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Community structure and functionalgroup classification of litter antsin the montane evergreen anddeciduous forests of Wayanadregion of Western Ghats, SouthernIndiaP. J. Vineesh a , Thomas K. Sabu a & K. A. Karmaly ba PG & Research Department of Zoology St. Joseph'sCollege , Litter Entomology Research Unit , Devagiri,Calicut , 673008 , Indiab Department of Zoology , St. Xavier's College , Alwaye ,683102 , IndiaPublished online: 05 Jan 2012.

To cite this article: P. J. Vineesh , Thomas K. Sabu & K. A. Karmaly (2007) Communitystructure and functional group classification of litter ants in the montane evergreen anddeciduous forests of Wayanad region of Western Ghats, Southern India, Oriental Insects, 41:1,427-442, DOI: 10.1080/00305316.2007.10417526

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Oriental Insects, Vol. 41: 427-442, 2007.

COMMUNITY STRUCTURE AND FUNCTIONAL GROUP CLASSIFICATION OF LITTER ANTS IN THE MONTANE

EVERGREEN AND DECIDUOUS FORESTS OF WAYANAD REGION OF WESTERN GHATS, SOUTHERN INDIA

P. J. VINEESH1, THOMAS K. SABU1

, & K. A. KARMALY2

1Litter Entomology Research Unit, PG & Research Department of Zoology St. Joseph's College, Devagiri, Calicut 673008, India. e-mail: sabukthomas@gmail.com

2Department of Zoology, St. Xavier's College, Alwaye 683102, India.

ABSTRACT. Community structure of litter ants based on feeding guilds and the more recent func­tional group classification, and also the role of abiotic factors in determining the community structure have been analyzed following 'Ants of Leaf Litter' protocol in a montane evergreen (shola) and deciduous for­ests in the Wayanad region of Western Ghats, southern India. Distinct variations in the guild structure of litter ant communities in shola and deciduous forests have been recorded. Predators dominated deciduous and omnivores in the shola forests. Cryptic species was the dominant functional guild in both litter stands, although hot-climate specialists have not been recorded from the shola forests. Rank-abundance plots at­tributed the difference in diversity between the forests to the dominance of Tapinoma sp. and Myrmicaria brunnea in deciduous forest. Physical characteristics of the habitat critically influenced ant abundance in both forest types. Functional group model classification was found to be a better model for the classifica­tion of litter ants than the conventional feeding-guild categorization as it enabled a meaningful comparison in relation to physical factors.

Key words: Litter ants, guilds, functional groups, abiotic factors, shola, deciduous forest, Western Ghats.

Introduction

Ant species that nest in ground and leaf litter are different from arboreal species, as the two groups exhibit divergent morphologies, which reflect their respective nesting habits (Wilson, 1959). The relative stability, moderate diversity and sensitivity to micro­climate of litter-dwelling ant community makes them a suitable group for measurement of biodiversity assessments and indicating ecosystem modifications in various habitats (Agosti et al., 2000; Bruhl et al., 2003). As important invertebrate predators, scavengers, seed dispersers, and competitors, ground-dwelling ants exert a strong influence on the arthropod community in tropical rain forests (Holldobler & Wilson, 1990). In addition, they play key roles in the movement of soil, transfer of organic materials, better aeration. (Agosti et al., 2000). Their nesting habits alter soil nutrient concentrations and biogeo­chemical cycles (Mac Mahon et al., 2000). Species-specific factors, viz., habitat require­ments, competition, dispersal ability, and dependence on other species, and stochastic stand features offer cues to habitat preferences of a specific ant species in a given com­munity (Punttila et al., 1996). Even seemingly minor changes in environmental condi­tions can be important to individual ants and these differences may explain some of the ant-community structure variations (Greenslade & Greenslade, 1977). Ant-community change has been correlated with vegetation and species turnover tends to increase with increasing habitat divergence. Since the foraging requirements of ants tend to overlap, trophic guilds are of limited use in ant community studies; hence, a functional group clas­sification based on a broad range of ecological characters was proposed (Andersen,

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1997). Subsequently Andersen (1997), King et al. (1998), and Morrison (1998) indicated that the functional group classification is more appropriate than a classification based on feeding guilds, since it substantially reduces the complexity of ecological systems and provides a basis for evaluating environmental change in relation to ant community struc­ture. In the present study we compared the diversity and community structure of litter ant communities based on traditional feeding guilds and recent functional group classifica­tion and analyzed the role of forest floor physical factors on distribution of litter ants in deciduous and montane evergreen (shola) forests in Wayanad region of Western Ghats, which is a recognized hot spot of biodiversity (Mayers et al., 2000).

Materials and Methods

Study sites are located at Thirunelli in Wayanad region of southern Western Ghats in the state of Kerala (Fig. 1) (11°58', l1°3'N; 75° 45', 76° 28'E). Biogeographically, Wayanad region of Western Ghats is a transitional zone between the moist-deciduous and dry-deciduous forests of southern Western Ghats, harboring many restricted habitats, en­demic species, as well as disjunctive populations of species that are found in moist­deciduous, evergreen and dry-deciduous forests (WWF, 2001 ). Thirunelli forests spread over an area of 20.55 km2 and occur at an elevation of 900 m amsl and above. No area records about the evergreen forests commonly referred as sho1a forests exists (Forests & Wildlife Department, 2001). Our estimates indicate that shola forests occupy an area of 6±2 km2 at 1300 m amsl. Northeast monsoon from October to November supplements the June-September southwest monsoon in this region. However, because of the deeply dis­sected topography with sheltering high ridges on the windward western and the eastern sides, the deciduous forests at Thirunelli receive less than 2000 mm/a rainfall whereas Periya and Vythiri regions on the western and shola forests on the eastern reaches receive more than 3000 mm/a. Rainfall data from the shola region is not available. Shola forests in the region are locally recognized as a high-rainfall region with greater wind velocity and higher evapo-transpiration rate compared with the deciduous forests (Forests & Wild­life Department, 2001).

Rainfall data was collected from the records of State Electricity Board office at Thi­runelli. Humidity and litter temperature was assessed with thermo-hygrometer (Barigo; Barigo Barometer fabric GmbH; Villingen-Schwenningen; Germany), moisture with moisture analyzer (Advance; M-3A deluxe; Advance Research Instrument Co; Ambala; India.), and litter depth with a standard 30 em ruler. Slope of the terrain was calculated using the trigonometric formula 'tan 9' (where '9' is the angle of inclination) (Jacobs & Meyer, 1972). Litter humidity, litter moisture, litter temperature, slope of the terrain and litter depth were calculated as the mean (arithmetic mean) of 30 sampling spots at each site (Table 1).

Obtaining exact values of evenness, richness and diversity indices, by conducting complete diversity inventories are an unachievable goal for invertebrate taxa, especially in the tropics (Longino et al., 2002). Alternatively, structured inventories based on lim­ited, but well-quantified sampling effort aim to reliably characterize communities (Longino et al., 2002; Alonso & Agosti, 2000; Leponce et al., 2004} For litter- ant studies the standardized protocol abbreviated 'ALL' (Ants of the Leaf Litter) (Alonso & Agosti, 2000) is widely recognized, which allows quantitative comparisons between litter- ant communities in space and time. For the collection of other fractions of local ant fauna complementary methods (pitfall traps, soil samples, wood samples, and visual search) are suggested (Fisher, 1998; Leponce et al., 2004). As per ALL method, a single-line transect

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2007 Vineesh et al.: Community structure of forest litter ants 429

(200 m) and a sampling interval of 10m (20 samples) followed by extraction in mini­Winkler apparatus (Fisher, 1998) for 24 h is the minimum sampling effort necessary for characterizing the leaf-litter ant assemblages. Based on this method, a preliminary line transect (300m) was constructed in both forests in November 2002. At intervals of 10m, leaf litter present inside a 1 m2 quadrate was collected, sifted through a wire sieve with square holes of 1.1 em x 1 em. Ants present in the sifted litter were extracted using a mini-Winkler apparatus for 24 h.

Ants were identified using Bolton (Bolton, 1994) and Fauna of British India (Bing­ham, 1903). Specimens were further compared with the collections at the museums of St. Xavier's College, Alwaye and the University of Calicut. Voucher specimens have been temporarily deposited at the museum of St. Xavier's College, Alwaye.

In the analysis of community diversity of colonial organisms such as ants what has been considered is the frequency of occurrence of species in each sample (incidence data) and not the number of each individual species encountered during the inventory. It is nec­essary as samples collected close to the nesting site of a rare ant species may lead to the recording of an extreme abundance of that rare species. Hence, we followed the presence or absence approach for species-count data (Bruhl et al., 2003; Leponce et al., 2004; Longino, 2000). Although non-quantitative in terms of numbers of individuals, occur­rence records at least provide an estimation of the probability of encounter with the vari­ous species and this procedure is commonly advised to evaluate the diversity of leaf-litter ants (BrUhl et al., 2003; Pfeiffer et al., 2003; Leponce et al., 2004). As per presence or absence approach, a species ( say for example species A ) present in all the 30 samples was given the incidence value of 30, species (species B) present in 20 samples was given the incidence value of 20 and another species (species C) present in only one sample was given the value of one. Hence the term 'abundance' in the current study means the total incidence (frequency) of a species in samples and not the total number of individuals of a species. Proportionate contribution (%) of individual ant species to the total ant abun­dance at each site was calculated from the overall incidence data. Sampled ants were categorized into the respective feeding guilds (Holldobler & Wilson 1990; Mack, 2005) and major functional groups as in Anderson's classification (Andersen, 1997). Abundance of specific guild means the sum of the incidence of all species included in the guild under consideration.

Rank abundance plots were plotted with abundance (log) of ants against ranks of in­dividual species and model fitting by linear regression (Magurran, 2003) was done. Alpha (a) diversity based on Pielou's evenness index (J'), Margalef species richness (d), Shan­non Species diversity (H'), Fishers alpha (a), and Simpson's dominance index (A.) was assessed using Primer software (Clarke & Gorley, 2001). Beta(~) diversity assessments for, both litter-ant assemblages and feeding and functional guilds were done with semi­quantitative Morisita Hom index and qualitative Sorenson index. Qualitative species richness estimators (Chao2, Jack1, Jack2, ICE, Bootstrap)(Colwell & Coddington, 1994) and ~-diversity were determined with EstimateS programme (Colwell, 2000).

Effects of physical characteristics of the forest vegetation types on ant abundance was tested with multiple regression (Zar, 2003) and the inherent collinearity (multicollin­earity) of explanatory variables was analyzed with auxiliary regression (Neter & Kutner, 1996). Variations in physio-climatic factors, a-diversity and functional and trophic guild wise ~-diversity between the forests types were analyzed with one way ANOVA (Zar,

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2003). The Gretl (Version 1.1; Cottrell, 2006) open-source software for Windows was used for all statistical analysis.

Results

Twenty-three ant species in 17 genera from deciduous and 20 species in 14 genera from shola forests were collected. Twelve species were common to both forests, 11 spe­cies were specific to the deciduous and eight to the shola forest. Higher abundance of lit­ter ants in deciduous forests was recorded (Table 2). Tapinoma (21%) and Myrmicaria brunnea (17%) were the dominant species in deciduous forest and Solenopsis sp.2. (12%) and Cardiocondyla sp.1 (12%) in the shola forest. Species belonging to seven functional groups were present in the deciduous and six groups in the shola forests (Table 2 & 3). Similar trends of abundance for feeding guilds and dissimilar trends except for the cryptic functional guild were evident in both forests (Fig. 2A & 2B). General predators and om­nivores were the dominant feeding guilds in the deciduous and shola forests. Functional guild scheme showed the dominance of Cryptic species in both forests, followed by gen­eralized Myrmicinae and dominant Dolichoderinae in deciduous forest, and an even dis­tribution of other guilds in the shola forest. Hot-climate specialists did not occur in the shola forest. All feeding guilds were present in both forests. Observed samples (Sobs) and other estimator curves failed to reach a perfect level-off denoting that more species in both forests remain to be found (Fig. 3A & B). Jack1 has the highest estimated value for both shola and deciduous forest (Table 4 ).

Alpha-diversity indices showed greater diversity, evenness, species richness and lower dominance for ants of the shola forests although greater ant abundance was re­corded in the deciduous forest (Table 5). Moderate qualitative and low quantitative simi­larity (~-diversity) between the ant assemblages, low similarity among five functional guilds (dominant Dolichoderinae, subordinate Camponotini, cryptic species, hot-climate specialists, generalized Myrmicinae) and three feeding guilds (omnivores, generalist predators, ant-preferring predators) were also recorded.

Species rank abundance plots for ants (Fig. 4) showed a log distribution (y = -2.70 Ln (x) + 7.61, F = 376.88, R2 = 0.95, p = 0.00 for the deciduous forest; y = -2.96 Ln (x) + 10.78, F = 620.59, R2 = 0.967, p = 0.00 for the shola forest) with the slope being more negative and the intercept being higher for ants from the deciduous forest. When the two abundant species (Tapinoma sp, Myrmicaria brunnea) from deciduous forests were ex­cluded, rank abundance distribution and the intercept of the slope became comparable in two forests (y = -3.14 Ln (x) + 8.96, F = 422.71; R2 = 0.9569, p = 0.00).

Multiple regression showed significant influence of physical factors on ant abun­dance in both forests (R2 = 0.93, F5, 24 = 62.18, P<0.05. for the shola forest; R2 = 0.85, F 5,

24 = 27.80, P<0.05 for the deciduous forest). Moisture and temperature in deciduous for­est and all except humidity in shola forest showed significant multicollinear effects (Ta­ble 6).

Discussion

Litter-ant communities in contiguous shola and deciduous forests varied considera­bly in terms of abundance and composition of feeding guilds and functional groups. A difference in the high number of unshared species and the dominance of different taxa, viz., Solenopsis sp. 2. (12%) and Cardiocondyla sp. 1 (12%) in the shola forest, and Tap­inoma (21%) and Myrmicaria brunnea (17%) in the deciduous forest was evident. High similarity between half of the six feeding guilds (Termite preferring predators, Collem-

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bola preferring predators and Seed eaters) and dissimilarity between 5 out of 7 functional groups (Subordinate Camponotini, Cryptic species, Opportunists, Generalized Myrmici­nae and Specialist predators) in the two forest vegetations supports the view that func­tional group scheme provides a more useful framework for differentiating ant communi­ties than trophically based feeding guilds (Andersen, 1997; Hoffmann & Andersen, 2003). High ~-diversity with 61% of unshared species and the dissimilar abundance pat­tern of functional guilds in geographically closely placed forests reflect the influence of forest vegetation in structuring the ant community composition in the Wayanad region.

As this study was a part of a wider investigation on altitudinal variation in forest­litter insect faunal diversity in Wayanad forests (Sabu, 2005), we observed comparatively higher abundance of larvae and all litter insect groups except termites in deciduous forest. Lower abundance of litter ants in shola forest is attributed to the low prey resource avail­ability (personal observations, First & second authors) especially for the predatory and omnivorous ants. As shola forest sampled in the current study was a smaller patch with a distinct boundary with limited accessibility compared with the sampled deciduous forest, it differs from the widely accepted view that smaller patches with distinct boundaries may carry lesser diversity (Bossart et al., 2006). However, the high diversity and evenness of litter ants in cold wet and moist shola forest with conditions less favorable for litter ants and low prey resource availability prompt us to hypothesize that the low diversity of ants in the low elevation deciduous forest might be related to the anthropogenic inferences of various sorts being close to agricultural frontiers and easy accessibility by roads. Undis­turbed climax evergreen and shola forests Wayanad region are the isolated islands of original residual forest and most of the low and mid land deciduous forests have been fragmented and prone to disturbances because of the conversion of the landscape into ag­ricultural plantations and monoculture plantation forests (Nair, 1991; WWF, 2001 ).

Earlier records from tropics indicated that excessive wetness and coldness associated with the litter habitat in high elevation stunted forests reduces the foraging area and time available for foraging ants (Olson, 1994; Bri.ihl et al., 1999), and the low-litter cover re­duces the foraging area and prey resources (Briihl et al., 1999). Our results agrees with the earlier observations on the regulatory effect of habitat specific physical factors on lit­ter ant abundance and indicates that high litter moisture and low litter depth is likely to be the major factors leading to the low ant abundance in shola forests .

Rank abundance plots suggest that difference in diversity between the two forests is mainly due to the dominance of Tapinoma species and Myrmicaria brunnea in deciduous forests. Abundance of Myrmicaria brunnea, a highly localized species often tending ho­mopterans for honeydew and forms conspicuous columns (Way, 1963), might be a re­gional pattern. Tapinoma sp. belonging to Dolichoderinae is the dominant litter ant group in low and mid elevations of Wayanad and is a well-known scavenger species of open forests world over with a strong preference for honeydew, often tending homopterans, (Buckley & Gullan, 1991; Mack, 2005; Sabu, 2005). Dominance of Tapinoma species and Myrmicaria brunnea in deciduous forest of the region is another instance of this pat­tern. Since members of Dolichoderinae are highly active and aggressive species prefer­ring hot and open habitats, their influence may have a negative impact on the abundance of other ant species in deciduous forests.

Abundance of termite preferring Leptogenys and Solenopsis (Davidson, 1998) in the shola litter habitat, we relate to the abundance of termites in the wet and humid shola for­est litter, which is well suited for isopteran dominance (Borror et al., 1989). Similarly, the

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abundance of termites and the seed availability in the surrounding grasslands may be leading to the abundance of omnivorous ants and the seed harvesting and occasionally termite feeding Phidole sp. (Briihl et al., 1999: Daniels, 1992) in shola forest. Higher abundance of general predators in deciduous forest in comparison shola forest we link to the high prey resource availability viz., collembola and larva (Sabu, 2005).

Abundance of opportunists (Tetramorium) and cryptic species (Solenopsis) recog­nized as a characteristic feature of disturbed sites (Burbidge et al., 1992; Lubertazzi & Tschinkel; 2003) in shola forest point towards the presence of habitat disturbances. His­torical and recent reports (Logan, 1887; Nair, 1991; personal observations of first and second authors) about seasonal summer fires in the shola forest region and the present records about the abundance of above two species associated with disturbed sites strongly indicate habitat disturbances arising from forest fires in the region. Abundance of Ant predators, Aenictus species, prevalent in ant abundant sites and specialized on feeding on other ants (Shattuck & Barnett, 2001), indicates the high abundance of litter ants in the regional deciduous forests (Sabu, 2005).

Failure of observed species accumulation curve to reach a perfect level off position, indicate the need for more sampling to record absolute richness. This prediction is not unexpected as even with the best methods only half the ant species could be effectively estimated unless extensive sampling is done (Delaine et. al., 2000). High beta diversity and dissimilarity for the functional guild, subordinate Camponotini arises from the higher richness of 5 species in shola against one species in deciduous forests. Moderate qualita­tive similarity indicated by Sorenson's index arises from the co-occurrence of 12 species (39% of the total ant species) in both the forests. However, the semi-quantitative Morisita Hom index (MH) indicates high Beta diversity (high dissimilarity) when the abundance data (expressed as incidence data in the present study) is also considered. Non-occurrence of dry habitat preferring hot climate specialists in wet shola forests and the dissimilarities between guilds become obvious only with functional group model classification. Current study reiterates the view (Andersen, 1997; King et al., 1998; Morrison, 1998) that since foraging requirements of ants tend to overlap, functional group classification based on broad range of ecological characters are of better application in ant community studies.

Recorded dissimilarities between ant assemblages of the two contiguous forest types emphasize the need for more vegetation based functional group categorization of ant fauna in other regions of the Western Ghats. However, dearth of information on the ecol­ogy, biology and colonization ability of many ant taxa endemic to Western Ghats may render the application of functional model of classification of ants a demanding task in the region necessitating the need for more ant ecology studies.

Acknowledgements

We thank Ministry of Environment and Forests (MoEF), Govt. of India, for financial support; the Chief Wildlife Warden, Kerala, for permission to enter the studied forests; K. T. Thomachan (Devagiri College, Calicut) for statistical analysis; C. A. Briihl and M. Pfeiffer for several clarifications, A. Raman for critical reading of a final draft of the manuscript and incisive comments and T.N. Ananthakrishnan for literature.

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Table 1. Physical characteristics of litter floor in deciduous and shola forests at Thirunelli in Wayanad

435

Parameters Deciduous Shola forest

No of Probability forest samples

(mean± s.d) (mean± s.d) Litter temperature (uC) 30.6 ±3.7 24.9 ±2.4 30 ***

Litter humidity (%) 59.5 ± 4.5 63.6 ± 2.7 30 ***

Litter depth (em) 7.9 ± 1.7 5.3 ± 1.1 30 ***

Slope of the terrain 16°.2' ± 3°.8' 28°. 8. ± 3°. 1 30 ***

Litter moisture (%) 48.4 ± 7.3 51.1 ±3.5 30 n.s.

* p ~ 0.05; ** p ~ 0.01; *** p ~ 0.001; n.s.- not significant

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436 Oriental Insects Vol. 41

Table 2. Functional group and feeding guild wise categorisation and incidence based abundance of litter ants in deciduous and shola forests at Thirunelli in

Wayanad.

Subfamily Species FG FuG D.F Shola. F Ref

Formicinae Camponotus angusticollis a 0 sc X 1 d Formicinae Camponotus compresses a 0 sc X 2 d

Formicinae Campo notus formaronis a 0 sc X 3 d

Formicinae Camponotus parius a 0 sc X 2 d

Formicinae Camponotus sericeus a 0 sc X I d Formicinae Camponotus radiatus b 0 sc 2 X d Myrmecinae Monomorium sp b 0 HCS 2 X e Myrmecinae Crematogaster sp c p GM 10 3 e Myrmecinae Solenopsis sp 1 c p (T) c 3 6 g Myrmecinae Solenopsis sp2 c P(T) c 8 9 g Myrmecinae Cardiocondyla sp c p c 7 6 d Myrmecinae Cardiocondyla sp 1 c p c 4 9 d Myrmecinae Strumigenys sp c P(Col c 7 2 d Myrmecinae Myrmicaria brunnea b p GM 24 X e Myrmecinae Myrmicaria spa p GM X 4 e Myrmecinae Myrmicaria sp 1 b p GM 2 X e Myrmecinae A1yrmicaria sp2 b p GM 5 X e Myrmecinae Phidole spc s GM 2 4 d Myrmecinae Leptothorax, sp 1 a 0 OP X 2 f Myrmecinae Tetramorium sp 1 c 0 OP 5 7 e Myrmecinae Tetramorium sp2 a 0 OP X 3 e Dolichoderi- Tapinoma sp c 0 DD 30 4 e Ponerinae Leptogenys sp c p (T) SP 2 2 e Ponerinae Pachycondyla sp b p c 1 X d Ponerinae Cryptopone sp b p c 10 X d Ponerinae Odontomachus sp b p HCS 3 X d Ponerinae Diacamma sp 1 c p c 7 1 d Ponerinae Diacamma sp2 b p c 3 X d Dorylinae A en ictus sp 1 b P(A) SP 2 X e Dorylinae A en ictus sp2 b P(A) SP 1 X e Dorylinae Dory/us spc P(A) SP 5 2 g

FG: Feedmg Gmld [0, Ommvores; P, General predators; P (Col), Collembola prefernng predators; P (T), Termite preferring predators; P (A), Ant preferring predators; S, Seed preferring ants]; FuG: Functional Group [SC, Subordinate Camponotini; HCS, Hot cli­mate specialists; GM, Generalized Myrmicinae; OP, Opportunists; DD, Dominant Doli­choderinae; SP, Specialist predators; C, Cryptic species] D. F, Deciduous forest; Shola F, Shola forest; Inc, Incidence based abundance data; Ref, Reference indicators; a, Specific to Shola Forest; b, Specific to Deciduous Forest; c, common to both forests; d, Pfeiffer et al. 2003; e, Mac 1998; r, Shattock and Barnett 2001; g, Samson et al 1997.

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Table 3. Functional group model classification of forest litter ant assemblages and characteristics of each guild in deciduous and shola forests at Thirunelli in Wayanad

Functional guild Taxa

Dominant Dolichoderinae: Prefer hot and open habitats. Abun- Tapinoma dant, highly active and aggressive species, exerting a strong com-petitive influence on other ants.

Snbordinate Camponotini: are behaviourally submissive to Dom Campo notus nant Dolichoderinae.

Hot Climate Specialists: Behaviourally specialized, which reduce Odontomachus interaction with dominant Dolichoderinae. Prefer arid environment.

Monomorium

Cryptic species: Forage predominantly within soil and litter, hav- Small myrmicines ing relatively little interaction with epigenic ants.

& Ponerines

Opportunists: Unspecialised, ruderal species characteristic of dis Tetramorium, turbed sites with low ant diversity.

Leptothorax

Generalized Myrmicinae: Present cosmopolitan, sub-dominant Crematogaster, ants occurring in most habitats with an ability to find and defend,

Phidole rapidly, clumped food resources.

Specialist predators: Little interaction with other ants due to spe- Aenictus, Dory-cialist diet. linus, Leptogenys

Cold climate specialists: Distribution centred on the cool- tern- Not recorded perate zone. Occur in habitats where Dominant Dolichoderines are generally not abundant.

Tropical climate specialists: Occur in habitats where Dominant Not recorded Dolichoderines are not abundant. Distribution centred on humid tropics.

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438 Oriental Insects Vol. 41

Table 4. Species richness estimator values of litter ant assemblages in deciduous and shola forests at Thirunelli in Wayanad. (Bias in parenthesis)

Richness estimators Deciduous forest Shola forest

ICE 23.97(0.04) 21.68(0.08)

Chao2 23.16(0.01) 20.46(0. 02)

Jack 1 24.93(0.08) 22.90(0.15)

Jack2 21.4(- 0.07) 20.29(0.01)

Bootstrap 24.64(0.07) 22.01 (0.1 0)

Table 5. Alpha and beta diversity of litter ant assemblages, and feeding and func-t" I "ld . d "d d h I :fi t t Th" II". W d 1ona 2u1 SID ec1 uous an s o a ores sa 1rune 1m ayana

a diversity Deciduous forest Shola forest Probability

Shannon diversity index (H') 2.70 2.79 *** Simpson dominance index(A.) 0.10 0.07 *** Margalef species richness (d) 4.42 4.43 *** Number of individuals (incidence) 145 73 *** Number of species (S) 23 20 n.s Evenness index (J') 0.86 0.93 Fisher's Alpha (a) 7.70 9.09 j} diversity Sorenson's index Morisita Horn

index Shola and deciduous 0.56 0.44

Assemblages

Feeding guilds Omnivores 0.31 0.41 * General predators 0.50 0.30 *** Termite preferring predators 1.00 0.97 n.s Collembola preferring predators 1.00 1.00 n.s Seed eaters 1.00 1.00 n.s Ant preferring predators 0.50 0.85 * Functional groups Dominant Dolichoderinae 1 1 *** Subordinate Camponotini 0.00 0.00 * Cryptic species 0.8 0.64 * Opportunists 0.5 0.82 n.s Hot Climate specialists• * Generalised Myrmicinae 0.5 0.22 *** Specialist predators 0.66 0.83 n.s

• not recorded from shola forest;* p ~ 0.05; ** p ~ 0.01; *** p ~ 0.001; n.s, not significant.

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Table 6. Auxilary regression analysis for the multicollinearity among physical characteristics in Deciduous and Shola forests at Thirunelli in Wayanad

Shola forest Deciduous forest

Physical factors R.l F42S p- value R.l F42S p-value Humidity 0.14 1.00 n.s 0.07 0.47 n.s Litter depth 0.39 3.96 * 0.22 1.77 n.s Moisture 0.59 9.06 *** 0.56 7.91 *** Slope 0.52 0.45 *** 0.14 0.99 n.s Temperature 0.39 4.05 * 0.62 10.04 *** * p:::; 0.05; ** p:::; 0.01; *** p:::; 0.001; n.s, not sigmficant.

(a) )"-'"*1 (c) N i. ~ Karnataka State ./ <, /) Kannur Dt. w4E ~ '""'-·5\ .. .l ;

\: f'"?j

v\J'/ s

(b) Kamataka ~ ..-

\ ,.J WayanadDt.

~ 3, \ t--'Jo

:2. Cochin (

Calicut Dt. Malappuram Dt.

"" 200 0 200 400 0 IOKM ----- L..--...J

Fig. 1. (a) Location of the Western Ghats in India. (b) The Western Ghats. (c) Study sites in Wayanad region of the Western Ghats.

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"' (.) s::

'" "C s:: ::s

60

40 ~--

~ 20 +---IOOiimriTIIr-- ------

0

60

8

Cl)40 CJ c ns

"C c :I

~20

- ~ !!! 0 "'­c: '" "'""' (!)!!!

0.

ci. C/)

0

~ (.)

C/)

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Oriental Insects

mm_ e""""'

feeding Guild

~~ ca-·u .g "' "' o.~ (/)O.

functional group

.l!! C/)

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Vol. 41

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c;:l Deciduous forest I

!ill Shola forest

m""""'

rJ]I __

1111111111

~ .l!! '" "' "C

"' "' (/)

Jl_' ~;§ c: 0 -- c: -eo 0 0. .o E " '" (/)(.)

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Fig. 2. Feeding guild (A) and functional group wise (B) ant abundance in shola and deciduous forests at Thirunelli in Wayanad.

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25 VI

:!! c 20-.s::. (,) ·;::

:!! 15 "(j G)

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5

B

Vineesh et al.: Community structure of forest litter ants 441

3 5 7 9 11 13 15 17 19 21 23 25 27 29

sample

35-.-----------------------------------------~

_.,_Sobs ---ICE ---+-Chao2

30

VI 25 -:!! c "5 20-·;::

5

3 5 7

~Jack1 --*-Jack2 -e-- Bootstrap ----- --l

9 11 13 15 17 19 21 23 25 27 29 sample

Fig. 3. Species accumulation curves for observed (Sobs) and estimated ant species richness in deciduous (A) and shola (B) forests at Thirunelli in Wayanad.

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12

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o+ 1 2

Oriental Insects

_._1). DF y= -2.70 Ln(x) + 7.61,F= 376.88, R2=0.95 p= 0.00

~2). Shofa y= -2.96 ,Ln(x) + 10.78,F=620.59, R2= 0.967 p= 0.00

• • • 3). DF* y = -3.14 Ln(x) + 8.96, F= 422.71; R2=0.9569 p= 0.00

3 4 5 6 7 8 9 rank

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Fig. 4. Rank and regression line for the litter ants species from shola and deciduous forests at Thirunelli in Wayanad. 1). DF, represents deciduous forest; 2). Shola, shola for­est; and 3). DF*, the hypothetical situation after excluding the two dominant groups from deciduous forest.

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