family Nymphalidae were
collected using bait traps. We found a clear negative effect on the ground
insect species diversity (Shannon index) and evenness (Shannon evenness index)
in pesticide treated plantations as compared to the organic plantations. A
similar negative effect was observed for butterfly diversity in plantations
using pesticides. Our results corroborate the value of organic plantations in
supporting higher levels of biodiversity.
Keywords: Biodiversity,
cardamom, coffee, conservation, insects, organic agriculture, pesticides,
Western Ghats.
doi: http://dx.doi.org/10.11609/JoTT.o3778.6186-94
Editor: Shonil A Bhagwat,
The Open University, UK Dateof publication: 26 August 2014 (online & print)
Manuscript details: Ms #
o3778 | Received 19 September 2013 | Final received 30 June 2014 | Finally
accepted 20 July 2014
Citation: Mone,
S., K.M. Kusha, D. Jathanna,
M. Ali & A. Goel (2014). Comparison
of insect biodiversity between organic and conventional plantations in Kodagu, Karnataka, India. Journal of Threatened
Taxa 6(9): 6186–6194;http://dx.doi.org/10.11609/JoTT.o3778.6186-94
Copyright:© Moneet al. 2014.Creative Commons Attribution 4.0 International License. JoTT allows unrestricted use of this article in any
medium, reproduction and distribution by providing adequate credit to the
authors and the source of publication.
Funding:We are indebted to The Third World Network (TWN),
Malaysia, for their financial support for this study.
Competing Interest:The authors declare no competing interests.
Author Contribution: SM
led field team, performed statistical analysis of data, contributed to writing
of paper: KMK assisted with fieldwork; DJ was involved at all stages of
project, especially initial design, statistical analysis, and manuscript
preparation; MA identified all the ant species and discussed the relevance of
the data; AG supervised the research plan and implementation of the field work
and wrote up the paper.
Author Details: Shamika Mone, MSc., Research director with Organic
Farmers’ Association of India (OFAI), Goa. K.M.Kusha, M.Sc., presently
employed with M/s. Metamorphosis Project Consultants Pvt Ltd., Bangalore. Devcharan Jathanna, Senior Research
Associate at Centre for Wildlife Studies, Bangalore, Musthak Ali Retired Professor of Entomology from UAS, Bangalore,
expert myrmecologist and still very active in trailing ants across India. Anurag Goel,
PhD, Research Scientist and Naturalist, co-founding director of ngo, WAPRED. Presently documenting biodiversity at
Mojo Plantation, Galibeedu, Madikeri,Kodagu District, Karnataka.
Acknowledgements: We
are indebted to the Organic Farming Association of India (OFAI) without which
this study could not have been implemented. We thank Prof. Viraktamath , University of Agricultural Sciences, Bangalore for his
generous time and expertise in identifying the enormous collection of insects.
We also thank our field assistant Arun Kumar and Aathira Perinchery (National
Centre for Biological Sciences, NCBS), Navendu Page
and Samira Agnihotri (Centre for Ecological Sciences,
CES) for their unstinting help in identifying the butterflies, plants and bird
calls, respectively. We thank Dr. Sujata Goel, Maya Goel, Archana Shetty and all the
interns at Rainforest Retreat for their ever helpfulsupport. Many thanks go to Rutuja Kate, Meera and Meghana who helped us
out with the R language. Finally, we are grateful to the land
owners who allowed us access to their plantations in order to conduct
this study.
For figures, tables -- click here
Introduction
Agriculture is a dominant human activity and occupies about 40% of
available land space globally (World Development Indicators online database,
World Bank), even more in India (World Bank Report 2010). Therefore, the decisions that farmers
make can dramatically affect biodiversity at all taxonomic levels. Modern
farming practices (mechanization, mono-cropping, hybrid varieties and
genetically modified GM crops) combined with the heavy use of agri-chemicals (fertilizers, pesticides and herbicides)
have resulted in a loss of biodiversity in agricultural landscapes and
surrounding areas (Andow 1983; Altieri& Letourneau 1984; Fuller et al. 1995; Krebs et al. 1999; Stoate et al. 2001; Benton et al. 2002, 2003). Agricultural ecosystems that are rich in
biodiversity possess greater resilience and are, therefore, able to recover
more readily from biotic and abiotic stresses such as drought, environmental
degradation, pests, diseases, epidemics, among others (Wilsey& Polley 2002; Wittebolleet al. 2009). Clearly, higher
community evenness—as found on organic plantations (Crowder et al.
2010)—enhances resistance to invasion and other forms of functionality
under stress (Wilsey & Polley2002; Wittebolle et al. 2009). Further, biodiversity conservation in
agricultural landscapes also promotes higher species richness (Bengtsson et al. 2005) and facilitates metapopulationprocesses between habitat patches (Perfecto & Vandermeer2010).
Insects have co-evolved with plants for millions of years and are
of enormous importance for agriculture. Some insects can damage crops, but others also provide pollination and
pest control services, or improve the fertility of the soil through feeding on
and assisting the decomposition of organic matter. Conventional agricultural pest-management
practices often lead to altered community structure (Macfadyenet al. 2009) and communities dominated by a few species, which contributes to
pest outbreaks. Organic farming
methods mitigate this ecological damage by promoting evenness among natural
enemies (Crowder et al. 2010) which then contributes
to a pest-predator balance. Hence,
species evenness was considered an important response variable in the present
study. While many studies in Europe,
Australia and Mexico (Bengtsson et al. 2005; Horne
2007; MacFadyen et al. 2009) have demonstrated that
organic plantations support a greater level of insect diversity, such studies
are lacking in tropical zones which harbour similar biodiversity. Studies on biodiversity in coffee
plantations in the Western Ghats have examined bird, mammal and butterfly
diversity (Bali et al. 2007; Dolia et al. 2007; Anand et al. 2008) in plantations at varying distances from
forests, but have not compared organic and conventional plantations. This study attempts to fill this gap in
our understanding of agricultural systems by comparing ground insect
biodiversity in organic and conventional plantations.
Study Area and Methods
This study was
carried out in the cardamom and coffee plantations of KodaguDistrict of Karnataka state, situated in the Western Ghats of southern
India. The average annual rainfall
in the area ranges from 1500–4000 mm and most of it occurs during the
southwest monsoon between June and September. The temperature ranges from a minimum of
110C in winters to a maximum of 280C in summers. The natural vegetation cover is
evergreen forest, which remains in the study landscape as fragments at varying
levels of degradation. Both
cardamom and coffee are cultivated under a two-tier mixed shade canopy comprising
leguminous and non-leguminous evergreen shade trees. Coffee requires about 40% shade whereas
cardamom requires 60% shade (Anonymous 1985). Therefore, in mixed systems coffee is
generally grown on slopes with pepper as an intercrop while cardamom is grown
in the moist valleys.
We selected 29
plots in different parts of Kodagu District (Fig.
1). These included 12 in completely
organic plantations that apply no pesticides or chemical fertilizers, five in
plantations using only chemical fertilizers (NPK) but not pesticides, and 12 in
conventional plantations that used NPK as well as chemical pesticides. Most (but not all) of the organic
plantations had been certified by an international agency for an average of six
years and conventional plantations had varying levels of pesticide use. We had originally intended to sample
using the powerful randomised block design (Quinn
& Keough 2002), but had to abandon this during
the course of the study since we were unable to find clearly and meaningfully
definable blocks. Because of this,
pairs of plantations of different types (organic and conventional) are sometime
located close together. However, we
are confident that the overwhelming effect of treatments will justify
statistical independence in such cases. The minimum distance between plantations of the same type is 1km. We collected ground insects and
butterflies from the months April to May (before the onset of the monsoons)
followed by collection from the months October to March (following the monsoon
rains). Wherever possible, one
organic and one conventional plot were monitored simultaneously, as explained
above.
Pitfall traps were
used to capture ground-foraging insects. A 1.21 to 2.02 ha (3–5 acre) plot was selected on each
plantation. The plot was selected
by the field team so as to cover a representative part of the estate but also
to ensure no edge effects from neighbouringplantations that may have been of a different type (e.g., pesticide runoff into
an organic plantation, effects due to spatial dependence in the response
variable). In each plot, five
equally spaced transect lines 20m apart were demarcated with string and mapped
using a global positioning system (GPS). Each transect measured 40m in length and five pitfall traps were placed 10m
apart on each transect. Hence, a
total of 20 pitfall traps were placed in each plot. Each pitfall trap consisted of a plastic
disposable cup, measuring about 10cm in height and 6cm in diameter. The cups were buried at ground level and
protected from rain by a plastic plate at a distance of about 2cm above the
ground. Each cup contained 15ml of
ethanol (50%) and 2–3 drops of glycerine to
prevent evaporation. Trap contents
were collected every 24h over four consecutive days, and preserved in ethanol (70%)
before identification. Ants were
separated from other insects for the purpose of identification.
We surveyed
fruit-feeding butterflies using hanging traps baited with over-ripe, fermenting
fruits (banana, apple, papaya). Each trap consisted of a cylindrical net with a
conical head and a wooden plank hanging 2.5cm below the bottom of the net. The bait dish was placed on the wooden
plank so that any butterflies visiting the bait were trapped within the net as
they flew upwards. Three traps were
randomly placed (equidistant from each other, approximately 30m apart) in the
same plot used for the pitfall traps. The traps were emptied and the bait replaced every 24 hours over four
consecutive days. The trapped
butterflies were photographed, counted and released. The photographed butterflies were then
identified using a field guide on butterflies of India (Kehimkar2008).
Total ground
insects and butterflies were identified to the lowest possible taxonomic
level. These data were used to
estimate mean species richness (not shown here), mean Shannon’s diversity
(which takes into account both species richness and evenness) and mean
Shannon’s evenness (data shown as evenness for each pitfall trap cumulative
over four days. Evenness data is
shown as it is considered an important response variable for effective pest
control on organic farms (Crowder et. al. 2010).
The data were analysed using linear modelling(Quinn & Keough 2002) in conjunction with a model
selection approach (Burnham & Anderson 2002; Johnson & Omland 2004). We chose the model selection approach over the traditional null
hypothesis testing as our data were derived from an observational study which lacked randomization of treatments and
controls. We carried out separate
analyses for the different response variables (species richness, diversity and
evenness), using linear models with treatment (three levels: organic, NPK,
pesticide) and crop type (cardamom or coffee) as the categorical
predictors. We fitted models where
the response variable was a function of only crop, only treatment, the additive
effect of crop and treatment and the interaction between crop and
treatment. The trap data were
combined to the level of the plot (=estate) prior to statistical analyses, so
random effects were not included in the models. Further, plantations were classified
into four categories as 0P, 1P, 2P and 3P depending on the number of different
pesticides used per year. (0P - No
pesticide or NPK; 1P - 1–3 pesticide applications; 2P - 4–7
applications; 3P - 8–14 applications). All statistical analysis was carried out
using the statistical programming package R (R Development Core Team 2008).
Results
Pitfall traps
Total Ground Insects: Diversity: A total of 32,484 ground
insects belonging to 467 different species, including 92 ant species and 123
beetle species, were collected using pitfall traps. The effect of treatment on the species
diversity index was observed to be the best fit model
(Table 1). Shannon’s species
diversity index (H’) is clearly higher in organic (G) plantations compared to
pesticide (P) plantations, while diversity in NPK (N) plantations overlaps with
that of other treatments (Fig. 1). The role of treatment in determining Shannon’s species diversity index
(H’) received further support from the next best model which included the
additive effects of treatment and crops. (ΔAIC=1.19; Table 1). Here we see that there is a clear
negative effect of pesticide treatment on Shannon’s species diversity index
(H’) when compared with organic plantations in both coffee and cardamom
plantations. There is no discernible effect of treatment on Shannon’s species
diversity index (H’) in NPK plantations (Fig. 2).
Total ground insects: Evenness: The additive effect of crop
and treatment on the Shannon’s species evenness index (E) was observed to be
the best fit model (Table 2). Shannon’s species evenness index (E) is
clearly higher in organic (G) plantations compared to pesticide (P) plantations
(Fig. 3). The role of treatment in
determining Shannon’s species evenness index (E) received further support from
the next best model which included only treatment (ΔAIC=1.36; see Table 1
and Fig. 3). The evenness index for
NPK (N) plantations is intermediate, overlapping both organic and pesticide
plantations.
Effect of chemical pesticides on ground insect species diversity
and evenness indices: Clear differences were seen in Shannon’s species diversity index
(H’) (Fig. 4a) between pesticide-free (0P) plantations and heavily sprayed (3P)
plantations (95% confidence interval [CI] for pesticide free (0P) and heavily
sprayed (3P) do not overlap).
Similar results were observed for Shannon’s species evenness index
(H’) (Fig. 4b) where there is a clear difference between pesticide-free (0P)
plantations and heavily sprayed (3P) plantations.
Pitfall Traps
Ants: Diversity and Evenness: A total of 6695 ants
comprising 92 species were collected from the pitfall traps. Similar to overall
ground insect data, we analysed patterns for just
ants by fitting and comparing the same set of models. The results for ant species diversity
and evenness are similar to those obtained for all ground insects and they
confirm that pesticide treatment (P) has a considerable and clear negative
effect on Shannon’s ant species diversity (Fig. 5a) and evenness (Fig. 5b)
indices compared to both organic (G) and NPK (N) plantations. As for total ground insects, Shannon’s
ant species diversity and evenness indices are not clearly different between
organic and NPK treatments.
Effect of number of pesticide applications on ant species
diversity and evenness indices: Large differences are apparent in both
Shannon’s ant species diversity (Fig. 6a) and evenness (Fig. 6b) indices even
between pesticide-free (0P) plantations and very low pesticide (1P) sprayed
plantations. In highly pesticide sprayed plantations (3P), the reduction in
both Shannon’s ant species diversity and evenness indices is very drastic.
Butterfly Bait
Trap
Nymphalidbutterflies: Diversity: A total of 1,259 butterflies comprising 25 species from the
family nymphalidae were collected using bait
traps. The effect of treatment on
the species diversity was observed to be the best fitmodel. Shannon’s butterfly species
diversity index (H’) is highest in organic (G) plantations (Fig. 7) and clearly
lower in pesticide (P) plantations. The role of treatment in determining Shannon’s butterfly species
diversity index (H’) received further support from the next best model which
included the additive effects of treatment and crops (Δ AIC=1.78). The data show a clear decrease in the nymphalid butterfly diversity in plantations sprayed with
pesticides but patterns in nymphalid butterfly
evenness are unclear.
All species data
will be published separately as a Data Paper.
Discussion
The
intensification of agriculture has been associated with a substantial loss of
biodiversity along with many important ecosystem services which include crop
production, pest control, pollination and decomposition processes, and soil
properties (Lal 1988; Daily 1997; Altieri1999; Schläpfer et al. 1999; Tilman et al. 2002; Wilby& Thomas 2002). The decline of
biodiversity affects ecosystem functioning and yield(Russell 1989; Daily 1997). Local intensification may affect biological pest control (Russell 1989; Matson et al. 1997; Thies & Tscharntke 1999; Östman et al. 2001; Symondson et al. 2002; Barbosa
2003; Donald 2004; Perfecto et al. 2004; Tylianakis et
al. 2004), grassland production (Bullock et al. 2001; Loreau & Hector 2001), pollination (Nabhan& Buchmann 1997; Kremen et al. 2002; Klein et al. 2003a,b)
and resistance to plant invasion (Lyons & Schwartz 2001; Kennedy et al. 2002; Levine et al. 2004; Zavaleta & Hulvey 2004). During the last decades, worldwide
losses of biodiversity have occurred at an unprecedented scale and agricultural
intensification has been a major driver of this global change (Matson et al. 1997; Tilman et al. 2001; Kremenet al. 2004). Hence, there is
considerable concern that intensive modern agriculture is not compatible with
the conservation of biodiversity (Robinson & Sutherland 2002).
Organic farming is
often thought of as a solution to the problems associated with biodiversity conservation
in intensive agricultural landscapes. Our study shows that there is greater level of insect diversity (ground
insects and butterflies) on organic plantations when compared to the
conventional (chemical fertilizers and pesticide-sprayed) plantations. Our study supports the contention that
organic farming enhances biodiversity (Paoletti et
al. 1992; Schönning & Richardsdotter-Dirke1996, Bignal & McCracken 1996; Plachter 1999; Sutherland 2002a,b). Conventional agricultural
pest-management practices often lead to altered food web structure and
communities dominated by a few common species, which together contribute to
pest outbreaks. Organic farming
methods mitigate this ecological damage by promoting evenness among natural
enemies (Crowder et al. 2010) which then contributes
to a pest-predator balance. Hence,
species evenness was considered an important response variable in the present
study. Our results confirm the hypothesis
that organic farming promotes species evenness of total ground insects.
The data generated
and analyzed here clearly show that pesticide treatment has a significant
negative effect on insect biodiversity as measured by Shannon’s diversity and
evenness indices. A comparative
effect of treatment on mean Shannon’s diversity index H’ for ground insects
within each crop type clearly indicates that organic (and NPK) cardamom
plantations have higher levels of biodiversity than corresponding coffee
plantations. This is expected
because cardamom is a native crop and grown under denser forest shade canopy
than coffee. However,
pesticide-treated cardamom plantations show the lowest levels of insect
biodiversity. This can be explained
by the very high levels (6–12 sprays per year) of pesticide use in
conventional (chemical) cardamom plantations as compared to 1–2 sprays in
conventional coffee plantations. There is no clearly observable difference in insect diversity between
organic and NPK plantations. This
result is probably because NPK treatment is limited to once per year and most
of the plantations in the district show high plant (weed) diversity and good
canopy cover. This produces a heavy
build up of mulch and ground leaf litter, and this combined with heavy rainfall
provides a good buffering capacity to the negative impacts of limited
applications and quantities of fertilizers.
One of the
interesting results of this study is that ants show a similar response to
pesticide use as total insects but the magnitude of the effect is much greater:
50% reduction in diversity compared to 20% for total insects in organic versus
pesticide-sprayed plantations. For
total ground insects, a significant difference was observed between
pesticide-free (0P) plantations and heavily pesticide-sprayed (3P) plantations,
but not with low or moderate pesticide treatment. For ants, a significant difference was
observed between pesticide-free (0P) plantations and even lightly
pesticide-sprayed (1P) plantations. These results indicate that ants are sensitive and rapid responders to
plantation management practices and hence are good biological indicators
(Campbell & Tanton 1981; Majer1983; Andersen 1990). This is
especially significant in light of the fact that tropical regions support very
high levels of insect diversity, which, combined with incomplete taxonomic work
(Narendran 2001), makes identification a difficult
task. This may account for the
lacuna of other studies on total ground insects. Ants, on the other hand, have been
extensively studied and their taxonomy is well understood (Narendran2001). Moreover, ants are
functionally important at different trophic levels (Alonso 2000) and play
critical ecological roles in soil turnover and structure (Humphreys 1981; Lobry de Bruyn & Conacher 1994), nutrient cycling (Levieux1983; Lal 1988), plant protection, seed dispersal and
seed predation (Ashton 1979; Beattie 1985; Christian 2001). Hence we propose, based on our results, that such future studies can be carried out more
cost-effectively by simply considering patterns in ant diversity.
Despite the clear
patterns in our results, we recognize that biodiversity in agricultural
landscapes is affected by many factors other than the farming system. Fallow areas, such as field margins,
habitat islands, hedgerows, natural pastures, wetlands, ponds and other small
habitats are important refuges and source areas for many organisms. Maintenance of biodiversity in
agricultural landscapes will depend on the preservation, restoration and
management of such habitats (Corbett & Rosenheim 1996; Stopeset al. 1995; Baudry et al. 2000; Tscharntkeet al. 2002, 2005). Landscape
structure and heterogeneity also contributes to biodiversity in agricultural
areas (Marino & Landis 1996; Fahrig & Jonsen 1998; Krebs et al. 1999; Weibullet al. 2000; Berg 2002; Steffan-Dewenter et al. 2002;
Benton et al. 2003; Dauber et al. 2003, Ricketts et al. 2004).
Our study shows
that organic plantations support greater diversity of ground insects and nymphalid butterflies, and that ants are a good indicator
taxon for ground insects. The
number of pesticide applications was seen to have a strong effect on both ant and
overall ground insect diversity. A
better understanding of how species interact within a community and how
communities function at the landscape level could be keys to the maintenance
and utilization of biodiversity in agri-ecosystems. Therefore, there is a crucial need to
conduct further similar research studies, at multiple spatial and temporal
scales, especially from tropical regions dominated by agriculture.
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