J. Sci. Univ. Kelaniya 7 (2012): 55-72 OCCURRENCE AND SPECIES DIVERSITY OF GROUND-DWELLING WORKER ANTS (FAMILY: FORMICIDAE) IN SELECTED LANDS IN THE DRY ZONE OF SRI LANKA R. K. SRIYANI DIAS AND K. R. K. ANURADHA KOSGAMAGE Department of Zoology, University of Kelaniya, Sri Lanka ABSTRACT Ants are an essential biotic component in terrestrial ecosystems in Sri Lanka. Worker ants were surveyed in six forests, uncultivated lands and, vegetable and fruit fields in two Districts of the dry zone, Anuradhapura and Polonnaruwa, from November, 2007 to October, 2008 by employing several sampling methods simultaneously along five, 100 m transects. Soil sifting, litter sifting, honey-baiting and hand collection were carried out at 5 m intervals along each transect. Twenty pitfall traps were set up throughout each site and collected after five hours. Air and soil temperatures, soil pH and soil moisture at each transect were also recorded. Use of several sampling methods yielded a higher value for species richness than just one or two methods; values for each land ranged from 19 – 43 species. Each land had its own ant community and members of Amblyoponinae, Cerapachyinae, Dorylinae, Leptanillinae and Pseudomyrmecinae were recorded for the first time from the dry zone. Previous records of 40 species belonging to 23 genera in 5 subfamilies for the Anuradhapura District are updated to 78 species belonging to 36 genera in 6 subfamilies. Seventy species belonging to thirty one genera in 9 subfamilies recorded from the first survey of ants in Polonnaruwa lands can be considered a preliminary inventory of the District; current findings updated the ant species recorded from the dry zone to 92 of 42 genera in 10 subfamilies. Consequent to this sum, the estimate of ant diversity of Sri Lanka rises to 202 species in 64 genera while 12 subfamilies remain unchanged. Corresponding author Email: [email protected] R. K. Sriyani Dias Keywords: Dry zone ant fauna, ant sampling methods, Anuradhapura ants, Polonnaruwa ants, rare ants INTRODUCTION Ants (Order: Hymenoptera; Family: Formicidae) are common and important elements of tropical terrestrial ecosystems because they act as seed dispersers, decomposers, janitors of the world and are functional as predators, prey, detritivores, mutualists and herbivores (Wilson 1971; Alonso 2000). Also, many ant species are useful tools for land management practices (Underwood & Quinn 2010) and ecosystem monitoring in the mining industry, sustainability of fire and grazing management in grasslands (McGeoch 1998; Bisevac & Majer 1999; York 2000). Medicinal properties of ants (Read 1982) as well as their ability to cause allergic reactions and the death of humans (Ratnatilake et al. 2011) have also been documented. Diversity and distribution of worker ant fauna in selected forests, cultivated and uncultivated lands in several wet zone Districts of Sri Lanka were documented by Dias & Perera (2005, 2007a, 2007b, 2007c, 2011), Dias (2006, 2008) and Gunawardene et al. (2008) by using several methods of collection simultaneously (Bestelmeyer et al. 2000; Ogata 2001). According to current records, 182 species belonging to 62 genera in 12 subfamilies have been recorded from Sri Lanka (Dias 2008). Forty species of ants of twenty three genera in five subfamilies have been recorded from four selected lands in Anuradhapura District (Dias & Gunathilake 2007a & b). Forests, uncultivated lands and vegetable and fruit fields in the dry zone appear to have rich ant diversity but very little information on the worker ant fauna of such lands has been documented. This paper presents the species richness and distribution of worker ants in six dry mixed evergreen forests, six uncultivated lands and six vegetable and fruit fields situated in two Districts of the dry zone of Sri Lanka. 56 Species Diversity of Ground-Dwelling Worker Ants METHODOLOGY Field and laboratory Methods The sites selected for this survey consisted of forests, uncultivated lands and vegetable and fruit fields from Anuradhapura and Polonnaruwa Districts (Table 1). Six forests were of dry, mixed evergreen type and F1, F3 and F5 consisted of a dense upper canopy. Among uncultivated lands, U1 and U6 were wild grasslands whereas other lands had trees occasionally. All cultivated lands had been applied herbicides, fungicides, insecticides and fertilizers by the owners. The lands are described in detail in Kosgamage (2011). Five locations of each land (Table 1) were surveyed for ants on the dates shown, using several sampling methods simultaneously along a 100 m transect laid at each location; ants were extracted by (a) soil sifting, (b) leaf-litter sifting (where leaf-litter was available), (c) honey baiting and (d) timed hand collection. Within each transect: (a) Twenty soil samples (each 10 x 10 cm; 5 cm deep) taken at 5 m intervals along a line which was parallel and 2 m left of transect, were sifted through mesh into a white tray. All ants seen with the naked eye were collected into glass vials filled with 85% ethanol. (b) Twenty leaf-litter samples (each approximately 20 x 20 cm wide; 4 cm deep), taken at 5 m intervals along a line which was parallel and 2 m right of the transect, were sifted into a white tray and the worker ants seen with the naked eye were collected into glass vials filled with 85% ethanol. (c) Twenty pieces of gauze (each 5 cm × 5 cm), each with a drop of honey, were placed on the ground at 5 m intervals along the transect, and the pieces of gauze and attending ants were collected after one hour into a plastic bottle filled with 85% ethanol. (d) Hand collection was done for 5 minutes, around a point approximately 5 m apart from the next, with twenty such points in a line parallel and 1 m right of the transect. At each point, worker ants crawling on the ground within a radius of about 80 cm were collected over five minutes and ants were preserved in 85% ethanol. In addition, twenty honey-baited cups were set in the soil, with the mouth of the cups flush with the surface soil level, throughout each sampling area. The cups and the attending ants were collected after five hours and ants 57 R. K. Sriyani Dias Table 1: Lands, GPS co-ordinates, sampling dates and number of samples collected by each method from each land B – Honey baiting; H – Hand collection; S – Soil sifting ; L – Leaf - litter sifting; P – Pitfall trapping. No. of samples Land GPS co-ordinates Date S L B H P 1. Kahalle – Pallekele Forest (F1) 08° 12’ N and 02/11/2007 100 100 100 - - 080° 31’ E 2. Unculltivated land 07° 51’ N and 03/11/2007 100 No 100 100 20 Pohoranwewa, Dambulla. (U1) 080° 37’ E litter 3. Bittergourd field 07° 51’ N and 03/11/2007 100 No 100 100 20 Pohoranwewa, Dambulla (C1) 080° 37’ E litter 4. Nachchaduwa Forest (F2) 08° 16’ N and 02/02/2008 100 100 100 100 20 080° 28’ E 5. Uncultivated land 08° 21’ N and 03/02/2008 100 100 100 100 20 Pulliyarahandiya, 080° 26’ E Anuradhapura (U2) 6. Vegetable and papaya field 08° 20’ N and 03/02/2008 100 No 100 100 20 Kawarakkulama Anuradhapura (C2) 080° 28’ E litter 7. Mihintale Forest (F3) 08° 20’ N and 21/04/2008 100 100 100 100 20 080° 30’ E 8. Uncultivated land 08° 21’ N and 22/04/2008 100 No 100 100 20 Mihintale (U3) 080° 30’ E litter 9. Brinjal field, Thulana (C3) 08° 20’ N and 22/04/2008 100 No 100 100 20 080° 28’ E litter 10. Giritale Forest (F4) 07° 58’ N and 02/07/2008 100 100 100 100 20 080° 54’ E 11.Vegetable, peanuts and corn 07° 57’ N and 03/07/2008 100 100 100 100 20 field, Nikawewa, Polonnaruwa (C4) 080° 56’ E 12. Uncultivated land 08° 00’ N and 03/07/2008 100 No 100 100 20 Jayanthipura, Polonnaruwa (U4) 080° 59’ E litter 58 Species Diversity of Ground-Dwelling Worker Ants Table 1 continued…. Land GPS co-ordinates Date No. of samples S L B H P 13.Nagalakanda Forest, 08° 03’ N and 05/09/2008 100 100 100 100 20 Minneriya (F5) 080° 55’ E 14. Surrounding area of 08° 02’ N and 06/09/2008 100 No 100 100 20 Minneriya tank (U5) 080° 53’ E litter 15. Papaya field 07° 59’ N and 05/09/2008 100 No 100 100 20 Sinhapura, 081° 00’ E litter Polonnaruwa (C5) 16. Somawathiya 08° 01’ N and 19/10/2008 100 No 100 100 20 Sanctuary (F6) 080° 05’ E litter 17. Grassland 08° 01’ N and 19/10/2008 100 No 100 100 20 Pulathisigama, 081° 05’ E litter Polonnaruwa (U6) 18. A field of vegetables, 08° 02’ N and 20/10/2008 100 No 100 100 20 corn and grapes 080° 57’ E litter Hathamuna, Polonnaruwa (C6) were preserved in 85% ethanol. The methods employed in each land and total number of samples collected by each method from each land is shown in Table 1. Ants in each collection were sorted and identified to the furthest possible taxonomic levels under a low power stereo-microscope at suitable magnifications, by reference to Bingham (1903), Bolton (1994) and Bolton et al. (2006) and the reference collection at the Department of Zoology, University of Kelaniya. Richness of ant species observed by each method and all methods from each land was recorded. 59 R. K. Sriyani Dias Measurement of environmental parameters During each survey, air and soil temperature at a representative point of each transect was measured using a thermometer and the mean value per land was recorded. A soil sample from each transect was brought to the laboratory and soil humidity (Brower et al., 1998) of each land was calculated from five mean values.