ABSTRACT. The ant community of Gilimale Forest Reserve in Sri Lanka is of special interest as a habitat of the island-endemic Aneuretus simoni. Ant community composition and aspects of A. simoni ecology in this forest were investigated using multiple sampling methods simultaneously, on six visits to Gilimale from February to December 2004. Daytime sampling of ants was carried out along ten 100 m transects by honey and canned-fish baiting, leaf litter and soil sifting, hand collection, pitfall trapping and mini-Winkler extraction. Honey baits at 1 m height on trees, and honey-baited pitfall traps on the ground, were set overnight. Air and soil temperature, depth of leaf litter and soil moisture during sampling were recorded on each occasion. Fifty species, in 38 genera, were recorded. Aneuretus simoni, Camponotus sp. 1, Carebara sp., Dolichoderus sp. 1, Lophomyrmex quadrispinosus, Monomorium sp., Myrmicaria brunnea, Odontomachus simillimus, Paratrechina (sensu lato) sp., Pheidole sp. 2, Pheidole sp. 7, Pheidolegeton sp., Polyrhachis sp., Solenopsis sp., Technomyrmex bicolor and Tetramorium bicarinatum were common and detected on all occasions. Detectability of A. simoni was consistently high and the species comprised 3-6% of worker ants collected on each of the six occasions.
Keywords: Aneuretus simoni Emery, Gilimale Forest Reserve, species richness, rare ants, multiple methods, repeated sampling
INTRODUCTION
Since 1955, Gilimale Forest Reserve in Sri Lanka has been known as a habitat of the Sri Lanka-endemic ant, Aneuretus simoni Emery (Wilson et al. 1956; Jayasuriya & Traniello 1985), the sole extant representative of Subfamily Aneuretinae. Gilimale Forest Reserve (6° 47' N and 80° 28' E, average altitude 152 m) occupies approximately 1147 ha and is situated in Ratnapura District, in Sabaragamuwa Province. This wet evergreen tropical forest receives on average 4758 mm of rainfall annually and is characterised by highly dissected terrain with numerous streams draining into several rivers. The average slope ranges from 9o to 15o but certain areas adjoining streams and rivers are extremely steep (Balasubramanium et al. 1991).
Eleven ant genera (Aneuretus, Camponotus, Crematogaster, Euponera (Brachyponera), Euponera (Mesoponera), Myrmicaria, Paratrechina (Nylanderia), Pheidole, Ponera, Polyrhachis and Technomyrmex) were recorded from the forest by Wilson et al. (1956) whereas ten genera (Aneuretus, Camponotus, Crematogaster, Monomorium, Odontomachus, Pachycondyla, Paratrechina, Ponera, Solenopsis and Tetramorium) were recorded by Jayasuriya & Traniello (1985). Our first survey of Gilimale Forest, in February 2004, revealed nine subfamilies (Aenictinae, Amblyoponinae, Aneuretinae, Dolichoderinae, Dorylinae, Formicinae, Leptanillinae, Myrmicinae and Ponerinae) and 37 species including A. simoni (Dias & Perera 2005a). Three visits in April, June and August 2004 collectively recorded nine subfamilies (Pseudomyrmecinae added; Dorylinae not found) and 35 species from the ground and lower canopy of the forest (Dias & Perera 2005b). The survey was extended through October and December 2004 and the results of the six visits are combined here to characterise the community of ground-dwelling ants observed by simultaneous multiple sampling in Gilimale Forest throughout 2004. We also report on several ecological aspects of A. simoni workers in this forest.
METHODS
Field and laboratory methods
Ten locations of Gilimale Forest Reserve were surveyed for ants, using several sampling methods along a 100 m transect laid at each location, on 23-26 February, 15-18 April, 24-27 June, 24-27 August, 29-31 October and 17-19 December 2004. At each location we carried out extraction of ants by (a) mini-Winkler sacks, (b) soil sifting, (c) pitfall trapping, (d & e) honey and canned fish baiting, (f) litter sifting by hand and (g) timed hand collection. Within each transect:
(a) Five polythene bags were each filled with leaf litter from five different 1 m2 areas, sampled at 20 m intervals along the transect, and the litter in each bag was transferred to a mini-Winkler sack kept in the laboratory. The worker ants emerging after 48 h were preserved in 85% ethanol.
(b) Ten soil samples (each 20 x 20 wide x 10 cm deep), taken at 10 m intervals along a line which was parallel and 1 m left of the 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.
(c) Ten cups (volume: 110 cm3), each half-filled with soap water, were set in the soil at 10 m intervals along a line parallel and 1 m right of the transect, with the mouth of the cups flush with the surface soil level.
(d, e) Twenty-five baits each of honey and canned fish (jack mackerel in natural juice with added salt), on a 5 cm x 5cm piece of gauze, were placed alternately on the ground at 4 m intervals along the
transect, and the pieces of gauze and attending ants were collected after one hour into a plastic bottle filled with 50% ethanol.
(f) Ten litter samples (each of one full sieve), taken at 10 m intervals along the transect, were sifted into a white tray and ants seen with the naked eye were collected into a vial filled with 85% ethanol.
(g) Hand collection was conducted for 10 minutes, around a point approximately 10 m apart from the next, with ten such points in each transect. At each point, ants crawling on the forest floor along a horizontal line which connects each point at 1 m left and 1 m right of the transect, were collected and ants were preserved in 85% ethanol.
Some of the locations were also sampled at night by different methods: (h) honey-baited pitfall traps on the ground and (i) honey baited small plastic vials hung on trees.
(h) In three of the transects used during the daytime, ten plastic cups of 110 cm3, each honey-baited and half-filled with 50% ethanol, were set in the evening in the soil along the 100 m transect.
(i) At the same three locations in February, and five locations on subsequent occasions, ten honey-baited small plastic vials were hung in the evenings (17:00-18:00 h) on ten trees, 10 m apart along the transects, and were collected at around 07:00 h the following morning.
Collected ants were preserved in 85% ethanol and the presence of A. simoni and other species was recorded. Ants were identified to the furthest possible taxonomic level using a low-power stereo-microscope at suitable magnifications with the assistance of Prof. Seiki Yamane, Kagoshima University, Japan, and by reference to Bolton (1994, 2003). Scientific names of the ants are given according to Bolton et al. (2006).
Measurement of environmental parameters during the sampling of ants
During each survey, air and soil temperature at the start, middle and end points of each transect were measured using a thermometer and the mean value per transect was recorded. Depth of the leaf litter layer was measured in the same manner using a ruler, and the mean depth (cm) per transect was recorded. Similarly, three subsamples of soil from each transect were brought to the laboratory and soil humidity (Brower et al. 1998) of each transect was recorded. The mean value of each parameter during the sampling period was calculated from the ten locations measured on each occasion.
RESULTS
Species richness and composition of worker ant community
Table 1 shows that worker ants belonging to 11 subfamilies, 38 genera and 50 species were recorded from the six visits to Gilimale Forest in 2004. The number of subfamilies observed on the six occasions was 9, 8, 5, 8 and 6, respectively. Seventeen species (Aneuretus simoni Emery, Camponotus sp. 1, Carebara sp., Dolichoderus sp., Lophomyrmex quadrispinosus (Jerdon), Leptogenys sp., Monomorium sp., Myrmicaria brunnea Saunders, Odontomachus simillimus F.Smith, Paratrechina (sensu lato) sp., Pheidole sp. 2, Pheidole sp. 7, Pheidolegeton diversus (Jerdon), Polyrhachis sp., Solenopsis sp., Technomyrmex bicolor Emery and Tetramorium bicarinatum (Nylander)) were common on all occasions and observed throughout the study period. In addition Acropyga acutiventris Roger, Cardiocondyla sp., Cerapachys sp., Dorylus sp., Pachycondyla sp. 3, Pheidole sp. 8 and Tetraponera allaborans (Walker) were observed on two or more of the six visits. The highest species richness was recorded in February whereas lowest species richness was observed in December (Fig. 1).
Table 1. Worker ant species observed on each visit to Gilimale Forest and overall worker ant community recorded in 2004. Bold letters show the species observed on all occasions. Species numbers are according to the first author's collection kept at the Department of Zoology, University of Kelaniya, Sri Lanka. *sensu lato. p = present.
Subfamily
Genus/ species
Visit
1
2
3
4
5
6
1. Aenictinae
Aenictus sp.
p
p
-
p
-
-
2. Amblyoponinae
Amblyoponesp.
p
p
-
p
-
p
3. Aneuretinae
Aneuretus simoni
p
p
p
p
p
p
4. Cerapachyinae
Cerapachyssp.
-
p
-
-
-
-
5. Dorylinae
Dorylus sp.
p
-
-
-
-
-
6. Dolichoderinae
Dolichoderus sp.
p
p
p
p
p
p
Tapinoma indicum
p
-
-
p
-
-
T. melanocephalum
-
-
p
p
p
-
Technomyrmex bicolor
p
p
p
p
p
p
Technomyrmex albipes
p
-
p
p
p
p
7. Formicinae
Acropygaacutiventris
-
-
-
-
-
p
Anoplolepis gracilipes
p
p
p
p
-
-
Camponotus sp. 1
p
p
p
p
p
p
Camponotus sp. 2
p
p
p
p
-
-
Lepisiota sp.
p
-
-
-
-
-
Myrmoteras sp.
p
-
p
-
-
p
Paratrechina*sp.
p
p
p
p
p
p
Paratrechina longicornis
p
-
-
p
p
-
Polyrhachis sp.
p
p
p
p
p
p
Pseudolasiussp.
-
-
p
p
p
-
8. Leptanillinae
Leptanilla sp.
p
-
p
p
p
-
9. Myrmicinae
Calyptomyrmex sp.
-
-
p
p
p
-
Cardiocondyla sp.
p
-
-
-
-
-
Carebarasp.
p
p
p
p
p
p
Cataulacus sp.
-
p
p
p
-
-
Crematogaster sp. 1
p
p
p
p
p
-
Crematogaster sp. 2
p
-
-
-
-
p
Crematogaster sp. 3
p
-
-
-
-
p
Lophomyrmexquadrispinosus
p
p
p
p
p
p
Meranoplus bicolor
-
-
p
p
p
-
Monomoriumsp.
p
p
p
p
p
p
Myrmicariabrunnea
p
p
p
p
p
p
Pheidolesp. 2
p
p
p
p
p
p
Pheidolesp. 7
p
p
p
p
p
p
Pheidolesp. 8
p
-
-
-
-
p
Pheidologetonsp.
p
p
p
p
P
p
Solenopsissp.
p
p
p
p
P
p
Strumigenys (Quadristruma) sp.
p
p
p
p
P
-
Tetramorium sp.
p
p
p
-
P
p
Tetramoriumbicarinatum
p
p
p
p
P
p
10. Ponerinae
Anochetus sp.
p
p
-
p
P
p
Centromyrmex feae
p
p
p
-
P
-
Hypoponerasp.
p
p
p
p
P
-
Leptogenys sp.
p
p
p
p
P
p
Odontomachus simillimus
p
p
p
p
P
p
Ponerasp.
p
p
p
p
-
p
Pachycondylasp. 1
-
p
p
-
P
p
Pachycondylasp. 2
-
p
-
-
P
-
Pachycondylasp. 3
-
-
-
-
-
p
11.Pseudomyrmecinae
50)Tetraponera allaborans
-
-
-
p
P
-
Total
39
32
34
36
33
29
Fig.1. Species accumulation curves for ten transects on each visit, and overall cumulative number of species recorded, from Gilimale Forest. (Night time baits were unsuccessful and did not collect ants on all occasions.)
Effects of using several sampling methods and transects on recorded species richness
Employing a combination of several simultaneous sampling methods yielded more ant species than using a single method on each occasion (Table 2). The cumulative number of species observed during this study increased with the number of transects (to ten) and visits (to six) (Fig. 1).
Table 2. Species richness recorded by each sampling method and the overall methods on each visit to Gilimale Forest in 2004. Only daytime sampling methods used at all sites are shown.
CB = Canned-fish Bait, HB = Honey Bait, LS = Litter Sieving, SS = Soil Sieving, HC = Hand Collection.
Month
CB
HB
LS
SS
HC
CB+HB+LS+SS+HC
February
19
24
27
22
17
39
April
17
19
22
14
24
32
June
20
19
20
15
20
32
August
22
21
23
12
16
36
October
16
21
17
13
22
32
December
11
13
15
11
14
29
Total
27
30
37
34
31
50
Environmental parameters
Slight differences in environmental conditions among sampling periods on the six occasions were noticeable (Table 3). The highest and lowest soil relative humidity were recorded on February and June visits, respectively.
Table 3. Environmental parameters of Gilimale Forest recorded on each occasion in 2004 (mean of ten measurements ± SD).
Parameter
Feb
Apr
Jun
Aug
Oct
Dec
Air temperature (oC)
27.0 ± 2.8
29.1 ± 1.2
26.0 ± 1.3
28.5 ± 2.0
27.6 ± 1.7
27.5 ± 2.5
Soil temperature (oC)
24.6 ± 1.3
26.5 ± 0.53
24.4 ± 0.53
26.0 ± 1.7
26.3 ± 1.8
25.3 ± 2.1
Mean litter depth (cm)
2.3 ± 0.89
4.7 ± 1.7
5.3 ± 0.44
3.9 ± 0.2
4.6 ± 1.0
2.6 ± 1.1
Soil humidity %
35.7 ± 2.2
32.1 ± 1.4
19.6 ± 0.19
23.3 ± 4.6
28.0 ± 2.1
33.0 ± 4.1
Aspects of the ecology of A. simoni
The sampling methods varied in effectiveness in catching A. simoni workers, between transects and between times of year (Table 4). No sampling method was effective in attracting these workers on all occasions. The species was recorded in all months at Transects 2, 3, 4, 5 and 7 and in all except December at Transects 1, 6 and 9. Percentage frequency of occurrence ((Number of transects positive for A. simoni / 10) x 100) of this species in Gilimale Forest ranged from 80% to 90% on the six occasions. The relative abundance of workers ranged from 3% to 6% of all collected specimens, with the highest proportion in February (Table 4). Table 5 shows that all methods except the tree traps were effective for detecting this species on each occasion.
Table 4. Sampling methods that caught A. simoni workers in each transect laid, percentage frequency of occurrence in transects, and relative abundance of this ant species in Gilimale Forest. Numbers in parentheses indicate the total number of ants encountered on each occasion.
CB = Canned-fish Bait, HB = Honey Bait, HC = Hand Collection, LS = Litter Sieving, PT = Pitfall Trapping, SS = Soil Sieving, WM = Mini-Winkler extraction.
Year 2004
Transect number
Frequency of occurrence (% of transects)
1
2
3
4
5
6
7
8
9
10
Feb
CB HB LS
LS PT
HB LS
CB SS
SS
HB
HB LS WM
HB
80
Apr
HB LS PT
CB HB LS PT
HB LS HC
LS HC
CB HB PT
CB HB
CB LS
LS HC
LS
90
Jun
HB
SS PT
HB LS
CB HB LS PT
CB HB
CB SS HB
LS SS HB
HB
LS
80
Aug
WM
HB LS PT
HB LS PT
HB LS PT
CB
HB LS
CB HB PT
HB
CB HB
90
Oct
LS HC PT
HB LS PT
HB LS HC
HB LS PT
HB CB HC
CB HB SS
CB HB LS
LS
LS
90
Dec
LS SS
HB LS HC
SS
LS
LS
LS
90
Table 5. Effective sampling method/s for each species. *sensu lato.
CB = Canned-fish Bait, HB = Honey Bait, HC = Hand Collection, LS = Litter Sieving, PT = Pitfall Trapping, SS = Soil Sieving, WM = Mini-Winkler extraction, TT = Tree traps.
Ant species
Effective methods
Aenictus sp.
LS, SS, HC
Amblyoponesp.
LS, SS
Aneuretus simoni
CB, HB, LS, SS, HC, WM, PT
Cerapachyssp.
SS
Dorylus sp.
CB,SS, HC
Dolichoderus sp.
CB, HB, LS, HC, PT, TT
Tapinoma indicum
CB, HB, LS, SS, HC, PT
T. melanocephalum
CB, HB, SS, TT
Technomyrmex bicolor
CB, HB, LS, SS, HC, WM, PT, TT
Technomyrmex albipes
CB, HB, LS, SS, HC, PT, TT
Acropygaacutiventris
SS
Anoplolepis gracilipes
CB, HB
Camponotus sp. 1
CB, HB, LS, HC, WM, PT, TT
Camponotus sp. 2
CB, HB, LS, HC, WM, PT, TT
Lepisiota sp.
LS, SS
Myrmoteras sp.
LS, SS
Paratrechina*sp.
CB, HB, LS, HC, WM, PT, TT
Paratrechina longicornis
LS, SS
Polyrhachis sp.
CB, HB, SS, HC
Pseudolasiussp.
SS
Leptanilla sp.
LS, SS
Calyptomyrmex sp.
SS, PT
Cardiocondyla sp.
SS
Carebarasp.
CB, HB, LS, SS, HC, WM
Cataulacus sp.
HC
Crematogaster sp. 1
CB, HB, LS, HC, PT, TT
Crematogaster sp. 2
CB, HB, LS, HC
Crematogaster sp. 3
CB, HB
Lophomyrmexquadrispinosus
CB, HB, LS, HC
Meranoplus bicolor
HB, LS, PT
Monomoriumsp.
HB, LS, WM
Myrmicariabrunnea
CB, HB, LS, SS, HC, WM, PT, TT
Pheidolesp. 2
CB, HB, LS, SS, HC, WM, PT
Pheidolesp. 7
CB, HB, LS, SS, HC, WM, PT
Pheidolesp. 8
CB, HB, LS, SS, HC, WM, PT
Pheidologetonsp.
CB, HB, LS, SS, WM, PT
Solenopsissp.
CB, HB, LS, SS, HC, WM, PT
Strumigenys (Quadristruma) sp.
LS, HC, WM
Tetramorium sp.
CB, HB, LS, HC, PT
Tetramoriumbicarinatum
CB, HB, LS, SS, HC, WM, PT
Anochetus sp.
HB, LS, SS, HC
Centromyrmex feae
LS, SS
Hypoponerasp.
LS, SS
Leptogenys sp.
HB, LS, SS, HC, PT
Odontomachus simillimus
CB, HB, LS, SS, HC, PT
Ponerasp.
CB, HB, LS, SS, HC, PT
Pachycondylasp. 1
LS
Pachycondylasp. 2
HC
Pachycondylasp. 3
LS, SS
Tetraponera allaborans
LS, HC
DISCUSSION
Twelve subfamilies of ants have been recorded from Sri Lanka (Bolton 1995, 2003) and all but Ectatomminae were observed during this survey. Aneuretinae, Dolichoderinae, Formicinae, Myrmicinae, Ponerinae and Pseudomyrmecinae were observed throughout the study period. Two subfamilies more rarely encountered in Sri Lanka, Cerapachyinae (detected only from soil sifting, Table 5) and Dorylinae (detected only from canned fish baits, soil sifting and hand collection, Table 5), were detected on single occasions, and Aenictinae, Amblyoponinae and Leptanillinae were observed on three to four visits (Table 1), probably due to their cryptic habit and lower effectiveness of these methods. All five ant subfamilies recorded from this forest by Wilson et al. (1956) and Jayasuriya & Traniello (1985), Aneuretinae, Dolichoderinae, Formicinae, Myrmicinae and Ponerinae (according to current classification), were recorded during the present survey.
Sixty-two genera of ants (Bolton 1995; Dias 2006, 2008) have been recorded from Sri Lanka and 38 of those were recorded from Gilimale Forest in 2004, indicating a high diversity of ants in this wet zone forest. This is the only survey of ants that has been conducted in Gilimale Forest recently using several sampling methods simultaneously and also with repeated sampling. Higher species richness was revealed by the simultaneous application of several sampling methods, as observed in other ant research conducted in Sri Lanka (Dias & Gunathilake 2007a, b) and elsewhere.
All ant genera reported previously at Gilimale by Wilson et al. (1956) were collected during this survey. In addition to the 11 ant genera reported by Wilson et al. (1956) this study recorded 26 additional genera from the Gilimale Forest. Pheidole, Monomorium, Tetramorium and Paratrechina were reported from this forest in 1979 by Jayasuriya & Traniello (1985) and were also observed in 2004 (Table 1). Other ant genera associated with A. simoni in "Pompekelle", Ratnapura (another habitat of this species) in May 2001, Anoplolepis, Cataulacus, Crematogaster, Pachycondyla, Pheidole, Pheidologeton, Solenopsis and Teramorium (Dias 2004), were also observed in the present collection. The results of the present survey suggest this forest reserve has continuously been a habitat of A. simoni from 1955 (Wilson et al. 1956) to 2004. It appears that environmental conditions such as soil temperature (24°C to 28°C in 2004) and soil humidity (19.6% to 35.7% in 2004) (Table 2) are favourable for this rare and endemic ant species when compared with those at a dry-zone forest (soil temperature: 30.6°C to 31.1°C; soil humidity 4.8% to 6.4%) where this ant was absent (Kosgamage & Dias, 2009).
Table 4 summarises the sampling methods that caught A. simoni workers along each transect laid on each occasion in 2004. The use of honey baits in daytime and leaf-litter sifting resulted in finding the workers of this species more often than the other methods. Although overall relative abundance seemed to be low (Table 4) this species made up a considerable proportion of individuals of this ant community. However this compound measure of abundance is influenced by the effectiveness of each method in detecting each species, and gives only an indication of actual relative abundance. Table 4 shows there is a high probability of detecting the species using these methods.
The species recorded in Table 1 can be considered a preliminary inventory of the ants of Gilimale Forest Reserve and the list can doubtless be extended. But it serves as a reference for ant researchers and ecologists. Clearing of this forest for cultivation or development should be prohibited, as such actions may affect the existing favourable conditions for this evolutionarily-important ant species as well as for other rare ant species such as Aenictus sp., Amblyopone sp., Cerapachys sp., Dorylus sp., Leptanilla sp. and Cardiocondyla sp. Further ant surveys are recommended to improve the current inventory and to investigate the nesting ecology of A. simoni.
ACKNOWLEDGEMENTS
Financial assistance from the National Science Foundation of Sri Lanka (RG/ 2003/ZOO/06) and field assistance from Zoology students and demonstrators are highly acknowledged. We thank the Forest Department, the Conservator of Forests and the Wildlife Conservation Department of Sri Lanka for granting permission to enter this forest to conduct the survey. Two anonymous reviewers and editors Dr Martin Pfeiffer and Dr John Fellowes, who contributed to improving this manuscript, are also acknowledged.
