resource utilization by two new guinea rainforest ants

Resource Utilization by Two New Guinea Rainforest AntsAuthor(s): Kristine P. PlowmanSource: Journal of Animal Ecology, Vol. 50, No. 3 (Oct., 1981), pp. 903-916Published by: British Ecological SocietyStable URL: http://www.jstor.org/stable/4145 .

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Journal of Animal Ecology (1981), 50, 903-916

RESOURCE UTILIZATION BY TWO NEW GUINEA RAINFOREST ANTS

BY KRISTINE P. PLOWMAN

Zoology Department, University of Queensland, St Lucia, Q, 4067, Australia

SUMMARY

(1) The resource utilization of two species of Leptomyrmex was observed (i.e. distribution of nests, foraging territories, colony size, items collected, daily activity patterns) in a Papua New Guinean montane rainforest.

(2) There was little temporal but some spatial separation in activity between the two species. The composition of items carried to the nest differed. Leptomyrmex lugubris displaced L. fragilis from nest sites without fighting and contact between individuals was avoided.

(3) Leptomyrmex lugubris had larger colonies with a few obvious trails traversing foraging areas specific to one colony, repletes were occasionally seen, plant matter and frass were items most commonly carried to the nest.

(4) Leptomyrmex fragilis colonies were small, trails were not obvious and foraging areas sometimes overlapped. Repletes were common and the majority of items carried to the nest was animal matter.

(5) Both species visited plants and gathered plant secretions. Both within and between species different colonies did not appear to share trees. The importance of trees as a resource is considered.

INTRODUCTION

Little is known of the ecology of the ant fauna of Papua New Guinea (Wilson 1959) and it is only partially surveyed. This paper presents data on the resource utilization of two dolichoderine species, Leptomyrmex lugubris Wheeler and L.fragilis (F. Sm.), living on the forest floor of a Papua New Guinean montane rainforest. Leptomyrmex species have been reported from a broad range of habitats in Papua New Guinea (Room 1975; Wilson 1959). This paper describes each species' distribution in space and its foraging strategy.

METHODS

The study was made on the southern slopes of Mt Sisa (lat. 6?9'S; 142?45'E) Southern Highlands Province, Papua New Guinea. The area selected was forest regrowth at an altitude of about 1100 m which had last been gardened about 20-25 years ago. It was approximately 1 km from the Etolo village of Bobole. This forest is lower Mountain forest (after Womersley 1978) characterized by plant families such as Lauraceae. Fagaceae and Elaeocarpeae. Tall stilt pandans occur in wetter places, epiphytes are common. Two seasons are recognized; (i) the cloud season, which begins in May, is characterized by low cloud and misty rain which increases in frequency until July and then declines through August and September and (ii) the pandanus season lasts from October until April, and has predominantly sunny days, afternoon thunder storms and an abundance of the fruit of the

0021-8790/81/1000-0903$02.00 ? 1981 Blackwell Scientific Publications

903



904 Ecology of rainforest ants

edible pandanus (Pandanus conoideus). From April 1979 to March 1980 rainfall recorded at Bobole was 4691 mm and temperature ranged from 31 ?C to 12.5 ?C; the mean monthly maximum was 26.2 + 1.8 ?C and the mean monthly minimum was 18.1 + 0.8 ?C.

A grid of 90 x 135 m (1.22 ha), marked at intervals of 15 m, was studied. Nests and trails of ants were identified by searching the eight grid lines, A-G (fig. 1). Foraging ants were encouraged to return to their nests by offering them mosquitoes. Leptomyrmex lugubris trails were usually conspicuous and nests were easily located. Three major censuses in April and June 1979 and February 1980 were supplemented by monthly checks of known nests. Between October and December 1979 activity counts were made

(a)

D -

C-

B- *

~~A-~~~~~x

! I . . . * . .

10 9 8 7 6 5 4 3 2 1

G - (b)

F - x

E - ,

B-

A _+:X

FIG. 1. The study area showing nests sites and trails of (a) L. fragilis and (b) L. lugubris. O, nest site used throughout the study; *, nest disappeared during the study; *, nest appeared

during study; 0, root parasite; x, tree.



through the day at two nests for each species. Between October 1979 and March 1980, items carried to three nests of each species were collected by trapping ants in a vial. To reduce bias towards large items the first ant seen with an item was taken. Collections were never made over a period exceeding 1 h; nor was the same nest sampled on consecutive days. Items were identified by eye in the field and were stored in alcohol for determination of dry weights.

RESULTS

Distribution of nests

Figure 1 plots the distribution of nests and of major trails for both species. It distin- guishes between nests that were present in both the June 1979 and the February 1980 censuses and nests that either disappeared or appeared in the intervening period. Nests that were located off the immediate area of the grid, but whose colony members foraged onto the grid, are also shown.

Thirteen colonies of L. lugubris foraged on the grid through the entire study period; at each of the June and February censuses, eleven of these utilized the grid. These colonies used twelve nest sites, the nest at G1 being occupied at different times, by two colonies. Eight colonies had their nests on the grid (seven nest sites). Five were present throughout the study, six were recorded in June and seven in February. Thus five of the nest sites located on the grid were occupied permanently, another (at G1) held very few L. lugubris between August and December and one was newly established after June. For colonies whose nest sites were located off the grid but which foraged onto it, four of five nest sites were occupied throughout the study while the fifth vanished during the study.

Twelve colonies of L. fragilis foraged on the grid and all but two had nests there. Shifts of nest site occurred for two of these colonies, near G1 and F8 respectively, between June and February. Seven colonies had their nests on the grid in June and 9 in February. Six of these were present throughout the study. In early February the colony at A3 divided with some individuals occupying a new site a few metres from the parent nest. The new site was abandoned within a few weeks.

There were only two of the fifty-four available grid squares (15 x 15 m) that held nests of both species (see G1 and BC89, Fig. 1). At G1 a colony of L.fragilis occupied the L. lugubris nest site during the period this species was absent. At other times the nests used by this L. fragilis colony were only a few metres from the L. lugubris nest. At grid square BC89 nests of the two species were 22 m apart and, although the foraging areas of these two colonies overlapped, the species were rarely seen together and no interactions were observed. For nests present on the grid throughout the study the mean nearest neighbour distances were 40 + 10 m for L. lugubris (n = 6, including G1) and 51 + 19 m for L. fragilis (n = 6). Nests of both species were overdispersed (L. lugubris R = 1 6, L.fragilis R = 2.2; Clark & Evans 1954).

Most nests of L. lugubris were in the bases of trees and tree stumps n = 9. Two were associated with both fallen logs and tree bases and 1, which disappeared during the study, was in soil beneath a fallen log. Entrances to these nests were usually concealed. Four L. fragilis nests were in the bases of trees, eight were in the ground and one was beneath a tangle of fallen logs. Nests in the soil usually had large entrances with a ring of ants visible just inside the entrance (cf. Wilson 1959).

Colonies of L. lugubris were considerably larger than those of L. fragilis. Estimates of the foraging population at different times of the day, for two colonies of each species, are

905 K. P. PLOWMAN



Ecology of rainforest ants

given in Table 1. Maximum foraging populations for L. lugubris are an order of magnitude greater than for L. fragilis. If the foraging population accounts for 10-20% of the colony (cf. Petal 1978) then these L. lugubris colonies included from 4000 to 10 000 individuals while the L. fragilis colonies included from 300 to 1000 individuals. Two observations of entire L. fragilis colonies on the move gave estimates within this range. Wilson (1959) estimated colony size for this species at about 300.

Daily activity The pattern of activity through the day appeared to be similar for both species. Ants left

the nest in relatively large numbers shortly after dawn, the rate of departure fell quite rapidly and through much of the day approximated the rate of return (Table 2). On some

TABLE 1. Estimation of (i) mean foraging population of two colonies of L. lugubris and of L. fragilis calculated by differences between the mean numbers entering and leaving the nest per hour for each sampling period and (ii) the population of colonies

assuming 10 or 20% forage (i) Sampling Period (ii) Estimation

8-9 a.m.

L. lugubris Nest 1 (10.8 h) Nest 2 (6-8 h)

L.fragilis Nest 1 (4-6 h) Nest 2 (6.0 h)

168 636

60 110

10-11 a.m.

1-3 p.m.

4-5 p.m.

336 402 1044 24 69 864

30 0

6 3

10%

10 440 8640

6 600 45 1100

20%

5220 4320

300 550

TABLE 2. The mean numbers of individuals per minute of (a) L. lugubris and (b) L. fragilis leaving and entering the nest and the percentage of those entering the

nest carrying items or that were replete during each sampling interval

Species L. lugubris

Nest 1 8-9 a.m. 10-11 a.m. 1-3 p.m. 4-5 p.m.

Nest 2 8-9 a.m. 10-11 a.m. 1-3 p.m. 4-5 p.m.

L.fragilis Nest 1

8-9 a.m. 10-11 a.m. 1-3 p.m. 4-5 p.m.

Nest 2 8-9 a.m. 10-11 a.m. 1-3 p.m. 4-5 p.m.

X entering X leaving % carrying nest nest items % replete

23.1 33.5 25.5 27.7

22.7 26.5 25.4 31-9

25-9 27.9 18.8 10.3

33.3 26.9 24.2 17-5

40 0 48 0 58 0 24 0

30 0 38 0 43 0 25 0

0.5 1-5 60 0 0.6 1.1 60 2 0.9 1.0 46 33 0.3 0.2 23 0

1.0 2.8 33 5 0.7 0.7 29 6 1.0 0-9 30 27 1-4 0.6 3 76

906



occasions, particularly if rain fell, the late afternoon return to the nest was conspicuous. There was considerable temporal variation in activity levels which reflected changing weather conditions and, presumably, short-term changes in resource availability. There was no evidence of nocturnal foraging in either species (cf. Stradling 1978; Lewis, Pollard & Dibley 1974).

Detailed information was obtained at one colony of L. lugubris. This colony was not on the grid. Activity records for 2 days are plotted in Fig. 2. The morning exodus entailed an initial period when the ants were highly excited and ran to and fro at the entrance of the nest until a column commenced moving along the trail that had been used the previous day. Emergence time varied with light intensity and the period of en masse departure occupied about 20 min. As it subsided individuals would commence returning to the nest carrying items. Thereafter, departures and arrivals were relatively even until late afternoon when departures fell virtually to zero and, with failing light, arrivals steadily declined. The last individuals returning to the nest were without items.

30 Jan., 1980

35 -

I I I I I I ,I I I ,I t-:Z I* I I I I _

1 I --

3 am 7am 8 am 9 am 4 pm 5 pm

I I II I I I I I I I I I I I I

8 am 9 am 4 pm

Time

5 pm 6 pm 6.30 pm

FIG. 2. Activity patterns of a colony of L. lugubris. A, individuals per min leaving the nest; *, individuals per min returning to the nest; t, first item carried to the nest; ;, no more items carried

to the nest; *, rain.

I \. t 1k;~ Fi

30

25

20

15

10

5

a)

V

V

H

-L 1)

H

29 Jan., 1980

40 -

6 pm 6.30 pm

35 -

30-

25

20

15 -

10

5

6 am 7 am

I I I

K. P. PLOWMAN 907

ll4

I I)- I4r-




Only 1 trail led from this nest. It went to a tree 45 m away. Some ants from the colony always moved directly to the tree while others digressed from the trail to forage. On one morning (not shown in Fig. 2) ants emerged from the nest at 7.28 a.m. and the leaders of the trail reached the tree at 8.50 a.m.; they had travelled at 1 m per 1.82 min. Within 2 min of reaching the tree seventy-eight individuals had climbed it; probably about one quarter of the initial group of ants. Fig. 3 shows the behaviour of ants at the 'tail-end' of this morning exodus. The upper portion of the figure shows rates of departure from and entry to the nest and the rates of movement to and from the nest at distances of 5, 15 and 45 m respectively. These latter values were obtained at the times when it was estimated that the ants counted out of the nest would be passing the recording station if they had remained on the trail (i.e. for 5 m the count was made 9 min after ants had left the nest). The lower portion of the figure shows that more than 60% of departing individuals had left the trail before they were 5 m from the nest and that only 9% reach the tree. The figure also shows that, for individuals returning to the nest, the proportion that were carrying items was greatest at 15 m. This latter value, however, may be correlated with time since departure rather than with distance travelled. Activity at the tree itself was sustained at a low level throughout the day. In the 5 min after seventy-eight individuals had been counted up the tree only two more individuals went up while seven came down. Later in the morning, at about 10.15 a.m., ants went up the tree at a rate of 1.2 per min. and came down at a rate of 0.9 per min (1 1-min count). Similar observations were made at other trees used by L. lugubris; after an initial early morning period when large numbers of individuals went up the tree, activity in either direction was relatively low. Fig. 4 gives data for one grid colony (nest 2 of Table 1). Over 300 individuals were counted going up a tree within a 10-min period; this represents approximately 30% of the estimated foraging population for this colony.

(a) 20-

E 15- 4

10-

100- (b)

80-

60-

40- -

20- ^ ~ r

Nest 5m 15 m Tree (45 m)

Distance from nest

FIG. 3. Foraging L. lugubris recorded at the nest, 5 m, 15 m and 45 m from the nest: (a) individuals per min entering (*) and leaving the nest (*), passing 5 m, 15 m and 45 m and (b) the percentage of individuals (-) which left the nest and passed 5 m, 15 m and arrived at the tree

(45 m) and the percentage of individuals returning to the nest carrying an item (*).

908



K. P. PLOWMAN

(a)

14'3 i 15 I

R 5.5 10- -

pm 2.00

(b) R 31 1

50-

40-

30

20-

10-

x 10'2

? 0

9 am 9.30 II 11.30 1.30 pm

t 4.5

2.00

FIG. 4. Numbers of L. lugubris per min tree visiting between 9 a.m. and 2 p.m. (Nest D4) on 12 December 1979. (a) Individuals leaving the tree; (b) individuals going up the tree.

Foraging behaviour

Figure 1 records the relationship between observed trails and nests sites for colonies of both species. The L. lugubris colony near D4 (No. 2) and the L. fragilis colony near A3 (No. 2) were studied in greatest detail. For L. lugubris the dispersion of trails around a nest site appears to be skewed. There is only one instance of overlap in the foraging areas of these colonies although, for this case, there was separation in time. Trails were of two types with some leading to trees and with others ending indefinitely on the forest floor. Ants would leave both types of trail and commence foraging nearby. A higher proportion of ants returning along the latter trail type carried items than occurred for trails that went to trees. Every L. lugubris colony utilized at least one tree within its foraging range. There was no known case of tree sharing. The distances from nest to trees varied from 8 to 45 m. Some of the colonies on the grid visited the same tree throughout the study while others used several. Concurrent use of different trees was observed. The colony near D4 (No. 2) visited nine different trees. One of these was used between May and September, another between October and December and the remainder for shorter periods. On the grid it was not

909

c E (n '5

T1 -2 "O




possible to confirm that the tree, or occasionally the vine, used to gain access to the forest canopy was in fact utilized by the ants at canopy height. Trees were visited by both workers and males.

The pattern of trail and of tree use could vary on both long- and short-term bases. Table 3 shows changes in routes followed for the D4 L. lugubris colony on two consecutive days in December 1979. On the first day three trails and two trees were in use; on the second day the frequency of use declined for trail A, increased for trail C and a fourth trail was used. Ants from trail A visited 1 tree on the first day and 2 on the second.

TABLE 3. Foraging activity of L. lugubris at nest 2 on 25 and 26 December, 1979 between 1-3 p.m. showing numbers per minute entering and leaving the nest, visiting trees and the percentage of individuals returning to the nest which were

replete or carried items Trail A tree A tree Trail Trail Trail

A 1 2 B C Ctree D Total 25 Dec. x ind/min

(i)entering nest 11.6 Not in use 6-2 5.7 Not in use 23.5 (ii) leaving nest 10.5 5-9 5.6 22 (iii) down tree 4.7 1.2 5.9 (iv) up tree 4.9 1.7 6.6 % carrying items 23 0 81 26 0 43.3 % replete 0.9 0 0 0 0 0.3

26 Dec. x ind/min.

(i) entering nest 5.8 5 10.1 Not 7.4 28-3 recorded

(ii) leaving nest 5.4 4.5 11-3 4.2 25.4 (iii) down tree 1.4 0.5 (iv) up tree 4.9 2.0 % carrying items 29 0 0 67 35 32 40.8 % replete 0 O 0 0 0 0 0

The foraging pattern of L. fragilis was difficult to monitor because colony sizes and the rates at which individuals moved along trails were low. Foraging ranges for different colonies sometimes overlapped but no interactions were observed. As for L. lugubris some trails led to the forest floor and individuals seemed to move considerable distances from these. For the colony at A3 (No. 2) as many as six different trails could be in use at the one time. L. fragilis appeared to range over most of the area within a 15-30 m radius of the nest. Other trails of this species led to trees or, in one case, to the male flowers of a forest floor root parasite (Balanophoraceae). Between March and April 1980 the A3 colony visited three different trees and one clump of root parasites. The travelling time from the nest to these points varied from 16 to 29 min (x = 21 min). Rates of movement up and down trees are given in Table 4; many individuals were replete when they left the tree. At the root parasite, individuals imbibed the contents of glands on the male flower. Their behaviour in the canopy could not be seen.

Food Table 2 shows rates at which ants of both species returned to nests carrying items or in a

replete condition. Only individuals with obviously swollen gasters were counted as repletes. An average of 38% of individuals of L. lugubris returned to nests carrying items. Higher

910



TABLE 4. Examples of the rates of tree visit by L.fragilis Repletes

X ind/min (% of those returning Tree Up tree Down tree to the nest)

Tree 1 (nest A3) 0-10 0.15 30 N= 67 min (10 fully replete) Tree 2 (nest A3) 0.6 0-1 0 Palm N = 10min Tree 3 (nest A3) 0.02 0.02 100 N = 60 min Tree 4 (nest F89) 0.45 0.30 100 N= 20 min

proportions carried items between 10 a.m. and 3 p.m. than at other times and the proportion carrying items declined markedly after 4 p.m. An average of 36% of individuals of L. fragilis carried items to the nest and the proportion appeared to decline through the day. A high proportion of individuals of this species entered nests as repletes (x = 19%); most of these were recorded in afternoon counts. Large numbers of L. lugubris repletes were observed on two occasions, once on a track near grass and secondary growth and once in a newly prepared garden. In both cases the ants present were highly excited and it seemed possible that an interaction had occurred between members of two colonies.

There were major differences in the types of items carried by the two species (Fig. 5). Leptomyrmex lugubris carried much plant material (57% of items) while L.fragilis carried much animal material (85% of items). For L. lugubris 28% of all items carried, that is, half of the plant material, comprised leaf fragments, particularly of ferns. Leaf fragments were conspicuous around the entraces to L. lugubris nests and especially abundant around evacuations, often in the soil a metre or so from the usual entrance, that appeared to be constructed for nuptial flights. It is not known whether these items were all food, materials for the production of food or materials used in nest construction. Leptomyrmex fragilis nests did not have ancillary evacuations such as those seen for L. lugubris. Most of the items carried by L.fragilis were insects and the cuticle of arthropods.

Although the classification of items used here is necessarily crude, being based upon visual determination in the field, it appears that the species utilize insects in different ways. Ants comprise 38% of the insect items carried by L. lugubris and 20% of those carried by L.fragilis while winged insects make up 19% of insect items for L. lugubris and 24% for L. fragilis. Leptomyrmexfragilis take more small items than do L. lugubris; the proportion of insect items classed as 'other insects' (because they were too small to identify further) was 24% of L.fragilis and 13% for L. lugubris. Further, the mean dry weights per item carried and per load (based on bulk samples) were 1.3 mg in each case for L.fragilis and 3.5 mg and 3.1 mg respectively for L. lugubris. L. lugubris co-operated in carrying items to the nest more often than L.fragilis did. General observations reinforced these data; thus 14 L. lugubris were once seen manoeuvering a spider and as many as 100 were seen hauling a large earthworm. No similar observations were made for L. fragilis. The species are of similar size with mean wet weights of 8.0 mg for L. lugubris and 10 mg for L.fragilis.

Competition andpredation Overt competitive interactions within species were not observed. Foraging ranges for

colonies of L. lugubris were sometimes within 5 m of each other but, with one exception

K. P. PLOWMAN 911




100- (a) L. lugubris (n=574)

% 50-

A B C L. frog//is (n=233)

A B C D E

FIG. 5. Composition of items carried to the nest. A, plant material; B, frass; C, insect; D other animals, E, arthropod fragments and unknowns; unknown L. lugubris 2%, L.fragilis 9%.

(Fig. 1), they did not overlap and interactions were never observed. Overlap of foraging ranges was seen for L.fragilis but again without interactions being recorded. Petal (1978) has suggested that when a species is seen carrying workers of its own kind to a nest then this may indicate intraspecific competition. For L. lugubris 23% of the ants carried to nests were of this species; for L.fragilis the equivalent figure was 5%.

Foraging ranges of L. fragilis often overlapped those of L. lugubris. The former species usually avoided possible interaction with L. lugubris, sometimes making extensive detours or pausing until a L. lugubris trail was clear and then crossing it. When encounters did occur, particularly on or near L. lugubris trails, this species usually chased but did not contact the L.fragilis.

On two occasions L. lugubris was observed to displace L.fragilis from a nest site. One occurred on the grid at G1. In August 1979 the L. lugubris colony at this nest site was virtually annihilated, apparently by an echidna, Tachyglossus aculeatus. Within a few weeks a neighbouring colony of L. fragilis moved into the now vacated stump and occupied it until December. On 11 December 1979, many L. lugubris, apparently from a colony that was off the grid and had not previously foraged there, were observed near the stump. On the following day, at 4.15 p.m., the L. lugubris had taken possession of the nest site and between 500 and 600 L. fragilis workers and males, many carrying larvae or

D E

912

nn



pupae, together with the queen, were milling about outside the nest within 1 m of it. Excitement level was high. Other L. fragilis, some carrying items of food and others replete, were still returning to the nest along trails. The displaced L. fragilis gradually formed into a tight mass, with the queen situated centrally surrounded by numerous workers that carried larvae or pupae. Unladen workers ringed this mass while others dashed short distances away from the mass, and from the nest, before returning to it. Many L. lugubris were present between the L. fragilis and the nest entrance. A shudder ran through the assemblage of L. fragilis and they commenced to move off; they were reminiscent of a large torch-carrying procession. They travelled about 1 m before stopping and L. lugubris followed in the rear. No obvious interactions occurred but it appeared that the L. lugubris were moving the L. fragilis entourage along. The L. fragilis moved short distances, paused while scouts rushed to and fro and then, in response to another shudder, moved on again. As darkness fell they had travelled about 2.5 m from the nest site to occupy a small hollow in the base of a tree trunk. The next morning they moved again and took up residence in the soil about 3 m from their original nest. Many L. lugubris spent some time 'examining' the place where L.fragilis had stopped for the night.

The second time (17 January 1980) that L. lugubris were seen to displace L.fragilis was underway when first noted. A trail of L. fragilis workers, some with larvae or pupae, together with the queen and males was moving ahead of a number of L. lugubris. They bunched and paused briefly and then moved on. The L. lugubris occupied the nest site that was known to have previously held L. fragilis; the new nest site for the latter species was not found.

Few acts of predation were observed. Attacks upon nests, presumably by echidnas, were recorded twice, once for each species. The L. fragilis nest was in a rotten stump and was destroyed. Nests of L. fragilis tend to be in more open situations then those of L. lugubris and may, therefore, be more vulnerable to echidna predation. A salticid spider was seen to capture an L. lugubris and, on a few occasions, ants of both species were seen carrying bodies of the other species.

Pigs foraging in the forest sometimes disturbed nests of L. lugubris. No disturbance by pigs to L. fragilis nests was observed. The fact that L. lugubris carry much plant material and frass to their nests and deposit matter at the nest entrance may render their nests more attractive to pigs. The foraging activity of L. lugubris appeared to be stimulated when trees were felled for gardens or when natural falls occurred.

Attraction to particular plants Ants were observed visiting plants in recently abandoned gardens where regenerating

trees were often only 3-4 m tall. In these habitats L. lugubris was observed moving about on many types of plants. These were:

(a) Homalanthus spp. (Euphorbiaceae). Leptomyrmex lugubris both gleaned the leaves of this species and visited glands on the leaves. Latex was obvious, especially if leaves were broken or had recently been attacked by insects. Bugs and weevils were common on the leaves. Homalanthus are early succession trees that are common in regenerating gardens and beside tracks; they live for about 20 years (J. Tracey, pers. comm.) and were present on the grid. Seedlings were found growing in tree fall areas within mature forest. When visiting Homalanthus, L. lugubris would stop briefly at glands they encountered (x = 0.07 min, n = 31) to taste or imbibe before moving on. Each gland might be visited by a number of individuals. Some repletes were seen leaving the plants. L. lugubris were seen visiting

K. P. PLOWMAN 913




Homalanthus in an area of regrowth that was about 10 years old: here the trees were about 15 m high.

(b) Urena lobata (Malvaceae). Ants visited glands on the leaves or wandered about on the plant. Urena lobata was only recorded in early regrowth or in disturbed areas near tracks. It was not recorded on the grid or in 10-year-old regrowth.

(c) Lauraceae (genera unidentified). Ants moved over the surface of the leaves, presumably gleaning. No glands were observed. These plants probably occurred on the grid.

(d) Callicarpa sp. (Verbenaceae). Ants were seen gleaning leaves. No glands were observed although Bentley (1977) reports glands for other members of the family. These plants probably occurred on the grid.

(e) Impatiens schechteii (Balsaminaceae). Ants visited the flowers of this plant which was common in gardens and in disturbed areas beside tracks. None were found in mature forests.

(f) Rubus sp. (Rosaceae). Ants visited flowers. The species was common in regrowth and alongside tracks both within and outside the forest.

(g) Fagraea sp. (Loganiaceae). Ants were found to be visiting the flowers of this tree, on the grid, after it had been blown down.

(h) Faradaya (?) sp. (Verbenaceae). Ants were seen visiting and gleaning the leaves of this vine which was present in regrowth and in mature forest. No glands were noted although they have been reported for other members of the family.

(i) Pandanus conoideus (Pandanaceae). Large numbers of ants were sometimes seen at fermenting fruits of this edible pandanus. Many of those departing were replete.

(j) Balanophoraceae. Ants visited glands in the male flowers of this root parasite which occurred in late regrowth and mature forest.

(k) Saccharum officinarum (Gramineae). Ants moved over the leaves and into the nodes of sugar cane. Some were replete when they left the plants.

Counts of plants that had ant visitors were made along 2 x 500 m transects in a recently abandoned garden. Thirty-six plants with five or more L. lugubris comprised twenty-five Urena lobata, ten Homalanthus and one laurel. Leptomyrmexfragilis were observed at the glands of male flowers of root parasites and licking droplets or exudates from the leaves of sweet potato (Ipomoea batatus).

DISCUSSION

The two species of Leptomyrmex investigated are relatively conspicuous members of the ant community. In their utilization of space and food in the regrowth forest they emerge as generalists. Indeed both species occur in the vicinity of villages, in gardens and in most phases of the post-garden succession through to mature forest. Elsewhere in Papua New Guinea species of Leptomyrmex (including L. niger and L. fragilis) are recorded in rubber, cocoa and coffee plantations as well as in mature forest (Room 1975; Wilson 1959). They are broadly based in their utilization of habitats and of resources within a habitat. The present study does, however, reveal differences in their use of the environment. Major differences between them are tabulated below.

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Characteristic: L. lugubris L.fragilis

Colony sizes large small Trails obvious, few at one time not obvious, several at

one time Foraging areas non-overlapping, nest often overlapping, nest

sites tend to be near sites tend to be central edge

Repletes occasional frequent Items carried to nests plant matter and frass animal matter common

common Major group of insects taken ants winged insects Mean weight/item carried 3.5 mg 1.3 mg Co-operation in carrying items frequent infrequent Competition for nest sites win lose

Figure 1 suggests some separation in space between the two species. There was no apparent temporal segregation but foraging strategies and the composition of items carried differed. Leptomyrmex fragilis once occupied a vacant nest site of L. lugubris and the latter species twice displaced L.fragilis from nest sites. It is possible that the species may compete for trees. On the grid there were no cases where the same tree was used by ants from more than one colony, either within or between species. If competition of this kind occurs then it is possible that access to trees might be a limiting factor in the ecology of the species: certainly there seemed to be a great excess of suitable nest sites. One direct observation supports this suggestion. Leptomyrmex lugubris were observed up to altitudes of about 1500 m; Nothofagus becomes a conspicuous component of the vegetation at higher altitudes. Leptomyrmex fragilis reaches to about 1300 m which is just above the zone that is used for gardening. On an area of 1.6 ha of mature forest at 1450 m four nests of L. lugubris were observed between April 1979 and April 1980. One of these nests was occupied through the entire period and the location of trails from it implied that only one tree was being utilized. The other three nests occurred within 75 m of each other. Only one of the three was extant at any time and it is probable, but not known, that these sites were successively occupied by the one colony. For the 12 months ants from these nests visited only one, and the same tree.

If access to trees is important to these Leptomyrmex species it is necessary to ask what function they serve. As indicated it was not possible to be sure that the trees used as routes to the canopy were those that were used in the canopy. Even with binoculars the behaviour of ants could not be followed. The problem was attacked laterally by observing the behaviour of ants in other habitats.

The observations made indicated that these Leptomyrmex species will visit a variety of plants and obtain secretions from leaf surfaces, flowers, fruit and glands. Such secretions are probably rich in sugars and, perhaps, amino acids (Bentley 1976). Sometimes the ants are replete when they leave these plants. On the study grid, this was a common occurrence for L. fragilis but less common for L. lugubris. Visits to trees appear to be a daily and essential occurrence in the lives of these species. Individuals from different colonies do not share trees. Bentley (1976) has observed that in the neotropics plants with extra-floral nectaries are more abundant in clearings than within forests. If this is the case for plants used by Leptomyrmex then the distribution of ant colonies within and between habitats may be

915 K. P. PLOWMAN




influenced by the relative abundance of suitable tree species. Within mature forest, patches of regeneration may be important locations for such trees. It may be significant in the context of this argument that these Leptomyrmex appeared to be absent from areas of early regrowth that had few trees and were dominated by tall cane grasses. The presence of these generalist species of ant in late regrowth and mature forests may require the presence of some individuals of generalist tree species. Where such trees are in short supply L. lugubris may dominate L.fragilis in gaining access to them.

ACKNOWLEDGMENTS

I would like to thank the Government of Papua New Guinea for permission to live in Papua New Guinea; Dr Lance Hill and Dr David Frodin, University of Papua New Guinea; Dr P. Room, C.S.I.R.O., Long Pocket Laboratory, Queensland; Dr R. Taylor, C.S.I.R.O., Canberra; Professor Jiro Kikkawa, Kay Solar, Jan Wilson of the University of Queensland; David, Elizabeth, Joy and Wendy Richards and Alf and Wilma Norman of the Asia-Pacific Christian Mission, Kangalu; Peter and Bruce Dwyer and the people of Bobole without whose hospitality this work would not have been possible-'nesegae'. This paper is dedicated to Didia and Aubelia.

REFERENCES

Bentley, B. L. (1976). Plants bearing extrafloral nectaries and the associated ant communities: interhabitat differences in the reduction of herbivore damage. Ecology, 54, 815-820.

Bentley, B. L. (1977). Extrafloral nectaries and protection by pugnacious body guards. Annual Review Systematics and Ecology, 8,407-428.

Clark, P. J. & Evans, F. C. (1954). Distance to nearest neighbour as a measure of spatial relationships in ecology. Ecology, 35, 445-453.

Lewis, T., Pollard, G. V. & Dibley, G. C. (1974). Micro-environmental factors affecting diel patterns of foraging in the leaf-cutting ant. Atta cephalotes (L.) (Formicidae: Attini). Journal of Animal Ecology, 43, 143-153.

Petal, J. (1978). The role of ants in ecosystems. Production Ecology of Ants and Termites (Ed by M. V. Brain), pp. 293-325. Cambridge University Press, Cambridge.

Room, P. M. (1975). Diversity and organisation of the ground foraging ant faunas of forest, grassland and tree crops in Papua New Guinea. Australian Journal of Zoology, 23, 71-89

Stradling, D. J. (1978). Food and feeding habits of ants. Production Ecology of Ants and Termites (Ed by M. V. Brain), pp. 81-101. Cambridge University Press, Cambridge.

Wilson, E. 0. (1959). Some ecological characteristics of ants in New Guinea rainforests. Ecology, 40,437-447. Womersley, J. S. (1978). Handbook of the Flora of Papua New Guinea, Volume 1. Melbourne University

Press, Melbourne.

(Received 5 March 1981)

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resource utilization by two new guinea rainforest ants

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